Volume 2: Full Reviews of Reports

OUSE WASHES LITERATURE REVIEW

VOLUME 2:

FULL REVIEWS OF REPORTS

May 2015

Mere Oak Ecology Mere Oak Farm Rowley Westbury Shrewsbury Shropshire SY5 9RY T. 01743 891492 [email protected]

OUSE WASHES LITERATURE REVIEW VOLUME 2 FULL REVIEWS OF REPORTS May 2015

Mere Oak Ecology Mere Oak Farm Rowley Westbury Shrewsbury Shropshire SY5 9RY T. 01743 891492 [email protected]

CONTENTS

1. ENGLISH NATURE, 1993. THE OUSE WASHES MANAGEMENT STRATEGY; INTRODUCTORY PAPER. LAMBERT, S.J.J...... 1 2. LAMBERT, S.J.J. UNDATED (1994?). OUSE WASHES MANAGEMENT STRATEGY – MANAGEMENT OF WOODY VEGETATION. ENGLISH NATURE...... 7 3. REPORT NO 49. RAMSAR ADVISORY MISSION (RAM) OUSE WASHES RAMSAR SITE, UNITED KINGDOM. 5-8 NOVEMBER 2001. ROEL POSTHOORN, ECKHART KUIJKEN & TOBIAS SALATHÉ ...... 8 4. CATHCART, R. 2001. EFFECTS OF NUTRIENT LOADING ON DITCH FAUNS AND FLORA IN THE OUSE WASHES: CURRENT IMPACTS AND POTENTIAL MITIGATION. INTERIM REPORT...... 16 5. CATHCART, R. 2002. EFFECTS OF NUTRIENT LOADING ON THE DITCH FLORA OF THE OUSE WASHES: CURRENT IMPACTS AND POTENTIAL MITIGATION. UNIVERSITY OF CAMBRIDGE M.Phil...... 17 6. OUSE WASHES WATER LEVEL MANAGEMENT PLAN, PREPARED BY HALCROW GROUP LTD FOR THE ENVIRONMENT AGENCY...... 33 7. ENVIRONMENT AGENCY ANGLIAN REGION, DECEMBER 2002. HYDRO-ECOLOGICAL REVIEW OF SELECTED EUROPEAN SITES. OUSE WASHES cSAC/OUSE WASHES SPA – OUSE WASHES SSSI CONCEPTUAL FRAMEWORK. ENTEC UK LTD...... 49 8. ENVIRONMENT AGENCY, OUSE AND NENE STRATEGIC STUDIES. OUSE WASHES: WATER AND NUTRIENT LEVEL ANALYSIS. DECEMBER 2003 (c), ENTEC UK LTD...... 77 9. BLACK & VEATCH, 2003. INVESTIGATIONS INTO SOLUTIONS TO WATER QUANTITY PROBLEMS AFFECTING THE SPECIAL NATURE CONSERVATION INTERESTS OF THE OUSE WASHES. ENGLISH NATURE...... 100 10. GRAHAM, J. 2003.OUSE WASHES – HYDRO-ECOLOGICAL PRESCRIPTIONS FOR FAVOURABLE CONDITION. ENGLISH NATURE...... 103 11. ENVIRONMENT AGENCY – ANGLIAN REGION. OUSE WASHES HABITAT CREATION: BUSINESS CASE FOR THE NEXT 5 YEARS OF INVESTIGATION, LAND PURCHASE AND PERMISSIONS. MARCH 2007...... 108 12. A SUMMARY OF THE WATER QUALITY INFORMATION AVAILABLE IN THE NATURAL ENGLAND OUSE WASHES FILES. BAYLISS, S. 2008...... 114 13. A REPEAT TRANSECT VEGETATION SURVEY OF THE OUSE WASHES – A REPORT FOR THE ENVIRONMENT AGENCY. JONATHAN GRAHAM, FENLAND BOTANICAL SURVEYS, 2008. .. 119 14. GREAT OUSE AND OUSE WASHES: CATCHMENT APPRAISAL REFRESH PROFORMA, 2009. DJL AGRONOMICS, FULSTOW, LOUTH, LINCLONSHIRE LN11 OXR...... 121 15. COMMON STANDARDS MONITORING CONDITION ASSESSMENTS OF THE OUSE WASHES SSSI, CSM SURVEY REPORT, OCTOBER 2009. WWT CONSULTING...... 126 16. BLACK & VEATCH, 2005. MONITORING OF THE WASH AND OUSE WASHES IN 2004 FOR THE NATURAL ENVIRONMENT PROGRAMME. SECOND ANNUAL REPORT. ESSEX AND SUFFOLK WATER...... 130

17. BLACK & VEATCH, 2010. MONITORING OF THE WASH AND OUSE WASHES IN 2008 FOR THE NATURAL ENVIRONMENT PROGRAMME. SIXTH ANNUAL REPORT. ESSEX AND SUFFOLK WATER...... 133 18. BLACK & VEATCH, 2010. MONITORING OF THE WASH AND OUSE WASHES IN 2009 FOR THE NATURAL ENVIRONMENT PROGRAMME. SEVENTH ANNUAL REPORT. ESSEX AND SUFFOLK WATER...... 135 19. OUSE WASHES AND PORTHOLME DIFFUSE WATER POLLUTION PLAN, NATURAL ENGLAND AND THE ENVIRONMENT AGENCY, 2010. NOTE THIS DOCUMENT IS STILL LIVE AND ON AT LEAST VERSION 11, 31 MARCH 2014...... 138 20. NATURAL ENGLAND. IMPROVEMENT PROGRAMME FOR ENGLAND’S NATURA 2000 SITES (IPENS). 18 DECEMBER 2012 & DIFFUSE WATER POLLUTION THEME WORKSHOP NOTE, NATURAL ENGLAND, 5 SEPTEMBER 2013...... 146 21. IMPROVEMENT PROGRAMME FOR ENGLAND’S NATURA 2000 SITES (IPENS). SITE IMPROVEMENT PLAN – OUSE WASHES. NATURAL ENGLAND, 19 DECEMBER 2014...... 149

1. ENGLISH NATURE, 1993. THE OUSE WASHES MANAGEMENT STRATEGY; INTRODUCTORY PAPER. LAMBERT, S.J.J. To ensure that traditional management continues English Nature is co-ordinating preparation of a Management Strategy for the Ouse Washes in partnership with the National Rivers Authority, the Hundred Foot Washes Internal Drainage Board, nature conservation organisations, wildfowling organisations and agricultural interests.

The Management Strategy will attempt to integrate the aspirations of all those people and organisations who have an interest in the Washes. This paper is the first in a series of discussion papers which will be produced during the coming year. It provides a statement of the conservation and flood defence value of the site, identifies the issues which need to be addressed to ensure the long term maintenance of these values and identifies the partners who will have a significant role in this process. It is also the first stage in what will be an ongoing consultation mechanism.

1.2 Background to the strategy

The concept of a management strategy for the Ouse Washes is not new. In the early 1970's, the Nature Conservancy assembled a group of interested parties who together produced a preliminary management strategy document. Unfortunately this initiative was not pursued, largely because of lack of resources.

In August 1991 the National Rivers Authority produced a document entitled "Ouse Washes Flood Control" which examined the possibilities for reducing the frequency of summer flooding on the Ouse Washes. An important part of the preferred flood alleviation option was the implementation of a management strategy for the site.

This proposal was very much in agreement with English Nature's thinking at the time, and it was agreed that these two statutory bodies should jointly promote the concept of a management strategy, in partnership with the other bodies who have a role in managing the site. English Nature are co-ordinating the strategy and appointed a Project Officer in July 1992.

1.3 The Management Strategy Process

The first stage in the management strategy process was to bring together all those bodies who have a major role in managing the Ouse Washes. In January 1992 a Management Strategy Group was established. Initially the group will guide production of the management strategy. Subsequently it will act as a forum for communication and will co-ordinate implementation of the strategy. Members of the group include: English Nature; The National Rivers Authority; The Hundred Foot Washes Internal Drainage Board; The Royal Society for the Protection of Birds; The Wildfowl and Wetlands Trust; The Wildlife Trust for Bedfordshire and Cambridgeshire; The British Association for Shooting and Conservation; Fenland Wildfowlers Association; Ely and District Wildfowlers Association; The National Farmers Union; The graziers.

It is envisaged that the management strategy will be progressed through a series of discussion papers. This general introductory paper is the first of the series. Subsequently detailed

1 discussion papers will be produced on each of the key issues identified in this introductory paper, see section 6. Completion of these is scheduled for February 1994.

1.4 Objectives of this paper.

The Introductory paper has five main objectives:

1. To provide a statement on the history, hydrology, and wildlife of the Ouse Washes; 2. To emphasise the importance of the Ouse Washes for nature conservation and flood defence; 3. To propose the key issues affecting the management of the Ouse Washes; 4. To identify the partners who have a role in the long term conservation of the site; 5. To provide a basis upon which interested parties can comment.

3. Hydrological overview

3.2 Operation during a major flood.

Under normal conditions water from the Great Ouse flows down the Hundred Foot River, with a small release to the Old West River through Hermitage Lock. When water levels in the Great Ouse upstream of Earith rise beyond a pre-set level, Earith Sluice opens automatically and water flows down the Old Bedford/Delph River. The levels which determine the opening of Earith sluice are set by Act of Parliament and are 3.17m ODN in the winter (November to March) and 3.77m ODN in the summer (April to October).

As levels in the Old Bedford/Delph rise water flows over its south-east or right bank onto the Washes. During major floods the Washes act as a broad, shallow river, with water flowing from Earith northwards towards the outfall of the Old Bedford/Delph at Welmore Lake Sluice. At very high levels in the Hundred Foot River water flows over the Cradge Bank onto the Washes. The worst floods occur when major rainfall or snow-melt in the Great Ouse catchment coincides with high tides in The Wash.

When water levels in the Old Bedford/Delph exceed those in the Hundred Foot River water is discharged through Welmore Lake Sluice, and eventually flows into the Tidal River. As levels in the Old Bedford/Delph drop, water gradually drains off the washes. The highest land on the Washes is at.the southern and northern ends so water remains longest in the area between Mepal and the Welney road. Flooding normally occurs each winter, but since the mid-1970's there have been a significant number of spring and early•summer floods.

There is a section describing summer management of water levels but this is well described elsewhere (eg ENTEC, 2002). It is however worth remembering that freshwater is only available for about six days every fortnight due to the tidal cycle. Freshwater flows into a header ditch and is then transferred through the Washes. The distribution of water can be finely controlled using a system of internal water-control structures. Over much of the site there are also control points at the outfalls of the ditches, which prevent ,water from flowing into the Old Bedford/Delph.

3.4 Summer flooding

During the latter part of the 1970's and the 1980's the Ouse Washes have experienced many incidences of early summer flooding. The National Rivers Authority have commissioned investigations into the likely causes of and possible solutions to the summer flooding problem. These are detailed in two reports: Summer Flooding on the Hundred Foot Washes (May 1990) and the Ouse Washes Flood Control Strategy Report July 1991). The latter examines various engineering options for improving the situation. The preferred option involves:

 implementation of a management strategy for the Ouse Washes;  modifications of Denver Sluice and operations*;  minor raising of the Cradge Bank;  partitioning of the Washes to create a flood storage area between Sutton Gault and Earith;  improvements to the right bank of the Old Bedford/Delph River;  modifications to Welmore Lake Sluice*; .  minor, phased raising of the Earith summer drawmark*.

An Environmental Assessment of the preferred option will be available shortly.

3.5 Middle Level Transfer Scheme

This scheme enables water from the Great Ouse to be fed into the Old Bedford River via slackers at Earith Sluice. This water may then be pumped into the Forty Foot Drain by a transfer pumping station near Welches Dam during the summer months only to meet agricultural abstraction needs.

4. Nature Conservation Importance

This is well described elsewhere and is not summarized here.

5 Flood Defence Importance.

The Middle and South Level Barrier Banks contain the flood overflow from the Bedford Ouse Catchment. They are vital for the flood protection of the Cambridgeshire Fens. Complete towns, villages and isolated dwellings, together with approximately 1500 square kilometres of agricultural land are protected from flooding by the Great Ouse River Defences, of which these embankments form a vital part. The National Rivers Authority are currently carrying out major engineering works, which are being grant-aided by MAFF, on the Barrier Banks to ensure that they are able to withstand a 1 in a 100 year flood. The works have a design projected life of 50 years.

6 Key issues affecting the Ouse Washes 6.1 Introduction

These issues have been identified by members of the Ouse Washes Management Strategy Group. Between April 1993 to February 1994 discussion papers will be produced on each of the identified topics. These papers will:  describe the biological interest of the feature (where appropriate);  review past and current management practices;  identify problems and opportunities;  identify future management objectives;  review management techniques which can be used to achieve those objectives;  consider the broad financial implications of management and identify sources of funding and  propose appropriate monitoring requirements.

The incidence of summer flooding has already been identified as a major factor affecting the management of the Ouse Washes. Whilst it is undoubtedly a 'key issue', a discussion paper on this topic will not be produced within the management strategy framework. Summer flooding is currently being addressed by the National Rivers Authority, and this process will proceed in parallel with preparation of the management strategy.

6.2 grassland management 6.3 water management 6.4 management of trees, scrub and osier beds 6.5 water quality 6.6 recreation and access 6.7 pest control 6.8 research, survey and monitoring

6.2 Grassland management, covered elsewhere, eg ENTEC 2002. 6.3 Water management, it has already been noted that summer water levels in the Old Bedford/Delph River have to be maintained at 0.5m AODN to enable optimum grassland management. In recent years the National Rivers Authority have had difficulty in keeping the river at this level. There are problems evacuating any excess water from the Old Bedford because of siltation downstream of Welmore Lake Sluice, and this causes localised nuisance flooding. In most years a pump is used at Welmore Lake Sluice to help reduce water levels more quickly. Works have since been carried out at Welmore Lake Sluice to remedy this situation, RK 050315.

The ditch system supports important communities of aquatic plants and provides feeding areas for breeding waders. Analysis of aerial photographs taken in 1971 shows that there were approximately 400 km of ditches present at some time in the 19th century. The 1927 Ordnance Survey maps show 194 km of functional ditches, and by 1974 this had reduced to 133 km. There are now estimated to be 108.06 km of ditches between Welney and Earith. Most ditches fell into disrepair after 1940, probably because reduced numbers of stock made it less necessary to drain away floodwater early in spring, and amalgamation of local farms had reduced the numbers of owners on the washes.

The ditch system requires regular maintenance to prevent deterioration. In recent years reed Sweet-grass has grown more vigorously than previously. This has necessitated a reduction in the period between slubbing out of the ditches, from once every 6 -8 years to once every 3-5 years. The water which enters the ditches from the Hundred Foot River is heavily silt laden. The silt rapidly settles out in the header dyke, which consequently has to be cleaned out every year. Disposal of the accumulated silt can cause problems.

The summer water table in the Washes must be kept high to encourage breeding waders. Water levels can be manipulated by various control points on the inter-wash ditches. Control points are fenced to protect them against stock damage. This fencing is badly affected by winter flooding and ice, and requires constant maintenance. Despite the erection of fencing, cattle gather round the control points and poach the dam soil, allowing water to run past it. Repair of dams is an ongoing requirement.

6.4 Management of trees, scrub and osier beds – a separate paper has been produced covering this topic. 6.5 Water quality, the quality of water in the river and ditch system directly affects plant communities. It is thought that raised levels of nitrogen are responsible for the accelerating growth of algae and reed sweet-grass in the ditch system, and the consequent decline in plant species diversity. The prospect of lowered residual flows in the Bedford Ouse catchment as a result of increased abstraction is of concern. This could increase the likelihood of saline water penetrating the Hundred Foot River and entering the internal ditch system of the Washes, causing damage to its freshwater ecology. This was a real risk identified by ENTEC 2002, RK 050315.

Interesting that high phosphate levels are not mentioned, RK 0503115.

6.6 Recreation and access 6.7 Pest control 6.8 Research, survey and monitoring, research and survey activities on the Washes have mainly concentrated on the ornithological and botanical fearures of the site. Here only less well known work is referred to, ENTEC give a full resume of this work. Grassland and habitat surveys were carried out by the Nature Conservancy Council in 1983 as part of the SSSI renotification exercise. In 1988 the National Rivers Authority commissioned river corridor surveys of The Old Bedford/Delph and Counter Drain/Old Bedford and vegetation and bird surveys of the Barrier Banks as part of the Environmental Assessment process. Other research carried out includes a srudy of the effects of wildfowling disturbance on bird populations which was undertaken jointly by the British Association of Shooting and Conservation and the Wildfowl and Wetlands Trust. Aquatic plant surveys of the Counter Drain/Old Bedford have been carried out by Glasgow University on behalf of the National Rivers Authority at the time of restoration work to Welches Dam lock to identify impacts due to increased boat traffic. There is very little information on water quality within the Washes. There is also a need to establish better ways of monitoring changes in the vegetation, and correlating this with other environmental variables.

7 The Strategy Partners

8 Aims of the Ouse Washes Management Strategy.

The overall aim of the Management Strategy is:  To ensure continuation of the traditional, sustainable management and use of the Ouse Washes, to enable it fully to realise its value as a wildlife habitat and to maintain its flood defence capability.  Other important objectives are:  To improve communications between and co-ordinate the actions of the various different groups who manage the Washes;  To establish and co-ordinate the implementation of an integrated research and monitoring programme to allow evaluation of the performance of the system;  To seek sources of funding for implementation of the required management.

9. Consultation process.

Summary, RK 5 March 5, 2015.

2. LAMBERT, S.J.J. UNDATED (1994?). OUSE WASHES MANAGEMENT STRATEGY – MANAGEMENT OF WOODY VEGETATION. ENGLISH NATURE. English Nature is co-ordinating preparation of a Management Strategy for the Ouse Washes in partnership with various organisations. The management strategy is to be progressed through a series of detailed discussion papers on key management issues and this paper on the management of woody vegetation is the first of the series to be produced.

Summary.

1. This paper considers management of woody vegetation within the Ouse Washes Site of Special Scientific Interest. 2. Six main types of woody vegetation are recognised: mature hawthorn hedges; pollard willows; mature white and crack willows; invasive willow and hawthorn scrub; osier beds, and recent plantations of cricket bat willow and poplar. The distribution of each type is mapped. 3. The extent of woody vegetation on the Ouse Washes has increased in recent decades as a result of planting and reduced grazing pressure. 4. Osiers, willow holts and hedges can be of high landscape and nature conservation value. However, localised areas of woody vegetation can impede water flow in flood conditions. 5. The overall management objective for woody vegetation is to maintain and enhance the existing structural diversity of woody vegetation whilst ensuring that there is no major impediment to flood flows. Specific management objectives for each habitat type are considered. 6. Management options are proposed to fulfil the overall and specific objectives:  restoring hawthorn hedges by coppicing;  repollarding existing willow pollards;  establishing new willow pollards;  maintaining existing mature willows;  bringing up to 50% of osier beds into active management;  removing invasive hawthorn and willow scrub, cricket bat willows and poplar plantations. 7. Advice is provided on the practical aspects of management including legal constraints, sources of labour and grant-aid. Countryside stewardship is considered the best option for the funding of management work. 8. Markets for willow are summarised. The most promising outlets appear to be thatching spars and brushwood faggots for sea defence.

RK, 5 March 2015.

3. REPORT NO 49. RAMSAR ADVISORY MISSION (RAM) OUSE WASHES RAMSAR SITE, UNITED KINGDOM. 5-8 NOVEMBER 2001. ROEL POSTHOORN, ECKHART KUIJKEN & TOBIAS SALATHÉ The Ramsar Convention gives special attention to assisting Contracting Parties in the management and conservation of listed sites whose ecological character is changing or likely to change as a result of technological development, pollution or other human interference.

On 23 October 2000, the Habitat Conservation and Ramsar unit of the European Wildlife Division in DETR requested the listing on the “Montreux Record” of the Ouse Washes Ramsar Site. In 1990, through Recommendation 4.8, the Conference of the Ramsar Contracting Parties established the Montreux Record as a list of Ramsar Sites where changes in ecological character have occurred, are occurring or are likely to occur. A Contracting Party may request inclusion of a site in the Montreux Record in order to draw attention to the need for action or support, e.g. through a Ramsar Advisory Mission (RAM).

The Habitat and Ramsar Team submitted a completed questionnaire providing information for assessing its possible inclusion in the Montreux Record plus a number of supporting technical reports, including six topic papers on the “Ouse Washes Management Strategy” prepared by a number of major stakeholders forming the Ouse Washes Strategy Group, some members of which are also represented on the Habitat Protection and Funding Group, published in 1994 by English Nature and the National Rivers Authority, plus updated information papers prepared in 2000. From this documentation it follows that the main ecological changes occurring at the Ouse Washes are a decline in the numbers of breeding waders and of wintering waterbirds and changes in vegetation communities.

There are two main, but inter-linked, issues that appear to be affecting the features of importance: 1) an increase in the incidence of summer flooding over the last 25 years, as well as high water levels in winter, and 2) a decline in water quality affecting the communities of higher plants within the rivers and ditches of the Ouse Washes.

In spring 2001, DETR submitted a report prepared for the Ouse Washes Habitat Protection and Funding Group by the engineering consultant company Posford-Duvivier providing an “Overview of various measures to alleviate summer flooding”. This report examines seven actions which may reduce the incidence and impact of summer flooding of the Ouse Washes. The purpose of the study was to identify which actions (if any), or combination of actions, merit further detailed consideration towards satisfying the various interests of the Ouse Washes Habitat Protection and Funding Group.

The Ouse Washes – from History to Present

Severe cyclical siltation in the tidal Great Ouse river is a factor affecting the drainage of the Ouse Washes. The new sluice at Welmore lake has however improved the speed of removal of water since its completion in 1999. Nutrient enrichment continues to be a problem, likely to result in the decline of some plant, fish and invertebrate species. Vegetation surveys (1972- 2001) show a marked change in plant communities of the open washes with a number of communities now scarce or extinct. These changes have been shown to be positively correlated

8 with periodicity of flooding and are likely also to be related to nutrient enrichment of the site.(13)

The Ramsar Advisory Mission

An on-site mission was originally planned for April 2001 but due to access restrictions during the outbreak of Foot-and-Mouth disease at that time, the mission was postponed to November 2001.

According to its Terms of Reference, the Ramsar Advisory Mission considered three main issues:

a) The hydraulics and water management of the Ouse Washes in the context of flood defence measures for the Fens rural area and drainage of summer floods in the catchment of river Ouse and its tributaries.

b) The nature conservation importance of the washlands, its dependence on the traditional grazing regime, grassland management, and its importance for vegetation development, plant species of conservation concern, breeding, migrating and wintering waterbirds and waders, and specific species of fish and invertebrates of conservation concern.

c) The quality of the water in the river and ditch systems, problems of eutrophication and water pollution affecting plant communities and species diversity.

Review of Current Management Activities

In the discussions it became clear that the Ouse Washes as a system as a whole is under threat. Hydraulic conditions and water quality are the key issues to both flood defense and ecological functioning. Therefore this report focuses on the water management in and around the Ouse Washes.

The Ouse Washes as Part of the Great Ouse River System

The increased flooding frequency indicates that the surrounding region depends more and more on the Ouse Washes for its safety. The extensive analyses undertaken by the Ouse Washes Habitat Protection and Funding Group make it clear that the problems inside the Ouse Washes mainly have external causes, and that the opportunities for improvement must be found mainly outside the area.

Therefore the mission recommends analysing the problems of the Ouse Washes in the context of the entire river basin of the Great Ouse. With regards to water management issues, the river system is divided into three sections to address the questions in the remainder of the report:

I. Great Ouse river upstream of Earith

II. The Ouse from Earith to King’s Lynn (Hundred Foot, Ouse Washes, Tidal River, Fens)

III. The Old West River, Ely Ouse and tributaries

The Great Ouse flows through a mainly agricultural landscape, passing through several towns and villages, like Huntingdon. Most of the sewage treatment plants in its catchment do not have an advanced phosphorus stripping facility. Also, it was stated that the capacity of the sewage treatment system was probably no longer sufficient for present-day requirements, as during peak rainfall periods untreated sewage regularly spills into the river. The Mission was also informed that under current investment programmes AM2 and AM3, all sewage treatment works over 10,000 population equivalent will be upgraded to include phosphorus control by the end of 2004. While this is not enough to control eutrophication on the Washes, it is considered a contribution to this goal.

The reports available to the RAM do not describe in detail the upstream part of the river Great Ouse. As water dynamics and water quality at the level of Earith (i.e. the inlet sluice to the Ouse Washes) are mainly dependent on the situation in the upstream part of the Great Ouse catchment, we consider it useful to undertake a new analysis, in this context, of the following parameters:

 The changes in land use practices in the upper catchment: The water retention (sponge) capacity of the catchment basin seems to be very poor. How does this relate to the loss of upstream wetlands, to agricultural practices, and to the expansion of built up areas and towns?  The discharge figures of the Great Ouse at Offord (and Earith), also in a historical perspective.  Q/h (surface water flows and human influences) relations at Offord and Earith: A hydrodynamic model of the river system could be useful to analyse and assess the effects of different flood mitigation options in the upstream area.  The water quality and to identify the sources of pollution and eutrophication.  The operating rules of the sluices under circumstances of normal and high discharge (and ecological aspects), taking the results of the analyses of the points above into account.

Section Earith – Kings’s Lynn For this section Earith-Kings Lynn of the Great Ouse catchment, further analysis of the following issues could be useful:  While existing studies have looked at flows in and out of the Washes in relation to arriving flow in the river Great Ouse, the following issues should be analysed in more detail: relative importance of the flow through the Washes, stationary inflow at Earith, and outflow at John Martin Sluice.  The siltation study concluded that there is a dynamic balance of the discharge capacity of Hundred Foot river in relation to its profile and reduced dimensions as a consequence of silting up. It was, however, suggested that the Environment Agency undertakes a repeat survey to clarify the discharge capacity.  A more accurate analysis, using entire annual periods, instead of summer periods only, of flooding frequency, duration and depth of the Ouse Washes could be undertaken. Is the period of 20 years of comprehensive data representative? Analysis of data from

other periods may provide different suggestions. A simple graph could present different scenarii, whether the Earith sluice trigger is released or not.  Water level monitoring in the Washes (install data loggers), taking into account that precise contour mapping, based on aerial photos, may be helpful to determine specific problem areas, given the fact that the Washes are not flat.  The station at Welches dam pumps discharge from the Middle Level Fens into the Washes. The pumping capacity is substantial (over 15 m3/s), but what is the actual impact on flooding frequency, flooding depth, and the duration of flooding of the Washes?  In order to analyze the influence of the water inlet during dry periods on the overall water quality in the Washes, figures of the amount and frequency of water inflow, etc. will be relevant. Are there options to increase the internal water storage capacity and reduce the need for intake?  A hydrodynamic model of the river system, in order to analyze and assess the effects of different options in this part of the catchment, would be useful.  With regard to water quality improvement, an analysis of the potential consequences of the control of slacker input would be helpful. Furthermore, the quantification of the sediment load deposited during flood events could provide helpful insight, as a significant proportion of phosphorus input arrives in particulate form.

Catchment planning and upstream storage of water should include other catchments that impinge on the Great Ouse catchment, such as the Cam. Flow from the Cam can be used to flush the tidal river, so preventing siltation, which has a significant impact on the rate at which floodwaters on the Ouse Washes can be discharged. Under flood conditions on the Washes, priority has to be given to discharging flows from the Washes through John Martin sluice at Welmore lake. Surplus flows in the Ely Ouse are diverted into the Cut Off channel. Therefore, upstream storage of water in the Cam, both to address current upstream urban flooding problems and to accommodate run-off from future development could be beneficial to this regime by providing an extended period over which this flushing can be achieved.

Old West and Ely Ouse

This is the section of the river that was cut off when the Ouse Washes were created. It now discharges into the Tidal River downstream of the Ouse Washes at Denver. The reports presented to the RAM indicate that during peak discharges of the Great Ouse / Hundred Foot, the water levels at Earith could be reduced by diverting part of the discharge to the Old West river. In this way a historical connection would be restored. Although at first glance an attractive option, there are at least two considerations: the first is related to the potential effects on the hydro-morphology of the Hundred Foot river (siltation). The second is related to the core of the river basin approach: It is not a pertinent solution to shift the high water level problems of the Ouse Washes simply to another subsystem within the Ouse River basin, without a prior integrated assessment. In this context, the following aspects should be considered:

 A description of the current state of the Old West river and Ely Ouse as a separate subsystem of the river Great Ouse, including the effects of diverting water through the Old West river.  In order to be able to analyze and assess the effects of flood relief options in this part of the catchment, the Old West and Ely Ouse should be included in the hydrodynamic model of the Ouse river system.  Effects of peak flow diversions into the Old West river (as investigated by the Environment Agency) as part of an integrated scenario with the creation of wetland habitat for water retention on the South Level Fens.

Working Towards Solutions: a Review The problems in the Ouse Washes are quite broad: the incidence of summer flooding, the deterioration of the water quality, as well as the loss of valuable habitat for breeding waders and grazing opportunities in summer. Also the higher water levels in winter and the longer duration of the winter floods are considered to have a negative impact on the grassland habitat.

In order to solve these problems in the Ouse Washes, an impressive effort has already been made. Several studies were carried out to deal with the increased summer flooding of the Ouse Washes and the siltation of the Hundred Foot river and Tidal river. In a report of July 2000 Posford Duvivier presents a brief overview of the options and measures that have been discussed and analysed so far (“Tidal River Great Ouse. Siltation and flood control: Options past and present”). The 58 options identified are summarized in the following categories:  training walls and dredging (8 options),  tidal barriers (8),  improve flow capacity in the river system (13),  storage (5),  improve drainage of the Washes (8),  operations / management (10),  others (6).

Most of the options were rejected because of their negative impact on other functions of the Ouse Washes (mainly navigation and agriculture), their environmental impact, their limited contribution to solving the problem, or their costs. Some of the study recommendations have already resulted in actions. In order to improve drainage of the Ouse Washes after a flooding period, the outlet sluice was replaced by a new complex, the John Martin sluice, with a 50% higher capacity. The measures carried out resulted mainly in a shorter duration of flooding of the Ouse Washes. However, further action was required. Thus, the most promising options to alleviate summer flooding of the Ouse Washes were analysed further and presented in October 2000 in a report of Posford Duvivier. The options considered are:  reprofile the Tidal river,  reprofile the Hundred Foot River,  install a tidal barrier on the Hundred Foot River,  divert summer floods via the Old West River,

 raise the Earith Sluice summer flood release drawmark,  attenuate summer flood flows,  divert summer floods via the Old West River combined with reprofiling the Tidal River,  reprofile Hundred Foot river combined with tidal barrier,  reprofile Hundred Foot River combined with attenuation of summer flood flows,  attenuate summer flood flows combined with other flow improvement options.

The report concludes that, although the effects of some of them are substantial, none of the options meet the desired reduction of summer floods to a frequency of not more than once in four years.

The outcome of the above-described process is not very satisfactory. In the process of designing solutions the problem was narrowed to “flooding in spring and summer, not more than once in four years (April to October)”. None of the considered options is able to solve this problem in an acceptable way. Thus, the objective was narrowed further to “flooding between May and September, not more than once in four years”. Also this objective cannot be achieved. Even when the aspirations are brought back to “flooding not more than once in three years between May and September” none of the considered options brings the solution.

In a broader perspective, this outcome is even less satisfactory, since other problems of the Ouse Washes, like eutrophication and the duration and depth of winter flooding, were not addressed at all. In this context, it should be noted that summer water has the highest phosphorus concentrations and therefore summer floods may have a disproportionate impact on the nutrient levels in the Washes and hence on the potential to cause eutrophication.

The strategy of reducing the problem by lowering the aspirations obviously does not work in the case of the Ouse Washes. In the process of designing solutions mainly technical options were considered and there was a strong focus on options in the downstream part of the catchment only. The problems, however, derive mainly from the situation in the upstream part of the catchment. Since purely technical options fail, a strategy of creating “more space for water” is relevant. This requires the elaboration of spatial solutions as part of an integrated river basin approach, notably the provision of increased storage capacity in the upper catchment. To this end a review of the existing land use and water use practices in the catchment is needed.

To define which options are promising and which are not, an integrated vision of the entire catchment basin, and the position of the Ouse Washes therein, is needed.

Towards an Integrated Systems Approach The outcome of all research so far shows that there is no single and obvious solution. As the approach followed so far, using very reduced ambitions (accept summer flooding once in three years) did not lead to a workable solution, we would like to recommend a different approach and perspective for the ecological situation in the Ouse Washes. Thus, the mission recommends a review of the problems of the Ouse Washes in the context of the river basin of the Great Ouse. Key elements of such an approach would be:

1. Integrated river basin planning, 2. Combining the integrated river basin planning for the Great Ouse with an ecosystem approach for the whole region of the Fens, notably also to define the functions of wet grasslands in this context. 3. A strategic approach to analyse the complex problems in the Ouse Washes is likely to propose solutions along multiple tracks. 4. The extensive analysis that has been carried out in the Posford Duvivier report provides a solid starting point for the development of a strategy for the Ouse Washes that is both ambitious and realistic. A further analysis of the options rejected in this report would be useful. 5. Retaining water upstream, flow diversion and restoration of the wetland ecosystem sponge capacity. Also parts of the Middle Level and South Level Fens are (through their pumping stations) functioning as upstream areas of the Ouse Washes. It is recommended that the Environment Agency models the upper catchment and uses this analysis to identify and progress wetland restoration sites for upstream retention. 6. Improving the water quality through the following measures:

Taking these in turn:

2. Cont. Wet grassland is rapidly decreasing all over Europe. Local imitiatives have promoted wetland habitat re-creation, eg “Wise Use of Floodplains” and “Wet Fens for the Future”. Restoration of fens, reedbeds and wet grassland can contribute to the sustainable development of the region. Such initiatives also provide opportunities to create additional habitat to maintain viable populations of godwits and other waders in the Ouse Washes and surrounding areas, as important indicators for the ecological quality of Fen wetlands. 3. Cont. Some contributions will be easy to implement (minor engineering and dredging works), others will need more time (habitat restoration). In order for the long term river basin and ecosystem approach to provide practical solutions for the actual problems in the Ouse Washes, we recommend a pragmatic step-by-step implementation of selected measures. In this context, the current experimental initiatives (of RSPB) to create new breeding habitats for waders adjacent to the Ouse Washes should be encouraged, as they are likely to provide useful experience. Given the urgency to find solutions to stop the habitat degradation, concrete actions need to be undertaken rapidly. 5. Cont. Wetland restoration can reduce the inflow in the Ouse Washes substantially through:  the creation of retention areas: one of the obvious locations is the area just south of the Ouse Washes (Ouse Fen), another the area just north and east of the Hundred Foot river (NE of the Hermitage marina),  improving the flow capacity of the Ouse river in such a way that the “Offord trigger” will be at about 35- 40 m3/s; (i.e. combining options 2.1, 4 and 5 of the Posford Duvivier report).  Creation of wetlands in the Middle Level and South Level Fens, in order to support the development of sustainable populations of typical fenland breeding birds and other wildlife. Such wetlands would also increase the water storage capacity of the Fens and thus reduce the pressure on the Ouse Washes.

6. Included are:  reducing flooding of the Ouse Washes, when the above mentioned measures are operational, by creating a storage buffer within the Washes upstream Sutton Gault and a limited improvement of the flow capacity of the Old Bedford/Delph river (improved through flow to John Martin sluice),  further reduce phosphorus inputs upstream,  reduce inflow into the Ouse Washes through the smart use of the sluices, increase the internal water storage capacity, and optimise the system of “wet fences”,  purify inflowing waters through buffer zones (reedbeds) within the Ouse Washes upstream of Sutton Gault. A useful drawing summarises these approaches.

Recommendations

The Ramsar Advisory Mission recommends the development of a multiple track strategy in order to prepare lasting solutions for the complex problems of the Ouse Washes. Elements of this strategy could be:

a) The development of an integrated river basin management plan for the Great Ouse and a new analysis of the problems in the Ouse Washes in this context. In order to be able to assess the effects of alternatives options more accurately, a hydrodynamic model of relevant parts of the catchment will be a powerful tool.

b) Since water quantity and water quality issues are closely related, we recommend integrating the strategy of improving the water quality in the Ouse Washes into planning process.

c) Encourage the development of an ecosystem approach for the Fens. In this man-made landscape only some three per cent natural fen habitat remain. The Ouse Washes are a core area of potential wet grassland habitat. Safeguarding the essential ecological functions of the Ouse Washes can be supported by the creation and restoration of wet grasslands, reedbeds and other fen habitats in the South Level and Middle Level Fens.

Summary, RK February 2015.

4. CATHCART, R. 2001. EFFECTS OF NUTRIENT LOADING ON DITCH FAUNS AND FLORA IN THE OUSE WASHES: CURRENT IMPACTS AND POTENTIAL MITIGATION. INTERIM REPORT. The cultural eutrophication of water bodies is characterised commonly by elevated phosphorous concentrations from sewage or agricultural run-off - an input that can lead to dominance by phytoplankton (Balls et al 1989). Resulting increases in turbidity lead to macrophytes being out-shaded, while increases in primary production and therefore amounts of decaying matter can lead to anoxic conditions (Phillips et al 1978). In short, the entire aquatic ecosystem can shift to an alternative state with greatly reduced diversity (Moss et al 1996). While the reduction of nutrient inputs to the system is the ideal remedy for eutrophication, it is generally costly and can take 10 years or more to have a perceivable effect. As an alternative, certain medium-term remediation techniques have been deployed, usually in shallow lakes, to buffer the effects of excessive nutrient loading by biomanipulation. A number of biomanipulation methods are identified as having possible application in the Washes' ditch system.

2. Aims and Objectives

The core aim of this project was conceived as a dual investigation of the extent of the nutrient loading in the Ouse Washes' ditch system and of potential mitigation techniques for buffering the effects of eutrophication. The principal objectives are:

2.1 Using selected ditch lengths, monitor water chemistry and nutrient status upstream and downstream of the following four mitigation trials and their controls: mussel filtration, fish removal, G. maxima filtration, limestone precipitation. 2.2 Survey the presence of aquatic and riparian macrophyte species in the trial ditches, using the controls for comparison. 2.3 Monitor the composition of phyto- and zooplankton communities in selected trial sites. 2.4 Undertake an physical survey of the trial ditches to measure channel dimensions and substrate. 2.5 Examine records of grazing and ditch management to assess their impact on ditch flora.

3.1. Mitigation Trials

An extensive water chemistry testing programme was designed to analyse samples from ditch trials. The sampling programme would simultaneously incorporate monitoring points used in a previous smaller-scale RSPB monitoring programme, thereby providing a spread of data from 1997 to 2001. It was recognised that a continual record of phosphorous levels, in particular, would be essential for informing any future remediation strategies.

In consultation with RSPB reserve management, 15 ditches spanning some 24 km of the Washes' system were selected for use as mitigation trials and their controls. The two known Tolypella prolifera sites - a ditch and a length of the external Counterdrain - were included as part of the water quality sampling programme.

As this Interim Report does not include analysis of all the results it is recommended to look at the final report, 2002. (Summary, RK 2 March 2015).

5. CATHCART, R. 2002. EFFECTS OF NUTRIENT LOADING ON THE DITCH FLORA OF THE OUSE WASHES: CURRENT IMPACTS AND POTENTIAL MITIGATION. UNIVERSITY OF CAMBRIDGE M.Phil. This study attempts to improve our understanding of the threat that eutrophication poses to ditches of conservation value. It seeks to identify patterns of change in ditch plant communities resulting from increased nutrient levels, and to compare those changes with the well- documented transitions in lake ecosystems. By understanding the eutrophication processes and mechanisms which are unique to ditches, it is hoped that bio-remediation techniques, a number of which are tested as part of this study, may be developed to help restore and protect these potentially rich aquatic communities of plants and animals.

Eutrophication: The Shallow Lake Paradigm

The cultural eutrophication of lakes is commonly characterised by elevated phosphorus and nitrogen concentrations from sewage or agricultural run-off, which lead to dominance of the water column by phytoplankton (Balls et al. 1989). Resulting increases in turbidity cause the out-shading and eventual disappearance of aquatic macrophytes, while increases in primary production and therefore amounts of decaying matter can lead to anoxic conditions (Phillips et al. 1978). In short, the entire aquatic ecosystem can be shifted to an alternative state with greatly reduced diversity among macrophytes and both the vertebrate and invertebrate fauna (Moss et al. 1996b).

The pursuit of methods to restore water bodies degraded by eutrophication is ongoing. Attempts originally focused purely on criteria for the reduction of external nutrient loading by analysing water chemistry conditions across a wide range of lakes (Vollenwieder 1968). However, it became apparent that sediments, where most phosphorus in aquatic ecosystems accumulates, could act as a major source of nutrient enrichment once the external loading had been reduced, thus ultimately producing only a marginal improvement in water quality. Moreover, studies began to reveal that the biotic composition and structure of turbid-water ecosytems, especially the large numbers of planktivorous and benthivorous fish and the absence of macrophytes, could create resistance to recovery (Shapiro 1980; Moss 1983). It became clear that an ecosystem approach, accommodating biotic and abiotic factors, was required in order both to understand the process of eutrophication and to intervene effectively to reverse its effects.

Eutrophication in Ditches

There is a limited literature available on the impacts of eutrophication on drainage ditch ecosystems. But there is some evidence that these small channels respond differently than shallow lakes to nutrient enrichment, and that floating macrophytes such as the Lemnaceae have a more important role.

The growth of L. minor resulted in a pH drop from 7 to 9 in June to between 5 and 6 in September, and generally anoxic conditions throughout the entire water column. Low oxygen concentrations resulted in low macrofauna diversity, either directly or as a result of an

17 increase in reduced substances. Indeed, the dominance of L. minor reduced the water column beneath to a zone where the only biological activity was decomposition.

Dominance by Lemnaceae cover in ditches has also been positively correlated with levels of agricultural nutrient inputs in adjacent fields (de Groot et al. 1987). Moreover, it is claimed that nutrient levels are more important than physical factors such as temperature and light in determining rates of growth.

The Ditch System of the Ouse Washes

The site slopes along its east-west axis, with the western edge of the Washes being approximately 1.2 metres lower than the eastern (figure 1.4) (Thomas el a/. 1981). The internal drainage of the Washes consists of a system of ditches which transfer water across this east- west slope and so drain away floodwaters in the Spring. In the process, they act as water fences between grazing meadows (figure 1.3). During the Summer, water levels in the ditch system are maintained at the required depth by topping up from the Header Drain which runs parallel to the Hundred Foot River for most of the length of the Washes. The Header, in turn, receives water when tidal conditions allow from the Hundred Foot through a series of inlet sluices known as "slackers". South of Mepal, water enters individual ditches through slackers directly from the Hundred Foot. Freshwater is available from the tidal Hundred Foot for only about six days in every fortnight due to the rise and fall of water levels dictated by the tidal cycle. There are 112 km of ditches between Earith and Welney and 16.7 km of header drain.

Management of the Washes

Management of the ditch system forms an integral part of the RSPB's conservation strategy, which aims to "maintain the wetland ecology of the site by managing existing ditches on a 3 to 8-year rotation to ensure that they function as wet fences and to conserve the nationally important ditch plant communities" (Carson & Cryer 1997). The clearance, or "slubbing out", of ditches is undertaken mechanically in a 3 to 8-year rotation pattern to ensure that ditches are in various states of vegetation growth ranging from open water to heavily overgrown. The RSPB has also introduced a selective ditch-widening and re-profiling programme under the Countryside Stewardship scheme that is aimed at improving habitat for wading birds and encouraging emergent macrophyte growth.

In summer, the washes are used as pasture for cattle, which are introduced in late April or May, water levels allowing, and removed in October and November to avoid the annual winter flooding. In a typical year on the RSPB reserve, cattle numbers peak at around 2,200 in August. Some 500 hectares of grassland, or 40 per cent of the total area managed by the RSPB, is grazed and topped (cutting to a short sward) at some point between July and November. About 600 hectares is grazed only. Hay-cutting takes place on 200 hectares, or 15 per cent of the RSPB- managed area, between July and August. About 30 hectares is cut for silage. Both the hay- cutting and topping techniques provide expanses of short sward for grazing wildfowl. In all, aftermath grazing takes place on 60 per cent of washes cut for hay or topped as part of a sward- management programme (RSPB 1999).

Flooding occurs when, due to high rainfall and tidal influence, the Hundred Foot is unable to discharge its waters. Flood relief is provided by opening the sluice gates at Earith, which allows the Washes to begin flooding from their southern end. When the level of the Inner River at Welches Dam is 1.75 metres above Ordnance Datum Newlyn, the Washes are flooded from bank to bank. Tidal conditions allowing, water is discharged from the Washes back into the Hundred Foot at Welmore Lake Sluice at the north end of the Inner River. Importantly for its ecology, the Outer River receives drainage water from farmland and not from the River Ouse which collects effluent from approximately 90 sewage treatment works upstream. When levels are high in the Outer River, water is pumped into the Inner River at Welches dam (adapted from RSPB el al. 1997).

The Soils of the Ouse Washes

Soil type is not only a key influence for terrestrial plants. As the substrate in ditch bottoms and as an influence on water chemistry, soil types are a factor in the distribution of aquatic macrophytes. The two most widespread soil types in the Washes are the riverine alluvium of the Midelney Series and the organic peats of the Adventurers' Series.

Most ditches in the central section of the Washes are sufficiently deep to cut through the upper alluvial deposits so that the ditch bottom commonly consists of peat overlain with an organic mud. The exception to this is in the Mepal and Sutton area where an outcrop of Ampthill clay, on which these Fen villages stand, protrudes into the Washes and provides a clay substrate to local ditches.

Conservation Status of the Ouse Washes

The 2,403 hectares of the Washes are the largest remaining area of lowland wet grassland in Britain, and support a mosaic of nationally and internationally important aquatic, marsh and grassland habitats.

Apart from the ornithological interest the invertebrate fauna includes 13 nationally rare species, including the Scarce Chaser dragonfly Libellula fulva and the globally-threatened Depressed River Mussel Pseudanodonta complanata.

The flora includes a host of nationally and regionally scarce plants associated with the ditch system and the river channels (table 1.2), and one species listed under Schedule 8 of the Wildlife and Countryside Act 1981, the Least Lettuce Lactuca saligna.

Table 12 usefully summarises the rare and scarce plants of drainage channels and pools on the Ouse Washes (Alder & Holmes 1986b; Alder & Holmes 1986a; Alder & Holmes 1986c; Cadbury el al. 1993; Cadbury 1997; Cadbury ela/. 2001).

In 1998, the Great Tassel Stonewort Tolypella prolifera, a Red Data Book charophyte species that has been observed on only seven sites in Britain since 1990, was recorded in a single Washes' ditch and a short stretch of the Outer River after a long disappearance (figure 1.6). It is a spring or summer annual and was historically found in slow-moving, shallow water in ditches, rivers and canals throughout Britain (Moore 1986). T. prolifera is the subject of a species

19 recovery programme under the auspices of the U.K. government's Biodiversity Action Plan (UK Biodiversity Group 1995).

Deterioration in the Ditch Flora

Large-scale vegetation surveys of the Ouse Washes' ditch system were carried out in 1978, 1992, 1997 and in 2001 (Grose & Allen 1978; Cadbury et al. 1993; Cadbury et al. 1994; Cadbury 1997; Cadbury et al. 2001). Aquatic macrophyte surveys were also conducted for the adjacent rivers in 1986 (Alder & Holmes 1986b; Alder & Holmes 1986a; Alder & Holmes 1986c).

At the time of the 1978 survey the aquatic and emergent flora were considered to be extremely diverse with species being recorded that were either nationally scarce • Myriophyllum verticillatum, Sium latifolium, Potamogeton compressus and Nymphoides peltata • or locally scarce • Baldel/ia ranunculoides, Alisma lanceolatum, Groenlandia densa and Potamogeton praelongus (table 1.2). The survey found that Glyceria maxima was the commonest emergent species, being recorded at 83 per cent of sites. Rorippa nasturtium- aquaticum, Mentha aquatica, Apium nodiflorum and Myosotis scorpioides were recorded at around 50 per cent of sites. L. minor and L. gibba were easily the commonest floating species, recorded at 79 per cent of the sites. Callitriche spp. (54 per cent of sites}, C. demersum (42 per cent}, Persicaria amphibia (35 per cent} and Elodea canadensis (25 per cent) were the next commonest (Grose & Allen 1978; Thomas et al. 1981).

The 2001 survey indicates that a shift in vegetation composition has taken place. G. densa, H. morsus-ranae and U. vutgaris are now almost certainly extinct from the ditch system (Cadbury et at. 2001). L. minor and the nutrient-loving grass G. maxima have strengthened their dominance, appearing in 95 per cent and 88 per cent respectively of the 603 sampled ditch sites. Over the same period, another surface-floating lemnid Spirodela polyrhiza has increased in occurrence frequency from zero to 48 per cent. C. demersum has doubled in frequency to 88 per cent and filamentous algae increased from 43 per cent to 67 per cent. Elodea nuttallii has entirely replaced E. canadensis over the period.

At the time of the 1992 survey, Cadbury et al (1993) cited nutrient enrichment, either directly or indirectly in the form of greater turbidity, as the possible cause for the decline or local extinction of species known to be sensitive to eutrophication (Cadbury et al. 1993):

Callitriche spp. Ranunculus circinatus

Chara vutgaris Rorippa nasturlium-aquaticum

Myriophyllum spicatum; Ranunculus aquatilis (extinct); Potamogeton compressus (extinct)

Groenlandia densa (extinct); Hydrocharis morsus-ranae (extinct) ; Utricularia vulgaris (extinct)

Indeed, a review, based on the known nutrient tolerance of species, of data from all surveys dating back to 1978 has suggested that eutrophication effects were already in evidence in the late 1970s (Newbold 1999). However, water chemistry data for the ditch system were not collected over the period of the surveys from 1978 to 1997.

Aims of this Study

Despite extensive floral surveys, the lack of water chemistry data for the Ouse Washes has limited our understanding of the mechanisms behind changes in the composition of the ditch vegetation communities. Thus, this project was initiated primarily to investigate nutrient levels in the ditches and assess the trophic status of the system as a whole. Water chemistry monitoring was designed to take place for an entire growing season, so that important seasonal trends could be examined.

Ultimately, the aim of this particular line of inquiry was to ask whether nutrient levels could be identified as the determining factor in the composition and structure of vegetation communities and of their location within the ditch system.

A subsidiary investigation would seek to establish the nutrient-tolerance range of the Red Data Book Charophyte Tolypella prolifera. Such information would assist in the development of the national species recovery plan for Tolypella and possibly aid selection of other Ouse Washes' ditches suitable for its introduction.

Identification of remediation methods for the restoration of macrophyte diversity in the ditches was considered a fundamental aim of the project. A range of biomanipulation techniques for restoring eutrophic lakes are available and a number of these were selected for field trials on the Washes. The intention was to monitor their application to ditch conditions and, hopefully, develop a practicable and affordable management tool that could also be applied to eutrophic ditches in a range of other conservation sites.

Chapter 2 Environmental Gradients and the Distribution of Aquatic Macrophyte Communities in the Ouse Washes Ditch System.

This study sought to identify those NVC community types occuring in the Washes' ditch system and their relative locations. It was considered that, in this way, it would be possible to investigate whether the distribution of vegetation community types was along environmental gradients, and to correlate those environmental variables, including nutrient levels, with NVC types. If a link could be established between particular vegetation communities and discrete levels of nutrients, then the first steps can be taken toward understanding eutrophication processes and impacts on community structure in ditch systems.

Thus the aims of this chapter were to investigate the location within the ditch system of distinct aquatic and emergent riparian vegetation community types, and to measure a range of abiotic and biotic environmental variables, including water chemistry determinands, at these locations.

Methods - Sampling Strategies

A total of 48 ditch sample points were identified and used to survey vegetation communities and water chemistry variables during late August and early September, 2001 (figure 2.1). The selected sites spanned 24 kilometres of the RSPB section of the Washes in order to accommodate the widest possible range of ditch types, and were also located at a range of distances from slacker inlet points.

Results

Macrophyte Survey

A total of 49 floating, submerged and emergent ri parian plant species was recorded (appendices 2.1 and 2.2; see appendix 1.1 for plant glossary).

The classification produced by Twinspan identified four discrete groups of floating and submerged aquatic macrophytes, which equated well with communities designated under the National Vegetation Classification. The map in figure 2.4 shows the distribution across the Washes of sites by group type. Groups 1 and 3 are mainly concentrated in the central and northern sections of the RSPB reserve where there is a peat substrate. Group 3 sites are generally situated closer to the header drain and slacker inlets than Group 1 sites.

Group 4 has sites that are all located in the header drain or in the first 50 metres of ditches, and which are therefore relatively close to slacker inlets. Group 2 sites tend to be concentrated in the southern half of the RSPB reserve, clustered on or adjacent to the area of clay substrate which protrudes into the Washes at Mepal.

Group 3 sites exhibit a tendency toward higher total phosphorus levels and, to a lesser extent, higher total nitrogen. Ditches in this group tend to be older and relatively short distances from slacker inlets compared with Groups 1 and 2. Group 3 ditches are also narrower and shallower than Group 1. Sites in Group 1 tend to have lower total phosphorus levels than Groups 3 and 4, and are located further from slacker inlets, with greater channel width and depth. There is also an association with higher levels of grazing and the gentler bank slopes of Profile 3.

Group 4 is associated with high levels of turbidity and shade. Group 2 sites have a very strong association with clay substrates, higher pH and steeper banks (Profile 1).

The distribution of these four vegetation community types across the ditch system followed a distinct pattern, with a clear zonation between groups. It was found that groups were associated with particular water chemistry regimes and that they could be clearly linked with different levels of nutrients, in particular total phosphorus.

Data Analysis: Emergent and Riparian Macrophytes

Classification

Classification produced four end-groups numbered 5 to 8 (figure 2.11 and table 2.5). The identification of groups which mirrored known plant community types proved more difficult than for in-channel species. This is doubtless because the data for emergent and riparian macrophytes reflected the gradient of species and community types along the ecocline from water level to bank top. However, the four groups could be assigned to NVC community types.

The distribution across the ditch system of Groups 5 to 8 shows some clear patterns (figure 2.12). Groups 5 and 6 are generally located in the central/northern peat ditches, though Group 6 has a few representatives in the clay area around Mepal and Sutton. Group 7 is found exclusively at header drain sites, while Group 8 is clustered on or near to the Mepal/Sutton clay incursion.

Discussion

The results of TWINSPAN classification show that distinct vegetation communities can be identified within the ditch system for both in-channel and emergent/riparian groups of species (tables 2.8 and 2.9). Moreover, these groups have a botanical and ecological integrity, equating well with recognised NVC types for aquatic and swamp communities (Rodwell, 1995). The mapping of sites by vegetation type shows some clear zonation, suggesting that the distribution of vegetation communities was along an environmental gradient (figures 2.4 and 2.14). Ordination of sites and species with environmental variables highlighted those water chemistry and physical parameters that were strongly associated with particular vegetation communities.

Group 4 ditches, encompassing just four ditches, is associated entirely with the header drain and sites very close (<50m) to the header-ditch inlets. These sites are narrow ditches with steep profiles that have recently been slubbed (2-3 years). Turbidity and pH levels are higher than for other groups, while the average Shannon-Wiener diversity score is the lowest at 0.66. The narrow profiles and young age are a reflection of management practices, which ensure that the header drain is regularly slubbed out to maintain flow. High turbidity and low plant diversity in these header drain sites may be a consequence of their proximity to the main slacker inlets from the Hundred Foot river.

Group 2 ditches – NVC A15 Elodea canadensis - are uniquely associated with clay substrates located in the area of the Mepal-Sutton clay incursion into the Washes' system. These deep and steep-sided ditches exhibit lower levels of total phosphorus and high pH. Although their average diversity score of 1.02 is comparable with Groups 1 and 3, Group 2 communities host all the nationally and locally scarce plants recorded in the survey, such as Nymphoides peltata and the rare stonewort Tolypella prolifera. The plant community is distinguished by the presence of a dominant shallow-rooting, submerged macrophyte, Elodea nuttallii, which occupies the mid- lower section of the water column but does not exclude other rooted aquatic macrophytes.

Group 1 ditches containing the NVC A5b community - C. demersum, L. minor - are associated with wide peat ditches that have an open aspect provided by gently sloping banks. This community tends to be located north of Mepal in the central and northern sections of the RSPB Washes and can be large distances (over 500m) from the slacker inlets toward the lower-lying areas of the Washes. This tendency to be located considerable distances away from the slacker inlets is reflected in the water chemistry as nutrient uptake over distance by macrophytes and phytoplankton may explain the lower nutrient levels recorded. The ditch sites showed an average age of seven to eight years since last slubbing. The plant community dominants are the rootless C. demersum which occupies the middle and upper reaches of the water column, and the floating L. minor. Few other macrophytes are able to survive under the extensive mats of these two plants.

Group 3 ditches have a number of similarities with Group 1. Again, they are associated with the peat substrate of the central and northern sections of the RSPB reserve and have an average age since last slubbing of 7 to 8 years. Although sharing with Group 1 the tendency to have gently sloping banks, these ditches are narrower and less associated with distance from slacker inlets. Group 3 sites have the highest average levels of total phosphorus and the lowest average pH. The Group 3 plant community - NVC A3 Spirodela polyrhiza-Hydrocharis morsus-ranae -

23 represents an extensive floating mat of various duckweeds with some submerged C. demersum and E. nuttallii.

Thus, it would seem that the in-channel plant communities form distinct groups that approximate to recognised NVC types. More importantly, these communities occupy different zones in the water column, moving from bottom-rooting Charophytes and macrophytes that receive their nutrients from the substrate, through rootless species such as C. demersum that thrive mid-column, to the pleustophytic Lemnaceae at the surface. It would appear that the occurrence of these different communities coincides with different environmental conditions and that the degree of nutrient-buffering at a particular ditch site may be determining which plant community is present. This survey enabled the identification of vegetation community types, but only provided a snapshot of water chemistry conditions that is insufficient in itself to confirm whether nutrient levels are significantly different between groups. Water chemistry data for a six-month period were therefore collected and are analysed in the following chapter.

Chapter 3 Seasonal Patterns in Water Chemistry Variables and Aquatic Macrophyte Communities.

Alms

Differences in water chemistry between the identifiable vegetation communities in the Ouse Washes ditch system were investigated using a large data-set of determinands collected over the entire growing season. It was hoped that this would confirm that certain communities were present at sites with particular water chemistry regimes and that the spatial dispersal of communities was determined by a nutrient gradient.

Methods - Sampling Strategies

Data were recorded from 17th May to 27th Septermber, 2001, on ten occasions at 27 sites.

Macrophyte Surveys

The ditch survey method outlined in Chapter 2 (p. 18) was employed to record percentage cover for in-channel macrophytes in 10-metre belt transects at each sampling site. Two surveys were conducted to monitor changes in communities over time: one at the end of June and a second in early September.

Seasonal Trends in Site Water Chemistry

To gain a summary view of water chemistry conditions on the site as a whole, means and minimum and maximum values were calculated for all determinands (table 3.2).

The overall mean values for the key determinands mask a wide variance both between different ditches and over a seasonal timescale. The plot for total phosphorus (figure 3.3) shows a rise in mean levels by survey date from 0.623 mg/I in early May to a peak of 1.024 mg/I at the end of August.

In contrast, mean values by survey date for total nitrogen reveal a steady decline over the course of the season from a high of 3.45 mg/I in May to a low of 2.23 mg/I in late August

(figure 3.4). This fall is mirrored by the trend for chlorophyll a, which drops dramatically from a very high early-season maximum mean of 131.5 µg/1, to just over 30 µg/1 by July and to less than 16 µg/1 by the end of September (figure 3.4). Dissolved oxygen displays a rapid fall in mean levels from the end of June, declining from a saturation of 128 per cent down to 50 per cent (figure 3.5). The levels of pH rise during May to a peak in early June of 8.5, and then fall back to just under 7.5 in late September (figure 3.5).

Correlations Between Variables

Total phosphorus has a significant negative correlation with dissolved oxygen (rs = -0.769, n = 37, P < 0.001) and pH (rs = -0.481, n = 37, P < 0.05). There also appears to be a relationship between total phosphorus concentrations and channel size since it is negatively correlated with width (r. = -0.609, n = 37, P < 0.01) and depth (r. = -0.465, n = 37, P <0.05).

Total nitrogen has a highly significant positive correlation with chlorophyll a (rs = 0.760, n = 37, P < 0.001) and turbidity (rs = 0.727, n = 37, P < 0.001). Chlorophyll a is also positively correlated with turbidity (r. = 0.814, n = 37, P < 0.001).

Seasonal mean values for water chemistry determinands were used to investigate the relationship between distance from slacker inlet and levels for key variables. Distance is negatively correlated with four of the water chemistry variables: total phosphorus (rs = -0.596, n= 37, P < 0.05), total nitrogen (r.= -0.706, n = 37, P < 0.001), chlorophyll a (rs = -0.642, n = 37, P < 0.001) and turbidity (r. = -0.703, n = 37, P < 0.001).

It is interesting to note that the greatest decline in each of the parameters is over the first 1000 m from the slacker inlet, after which the parameter shows little change.

Tolypella prolifera - Water Chemistry Range

A few individual plants of the Great Tassel Stonewort Tolypella pro/ifera were recorded in June and September at both site 33 and 38. Site 33 is located in a clay-substrate ditch in the Mepal/Sutton area of the Washes and hosts a Group 2 Elodea-ty pe community. It is positioned downstream in the last 15 metres of the channel before its outfall into the Inner River. Site 38 is outside the ditch system. It is located on the Outer River at a distance of no more than 50 metres from site 33 but is, in fact, part of a different hydrological system, receiving its waters solely from agricultural run-off rather than the Hundred Foot River.

There were significant differences between sites for all water chemistry variables except pH (table 3.13 and figure 3.18). Further analysis revealed that total phosphorus levels at site 38 were significantly lower than at site 33 (Wilcoxon signed rank, W = 0.0, n = 9, P = 0.014).

Site 33 displayed a unique pattern in its seasonal trend for total phosphorus when compared with other study sites (figure 3.18). It is apparent that site 33 experiences a period of very low values in the early part of the season, which then begin to rise toward the system mean from early August. Low total phosphorus is accompanied during this phase by relatively low chlorophyll a and turbidity.

In addition to supporting the only ditch-based population of T. prolifera, site 33 exhibited open• water conditions without evidence of any Lemnaceae at all. Bottom-rooting macrophytes E. nuttallii and P. trichoides were the dominant submerged species.

The in-channel vegetation of site 38 in the Outer River also differed from the ditch system. It supported populations of the pondweeds Potamogeton crispus and Potamogeton natans, neither of which were recorded in the ditch surveys. There were no Lemnaceae observed at site 38 or along the adjacent stretches of the channel and, instead, there were abundant floating populations of the water lilies Nuphar lutea, unrecorded in the ditch system, and the nationally scarce Nymphoides peltata, which was also observed at just one ditch site.Discussion

It should be mentioned at the outset that, based on data spanning a complete season, the mean level of 0.684 mg/I for total phosphorus was extremely high. Comparisons are problemmatic in that the impact of a particular concentration may vary with the volume of a water body (Moss et al. 1997). However, this level is certainly far above the value of 0.1 mg/I total phosphorus recognised as a criterion for eutrophic waters (Vollenwieder 1968). To use a local comparison, total phosphorus levels at Cockshoot Broad in Norfolk were at an annual mean level of 0.166 mg/I in 1980 before remedial treatment was undertaken (Moss et al. 1996). The increase in mean total phosphorus levels over the season from 0.623 mg/I in early May to 1.024 in September suggests that high input levels from the Hundred Foot River are in excess of the system's capacity for uptake of this nutrient (Harper 1992). Normally, nutrient levels can be expected to fall from the high levels of early Spring as the growing season gets underway and phosphorus is incorporated into plant matter. Indeed, this pattern is exhibited by total nitrogen, which declines from an early May mean value of 3.45 mg/I to 2.23 mg/I in September. Total phosphorus is frequently the nutrient limiting macrophyte and algal growth in freshwaters (Mason 1981; Scheffer 1990; Mainstone et al. 2000). However, it seems clear that in the Ouse Washes system excess levels of total phosphorus are allowing plants to maximise uptake of total nitrogen.

The trend in mean levels of chlorophyll a followed a downward curve similar to that of total nitrogen. Analysis confirmed that there was a highly significant correlation between the two, and that early-season levels were significantly higher than those of middle and late summer. It is suggested that immediately following the run-off of floodwaters, the newly exposed ditches support rapid increases in the growth of phytoplankton populations for a limited time period during this early part of the year. It has been noted in a ditch experiment elsewhere that, while increases in phosphates led to enhanced macrophyte growth, high levels of nitrate enrichment resulted in the development of phytoplankton blooms (Daldorph & Thomas 1991).

Interestingly, in the Ouse Washes' ditches the algal blooms do not persist at the same high densities, as the dramatic decline in chlorophyll a levels from around June indicates. This is a key point. In the case of the Washes', it appears from vegetation survey data discussed later that the phytoplankton is out-competed by macrophytes, in particular the surface mat- forming Lemnaceae and the mid-column floating C. demersum, a phenomenon for which there is some evidence in other studies (de Groot et al. 1987; Mjelde & Faafeng 1997).

Water Chemistry by Vegetation Community Type

Results showed that the four distinct vegetation communities, identified by TWINSPAN classification and matching NVC community types, exhibited significant differences in their water chemistry, but also in other environmental parameters (table 3.14).

Group 4 sites are particularly associated with the header drain and locations close to slacker inlets. They have high nutrient levels because of their proximity to the point source, and high turbidity levels reflecting a higher degree of phytoplankton growth than other ditches, but also a higher level of suspended sediment caused by the infiow from the Hundred Foot River and by the regular dredging regime needed to keep the header drain clear. Group 4 sites are the only ones that have any substantial shade, provided by bankside trees and by the steep banks (Profile 1). The Callitriche vegetation community of this group is a refiection of these factors. Plants from this family are shade-loving and, as a shallow-rooting species, are willing colonisers of disturbed substrates (Preston & Croft 1997). The shady conditions and greater turbulence from higher fiows prevent colonisation by the Lemnaceae, which do not tolerate either of these conditions (Sculthorpe 1971). Generally, Group 4 ditches have sparse vegetation other than Callitriche and some C. demersum, and this is refiected in the group having the lowest diversity score.

Group 3 sites are further from slacker inlets than Group 4, but closer than the two other groups. Nutrient levels are thus less depleted by uptake over distance by ditch vegetation. Mean total phosphorus levels are the highest of all groups at 1.08 mg/I. The vegetation is dominated by extensive surface mats of Lemnaceae, beneath which little grows. Conditions in the water column below the mats are often anoxic, as the low dissolved oxygen scores confirm. These sites then are characterised in terms of their vegetation structure by a zone of production at the surface, where Lemnaceae capitalise on their ability to take nutrients from the water column and to maximise light capture by a horizontal growth strategy. L gibba and S. polyrhiza, two of the key components of floating mats, are both positively correlated with high total phosphorus levels.

Group 1 sites are located in the same areas of the ditch system as Group 3 but are, on average, some 300 metres further away from the slacker inlet. The increased nutrient uptake over distance by channel plants effectively lowers the levels of total phosphorus and total nitrogen. Lemnaceae are present on the surface but do not dominate as in Group 3, and C. demersum occupies the main zone of production in this type of community in the middle to upper reaches of the water column. Dissolved oxygen levels are higher, reflecting the lack of a complete Lemnaceae cover.

Group 2 is the only category to contain ditches with clay substrates, and this may be a key influence on their water chemistry and ecology. A number of plants show preferences for mineral substrates (Newbold et al. 1989). Moreover, clay particles have the ability to bind phosphorus into the sediment through a process of adsorption (Marsden 1989; Alloway & Ayres 1993). Although closer to the slacker point source of nutrient pollution than Group 1, Group 2 sites have comparably low total phosphorus levels, indicating that the substrate binding of phosphorus is having a buffering effect. The Elodea community based in these ditches is

27 characterised by bottom-rooting macrophytes, taking their nutrients from the substrate, and there is an absence of dominant floating species at the surface.

Table 3.14 is a useful summary of the in-channel floating and submerged vegetation community types and associated environmental attributes.

Seasonal Change in Aquatic Macrophyte Communities

The flooding of the Ouse Washes each winter entails the complete submersion of the ditch system. It is unclear what happens to all the resident macrophyte species during this period, but certainly the floating Lemnaceae are swept away on the first floods and must re-establish themselves the following Summer. Thus, the annual flood initiates a form of secondary succession in the ditch vegetation every year. The results of the June and September surveys show clearly that plant communities in some ditches change their composition and that, generally speaking, this succession involves shifting to a community type associated with higher nutrient levels. Importantly, Group 3 sites are the only ones that do not change, suggesting that the Lemnaceae community can be described as the climax community for the ditch system given the current levels of nutrient loading.

Nutrients and Light: Competition for Resources

The shifts in vegetation community are along an environmental gradient represented by an increase in total phosphorus levels in the water column. It is assumed that this occurs as the buffering capacity of particular sites for total phosphorus is exhausted. But there is also a parallel shift in the location of growth, or the zone of production, within the ditch channel itself (figure 3.19). The community types occupy distinct compartments of the channel that reflect their mode of nutrient uptake, either from the substrate or water column. High nutrient levels in the water column favour those species which can derive their supply from the open water. In addition, plants which can position themselves higher in the channel have a competitive advantage in respect to light interception. Overall, an increase in nutrients favours those plants that are productive near or at the water surface. Once established, mat-forming plants such as the Lemnaceae outshade competitors from below.

The distribution of vegetation community types across the Washes ditch system is a function of the nutrient-buffering capacity of a particular site. Through loss processes, such as phosphorus adsorption to clay mineral particles or uptake as a function of distance from the point source, the physical environment can buffer nutrient loading and so arrest the re• structuring of the plant community at a particular ditch site. The capacity of the local environment to buffer the nutrient load is manifested in the composition of the vegetation community present, which directly refiects the levels of total phosphorus in the water column (figure 3.20).

Tofypella prolifera: A Relic Species?

The water chemistry regime at site 33, the only ditch section to contain examples of Tolypel/a prolifera at the Ouse Washes, appears to be unique within the system. Indeed, its extremely low total phosphorus can only be compared with levels at site 38 on the Outer River, with its separate water source. Clearly, local environmental factors, such as the clay substrate, are

28 buffering total phosphorus levels. The site is also at the very end of the ditch, some 1050 metres from the slacker inlet, and nutrient levels could be expected to fall considerably over this distance. The ditch has very steep banks and the shading provided may also help to limit productivity and ensure that a low-growing charophyte is not out-shaded.

Chapter 4 Biomanipulation of Ditch Systems: its Potential as a Tool for Restoration

Discussion

The methods employed to reduce directly nutrient levels or turbidity all achieved some degree of success. Biofiltration by mussels produced significantly lower levels of turbidity and total phosphorus at trial site 9. It is likely that the phosphorus removed from the water column would have been both the component contained within the phytoplankton consumed by the mussels and also that bound to suspended sediment particles and deposited as mussel pseudofaeces.

The 100 per cent mortality of the mussels located at trial sites 18 and 28 is explained by the presence at both of extensive Lemna blankets. The decay of dead vegetation matter beneath these mats, which achieved comprehensive coverage of the ditches from mid-June, caused severe reductions in oxygen levels. Freshwater mussels were unable to survive where the Lemna cover was extensive, a fact limiting their use in ditch systems.

Limestone precipitation of phosphorus had a significant effect in reducing levels at two of the three trial ditches. However, the change in total phosphorus levels was insufficient to shift the vegetation type away from surface domination by Lemnaceae. It is clear that one of the problems with using limestone chippings is that a huge tonnage would be required to line ditches extensively enough for inflowing water to have substantial contact time with the chippings in order to cause precipitation.

In the Glyceria maxima filtration ditches, total phosphorus was significantly reduced between the slacker inlet point and the most distant sampling site in two of the ditches. Further research is required to investigate the rate of decline in phosphorus levels in relation to vegetation cover and length of channel. Residence times as governed by rate of flow will also be an influence.

Biomanipulation by fish removal did produce decreases in turbidity and chlorophyll a between the paired control and the fish removal sites in two ditches, but the expected pattern of chlorophyll a decreases in fish-removal enclosures and increases in added-fish enclosures did not occur. As has already been noted, eutrophication in the Ouse Washes' ditch system appears to result in dominance by surface-floating aquatic macrophytes rather than phytoplankton. Clearly, fish removal designed to increase algal grazing, a technique developed for shallow lakes, is unable to address this problem.

Chapter 5 Conclusions

Trophic Status of the Ouse Washes Ditches

This study represents the first detailed and season-long investigation of water chemistry parameters within the Ouse Washes ditches. As such, it has been able to assess the trophic status of the system as a whole and to shed some light on the changes in the composition of

29 aquatic plant communities that have been detected in periodic surveys from 1978 onwards (Cadbury et al. 2001). Nutrient levels within the ditch system are very high, far above widely accepted criteria indicating polluted status (Vollenwieder 1968) and even in comparison with other eutrophic waterbodies (Moss 1987; Madgwick 1999). Total phosphorus is particularly high and shows a pattern of increase through the growing season. The latter indicates that phosphorus, normally the limiting nutrient in aquatic ecosystems, is not depleted or even reduced by plant and phytoplankton growth during the summer and remains in excess within the Ouse Washes' system as a whole. Levels of both total phosphorus and total nitrogen are highest at sites near the inlet sluices from the Hundred Foot River that supply the ditch network. It can be inferred that, while internal phosphorus loading from sediments may be playing a part, the ditches are being polluted primarily by water fiowing in from the Great Ouse system.

The aquatic macrophyte species and communities present are, as a whole, further confirmation that the system is eutrophic (Newbold & Palmer 1979; Haslam 1990; Demars & Harper 1998). There can be little doubt that those species recently lost to the Ouse Washes, such as Hydrocharis morsus-ranae and Utricularia vulgaris, have been out-competed by others more suited to higher nutrient levels. Certainly, historic data confirm that the mat• forming Lemna minor and Spirodela polyrhiza have increased considerably over time (Cadbury et al. 2001), and it is clear that few other plants can survive below these mats where they are extensive. L. minor was present at over 80 per cent of the sites surveyed in the current study, and there must be concerns that it will only continue to extend its domination while nutrient levels remain high to the further cost of species of greater conservation value. At the time of the first comprehensive ditch survey in 1978 (Grose & Allen 1978), the Ouse Washes ditch system was viewed as supporting a rich and diverse community of aquatic macrophytes. In 2001, it is difficult to claim that this is still the case.

And if the submerged plant community is deteriorating because of high nutrient levels, either directly or indirectly through competitive disadvantage, then there must also be fears for the health of aquatic invertebrate populations. Indeed, a number of studies have linked the species richness of macrophytes and macroinvertebrates (Moss & Timms 1989; Bass el al. 1997; Painter 1999). In ditches in particular, it has been shown that the distribution of invertebrate species is greatly influenced by patterns of submerged and emergent macrophyte growth (Scheffer et al. 1984). The loss of submerged plants beneath Lemna mats at the Ouse Washes must therefore be having an impact on the ditch fauna. It is felt that a comprehensive survey of invertebrates in the ditch system should be undertaken as a priority in order to establish baseline data for further monitoring.

Distribution and Succession of Aquatic Macrophytes Along a Nutrient Gradient

The study identified four discrete groups of floating and submerged (in-channel) aquatic macrophytes, which equated well with communities designated under the National Vegetation Classification (Rodwell 1995). The distribution of these four vegetation community types across the ditch system followed a distinct pattern, with a clear zonation between groups. It was found that groups were associated with particular water chemistry regimes and that they could be clearly linked with different levels of nutrients, in particular total phosphorus.

A key finding of the study was that the mat-forming Lemna community represented the climax ditch vegetation community given the high levels of nutrients occurring in the Ouse Washes' ditches. Other communities represented intermediate phases in a succession of community types along this nutrient gradient. Where local environmental conditions were able to buffer nutrient levels, maintaining them at lower levels, the succession of the in-channel macrophyte community toward one dominated by Lemna was arrested.

This succession of macrophyte communities also entails a vertical movement toward the top of the water column. In this change of location within the ditch channel there is further clear evidence that succession in ditch systems is nutrient-driven. As nutrient levels rise, macrophyte communities change from those dominated by bottom-rooting species to those dominated by rootless species occupying the middle to upper layers of the water column. With higher levels still, the climax community of lemnids dominates by occupying the surface layer.

The zone of production rises vertically as those species which can take nutrients directly from the water column begin to gain a competitive advantage. Competition for light is also a factor with species able to grow nearer the surface having an advantage, but it is the initial increase in nutrient levels in the water column that triggers the process of succession. And increased nutrient levels in the water column are a result of overload in the ecosystem's phosphorus• storage capacities. These loss processes, be they nutrient uptake by plants or sediment binding, have been overwhelmed in the face of continuing high external inputs of phosphorus.

Ditches Are Different

The study has found that, even with high phosphorus loads, ditch systems can remain dominated by macrophytes but that a succession takes place in community composition leading ultimately to domination at the surface by floating species. Although there was evidence of high phytoplankton productivity in the Spring, this was not sustained and free• floating algae were generally out-competed for light and nutrients by the Lemnaceae. This is clearly different to the shift from macrophyte to phytoplankton domination that has been described for shallow lakes (Scheffer et al. 1993).

Blomanipulation of Eutrophic Ditch Systems

The study indicated that phosphorus levels can be buffered by binding with sediments in clay based ditches. Given that clay deposits extend beneath the whole site at a variety of depths beneath the overlying peat, total phosphorus levels could be reduced by the expedient of digging ditches sufficiently deep to reach the clay stratum. This might only be practicable in particular areas, according to peat depths, and restricted to use for selected ditches, but it may be a form of mitigation worthy of further investigation.

Reduction of External Phosphorus Loading

As other studies have showed, biomanipulation is most effective when it is applied in the context of reductions in nutrient levels at source (Perrow et al. 1997). And at the Ouse Washes, the unique features of the site make this reduction in total phosphorus input all the more vital. As has been noted, current biomanipulation techniques have limited application in ditch ecosystems. Moreover, the annual flooding of the entire site limits management of the ditches

31 to just six months of the year and means that any biomanipulation scheme has to start from scratch each Spring. Internal sources of phosphorus can be tackled by sediment removal but this costly exercise, which would be a huge undertaking for over 100 km of ditches, is pointless without reductions in inputs from external sources.

The conclusion cannot be avoided that a reduction in nutrient levels in the Great Ouse system is required before a subsequent decrease in the Ouse Washes ditch system can be achieved to the extent that restoration of ditch communities becomes feasible. Phosphate-stripping technology has been installed in some sewage treatment works in the upper part of the catchment with immediate improvements in water quality (Mainstone et al. 2000). The plight of the Ouse Washes can only serve to strengthen the conservation argument for further investment in this technology, which so effectively removes a large proportion of phosphate pollution from point sources. Diffuse sources of nutrient pollution are also contributing to eutrophication in the catchment but, in contrast, are more difficult to counteract.

In 2002, negotiations begin in earnest between the government, the Environment Agency and the Office of Water Services (Ofwat), the industry regulator, on the spending allocated to environmental improvement in the water industry for the years 2005 to 2010. The warning contained in this study over the threat to the flora and fauna of an internationally important wetland is perhaps a timely one.

RK Summary, April 2015.

6. OUSE WASHES WATER LEVEL MANAGEMENT PLAN, PREPARED BY HALCROW GROUP LTD FOR THE ENVIRONMENT AGENCY. Introduction.

The Ouse Washes Water Level Management Plan (OWWLMP) was prepared by Halcrow Group Limited for the Environment Agency to review and update the previous edition of the Ouse Washes Water Level Management Plan (Environment Agency, 1998).

2.1 Purpose and Background to the Plan

Water Level Management Plans (WLMPs) provide a means by which the water level requirements for a range of activities in a particular area, including agriculture, flood defence and conservation can be balanced and integrated. WLMPs are Department for the Environment, Food and Rural Affairs (DEFRA) initiatives; WLMP production is the responsibility of the relevant flood defence operating authority. In this case the operating authority is the Environment Agency (Anglian Region, Central Area) due to the site's proximity and interaction with statutory main river.

The main requirement of WLMPs on Sites of Special Scientific Interest (SSSI) and sites with international conservation designations is to maintain or rehabilitate their designated features of conservation interest, by managing water levels.

Although WLMPs focus on the management of water levels by flood defence and land drainage authorities, other aspects of hydrological management that may impinge on the regime should also be considered. Where these aspects lie outside the WLMP process, reference to other Agency initiatives will be made.

A WLMP is a written statement that outlines the water level management objectives for the area and the means by which those objectives may be achieved; it is not meant as a pre- feasibility study for any possible solutions. Its production should involve all those parties whose interests may be affected by water management within the area covered by the WLMP. A WLMP is deemed complete only when it has been formally endorsed by English Nature, although in addition to this the Agency will seek to gain endorsement from other relevant bodies.

While WLMPs have no statutory status they are a DEFRA High Level Target and are considered as a central component of an operational plan for a given area.

2.2 Contents of this Plan

This WLMP reviews and updates the previous Ouse Washes Water Level Management Plan (Environment Agency, 1998) and forms a written statement outlining the objectives for the Ouse Washes and the means by which these objectives can be achieved.

2.3 Methodology

The Water Level Management Plan (WLMP) was been prepared in accordance with the DEFRA procedural guide for preparation of Water Level Management Plans.

Once the 1998 WLMP was finally agreed and endorsed, then English Nature, the Environment Agency and other organisations with primary interests on the Washes, agreed that the most appropriate forum for future updates and reviews would be the Ouse Washes Management Strategy Group. The group has been consulted throughout this review of the Plan.

The existence of this WLMP will ensure that the agreed management regime is recorded for future reference, and all parties will be fully aware of the site's water requirements, and what their own particular responsibilities are in maintaining, restoring or enhancing the interest of the site.

The WLMP is a working document, which is reviewed on a regular basis and updated or revised if the objectives are not being met or if circumstances change.

2.6 The importance of the Ouse Washes

This information is not repeated this here.

2.7 WLMP.

This Water Level Management Plan updates the 1998 WLMP, reviews the management procedures for the Ouse Washes and sets out new objectives and procedures.

3. Description of the area.

Although useful and thorough this information is not replicated here as it has already been presented elsewhere, unless there is new or particularly relevant information.

The Ouse Washes are primarily a very large flood storage reservoir and as such come under the ambit of the Reservoirs Act 1975. The Act sets out mandatory regulations to ensure that the reservoir is operated and maintained in a manner that will not compromise public safety. These regulations principally relate to the flood banks owned by the Agency ("The Undertaker") which form the reservoir site (i.e. the Middle Level Barrier Bank and the South Level Barrier Bank).

The Conservation Objectives for the European Interests of the Ouse Washes SSSI are included in Appendix 5. Favourable Condition Tables (Appendix 6) are developed by English Nature and other appropriate authorities and set a series of targets for the condition of the habitats within a SSSI. The targets are aimed to permit the continued support of species and features for which the site is designated.

3.4 Area covered by this Plan

The drainage system within the Ouse Washes SSSI can be divided into four parts as shown on Figures 2 and 3:

 The Hundred Foot River;  The river within the Ouse Washes, which is called the Old Bedford River upstream of Welches Dam and the Delph River downstream and is referred to in this WLMP as the Old Bedford/Delph River;  The Ouse Washes internal ditch system; and  The river to the west of the Old Bedford/Delph River, which is called the Counter Drain upstream of Welches Dam and the Old Bedford River downstream of this point. This river will be referred to as the Counter Drain/Old Bedford River in this WLMP.

In addition to these watercourses within the area of the Ouse Washes SSSI the following three channels are directly connected to the Ouse Washes are therefore also included in this WLMP and shown on Figure 2:

 The Bedford Ouse between Brownshill Staunch and the Hundred Foot River;  The Tidal River between the Hundred Foot River and Salters Lode; and  The Cranbrook Drain between Copens Corner and the Counter Drain/Old Bedford River.

The limits of the WLMP on each of these watercourses is shown on Figure 2. The main watercourses and control structures of the Ouse Washes and Counter Drain/Old Bedford River systems are summarised on Figure 4 and shown in detail on Figure 5. Table 1 summarises the operations of the principal structures within the Ouse Washes, and is referred to in Figure 4. Figure 6 shows how water moves through the system.

Each of these rivers is described in detail.

3.5 Operating Authorities.

3.5.1 The following nine Operating Authorities have responsibilities within the area of the Ouse Washes WLMP or can impact within the area by the control of discharges or abstractions from the Bedford Ouse and the Hundred Foot River. Their activities can affect the capacity, water level and the salinity of the tidal watercourse:

• The Environment Agency Anglian Region (Central Area).

• The Hundred Foot Washes IDB.

• Sutton & Mepal IDB.

• Manea & Welney DDC.

• Upwell IDB.

• Haddenham Level IDB.

• Littleport & Downham IDB.

• Over & Willingham IDB.

• Bluntisham IDB.

The watercourses and structures for which each authority is responsible are listed in Appendix 7.

4. Relationship of the Water Level Management Plan with Other Strategies

4.1 Introduction

The Ouse Washes have been subject to a number of major studies in the past. There are also a number ongoing and programmed for the future. The outcomes and recommendations of the completed studies have been incorporated into this WLMP and the recommendations of those, which are still to report, should be included in future.

4.2 Ramsar inspection

The RAM considers that the ecological problems of the Ouse Washes have external causes, that the situation is not as a result of causes within the Ouse Washes but the underlying situation in the Great Ouse catchment as a whole. It therefore recommends the development of a multiple track strategy in order to prepare lasting solutions for the complex problems of the Ouse Washes. Elements of this strategy would include:

 The development of an integrated river basin management plan for the Great Ouse and a new analysis of the problems in this context, for example the production of a hydrodynamic model.  Integration of the strategy for water quality improvements into the Ouse Washes planning process.  Combining the integrated river basin planning for the Great Ouse with an ecosystem approach for the fens. This would include restoration of fens, reedbed and wet grassland and the creation of additional habitat to maintain viable populations of waders.

The draft report is currently being reviewed by the stakeholders of the Ouse Washes and may be subject to some changes. It is anticipated that the final report will be issued in late summer 2002.

Overview of Various Measures to Alleviate Summer Flooding

In October 2000 the Overview of Various Measures to Alleviate Summer Flooding (Posford Duvivier, 2000) was produced on behalf of the Ouse Washes Habitat Protection and Funding Group assessing the impacts of summer flooding on the Washes, and identifying measures which would alleviate this. This report is, however, still a draft version, to be updated following the publication of the findings of the Ramsar Advisory Mission. The Overview focuses on two approaches:

 to improve drainage from the Washes; and  to prevent water entering the Washes.

For further information on this suggest that Investigations into solutions to water quantity problems affecting the special nature conservation interests of the Ouse Washes. English Nature, 2003 is looked at which updates the Posford Duvivier report.

Ouse Washes Flood Control Strategy

The Ouse Washes Flood Control Strategy (1995) went out to public consultation in October 1995. This addressed the issue of summer flooding and suggested a number of engineering options to alleviate this problem, some of which have already been carried out.

 Renew John Martin (Welmore Lake) sluice (completed 2000);  Improve drainage characteristics of John Martin (Welmore Lake) sluice (completed 2000);  Provide a permanent pump station at John Martin (Welmore Lake) sluice (completed 2000);  Strengthen the Cradge Bank to prevent overtopping and erosion, therefore preventing tidal inundation of the Washes;  Minor enlargement of the Hundred Foot River to improve capacity and prevent the Earith sluice from opening too soon;  Direct 5m3/s of summer floods into the Old West River; and  Raise Earith Summer Drawmark by 0.04m.

Assessment of the last two items as part of the draft Overview of Various Measures to Alleviate Summer Flooding (Posford Duvivier, 2000) has shown that they are no longer considered to offer significant benefit in the reduction of the large volumes of water necessary to eliminate summer flooding in the Ouse Washes. These two options are unlikely to be developed further, however, they have not been fully dismissed.

A Flood Control Strategy for the Counter Drain/Old Bedford River has also been developed, resulting in the modernisation and automation of Welches Dam Pumping Station (para 7.3.2).

The following are also discussed: Catchment Abstraction Management Strategies; Review of consents; AMP 3; Local Environment Agency Plan;

Ouse Washes Management Strategy

The Ouse Washes Management Strategy Group was formed in 1991 from individuals and organisations involved in the operation and organisation of the Ouse Washes. The Ouse Washes Management Strategy was produced to ensure the traditional management of the Ouse Washes. The strategy was co-ordinated by English Nature and the National Rivers Authority in partnership with other interests.

In 1994 the Group guided the production of a series of seven Topic Papers which together cover the existing practices and form the basis for future management of the Ouse Washes. These Papers:

 Describe the nature conservation, flood defence and other features of interest;  Review past and current management practices;  Identify problems and opportunities;  Identify future management objectives;  Review management techniques which can be used to achieve those objectives; and

 Consider the broad financial implications of management and identify sources of funding and propose appropriate monitoring requirements.

The Topic Papers cover the following subjects:

 Introductory Paper;  Water Management;  Grassland Management;  Wood Vegetation;  Pest Control;  Recreation and Access; and  Research, Survey and Monitoring.

4.9 Ouse Washes Site Management Statement

The Ouse Washes Site Management Statement (OWMS), prepared jointly by English Nature and the Agency in consultation with nature conservation, recreation and agricultural interests, was launched in 1995. The statement outlines the objectives of English Nature and the landowners for management of the Ouse Washes to maintain the site as a SSSI. The statement also agrees the management activities for each landowner's part of the Ouse Washes. Site Management Statements are now outdated due to the amendments to the Wildlife and Countryside Act as a result of the CROW Act and the introduction of management schemes. The recommendations for the appropriate management of the site may still, however, be applicable.

4.11 Catchment Flood Management Plan

A Catchment Flood Management Plan (CFMP) is a strategic planning policy document, which will provide a proactive approach to flood risk management and will promote a suite of sustainable flood risk management options. The options will consider a move away from the traditional hard engineering to focus on flood management and encourage the consideration of the more sustainable, opportunities for holistic environmental enhancements.

6. Water Level management Objectives

Status of Objectives for the Ouse Washes

The objectives in this Water Level Management Plan fall into two categories:

Objectives identified in the Ouse Washes Management Strategy, which was launched in February 1995, and has been agreed by English Nature, the Environment Agency (as the National Rivers Authority), the Hundred Foot Washes IDB, the Royal Society for the Protection of Birds, the Wildfowl and Wetlands Trust, the Wildlife Trust for Cambridgeshire, wildfowling and farming interests.

Additional objectives for conservation, water resources, water quality, flood defence, recreation and navigation for the watercourses of the Ouse Washes identified during development of the 1998 WLMP and this review. Not all objectives have, at this stage, been agreed by all parties.

6.2 Ouse Washes Management Strategy Objectives for Water Level Management

The overall objective of the Management Strategy is:

To ensure continuation of the traditional, sustainable management of the Ouse Washes to maintain its primary function as a flood storage reservoir and to enable it to fully realise its value as a wildlife habitat.

The overall water level management objective is:

To maintain the traditional water management regime which accommodates flooding in winter, produces moist soil conditions in spring and drier soil conditions in the summer, so that the Washes may fully realise their function as a flood storage reservoir and value as a wildlife habitat whilst also fulfilling agricultural and recreational requirements.

Specific objectives are:

 To maintain the Ouse Washes in a condition to accept flood waters when flows in the River Ouse at Earith exceed acceptable levels.  To drain the majority of surface floodwater from the Washes by the end of April through a gradual lowering of levels in the Old Bedford/Delph River, with optimum levels at Welches Dam of . 0.8m OD to 7 April . 0.7m OD to 14 April . 0.6m OD to 21 April . 0.55m OD to 28 April.  To maintain water levels in the Old Bedford/Delph River at 0.5m OD at Welches Dam between May and October.  To maintain the average soil water table at between 20 and 30cm below the soil surface between April and July.  To maintain high, relatively stable water levels in internal ditches for wet fencing and cattle drinking.  To carry out routine maintenance of rivers in accordance with the Agency’s Conservation Guidelines.  To control weed growth in the Old Bedford/Delph River by cutting in early autumn.  To properly maintain internal ditches and in particular to slub out internal ditches on a rotational basis so as to fulfil drainage, agricultural and ecological functions.  To maintain limited areas of temporary pools in autumn and spring for the benefit of breeding waders and wildfowl, passage migrants and wintering wildfowl.  To maintain existing permanent pools, but not to seek to create any additional areas of permanent open water.

Other Water Level Management Objectives

Objectives for Nature Conservation

 For the Agency to maintain and enhance the nature conservation value of the site in the course of its duties and to actively progress a solution to the issue of summer flooding

to remedy the deterioration occurring on the site and maintain favourable condition in accordance with its legal obligations.  To maintain the aquatic flora and fauna of the Counter Drain/Old Bedford River (particularly the population of spined loach) which qualify the area as an SSSI and cSAC.  To maintain stable water levels in the Counter Drain at Welches Dam during the summer months, with a target level of 0.91m OD and a minimum level of 0.75m OD. These stable levels are required to promote marginal vegetation and invertebrates living on the water margin and provide appropriate soil water levels in the Counter Wash (the area between the Counter Drain and the Middle Level Barrier Bank).  To ensure that the effects of salinity on the aquatic flora at the downstream end of the Counter Drain/Old Bedford River are minimised.  To maintain water levels in the Old Bedford/Delph River at the target of a minimum of 1.0m OD from November to April to provide shallow flooding to attract overwintering birds.

Other objectives for many other purposes are then set out.

7. Water Level Management Practices.

This summarises the key current management practices occurring in the Ouse Washes and Counter Drain/Old Bedford River systems. Further details on structures and their operation can be found in Appendix 10. A fuller description of the rationale underlying the current maintenance regimes is available in the "Ouse Washes Management Strategy Water Management Topic Paper" (1994).

Ouse Washes Main Rivers

Earith Sluice

Earith sluice has three 6.71m wide radial gates, which open automatically when Bedford Ouse levels are high, to let excess water into the Old Bedford/Delph River and the Ouse Washes. From 1 April to 31 October Earith sluice opens when levels upstream are above 3.77m OD and closes when levels are below 3.72m OD. From 1 November to 31 March the corresponding levels are 3.17m OD and 3.12m OD. Water levels upstream are checked every 5 minutes by a telemetry system, and if necessary the gate opens or closes by approximately 0.075m. This process is repeated every 5 minutes as the gates open and more frequently as the gates close. The centre gate is opened earlier and closed later than the outer gates.

I understand that these set levels are currently being reinvestigated by the Environement Agency – RK.

John Martin (Welmore Lake) Sluice

The John Martin (Welmore Lake) sluice was officially opened in April 2000 and provides the only means of evacuating floodwater from the Ouse Washes. It contains three 7.3m wide vertical lift gates and three mitre gates, which are used to prevent tidal incursion. The tidal gates work on water pressure allowing water to discharge when levels in the Old Bedford/Delph River are above those in the Tidal River. The lift gates are operated by sluicekeepers based at Denver who

40 visit the sluice daily. The lift gates are normally set to project some 300mm into the water surface in winter to act as booms to collect floating debris to prevent it from getting caught in the mitre gates, and also to push water downwards to remove silt. Between November and March the lift gates follow the water level. From April to October the gates are used to maintain the retention level of 0.5m OD in the Old Bedford/Delph River.

The sluice structure also contains two permanently installed 0.75 cumec capacity submersible pumps, electrically powered but manually controlled. Their function is to remove floodwater from the Washes that cannot be evacuated by normal gravity discharge. They are not intended to be used while gravity discharge is still possible through the sluice. These pumps may be used between April and November to ensure that the water in the Old Bedford/ Delph River is lowered to its summer retention level of 0.5m OD.

Denver Sluice

Denver sluice allows the Ely Ouse to flow into the Tidal River when the Tidal River level is lower than the Ely Ouse level. Denver sluice does not directly control water levels within the Ouse Washes system, but is a major factor influencing water levels. Flow of water from the Ely Ouse through Denver sluice is important for reducing siltation of the Tidal River, which benefits drainage of the Ouse Washes in summer and winter. However, when Denver sluice is discharging it is more difficult to evacuate water through John Martin sluice, because levels in the Tidal River are raised. There are conflicting pressures to maintain flows through Denver sluice and reduce the siltation, and also pressures to evacuate water from the Ouse Washes as quickly as possible. The operating rules for Denver sluice (detailed in Appendix 11) seek to resolve these conflicts and have been revised to take into account the many complex factors which affect its operation on a day to day basis.

Middle Level Transfer

This transfer is used only when the Middle Level Commissioners request water during a drought. There are 3x300mm inlet valves under the centre gate at Earith, which are operated only if the level in the Bedford Ouse is above 2.13 OD. Water flows down the Old Bedford/Delph River and then four 6" pumps at Welches Dam transfer the water into the Forty Foot River. There are flow meters at both points, so that the water coming in is balanced by that going out.

Routine Maintenance

Routine maintenance operations such as dredging, bushing and weed cutting in the Ouse Washes, Hundred Foot River and Old Bedford/Delph River, are carried out in accordance with the responsibilities agreed between English Nature and the Agency. This ensures that maintenance operations maintain the conservation value of the Ouse Washes.

The Old Bedford/Delph River is subject to a programme of dredging to remove excessive silt build up, in order to maintain channel capacity. Dredging practice follows the Agency’s Conservation Guidelines. Operations are limited to the period between July and September. The dredger works only from one bank to avoid disturbance to the toe of the opposite bank. Spoil is disposed of appropriately to avoid important conservation features.

The Hundred Foot River is regularly surveyed and subject to a programme of dredging, where required, with silt being removed from the Cradge Bank margin. Spoil from dredging the Hundred Foot River is used to strengthen and improve the Cradge Bank.

Aquatic vegetation is cut once a year in the Old Bedford/Delph River, between September and November. Under exceptional circumstances weed may have to be cut outside this period, and prior agreement from English Nature would then be necessary. An uncut margin equivalent to 1/4 of the channel width is left at each side of the channel. From time to time it is necessary to remove cott using a weed-rake.

Summer Water Levels

The Ouse Washes have been subjected to an increase in the incidence of summer flooding since the late 1970's. This is indicated in Table 2. As a result of the increasing summer flooding the Ouse Washes RAMSAR site was placed on the Montreux Record in October 2000. The summer flooding is considered to be changing the character of the site, or is likely to cause changes, since its designation and therefore have impacts upon the habitats and wildfowl of the site. The site was inspected by the Ramsar Advisory Mission and the final report is expected in late summer 2002. The recommendations resulting from this inspection should be incorporated into the assessment of options for the reduction of summer flooding.

Ouse Washes Internal Ditch System

Ditch Water Levels

High water levels are retained in the internal ditch system to provide stock fencing and watering. Stable, relatively high water levels are an essential feature of many of the most ecologically valuable wildlife ditches. High ditch water levels also maximise suitable wader breeding habitat. Ideally this habitat requires that the water table in the surrounding grassland should be held 0.2 to 0.3m below the soil surface between April and July, which is achieved by filling ditches to field level where possible. Fluctuating water levels in ditches considerably restrict the range of marginal species. From an ecological viewpoint summer water levels in ditches should not vary by more than 0.15m. However it is not possible to achieve this stability in all ditches, because of the way that water enters and is transferred throughout the site.

During very dry years artificial autumn flooding may take place to create flashes to be used by overwintering birds. This process anticipates the eventual natural flooding. Water is allowed in from the slackers in exactly the same way as it is during the grazing season, but slightly more is allowed so that the ditches overflow. Natural lows fill first as a result of the groundwater table being raised.

Cradge Bank Slackers

The Hundred Foot River is the only available source of water for maintaining water levels in the internal ditches. The river is tidal and water can be drawn only during high tides, a period of between six and seven days each fortnight. The total amount of water available depends on a combination of the tide height, fluvial flow and weather conditions. During dry summers

42 there may be insufficient water available to top up ditches to the optimum level, and compromises have to be made.

Water enters the internal ditches through the seventeen inlet slackers in the Cradge Bank, the locations of which are shown on Figure 5. The slackers are of varying designs and dimensions, and are situated at different levels. Details of construction and state of repair as at June 1995 are given in Appendix 10c. The IDB has an ongoing programme to replace or repair faulty slacker control equipment.

Water comes through the slackers into a header dyke, which runs parallel to the Cradge Bank. The aim is to bring water into the system as steadily as possible. If the slackers are opened too wide, particularly on a high tide, water enters the system too fast. Fast-flowing water carries a large silt load, erodes dams and fills ditches too quickly, causing localised nuisance flooding.

Once water has entered the system it is necessary to distribute it in the most efficient and equitable way. Water in the header ditch can flow in either direction. Each slacker feeds a defined section of the Washes. The area of the different sections varies considerably (see Appendix 10c). In order to get water to the most distant ditches it is necessary to use the temporary head created by tidal influx to best effect by expediting its passage through dams, culverts and water control pipes. The controls in ditches nearest the inlet are set at the highest position early on in the cycle, to enable water to flow into the more distant ditches. Ideally the most distant ditch should start to take water at the same time as the nearest one, although in practice the nearer ditches usually receive water earlier.

There is a natural, albeit small (0.3 to 0.45m), gradient across the Washes from the Hundred Foot River to the Old Bedford/Delph River. Most ditches crossing the Washes have four or five water control points along their length, including one at the junction with the Cradge Ditch and another at the bottom of the ditch by the Old Bedford/Delph River.

For the slackers and ditch systems operated by the Hundred Foot Washes IDB, annotated maps on a 1:10,000 scale have been produced giving outline details of the current working procedures. These are not included in this document, as they are working documents subject to continual amendment, but further information can be obtained from the Hundred Foot Washes IDB Wash Superintendent at the RSPB Ouse Washes Reserve.

Ditch Maintenance

Ditches in the Ouse Washes are cleaned out regularly, otherwise they soon become infilled as a result of silt deposition during flooding, bank erosion from cattle trampling, accumulation of detritus and growth of vegetation, particularly reed sweet-grass. The majority of ditches are between 2 and 4m wide at water level, and are between 1.5 and 2.5m deep. These dimensions were probably optimal in the past, when vegetation grew less aggressively in the ditches, but wider, shallower edged ditches which will last longer between clearance are more desirable now. The width of the ditches must be sufficient to prevent cattle crossing them, but must also allow management from one side with a tracked hydraulic excavator and the provision of bridges for access. The Ouse Washes Management Strategy Water Management Topic Paper (1994) details good practice in ditch maintenance.

Silt accumulation in the Cradge Ditch is very rapid, particularly close to the slackers. The Cradge Ditch requires maintenance almost annually. The Hundred Foot Washes IDB carries out this work, and also cleans silt from internal ditches immediately opposite slackers, for 50 to 100m downstream.

Counter Drain/Old Bedford River

Land Drainage Inflows

There are five IDB pumping stations and one private pumping station which discharge water into the Counter Drain/Old Bedford River from neighbouring arable land. These pumping stations are listed in Appendix 11d and their locations are shown on Figure 5. The Counter Drain/Old Bedford River also receives effluent and gravity drainage from the Cranbrook Drain, which drains the Somersham area. In the past Black sluice could only be used to drain the Counter Drain/Old Bedford River into the Old Bedford/Delph River by gravity. In 2000 the original flap in the sluice was replaced with a penstock. This enables water to be transferred between the two rivers in either direction as required. This process can only be used when water levels are appropriate, as there is no active pumping.

Welches Dam Pumping Station

During flood conditions, water levels in the upper part of the Counter Drain/Old Bedford River are controlled at Welches Dam Pumping Station. The station uses diesel pumps to transfer water from the Counter Drain/Old Bedford River into the Old Bedford/Delph River. The station was automated in 2000 and one diesel pump was also automated.

Old Bedford Sluice

Old Bedford sluice near Salters Lode was built to permit navigation between the Tidal River and the Counter Drain/Old Bedford River. In 1995 the doors at the Counter Drain/Old Bedford River end of the lock were replaced by a vertical lift gate. The original tidal doors remain at the Tidal River end. In winter the sluice is primarily used to provide gravity drainage for the Counter Drain/Old Bedford River when levels in the Tidal River are low. The lift gate is operated to maintain winter levels in the Counter Drain/Old Bedford River at the lock above 0.8m OD.

The main source of summer water for the Counter Drain/Old Bedford River is from the Tidal River through the Old Bedford sluice. The transfer takes place after a high tide when water levels are falling. This prevents excessive silt entering the Old Bedford River. The transfer occurs only when the salinity is below an agreed threshold of 1500S/cm at the Salters Lode automatic monitor. This threshold assumes dilution and is based upon the tolerance of crops to sodium chloride/ chlorine. Automation of the Old Bedford sluice has improved the raising of Counter Drain/Old Bedford River levels to 0.91m OD, by allowing more opportunities for transfer.

Welney Gate

Welney Gate is closed before the Welches Dam pumps operate. This can now be operated automatically as it is linked to the automatic pump at Welches Dam, to ensure that water from Upwell IDB does not flow back up the Counter Drain/Old Bedford River to the pumps. It remains

44 shut until the downstream level is lower than the upstream level. Navigation past this point is not possible when the gate is shut. Prolonged closure of Welney Gate can cause silt accumulation in its vicinity, which exacerbates the effect of low summer water levels.

Well Creek Weir

If the Old Bedford sluice is tide-locked, water from the Counter Drain/Old Bedford River can flow over a 3m long weir set at 1.65m OD close to Salters Lode, and enter Well Creek which is part of the Middle Level system. The Middle Level Commissioners are consulted before water is diverted across the weir so that they can adjust their weirs in Well Creek.

Slackers

The IDBs take water from the Counter Drain/Old Bedford River through three main slackers (Glenn House, Argent's Farm and Fortrey's Hall), and by backfeeding through the Glen House Pumping Station. In addition water is taken from the Old Croft slacker further downstream. Water is also abstracted from the Cranbrook Drain at the Holwood Farm slacker.

Welches Dam Lock

The Welches Dam lock was refurbished and officially reopened in April 1991 to open the navigation between the Middle Level and the Counter Drain/Old Bedford River via the Forty Foot Drain. The Forty Foot Drain has high seepage losses and so this navigation can be used only at weekends, on special request, when the Agency and the Inland Waterways Association agree, and provided there is sufficient water available.

Maintenance

Aquatic vegetation in the Counter Drain/Old Bedford River is routinely managed in accordance with the responsibilities agreed between English Nature and the Agency. Weed is normally cut between September and November.

Summer Water Levels

With a succession of dry summers in the 1990s, the summer management of the Counter Drain/Old Bedford River has been developed. Control at the critical level of 0.75 m is difficult and has not always been achieved because the varying inflows and outflows can cause daily fluctuations of up to 0.08 m; however, the installation of cills at 0.75m on the slackers has gone some way to alleviate this problem. It has been observed that when all the slacker transfer has ceased the water level can continue to fall, probably due to seepage.

8. Key Issues and Proposed Actions.

I have set out the Proposed Actions as presented in the Summary of Recommendations, rather than in this chapter.

9. Monitoring and Review

Monitoring

Monitoring is essential if review of the Water Level Management Plan (WLMP) is to be meaningful. Monitoring is seen as a key part of many of the current and future strategies for the Ouse Washes, and many of the monitoring results from these will be pertinent to review of the WLMP. Particularly relevant projects are detailed in Appendices 12 and 13.

The quantity of water required to maintain the internal ditch system of the Ouse Washes is not known, and the final destination of this water is of some concern to the Agency. While some data are available, at present there is insufficient data to address this issue and so the report proposes that a range of survey and monitoring work is carried out to investigate this issue.

In summer, water is transferred from the Hundred Foot River to supply the Ouse Washes and parts of the South Level. In addition, the Tidal River provides the only source of summer water for the Counter Drain/Old Bedford River. All these users essentially rely on the same water, the source of which is the flow of the Bedford Ouse through Brownshill Staunch, supplemented, when available, by Ely Ouse water released through Denver sluice. This water supply is severely limited in dry years but there is no information available on how this water is currently divided between users. Metering of slackers drawing water from the Hundred Foot River and Counter Drain/Old Bedford River is recommended, subject to a feasibility study, so that the needs of the Washes and of different users can be better balanced (this work was subsequently done for EA by Entec in 2002 and 2003, RK comment).

10. Summary of Recommendations

Table 3 Target Water levels

Water Course Target Levels Hundred Foot River  No control (tidal) Tidal River  No control (tidal) Bedford Ouse at Earith  No control (tidal). Navigation level of 2.13m OD maintained whenever possible.  Earith sluice opens if levels exceed 3.77m OD 1 April to 31 October and closes when levels are below 3.72m OD  The sluice opens if levels exceed 3.17m OD 1 November to 31 March and closes when levels are below 3.12m OD Old Bedford/Delph River at Welches Dam  0.8m OD 7 April reducing to 0.5m 1 May  0.5m OD 1 May to 31 October Counter Drain/Old Bedford River at Welches  Minimum level 0.75m OD Dam  Target level 0.91m OD  Welches Dam pumps switch on 1.10m OD Ditches within Ouse Washes  High stable water level to maintain the average soil water table 0.2 to 0.3m below the soil surface between April and July

Recommendations

The recommendations that have arisen through the production of the WLMP are shown in Table 4. The table also has a column in which dates can be identified by which the recommendations are to be commenced. I have simply taken the recommendations from Table 4 and set them out as follows below. All of the Actions simply have TBC against them, to be commenced by, with no dates given. There is a column for the organisation responsible which I have omitted.

OUSE WASHES

1. In the short term to investigate and develop alternative habitats for birds with European Conservation Status which are affected by the regular occurrence of spring/summer flooding (8.1.8) 2. Further study of the environmental implications of summer flooding, to be undertaken before recommendations from the draft Overview of Various Measures to Alleviate Summer Flooding (Posford Duvivier, 2000) and the Ramsar Advisory Mission report are implemented, to identify the most environmentally, technically and economically viable solution (8.1.1) 3. Analysis of the tolerance to flooding regimes for each of the designated interest features to be undertaken (8.1.2). 4. Review results of monitoring of Ouse Washes water use. (9.1.2) 5. The effectiveness of the recommendations from the 1995 Ouse Washes Flood Control Strategy to be assessed. (8.1.4) 6. The effectiveness of the adjustments to the Earith sluice operating sequence should be monitored to establish the benefits that have resulted and to assess whether further adjustments are necessary. (8.1.6) COUNTER DRAIN/ OLD BEDFORD RIVER 7. Water levels will be managed to a target level of 0.91m and a minimum of 0.75m. If retention of the target level is not possible following changes in the slacker cill levels, further changes to the system should be considered (8.2.2) 8. Measure slacker transfer from the Counter Drain/Old Bedford River, subject to a feasibility study (9.1.3) 9. Review effect of Old Bedford sluice improvement and the new automated pump control system at Welches Dam pumping station on water levels in the Counter Drain/Old Bedford River (9.2.3) 10. Implement recommendations resulting from investigation into losses from Counter Drain/Old Bedford River and Cranbrook Drain due to seepage and evaporation (8.2.4) OLD BEDFORD/ DELPH RIVER 11. Subsequent to construction of the John Martin Sluice and improved discharge from the Washes, monitoring should be undertaken to identify whether de-oxygenation is still a problem (8.3.1) HUNDRED FOOT RIVER AND CRADGE BANK 12. Spoil from dredging the Hundred Foot River will be used to strengthen and improve the Cradge Bank where appropriate (7.1.11)

13. Carry out such improvements and modifications to the existing slackers through the Cradge Bank as may be appropriate(8.4.2) 14. Identify cill levels of all Cradge Bank slackers (9.1.3) INTERNAL DITCH SYSTEM 15. A programme will be ongoing to replace or repair faulty slacker control equipment (7.2.4) 16. An operational statement identifying when, how and why water moves onto the Washes will be written, and agreed by all interests that regulate water levels by outfall pipes (8.1.5) 17. Analysis of the capacity of outfall structures discharging into Old Bedford/Delph River will be carried out as part of the operational statement including a review of the 'fall' available from the Wash ditches to the Old Bedford/ Delph River during evacuation periods. (8.5.1) 18. If necessary, following the analysis of the capacity of structures (action 20 above), a design should be produced for an enhanced control structure to replace existing structures (8.5.1) 19. All ditches discharging to Old Bedford/Delph River, will be identified and mapped (9.1.3) 20. Ditches to be restored in areas that may be underlain by gravel will have shallow, wide profiles rather than deep narrow profiles to ensure high water tables can be maintained without seepage losses (9.1.5) 21. The effect of re-opening the ditches should be monitored to ensure they are performing as desired and to detect any suspected seepage through the underlying gravel stratum (9.1.5)

Numbers in brackets refer to paragraphs in the main WLMP report.

Fuller details are given in Chapter 8, Key Issues and Proposed Actions.

RK Summary, May 2015.

7. ENVIRONMENT AGENCY ANGLIAN REGION, DECEMBER 2002. HYDRO- ECOLOGICAL REVIEW OF SELECTED EUROPEAN SITES. OUSE WASHES cSAC/OUSE WASHES SPA – OUSE WASHES SSSI CONCEPTUAL FRAMEWORK. ENTEC UK LTD. This report was undertaken for EA by ENTEC as part of its requirement as a ‘competent authority’ to review the effects of existing consents, permissions and authorisations that it (or its predecessor bodies) has granted on the European features of interest for which the site has been designated. It is particularly concerned to review the impact of abstraction licences on wetland sites.

It is based largely on desk-study and provides baseline hydro-ecological information that will be used to provide:

 A preliminary understanding of the key hydrological and hydrochemical processes affecting the wetland and the sensitivity of the site's European features to these processes.  A preliminary assessment of whether there are likely to be any existing licensed surface water or groundwater abstractions that could adversely affect the wetland under study. The assessment is based on review of licensed abstraction quantities, rather than actual abstractions.  An indication of where additional investigations may be required to fill shortfalls in knowledge for: o improved strategic (catchment scaled) management; o understanding appropriate conditions and/or management targets for the site.

For the Ouse Washes site it is considered that the principal water resources related factors which likely affect the site are primarily influenced by strategic catchment management rather than by impacts from consents. Therefore, in this assessment, due regard is given both to strategic issues as well as the standard requirements for the Review of Consents under the Habitats Directive.

The Executive Summary has a useful summary of the key features of the site.

On a site visit with partner organizations to prepare for the work the following issues were identified:

 Shortage of water in the summer due to resource issues;  Increased frequency of spring and summer flooding which adversely affects washland plant communities and the breeding waders;  Poor water quality that is adversely affecting washland plant communities in the Washes.

3.1 Conservation Status and Conservation Objectives

National

The Ouse Washes was first notified as an SSSI (Bedford Wash) in 1955; it was re-notified in 1984.

International

Candidate Special Area of Conservation (cSAC)

The European feature of importance in the Ouse Washes cSAC, which comprises only the Counter Drain and Old Bedford Delph parts of the SSSI (see Figure 2.2), is: Spined loach (Cobitis taenia. Definition: The spined loach is a small bottom-living fish restricted to the catchments of five east-flowing rivers in central England and East Anglia.

Representation on site: Spined loach is present in the Counter Drain and Old Bedford Delph. On the basis of recent survey work, it is very unlikely that the spined loach can persist within the internal ditches of the washes (Perrow & Tomlinson, December 2001).

Special Protection Area (SPA) The Ouse Washes are also designated as an SPA (Ouse Washes SPA). Unlike the cSAC, most of the SSSI is included in the SPA (see Figure 2.1). The SPA citation is included in Appendix E. This site has been identified as being used by, or capable of supporting, the following features from the SPA Citation:

Annex I Bird Species:

Bewick's swan (Cygnus bewickii) (wintering); whooper swan (Cygnus cygnus) (wintering); hen harrier (Circus cyaneus) (wintering); spotted crake (Porzana porzana) (breeding); ruff (Philomachus pugnax) (breeding and wintering).

Migratory Species of European Significance: black-tailed godwit (Limosa limosa 10 (breeding); pintail (Anas acuta) (wintering); shoveler (Anas clypeata) (breeding and wintering); wigeon (Anas penelope) (wintering); gadwall (Anas strepera) (breeding and wintering); black-tailed godwit 10• pochard (Aythyaferina) (wintering);

Species that Contribute to the Wintering Assemblage: lapwing (Vanellus vanellus); teal (Anas crecca); tufted duck (Aythyafidigu/a); mallard (Anas platyrhync/ws); cormorant (Phalocrocrax carbo); coot (Fulica atra).

The European features that qualify a site for inclusion in an SPA are identified primarily from a review of survey information and also the presence on site of the appropriate habitat types. Indeed, it is the habitats used by the species which form the basis of the conservation objectives.

The Ouse Washes have been identified as an SPA because the species listed above have been recorded from the site and because the habitats on site are considered to be those that are required by the species, as follows, here the habitat requirements of the Annex 1 bird species and of the migratory species of European significance are presented.

Ramsar Sites In addition to the cSAC and SPA designations, the Ouse Washes are designated as a Ramsar site. The Ouse Washes qualify for Ramsar status under the following criteria:

Ia - being a particularly good representative example of a natural or near-natural wetland characteristic of its biogeographic region;

3.1.2 Conservation Objectives

International Objectives

Candidate Special Area of Conservation The conservation objectives for this site, in respect to its contribution to the Ouse Washes cSAC, are as follows:

o to maintain, in favourable condition, the habitats for the population of spined loach. Note: maintenance implies restoration if the feature is not currently in favourable condition.

The draft criteria that will be used to assess 'favourable condition' are included in Appendix G of the report.

Special Protection Area The conservation objectives for the Ouse Washes, in respect to its contribution to the SPA, are as follows:

o to maintain, in favourable condition, the habitats for the population of Annex I bird species of European importance (Bewick's swan, whooper swan, hen harrier, spotted crake, ruff) with particular reference to: . grassland/marshy grassland with ditches; . open water. o to maintain, in favourable condition, the habitats for the population of migratory bird species of European importance (wigeon, gadwall, shoveler, pintail, pochard, black- tailed godwit) with particular reference to: . grassland/marshy grassland with ditches; . open water. The draft criteria that will be used to assess 'favourable condition' are included in Appendix G of the report.

National Objectives At the time of writing the national conservation objectives for the Ouse Washes SSSI (as opposed to those relating to the SAC/SPA/Ramsar designations) had yet to be produced by English Nature.

3.3 Site Management

3.3.1 Conservation Management The general management aims and objectives for the Ouse Washes are described in a series of Topic Papers produced in the early 1990s by English Nature and the then National Rivers Authority (NRA). The topic papers considered the following topics:  Introduction (Overview of the system) (May, 1993);  Grassland management;  Management of woody vegetation;  Water level management;  Recreation and access;  Research, survey and monitoring.

There is a good general description of the management of the site:

The management of the vast majority of the Washes comprises grazing, mainly by cattle but with some horses, with the aim being to produce some areas of short sward (up to 15 em tall) and some of medium length (I 0-25 em). The normal grazing period is from mid-May to the end of October. Some areas are however not grazed until hay has been taken in July/August'6  When necessary areas are topped to control rushes, thistles, dock etc.  When necessary hedgerows are coppiced and willows pollarded. Invasive scrub is removed and predator control is practised.  Water levels are managed, wherever possible, for the benefit of the features of interest. Details of target water levels are described in Sections 4.1.4 and 4.1.5 of this report.  Ditches are cleared on a 5-7 year rotation. Clearance is undertaken between July and October. On the RSPB reserve, if re-shaping is necessary the aim is to produce ditches 3-4m wide and about I m deep with gently sloping edges.  The aquatic flora of the Old Bedford Delph and the Counter Drain are cut annually by the Environment Agency between September and November to maintain hydraulic continuity in the watercourses. The aim is to cut the flora in the middle half to two thirds of the channel leaving a fringe of marginal vegetation.  When dredging of the main watercourses is required it is undertaken from one bank only and takes place in late summer.

3.3.2 Previous and On-going Ecological Monitoring There is a useful section on recent monitoring that has been carried out. This starts with the statement that “The RSPB and Wildfowl and Wetlands Trust carries out virtually all the monitoring that is currently undertaken on the Ouse Washes” 4. Hydrology.

The hydrological description given in this Section is structured by splitting the whole Ouse Washes site into two hydrologically distinct components: i) the Ouse Washes (including internal ditches and the Old Bedford Delph);

52 ii) the Counter Drain. As part of the hydrological assessment any regard to water quality is limited to standard sanitary determinands (used for the RE classifications), nutrients and salinity. No particular attention will be given to pathogens, metals, pesticides, or hydro-carbons and any issues associated with these pollutants will only be reported if they arose as a specific issue during consultations.

4.1.3 Hydrogeology

Within, and in the immediate proximity of, the Ouse Washes the River Terrace Gravels form the most notable aquifer. These deposits exist in the southern part of the Ouse Washes (south of Mepal), where they are semi-confined by the overlying alluvium, and here these deposits may potentially help sustain a wetland regime in the Washes during prolonged dry (and low flow) periods.

4.1.4 Flood Drainage and Navigation

The background to the construction of the Washes is set out.

Flood Operations Considerable detail is given in the WLMP on the flood control operations for the Ouse Washes. These details are supplemented and updated in Posford-Duvivier, 2000a (Overview of Various Measures to Alleviate Summer Flooding 2000). Summary details of these operations are given schematically in Figure 4.3 with supplementary details given in Table 4.2 and these are outlined as follows:

Flood inflows to the Ouse Washes are conveyed from the Bedford Ouse through Earith Sluice. Earith Sluice is activated when upstream levels on the Bedford Ouse:

. >3.77 m AOD in summer {April to October); . >3.17 m AOD in winter (November to March).

In exceptional flood conditions further floodwaters can be conveyed into the Ouse Washes by:

. pumping at Welches Dam from the Counter Drain; . overspill of the Cradge (inner) Bank from the Hundred Foot River which can occur during tidal high-water

Flood outflows from the Ouse Washes are conveyed to the tidal Great Ouse through Welmore Lake Sluice (also now referred to as John Martin Sluice). This structure has recently been uprated incorporating greater (50% more sluicing) capacity and also facilitates permanent pumping equipment.

Fig 4.3 is a very useful diagram for understanding the hydrological functioning of the Washes and also appears in the Water Level Management Plan, while in a similar vein Table 4.2 is a useful Schedule of river controls and pumped drainage systems relevant to the Ouse Washes site.

Flood Issues

The RSPB have charted the incidence of summer flooding in the Ouse Washes and their findings are summarised here as Table 4.3. This shows a marked increase in the incidence of summer flooding in the period 1977 to 2000 compared with 1957 to 1976. This is particularly so for the period April to June which is considered to be highly detrimental to the bird (breeding waders and wildfowl) populations of the Ouse Washes. In addition, such 'unseasonal' flooding is also detrimental to the Ouse Washes concerning:  stock (cattle and sheep) grazing;  hay cutting;  invasion of grazing meadows by poorer swamp flora;  poor water quality in the internal ditches of the Washes and then subsequently in the receiving rivers when the Washes are drained.

This is of course a key section of the report and Table 4.3 referred to above is important in this regard.

The reason for this increase in undesirable summer flooding of the Ouse Washes may be the result of climate variance and resultant fluvial flood flow response to an increase in notable storm/rainfall events. There are however differing views on this issue and other localised factors which may have exacerbated this effect and are thought to include:  Increased siltation along the tidal Great Ouse and part of the Hundred Foot River has undoubtedly affected the drainage of floodwaters from the Ouse Washes through Welmore Lake Sluice and extended the duration of effect from flooding. Additionally, it is perceived by some that the above siltation also raises flood levels (for a given flow) at Earith (the intake to the Ouse Washes). This effect could potentially increase the incidence of flooding into the Ouse Washes but Entec regard the likely significance of this effect to be minor.  Urbanisation (i.e. Milton Keynes and Bedford) coupled with land use/drainage changes in the Bedford Ouse catchment may have marginally affected (increased) the flood response of the Bedford Ouse.

In order to mitigate the effects of siltation on the tidal Great Ouse/Hundred Foot River the following actions have been taken:  Welmore Lake Sluice has been uprated (see Figure 4.3);  operations at Denver Sluice, on the Ely Ouse River, have been modified to help control the problem of siltation;  some dredging of silts have been undertaken . Additional schemes are also under consideration which may give further alleviation of summer flooding (Posford-Duvivier, 2000a).

The siltation of the tidal Great Ouse (extending into the Hundred Foot River) probably relates largely to the introduction of a major flood relief scheme on the Ely Ouse in the 1950s/1960's. This diverted significant flood flows away from Denver Sluice and along 18 km of the tidal Great Ouse between Denver and the Tail Sluice (see Figure 4.3 and Table 4.2).

Navigation The Ely Ouse has a Statutory Navigation. The Counter Drain and the Old Bedford (outer river and which is within the Ouse Washes) has a statutory right of Navigation from Salters Lode to Welches Dam. From Welches Dam, the navigation runs west away from the washes along the

Forty Foot Drain. The Hundred Foot River, links the navigation lock at Denver Sluice with the Old West River through Hermitage Lock (see Figure 4.3).

4.1.5 Summer Water Resources

The target water level regimes for the Ouse Washes are detailed in the WLMP and summarised in Figure 4.3. In brief, for the Ouse Washes component of the designated European site the targets include:  Old Bedford Delph at Welches Dam: . Falling level during April from 0.8 to 0.5 m AOD; . 0.5 m AOD (May to October).  Internal ditch levels over the period April to July 0.2 to 0.3 m bgl (metres below ground level).

Over the summer period, the only controlled inflows to the Ouse Washes involves slacker transfers (gravity fed discharges through pipes or culverts controlled by penstocks or gate valves) from the Hundred Foot River. There are 17 such slackers with 13 operated by the Hundred Foot Washes IDB and four (the most downstream slackers) operated by the Wildfowl and Wetlands Trust. An issue relating to these latter four is picked up later in the report, eg see 7.31. Cross reference also to Section 4.3, Figure 4.7, and Table 4.5 will also provide further details.

There are no definitive flow data or operating schedules available for these slackers and therefore considerable uncertainty exists concerning actual transfer quantities involved. A very approximate flow estimate based on anecdotal information from the RSPB (pers com. C Carson - RSPB and A Papaioannou - Entec) suggests the typical values may seasonally average 30 Ml/d and gross 3000 Ml per season. It was indicated that discharge to the Ouse Washes is limited to high-water periods in the Hundred Foot River and sufficiently high river levels only occur over the spring tide regime, thus significantly limiting the available duration of such operations. (NB This lack of data on flows for the slackers was remedied by an ENTEC Report in 2003 specifically on this topic).

During periods of very low flow in the Bedford Ouse and on into the Hundred Foot River, estuarine saline intrusion may extend upstream to Welney or beyond and affect slacker operations. In recent years electrical conductivity monitoring has been undertaken and slacker transfers are ceased when values >1500 µS/cm. This value is used by the Agency for the transfer onto the Counter Drain at the Old Bedford Sluice. It is also used by the RSPB IDB superintendent (Cliff Carson pers comm).

The slacker transfers are discharged into an extensive soak dyke system located to the west of the Cradge Bank within the Washes. These waters then serve the internal ditches of the Washes aimed at maintaining high surface and groundwater levels throughout. However, the operations also aim to minimise the extent of residual drainage entering the Old Bedford Delph which effectively acts as a sump, over the summer, for the Ouse Washes system.

The nature of the river banks and general ground conditions of the Ouse Washes means that potential for seepage losses occur which can be quite significant over a 32 km system; details are given of these.

4.1.6. Water Quality

A limited period of water quality data has been obtained from the Environment Agency for the Old Bedford Delph (which has a RE3 classification) at Welches Dam from Spring 2000 to Winter 2001. These data indicates that the only water quality issue, within the recent period, for the Ouse Washes is with respect to nutrients and this is well recognised as a major concern as detailed in:

 English Nature, 1999a (Water Quality and the Aquatic Flora of the Ouse Washes; C Newbold;  ONSS, 2000 (Ouse and Nene Strategic Studies Ecological Risk Assessment Final Report; WRc).

The major problem concerning nutrients is with respect to phosphorous loading of the water environment. The high levels of phosphorous allow:  nutrient tolerant macrophytes to invade the water environment;  seasonal algal proliferation within the water body which can give rise to blue-green algal development.

Other water quality issues which are not evident from the recent data, during which flows have been generally high, are summarised (in Figure 4.10). In outline, additional issues arise under very low flow conditions when:  BOD concentrations fail;  dissolved oxygen levels become marginal;  saline ingress is extensive (although it is noted that saline ingress on the Hundred Foot River is to be expected under low flow conditions and hence this is regarded as a marginal issue for the river. However, this may give rise to significant consequences for areas served by slacker transfers from the river).

Dissolved oxygen levels also become depleted following unseasonal late spring/early summer flooding of the Ouse Washes. As the floodwaters are drained from the Washes the internal ditches and receptor rivers can be significantly affected.

It is noted that a larger dataset exists (1981-2000) which shows higher maximum P levels and that the internal ditches have had a higher eutrophic status. Unfortunately this datasetdoes not appear to be referenced.

Further details on the water quality issues for the Ouse Washes arc given in Section 4.3.

4.2 Counter Drain

The part of the Counter Drain which is within the European designated site lies between Black Sluice and the Old Bedford Sluice. The Counter Drain normally discharges to the tidal Great Ouse at Old Bedford Sluice. The Counter Drain is designated as a cSAC for its population of spined loach.

The drainage area served by the Counter Drain is approximately 105 km2 , mainly draining part of the Middle Level fen, and includes the drainage areas of: Cranbrook Drain; Manea & Welney IDB; Sutton & Mepal IDB;Upwell & Outwell IDB;Lake Farm (Private drainage area). All but one of the above drainage areas, the exception being the Cranbrook Drain, discharge to the Counter Drain by means of pumping. The private drainage system at Lake Farm, which is not part of the Middle Level fen, serves land located between the Counter Drain and Hundred Foot River north of the Ouse Washes from Welmore Lake Sluice to Denver Sluice.

Under high flood flow conditions, when levels in the Counter Drain reach 1.15 m AOD, Welches Dam pumping station is activated in conjunction with Welney Gate, located to the north, forming a barrier across the Drain. Under these conditions pumped discharges of up to12.6 m3/s, from the Upper Counter Drain into the Old Bedford Delph (the Ouse Washes) occur. This operation aims to give a flood defence standard for the 1in 25 year flood for the drainage area served by the Upper Counter Drain.

When Welches Dam pumping station and Welney Gate are in operation the Lower Counter Drain mostly continues to be drained through Old Bedford Sluice. However, if levels exceed 1.65 m AOD an overflow into the main Middle Level drainage system can occur. Under high flow conditions, possible exceedence of the 1.65 m AOD level is likely under tide-lock conditions at Old Bedford Sluice and overflows will result.

During typical or dry summers very little positive discharge from the drainage areas served by the Counter Drain occurs. In fact, the IDB drainage areas regularly draw water from the Counter Drain, by means of several slacker transfers, to make up for seasonal deficiencies in water resources (see Section 4.2.2).Presumably permission for these transfers was reviewed for the Ouse WashesROC?

The target retention level for the Counter Drain is 0.91 m AOD. This level can usually be retained in winter but is virtually unsustainable in summer (see Section 4.2.2). This also has implications for Statutory Navigation along the Counter Drain which runs from Welches Dam to the Old Bedford Sluice. This system links to the:  navigation along the Forty Foot at Welches Dam Lock and into the Middle Level navigation system;  tidal Great Ouse. However, the link with the Forty Foot is very restricted because severe operational difficulty is experienced with maintaining adequate levels in this system.

4.2.2. Water Resources

The water resources of the Counter Drain system are very scarce and usually inadequate over the summer season. The natural flows in the catchment are negligible in summer and the only significant input is introduced artificially as a transfer from the tidal Great Ouse at Old Bedford Sluice. This operation is constrained as flows to the tidal Great Ouse become very low and saline intrusion becomes a significant issue. In recent years transfers have ceased when electrical conductivities in the tidal Great Ouse ≥500 µS/cm.

The target level for the Counter Drain of 0.91 m AOD is virtually impossible to sustain. Because the Drain is subject to significant abstractions (to meet slacker transfer operations into adjacent IDB areas) and it is also likely that significant seepage losses occur both to the Old Bedford Delph and into the Middle Level fens (see Sections 4.1.3 and 4.1.5) a more realistic operational

57 objective in summer is to maintain a level of 0.75 m AOD. However, in very low flow conditions, as occurred in 1995, even this level was not maintained. As a result the Environment Agency introduced Drought Restrictions, on spray irrigation abstractions, to reduce the demand for slacker transfers and to mitigate the situation. As a result levels of 0.75 m AOD were restored in the Counter Drain. This issue is examined further in Section 4.2.3.

An argument is presented to suggest significant upstream flow into the Counter Drain towards Welches Dam from Old Bedford Sluice. This may support the argument that significant transfer flows are input to the Counter Drain from the tidal Great Ouse at Old Bedford Sluice.

4.2.3. Water quality

Water quality data for the period 1990-2001 have been obtained from the Environment Agency for three locations on the Counter Drain which has a RE3 classification. The three locations include: Welches Dam; Welney; Old Bedford Sluice (upstream). As far as nutrient loadings are concerned these are seasonably high with oxidised nitrogen being high only in winter when indigenous IDB drainage from intensively arable land is actively discharging. Conversely, ortho- phosphate values are normally low and are only elevated in summer and this is probably as a result of water input to the Counter Drain from the tidal Great Ouse through the Old Bedford Sluice. Associated with the summer increases in ortho-phosphate moderate chlorophyll-a concentrations either develop or are introduced as part of the transfer. However it is noted that there is a lack of detailed data available so true comparisons between sites is difficult.

Salinity levels in the Counter Drain are seasonally elevated by the transfer of brackish water from the tidal Great Ouse at Old Bedford Sluice. The values attained are excessive and this is particularly so in the low flow years of the early to mid 1990's. It should also be noted that electrical conductivity values are elevated by significant sulphate values which appear to be indigenous to the Counter Drain catchment.

Recent SIMCAT modelling predicted that P removal in line with UWWTD would reduce the phosphate at Earith by 29%. Loading calculations predicted a 67% reduction in phosphate from point sources if all 20 qualifying discharges were set to UWWTD standards.

4.3 River Great Ouse

This section provides a strategic overview assessment of quantity and quality regimes and management for the River Great Ouse as is relevant for appraisal of the site which includes the Ouse Washes and Counter Drain. The overview concentrates on quantity and quality management of the Bedford Ouse extending down in to the Hundred Foot River. Additionally, some consideration is also given to the management regime of the Ely Ouse at Denver.

4.3.1 Water Resource Management for the Bedford Ouse to Offord

Water resource management for the Bedford Ouse (see Figure 4.5) focuses around operating a minimum control flow (met) regime at Offord gauging station (GS) located immediately downstream of AWSs major abstraction intake to Gratham Reservoir authorised under abstraction licence 6/33/22/*S/0061. Singly, this is by far and away the most major operational abstraction in the Bedford Ouse catchment. The mcf regime is analogous to the Hands Off Flow concept which is commonly referred to for this method of river management.

The AWS abstraction licence at Offord is governed by a mcf control of 1.579 m3/s (136.4 Mlld) requiring:  any daily abstraction rate (A) up to the daily authorised quantity (of 459.15 Mlld)to only occur providing the residual flow at Offord GS ≥: mcf + (A/3);  cessation of abstraction during weekend periods over the summer period (June to September inclusive) if the flow in the Bedford Ouse before any abstraction at Offord Intake falls below 2.63 m3/s (227.3 Ml/d). The AWS Offord licence was granted in the late 1960's upon full commissioning of the Grafham Reservoir scheme. In the early 1990's growing concern was being expressed by AWS to the NRA that abstraction authorisations granted in the Bedford Ouse upstream of Offord were potentially eroding the reliability of their interests at Offord. As a result of this the NRA imposed a general embargo on new licensed abstractions and introduced a Clause to be applied to the renewal of consumptive (mainly spray irrigation) abstraction licences which: . limited abstractions to a mcf of 2.9 m3/s (-250 Ml/d) upstream of the AWS intake to Grafham at Offord (note: in some instances more localised and equivalent mcf's are imposed); . required the applicants of larger abstractions (>20 Ml/d) to negotiate/agree proposals with AWS.

Additionally, it should be noted that it has been standard practice for over 30 years in the whole of the Bedford Ouse and Ely Ouse catchment to only grant spray irrigation abstraction licences on a temporary, I 0 year duration, basis. Therefore, as temporary licences come up for renewal which do not include the above clause it is applied as a standard condition as part of the renewal process.

Allowing for the conditions placed on the AWS abstraction licence at Offord the Offord Clause effectively equates to a second mcf at Offord GS (downstream of the AWS intake) of -1.91 m3/s (-165 Mlld). The Offord Clause is aimed at protecting AWS interest and enabling them to maintain abstraction at Offord Intake through the smallest of their pumps and satisfY the conditions of their abstraction licence.

AWS also have a major, but dormant, abstraction licence at Brownshill (ref 6/33/26/*S/0107). This is located downstream of Brownshill Staunch and upstream of Earith Sluice. This abstraction would aim to provide a secondary abstraction intake from the Bedford Ouse to Grafham Reservoir to work in conjunction with Offord Intake. It must be emphasised that the works necessary to enable this abstraction are not in place and are of a very major nature. Such works are believed to require a Parliamentary Order and may also be subject to Planning Consent. It is also thought likely that the enabling of the whole operation would be subject to Environmental Impact Assessment.

The combined factors of:  operating Grafham Reservoir (with serving abstractions subject to mcf);  effluent discharge recycling (with less than 10% consumption);  other operational leakage losses returning to the hydrological cycle. mean that the overall loss of water resources from the catchment is relatively small. Further, because of the Offord Clause and the above it is thought likely that actual low flows above Offord are probably elevated compared to what would occur naturally.

The Brownshill Intake mcf shows that if the AWS Brownshill licence were ever to become active, then in flow control terms, there would be virtually no restriction on the licensed abstraction, except for control levels of Earith, in its present form.

4.3.2 Water Management for the Bedford Ouse Downstream of Offord

Beyond the dormant abstraction licence held by AWS at Brownshill the actual operational use of (or demand for) available water resources from the Bedford Ouse downstream of Offord (including the Hundred Foot River) are virtually all for either agricultural or environmental purposes. Agricultural purposes largely include spray irrigation (which is licensable) and 'land drainage' use (which is licence exempt) incorporating sub-surface irrigation, wet fencing and riparian losses. The generic locations of the major uses are shown schematically in Figure 4.7, with further details provided in Table 4.5 outlining use and magnitude of operations etc. A very approximate and modest evaluation of unconstrained seasonal (summer) requirements for water resources from the Bedford Ouse downstream of Offord, much of which is exempt from abstraction licensing (see Table 4.5 for details), is summarised as follows:  Slacker transfers to IDB's 75 Ml/d  Slacker transfers to Ouse Washes 30 Ml/d  Hermitage Lock transfer 100 Ml/d  Old Bedford Sluice Transfer 50 Ml/d These estimated demands give a total of -250 Ml/d (-2.9 m3/s). Even if the estimate for these non licensed operations is a little conservative there are a number of private seasonal abstraction licences. The Environment Agency's (Bedford Ouse to Middle Level) transfer licence has now expired.

Therefore, even allowing for fairly modest seasonal (June to September) operational abstraction demands (and for losses) the total requirement is assumed to be at least 250 Ml/d (-2.9 m3/s) from the Bedford Ouse downstream of Offord and this can only be reliably met approximately 50% of the time in the seasonal period considered. It is also worth noting that in extreme conditions, for the crude assessment considered, a flow deficit of at least 1.5 m3/s (-130 Ml/d) may occur.

In the severe drought year of 1996 the Environment Agency enforced a widespread Drought Restriction which:  severely limited, and at times prevented, spray irrigation abstractions;  sought voluntary actions from IDB's to limit slacker transfer operations. This action did help restore more appropriate river flows and levels which otherwise became significantly depleted in the lower reaches of the Bedford Ouse into the Hundred Foot River.

4.3.3 Ely Ouse at Denver

Operations for the Ely Ouse at Denver Complex can have some significance to the site in terms of:  flood flow (or high flow) management which may influence siltation of the tidal Great Ouse and possibly the Hundred Foot River;  low flow management which may: . improve saline ingress control along the tidal Great Ouse and Hundred Foot River; . improve water resource availability (quantity and quality) for water transfer operations in to both the Ouse Washes (from the Hundred Foot River) and the Counter Drain (from the tidal Great Ouse).

The significance of flood flow (or high flow operations) at Denver Complex on siltation to the tidal Great Ouse and Hundred Foot River is outlined in Section 4.1.4. In essence siltation affects drainage from the Ouse Washes and can significantly extend the period of effective drainage. If this occurs in the April to June period it can lead to undesirable environmental consequences. In recent years, operations at Denver Complex have been modified to help reduce this problem.

The major water resource abstractions and controls for the Lower Ely Ouse system are shown schematically in Figure 4.7 and further detailed in Table 4.5. In summary, the major abstractions from this part of the river system include:  transfers from the Ely Ouse into the Cut Off Channel at Denver to service the Ely Ouse to Essex Transfer Scheme (EOETS). These abstractions are subject to mcf control at Denver.  Widespread slacker abstractions from the Ely Ouse and tributaries into surrounding IDB areas. Seasonally, these abstractions are estimated to average -7000 Ml and peak at - 10000 Ml (Entec, 2000a). The standard Denver mcf is applied to the EOETS abstraction licence although this is subject to a temporary variation at present. Additionally, the granting of new abstraction licences (including renewals) for spray irrigation licences in the lower Ely Ouse are all subject to the standard Denver mcf. In summary, the standard and temporary Denver mcf controls are given in Table 4.6.

Since this report was written the Denver mcf has been varied to allow increased abstratction to Abberton reservoir and as a consequence a requirement for the implementataion of a detailed monitoring programme has been placed on Anglian Water.

Actual monthly average gauged flows at Denver for the period 1980 to 1997 are shown hydrographically together with the standard mcf for the period 1980 to 1997 in Figure 4.9. These data reveal that the flows fell below the mcf in the summers of 1990, 1991, 1995 and 1996. In 1990 and 1991 the occurrence of mcf breaches extended into the autumn period. In1996, flows were so depleted that a period of zero flows through Denver were actually recorded. During these very low flow years problems with maintaining the mcf occurred despite the Environment Agency:  imposing widespread Drought Restrictions/Bans on spray irrigation abstraction;  undertaking significant river support operations utilising the Great Ouse and Lodes- Granta Groundwater Schemes.

The introduction of Drought Restrictions/Bans on spray irrigation abstractions did help reduce the extent of slacker transfer operations undertaken in these dry years but does not prevent them altogether as they are exempt from licensing and are also operated to service water resource demands other than for spray irrigation abstraction. In addition, under very low flow conditions the significance of seepage losses from the Ely Ouse rivers which transect fenland are believed to be very high equating to approximately 80 Ml/d (Entec, 2000a).

Conditions associated with the standard EOETS abstraction/transfer licences require the Denver mcf to be discharged via a purpose built residual flow structure from the Ely Ouse into the Relief Channel at Denver, thus bypassing approximately 18 km of the tidal Great Ouse from Denver to near Kings Lynn (see Figure 4.7). In 1997 when the present temporary variation was taken out for the EOETS abstraction/transfer licences (see Table 4.5 for details) flexibility was also

61 introduced enabling the Denver mcf to be discharged either into the Relief Channel or through Denver Sluice into the tidal Great Ouse. This operation has the benefit of making:  additional water resources available for the transfer of water from the tidal Great Ouse, through Old Bedford sluice, into the Counter Drain;  improving saline ingress control into the tidal Great Ouse (in the vicinity of Denver) and upstream into the Hundred Foot River. These improvements are relevant for transfer operations to the site including:  the Ouse Washes (see sub-sections 4.1.4 and 4.1.5);  the Counter Drain (see sub-sections 4.2.2 and 4.2.3). However, since the temporary licence variation was introduced (1997 to 2002), it has not been possible to directly assess significance under very low flow conditions as these have not occurred to date. Further, as can be seen from the drought periods recorded in the early and mid 1990's the Denver mcf is not always reliably available to enable the required quantity/quality regimes outlined above to be maintained at all times.

4.3.4 Water Quality in the Bedford Ouse

Certain problems are experienced with saline ingress upstream of Denver along the Hundred Foot River. This can sometimes affect abstraction use through slacker transfers to both the Ouse Washes and also the South Level fens. As a rough rule of thumb an equivalent electrical conductivity trigger level of approximately 1500 µS/cm is used as a guide above which such transfers are ceased (or become very controlled). Similar, and somewhat more severe, problems are also experienced with transfers from the tidal Great Ouse to the Counter Drain at Old Bedford sluice (located downstream of Denver Sluice).

Saline ingress is a problem that becomes exacerbated by low flow occurrence. In exceptional circumstances elevated chloride concentrations have been recorded as far upstream as Earith. Norrnally saline ingress will seasonably affect the Hundred Foot River up to Welney. It should be noted that salinity profiles in the Hundred Foot River are well mixed with little top to bottom gradation Since modified mcf operations have been introduced at Denver Complex, its significance to saline ingress has been difficult to assess as very low flows have not occurred from 1997 to date.

The main water quality issue for the Bedford Ouse concerns eutrophication and nutrient loading of phosphorous (see also sub-sections 4.1.6 and 4.2.3). Available data (WRc report February 2001) suggests that at least 80% of the ortho-phosphate loadings to the Bedford Ouse is derived from point (mainly STWs treated effluent) sources. For the Bedford Ouse these loadings most notably come from Cotton Valley (Milton Keynes), Bedford and several other STWs.

Ortho-phosphate concentrations in the Bedford Ouse at Earith over the period 1992 to 1997 averaged approximately 1.0 mg/1 (P) with significant seasonal and annual variations as shown hydrographically in Figure 4.11. Over this period, annual average values have varied from approximately 0.6 to 1.6 mg/1. These values together with annual ranges and a commentary are given in Table 4.7. Typically, for the range of values given above, the peak values occur in summer (co-incident with the lowest flows) and minimum values in winter (co-incident with the highest flows).

Ortho-phosphate levels longitudinally along the Bedford Ouse are found to be fairly constant downstream of Cotton Valley (Milton Keynes) STWs. However, this is not the case concerning

62 chlorophyll-a concentrations which generally increase down river. Seasonal highs of chlorophyll- a at Earith typically reach 200 mg/1. In the late spring/summer period algal proliferation can lead to problems associated with the blue-green algae as notably occurred in 1996.

For macrophytes associated with the:

 Internal ditches of the Ouse Washes;  Old Bedford Delph.

Ideal ortho-phosphate levels would not exceed 0.1 mg/1 though a more pragmatic target may be -0.2 mg/1. As can be seen from the data, values of 0.1 mg/1 are never achieved and values as low as 0.2 mg/1 are seldom achieved. The highest values tend to occur in summer when transfers from the Hundred Foot River to the Ouse Washes and the tidal Great Ouse to the Counter Drain are in operation.

During winter, when flooding of the Ouse Washes occurs, although ortho-phosphate levels will usually be lowest, additional phosphorous loading by way of sediment will be introduced. This phosphorous loading has not been quantified but is likely to be fairly significant. Because of the stilling action on flood waters within the Washes virtually all of the introduced sediment will remain in place.

Target phosphorous loading from STWs in the Bedford Ouse catchment should reduce from present phosphorous loadings by -57% (from -913 to -393 kg/day). Further SIMCAT modelling carried out by the Agency predicted that phosphate removal at qualifying discharges upstream of Earith will reduce the mean concentration of phosphate at Earith from 1.57 mg/1 to 1.11 mg/1, a reduction of 29%. In terms of the total phosphorous loadings to the river it can be anticipated that, in general, future ortho-phosphate levels should reduce to approximately half of their present levels.

Although this is a notable improvement on the present situation, future phosphorous levels will still, in general, significantly exceed the ideal (or even the pragmatic) target levels considered appropriate for the site and phosphorous loadings plus associated eutrophication problems are likely to remain as a significant problem. 5. The Relationship Between Ecology and Water Resources

5.1 Relationship of Flora and Fauna to Water Supply

5.1.1 Flora Although the flora of the Ouse Washes is not designated as part of the SAC or SPA in its own right the grassland/marshy grassland is identified as a habitat to be maintained in favourable condition for the SPA features and a number of the species that are present in the grassland are required as food for the SPA features, as are the species found in the ditches, as follows (from the Conservation Objectives - see Appendix G):

 Food availability - Presence and abundance of soft-leaved plants - No significant reduction in presence and abundance of food species in relation to reference level. For example: . Lolium perenne, Glyceria jluitans, Phleum pratense, Rorippa amphibia, A/opecurus geniculatus for Bewick's Swan; . Eleocharis palustris, Rumex, Glyceria spp for Pintail;

. Lolium, Glyceria, Agrostis, Alopecurus spp for Wigeon (See Appendix G for further species requirements);

 Food availability - Presence and abundance of aquatic plants - No significant reduction in presence and abundance of food species in relation to reference level. For example: . Scirpus, Eleoclwris, Carex, Potamogeton, Glyceria for Shoveler; . Potamogeton, Ceratophylum, Zannichellia, Myriophyllum, Chara spp. for Bewick's Swan; . Chara, Nitella, Potamogeton spp for Pochard.

Grassland The NVC communities present on the Washes, particularly in the RSPB reserve area, were identified previously and comprise mainly a combination of inundation grasslands and swamp communities. These inundation grasslands (MG8, MG9, MG!l and MG13) comprise a number of preferred plant species eaten by the wildfowl and tend to occur on permanently moist soils that are often inundated. However persistent flood periods, particularly extending into the spring, will result in the spread of swamp communities and the consequent reduction in the finer- leaved grassland communities. For example it is known that, with the spring flooding that the Washes have been experiencing, swamp communities such as the reed sweet grass S5 swamp have been increasing at the expense of the inundation grassland communities. Preliminary results from the work commissioned by English Nature in 2001 suggest that creeping bent (Agrostis stolonifera), which is one of the constant species of the inundation communities MG11 and MG13 and is also common in MG8 and MG9 has been virtually totally lost form the Washes (Prosser and Wallace 2001, survey report). Both MG11 and MG13 are still present on the site but MG13 areas have undergone a huge contraction in area for the period 1972-2001. In contrast the reed sweet grass swamp (S5) has been spreading rapidly on the Washes in recent years. This is considered likely to be due to the eutrophic status of the water supply to the site and also as a result of the increased frequency of spring flood events. Reed sweet grass tends to occur over nutrient rich substrates and where the water supply replenishes the nutrient levels (Preston and Croft, 1997). It can tolerate water up to 0.8 m deep but also a water table 0.6 m below the surface in summer (Preston and Croft, 1997). Hence it is ideally suited to washlands that have a nutrient rich water supply.

Further comment on the status of the inundation grassland communities on the Washes will be possible when the results of English Nature's work become available in the near future. Nonetheless, it is worth noting that an increase in the reed sweet grass (S5) and other swamp communities at the expense of areas of inundation grassland communities and hence a reduction in the abundance of fine-leaved grass species, is considered an adverse effect on the condition of the Washes for the SPA features. As noted above, methods for assessment of the abundance in the food species present have yet to be determined by English Nature however quantification of the change in the extent of inundation communities may provide an appropriate measure.

Ditch Communities

The ditch communities which provide some food plants for a number of the SPA species were described above. Consistently high ditch water levels are important for the macrophyte communities on the Ouse Washes and the target water levels on the Ouse Washes are 0.2-0.3 m below ground level in the spring/summer. These levels are maintained, when necessary, by slacker transfers from the Hundred Foot River and are maintained by control structures within the internal drainage system. Neither the RSPB or WWT report that low water levels in the

Hundred Foot River significantly limit their ability to maintain water levels in the ditches (although poor water quality (salinity) sometimes does).

It should be noted that the late spring flooding experienced by the Ouse Washes in recent years probably does adversely affect the macrophyte flora. Flooding up to 2 m deep is experienced and this probably retards the growth of the macrophytes in the spring by reducing the light reaching them. Persistent spring floods may lead to a reduction in vigour of the macrophyte species, which over many years may lead to the loss of some species from the site.

Eutrophication

Grazing marsh ditch communities support the greatest variety of macrophytes when the water supply is of a low nutrient status, and in particular, when the level of P is low, ideally in the range 0.1 mg/1 or less". P levels significantly higher than this (i.e. around the 1 mg/l level such as are experienced in the Hundred Foot River and hence are transferred onto the Ouse Washes) tend to result in a dominance of algae species that out-compete the macrophytes and often result in virtually mono-specific communities of duckweed and/or blanket-weed that block out light killing submerged macrophytes. There is reference to research at Cambridge University by Cathcart 2001 and that English Nature has commissioned a contract to further develop this work.

Salinity

Increased levels of salinity, indicated by higher conductivities, can also adversely affect the macrophyte flora. In general the most diverse macrophyte communities occur where the conductivity is <1000 µS/cm and higher salinities tend to result in less diverse communities. Studies in Broadland, that have related community type to conductivity level, indicate that communities and species such as those found in the Ouse Washes (NVC types A2 and AS predominantly) mainly occur in situations where conductivities are <1000 µS/cm in the summer, although examples are also found at higher levels.

Therefore, whilst it is desirable to have low conductivities (ideally <1000 µS/cm) for the macrophyte flora it is difficult to define an absolute upper limit although levels above 1500 to 2000 µS/cm are considered likely to result in greater adverse effects on the macrophyte flora. Electrical conductivities of this order and higher were widespread throughout the Washes in the 'dry years' and low flow summers experienced in the early 1990s.

5.1.2 Fauna (Ouse Washes cSAC)

The internationally important feature for which the site is included within the Ouse Washes cSAC is the spined loach. Some guidance on the water levels (and quality) required by the SAC feature is provided in the draft favourable condition tables for the site (see Appendix G). The guidance, summarised below, applies to the Counter Drain and Old Bedford Delph only, as these are the only parts of the Ouse Washes included in the cSAC.

 Flow - River flow has a major bearing on key environmental factors, such as dissolved oxygen levels (in the water column and substrate), phytoplankton standing crop (by dictating residence times) and water temperature. Maintenance of adequate flows through the summer is therefore important. In the absence of a complete

understanding of flow requirements at this site, existing summer flows should be maintained as a minimum requirement.

 Water Quality:

Soluble reactive phosphorus (ortho-phosphate) - 0.1 mg/1 annual mean".

There follows a section setting out the known ecology of the species (p46-47). It concludes that the conditions most likely to meet the reproductive and feeding requirements of spined loach and thus ensure the long-term stability of age-structured spined loach populations, is a diverse food web containing submerged macrophytes. Thus, the continued high loading of nutrients and fine sediments is likely to be detrimental in the long term. It may be for this reason that spined loach appears to be absent in the wash ditches themselves.

Whilst spined loach is poorly adapted to high flows m a rivenne situation, it may utilise submerged and littoral emergent macrophytes as cover. The flows encountered in the Ouse Washes are thought unlikely to have a detrimental effect, particularly where cover is present, whilst flushing flows which decrease residence times, and thus the potential for domination of planktonic algae, are likely to be beneficial. However, extensive flooding is likely to re• distribute spined loach, with loss of fish into the wash ditches which may be unable to support them in the longer term.

5.1.3 Fauna (Ouse Washes SPA)

The internationally-important features for which the site has been designated as an SPA are:

 Annex 1 Bird Species (Bewick's swan, whooper swan, hen harrier, spotted crake, ruff);

 Migratory Species of European Significance (Pintail, shoveler, gadwall, pochard, wigeon, black-tailed godwit);

 Species that Contribute to the Wintering Assemblage (teal, tufted duck, mallard, cormorant, lapwing, coot).

Some guidance on the water levels (and quality) required by the SPA features is provided in the draft favourable condition tables for the site (see Appendix G). The headline guidance is summarised below for all species together:  Hydrology/flow - No significant reduction in soggy or flooded areas in relation to reference level;  Hydrology/flow - Range of water levels providing a succession of surface water areas (feeding) in relation to reference level;  Hydrology/flow - Dropping water levels providing a succession of surface water areas for feeding, in relation to reference level;  Water depth- should not deviate significantly in relation to reference level;  Water area- No significant reduction in water areas from a reference level;  Food availability - No significant reduction in presence and abundance of food species in relation to reference level. Examples are given;

SPA Features Water Supply Requirements

Wintering Species

The majority of the SPA features, for which the site has been identified as an SPA are present in the winter months and, as described above, the species generally require soggy or flooded conditions. The Washes flood bank to bank and/or partially flood every year, and in recent years the periods when flooding is absent has been decreasing (see Table 4.3 shows the pattern of flooding).

Given the regularity of the flooding conditions should be ideal for wintering species. However it is worth noting that the conditions required by one species are often not desirable for another species. This is usually resolved by species that require shallow flooding (e.g. ruff, gadwall, shoveler, wigeon) tending to use areas around the edges of any more extensive floods whilst those species requiring deep floods (e.g. pochard) tending towards the middle of flooded areas. Excessively deep floods however will favour diving ducks and reduce the value of the habitat for dabbling ducks and in recent years flooding has become very deep (between 1.5 and 3m in parts), which means that conditions for the dabbling species are not appropriate and hence they are often forced to find food on shallower flooded land outside the Washes. Minimal flooding will have the opposite effect, favouring dabbling ducks.

Breeding species

The ideal requirements, identified in the Favourable Condition Tables for the site, are presented in the report, p47-48. Breeding waders require a high soil water table resulting in soggy or flooded conditions which enable them to probe for soil invertebrates.

Water levels are maintained in the ditches on site at about 0.2 m below ground level during the spring/summer period once the winter flooding has subsided. Spoor and Chapman ( 1992) determined that the ideal soil water levels for breeding waders on the Nene Washes were above 0.25-0.2m below ground level and this was best achieved by maintenance of ditch water levels close (within 15 cm) to the field surface. Maintenance of ditch water levels at 0.2 m below ground level may also provide similarly suitable conditions for the breeding Waders on the Ouse Washes, although perhaps 0.15 m below ground level may be better. However, this needs to be validated for the Ouse Washes. It is worth noting that Spoor and Chapman (1992) found areas which had soil water tables lower than 0.3 m below ground level supported fewer pairs of breeding waders.

Provision of suitable ground conditions for breeding waders has been relatively easy in recent years because of the flooding as the Washes stay water-logged well into the summer. However the incidence of late spring flooding adversely affects the breeding success of the waders because it washes out many if not all the nests. Whilst many of the birds will attempt to nest for a second and even a third time if the nests are lost, spring flooding is not desirable for the breeding waders of the site and the condition of the Washes for breeding waders will not become favourable until the spring flooding issue is resolved. Another consideration is that heavy waterlogged conditions over a prolonged period (i.e. continued flood conditions in spring/summer) will have a detrimental effect on the invertebrate population, thus over time, reducing the food source of the breeding waders.

5.1.4 Summary of Evidence of Ecological Change Flora - Grassland

It is known that the flora of the Washes (and the ditches) has been changing (deteriorating) over at least the last 20 years and that these changes are thought to be caused by the regular and persistent spring flooding and high nutrient loadings.

With reference to vegetation data collected for the Ouse Washes between 1972 and 2001, major changes in species (and hence community) composition are a feature of the washes. The vegetation is unstable and tending to be increasingly composed of more flood-tolerant species capable of colonising bare wet areas. Such species form the plant communities OV28, 29, 30 and 32 which have become prominent on the site since the early 1990's. The Bidention communities (OV30 and 32) have shown the greatest expansion in area over the last 10 years and have been positively linked with areas of extended floodwater retention, although it may also be linked to nutrient loading of substrates. In contrast, species with more summer drought resistance and those of closed inundation swards are in general decline. During the period 1972-2001, there has been a marked increase in the area ofS5 (Glyceria maxima) swamp, and major contractions in the areas of MG9 (Holcus lanatus-Deschampsia caespitosa) grassland, MG 13 (Agrostis stolonifera-Alopecurus genicula/us) grassland and S28 (Phalaris a11mdinacea) swamp. The 2001 survey of the washes also failed to find significant areas of MG8 (Cynosurus cristatus-Caltha palustris) grassland and S6 (Carex riparia) swamp.

Flora - Ditches

Following the 1992 survey of the ditch flora of the Ouse Washes Cadbury, Halshaw and Tidswell (1993) compared their results with those from the 1978 survey. They reported, at that time, that at least 10 species may have become extinct on the site. Of these 10, seven were aquatics and included: Ribbon-leaved water-plantain; Canadian pond weed (Elodea canadensis) - transition to Nuttall's pond weed (Elodea nuttallii); Frogbit (Hydrocharis morsus-ranae); Red pondweed (Potamogeton a/pinus); Flat-stalked pondweed (P friesii); Common water-crowfoot (Ranunculus aquatilis);Greater bladderwort (Utricularia vulgaris).

Of the 31 species recorded as associated with internal ditches during the 2001 survey, 18 have increased and 13 have decreased in frequency. Twelve of the 18 species which have increased have an Ellenberg nitrogen index value 7+ implying that they are increasing in response to increasing eutrophication of the site. Six of the 13 species shown to be decreasing also have an Ellenberg nitrogen index of 7+. For these species, which includes water mint and common spike rush, their distribution within the site is thought to be related to other factors such as water quality.

Care must be taken in interpreting the relationship between ditch flora and water quality. Many of the species which show a recovery in the 2001 survey (such as hairlike pondweed (Potamogeton trichoides) and horned pondweed (Zanichellia palustris)) have responded to positive ditch management such as widening and re-profiling. Cathcart (Interim Report 2001) has observed that there is a seasonal succession of plant communities which respond to eutrophic conditions (particularly total Phosphorus levels) and are related to low oxygen levels. It is likely that this seasonal succession of communities is detrimental to a number of key

68 macrophytes formerly more widespread within the site. Cathcart also observes that the BAP priority species, great tassel stonewort (Tolypel/a prolifera), is restricted to a single drain within the washes where water quality is within the biological threshold for this species (0.058 - 0.09 mg/1 total phosphorus). EN has set up a contract with Cambridge University / Rob Cathcart to further develop this work incorporating additional plant and water quality data sets.

Of the 16 previously recorded nationally scarce species the following 5 species were not recorded by any of: Perrow & Tomlinson; Prosser, Wallace and Cadbury; or Prosser and Wallace in 2001: Marsh sow -thistle (population reported as sick in 1997); Whorled water milfoil; Narrow leaved water dropwort; Tasteless water-pepper; Fen ragwort.

Newbold's (1999) paper (see Appendix M) on the links between the aquatic flora of the Ouse Washes and water quality describes the effects of an increase in nutrients in the water column on aquatic flora and relates this to changes in the flora on the Ouse Washes. Newbold indicates that the changes in the flora of the Washes have followed predictable eutrophication processes and that in fact the flora may have been changing prior to the 1978 survey which Cadbury et a/ compared their 1992 results against. Newbold ( 1999) suggests that the system was moving from Level 1 (21) to Level 2 (22) in 1978 and was approaching Level 3 (23) when Cadbury et al undertook the work mentioned above.

Newbold (1999) also indicates that the Old Bedford Delph has undergone similar changes in flora to the ditches although it was not originally as diverse as that in the ditches on the Washes.

Fauna - Spined Loach

Perrow & Jowitt (1997) reported reasonable population densities of spined loach throughout the Counter Drain. The population density was significantly lower in the Old Bedford Delph and generally lower than that thought to represent a good and viable population. Although the data from the survey in 2001 are still undergoing analysis, it is clear there have been changes in the density of loach at some previously monitored sites, taking the differences in timing of the surveys into account. However, the trend is not consistent and some sites (e.g. Earith and between Welches Dam and Welney) showed improvement and others showed decline (e.g. Mepal). Whether loach increased or decreased was consistent between rivers despite their ecological differences and the fact that they are unconnected. A better understanding of the loach and its habitat will only be achieved by undertaking more survey work.

Fauna – Birds

In general peak counts in wintering species have been increasing. However it is difficult to identify trends in the numbers of birds using the site from peak count data because a high count only needs to be made on one day over a whole season. A better measure of the bird use of the site would be to convert the numbers into bird months. In the absence of such data it is only possible to make one or two general comments on the use of the site by wintering species:

 Wigeon numbers have declined in recent years because the flood water has generally been too deep to provide them with suitable feeding areas;

 Gadwall and shoveler numbers have been reduced recently because the flood water has generally been too deep to provide them with suitable habitat;  Lapwing and black-tailed godwit numbers have been reduced in the last couple of years for a similar reason;  Conversely numbers of pochard and tufted duck have been generally high in recent years because the deep water favours these species.

Breeding bird numbers on the Earith to Welney Wash Road section of the site were relatively stable between 1996 and 1999 however the summer flooding in 2000 resulted in a significant reduction in the success of breeding birds on the Washes. It is also notable that average breeding numbers for the period 1996-2000 are all reduced compared to the 1991-1995 period when bank to bank late spring flooding was less prevalent, although partial flooding did still occur.

Most notable amongst the breeding species are the black-tailed godwits. During the 1996-1999 period numbers of territorial pairs remained relatively stable although this declined markedly in2000 when the site remained flooded into June. A study of black-tailed godwits on the Ouse Washes by Ratcliffe and Schmitt (2001) has found that the numbers of breeding pairs and productivity of the species has fluctuated enormously over the last 30 years due to flooding and that productivity was below the level required to maintain a stable population in 17 of the last 30 years. In years that were not subject to flooding, predation depressed productivity to levels that precluded population increase. Ratcliffe and Schmitt concluded that if the trend in spring flooding continues black-tailed godwit will eventually be lost as a breeding species on the Washes.

5.2 Summary of Main Water Resource Issues for the Ouse Washes Site

There is major concern for the Ouse Washes regarding the increased incidence of late spring/early summer flooding post 1977. The cause of this phenomenon is not fully understood but may be the result of a number of factors including climatic changes resulting in increased storm-rainfall, increased urbanisation, increased siltation or management changes. There is little doubt that flooding problems in the Ouse Washes have been exacerbated by increased siltation in the tidal Great Ouse and Hundred Foot River. The most significant step recently undertaken to mitigate this concerns the major uprating of Welmore Lake Sluice which provides the outlet from the Ouse Washes into the Hundred Foot River. Other actions taken to improve the situation includes some dredging and modified high-flow operations at Denver Sluice. Additional schemes are also under consideration aimed at further reducing the problem.

There are two distinct hydrological components to the European designated (Ouse Washes) site including:

 The Ouse Washes (Old Bedford Delph and internal ditches) which is typically flooded in winter through a major intake from the Bedford Ouse at Earith into the Old Bedford Delph. In summer, water resource replenishment to this part of the site is maintained through slacker transfers from the Hundred Foot River

 The Counter Drain which has very little natural water resource in summer and this is seasonally supplemented by transfers from the tidal Great Ouse through Old Bedford Sluice.

A brief assessment of water resources (quantity and quality) for the Bedford Ouse reveals that:  Target mcfs are very reliably sustained at Offord GS downstream of the AWS intake to Grafham Reservoir;  The mcf at Offord is not sufficient to reliably meet seasonal (June to September) demands for water resources in the lower Bedford Ouse extending into the Hundred Foot River. Much of this demand, which is met by various (slacker and other) transfers is mostly exempt from abstraction licensing;  In periods of very low flow the situation can lead to significant saline ingress which will affect both transfer operations to the site and other transfer demands;  There is a very high phosphorous loading to the Bedford Ouse largely introduced via STW discharges, which makes the river eutrophic and liable to seasonal algal proliferation. This situation is detrimental to the site flora/fauna and causes concern. Plans under the UWWTD will significantly reduce future phosphorous loadings but this will not be sufficient to remove present concerns or significantly reduce associated impacts to the site.

Regard is also given to a dormant abstraction licence held by AWS, which if activated, would allow very significant secondary abstraction to service Grafham Reservoir from the Bedford Ouse at Brownshill. If this abstraction were allowed, as currently conditioned, then theoretically it could substantially deplete the residual water resources in the lower Bedford Ouse. This could have very serious consequences in the June to September season for the site and other abstraction users.

In the Counter Drain there is a lack of natural (indigenous) water resources in summer and there are some local water quality problems. The seasonal transfer of water from the tidal Great Ouse at Old Bedford Sluice is primarily aimed at sustaining the water level at 0.75 m AOD to support the conservation value, with secondary aims of servicing slacker transfer to adjacent IDBs mainly to provide water resources for sub-soil and spray irrigation abstractions (see Figure 4.3 for details on target levels) as well as navigation within the Counter Drain.

This transfer has two notable (and undesirable) effects on the site including the elevation of both salinity and phosphorous levels. It should be noted that despite some local water quality problems in the Counter Drain, data provided by the Agency (1990-2001) suggest that indigenous phosphorous levels are quite low and this should be borne in mind.

There is the potential for the River Terrace Gravel aquifer to help sustain wetland conditions, during late summer months, in the southern Washes (between Earith and Mepal).

5.3 Potential Vulnerability to Changes in Water Levels and Flow

This section is a useful summary but no new information is presented.

6 Review of the Impact of Environment Agency Water Resources Management and Abstraction Licences

6.1 Strategic Management

The water resources available to the Ouse Washes site are essentially determined by catchment management for the:

 Bedford Ouse (including the Hundred Foot River);  Counter Drain;  ElyOuse.

In summer, the two main hydrological components to the site:

 the Ouse Washes (incorporating internal ditches and the Old Bedford Delph);  the Counter Drain (in average to dry years); are sustained by water resources substantially derived from the Bedford Ouse supplied by respective transfers from:

 the Hundred Foot River through a series of slackers, and,  the tidal Great Ouse through Old Bedford Sluice.

The freshwater that can be discharged to the above systems is nutrient rich and this introduces eutrophication problems to the site (see Section 7.2). Additionally, the points of transfer are tidally influenced and, under low flow conditions, are prone to extensive (saline) intrusion. In general, such transfers are ceased (or become highly controlled) when electrical conductivities (a surrogate measure for salinity concentration)>1500 µS/cm.

At present, there is no minimum flow target set for either the Hundred Foot River or the tidal Great Ouse (downstream of Denver Sluice) in order to check the extent of estuarine (saline) intrusion or to meet the environmental needs of the tidal Great Ouse.

The major non-licensed transfer operations in the Bedford Ouse/Hundred Foot River/Tidal Great Ouse (see p 60) place total demands on summer water resources which are considered likely to regularly and sometimes significantly exceed residual flows permitted at Offord. At present, the only controls possible on these operations which are sometimes implemented to help protect the water environment involve either imposing Drought Bans/Restrictions on spray irrigation abstractions or on seeking voluntary reductions on slacker transfer operations.

There is a detailed consideration under 6.2 Surface Water Abstractions, 6.2.2 Non Licensed Operations, of how best to deal with the summer low flow problems which encourage the use of saline water to maintain river levels but the key recommendation is that “It is considered essential that a Low Flow Operating Policy for the Lower Bedford Ouse/Hundred Foot River is developed, in order to more effectively manage the flow/transfer needs of the river. Further details on possible recommendations are given in Section 9”.

Counter Drain

As already indicated, the Counter Drain is supplemented in summer by transfers from the tidalGreat Ouse. A significant proportion of this transfer is required to:

 Replenish water resources to enable slacker transfers into local Middle Level fen IDBs to service "land drainage" requirements and spray irrigation demands;  Make good for water resources losses arising from other direct abstractions from the Cranbrook Drain/Counter Drain for spray inigation use.

Associated with these transfers, partly driven by spray irrigation abstraction demands is a need to import high nutrient and sometimes brackish/moderately saline water into the Counter Drain. Therefore, all the licensed (and non-licensed) demands which drive these transfer operations are likely to be having an effect on water quality in the Counter Drain and these potential effects need to be quantified. Outline details on possible recommendations to improve this situation are provided in Section 9.

6.4 Preliminary Assessment of the Potential Risks Resulting from Environment Agency Water Resources Consents

Attention should be drawn to Table 6.4 which summarises the “Potential Risk due to EA Licensed Abstractions and Strategic Water resources Management”.

7. Review of Other factors Potentially Affecting the Ouse Washes

7.2 Other Environment Agency Consents

7.2.1 Consented Water Discharges

The major STWs discharges affecting the Bedford Ouse give rise to some relatively minor RE quality problems but significant nutrient (phosphorus-loadings) issues for the river and the site. The results from treatment works improvements to reduce phosphorus loadings from qualifying STWs under the UWWTD are yet to come to full fruition and be observed but ortho- phosphate levels, in the lower Bedford Ouse, are expected to reduce from an average of -1.0 to -Q.S mg/1 (P). This will give some improvement to eutrophication problems but this is not considered to be significant enough to reverse undesirable trends at the site associated with the invasion of poorer wetland/aquatic flora. This is considered to have been a significant effect on the site and is anticipated to remain so despite UWWTD implementation.

Locally, the Hundred Foot River and Counter Drain are influenced by relatively small STWs discharges including:

 Witchford and Witcham STWs to the Hundred Foot River;  Somersham and Manea STWs to the Counter Drain.

None of these STWs are qualifying discharges under the UWWTD and therefore no reduction innutrient loadings to the receiving rivers from these treatment works can be anticipated. However, the Environment Agency report that improvements were introduced to Somersham STW (circa 2000) under AMP2 and this has brought about local water quality improvements to the Counter Drain and very recent compliance with it's RE3 target.

7.2.4 Flood Defence

Concern about the impact of bank to bank spring flooding on a regular basis on the breeding waders has been set out above as has concern about the excessive depth of the floods in winter because deep water is unsuitable for many species that should use the site.

Any exacerbation of prolonged flooding to the site as a result of siltation in the tidal Great Ouse extending into the Hundred Foot River is predicted to have been mitigated by the renewal/uprating of Welmore lake Sluice. Despite this, given a continuation of recent Spring storm events then further undesirable flooding of the Washes is anticipated. Further schemes are under review by the Environment Agency and other interested parties to consider further mitigation measures which may reduce this problem. The risk from this effect is considered to be high and is likely to remain so in the absence of further and significant mitigation or a change to Spring weather.

7.3 Other Competent Authorities

7.3.1 Internal Drainage Boards

The Hundred Foot Washes !DB controls water levels in the dykes in the Washes. Levels are controlled via a series of slackers from the Hundred Foot River. When this report was written The Superintendents of the IDB were staff of the RSPB and WWT ; it is not known if this is still the situation. In their opinion at the time the report was written water levels were managed to optimise the nature conservation potential of the site. The risk to the site from IDB management should therefore be minimal, however telephone conversations with the operations staff for the WWT indicated no particular awareness of saline ingress along the Hundred Foot River being a potential issue for slacker transfer operations to the northern Washes. Release of water onto site with a high salinity will adversely affect the flora and fauna of the ditches and hence the risk from IDB management is considered to be medium.

7.5 Preliminary Assessment of the Potential Risk Due to Factors Other Than Licensed Abstractions

Table 7.1 is significant as it lists “Potential Risks due to Other factors”.

8.0 Summary

8.2 Potential Risks

8.2.2 Other Environment Agency Consents

Consented Water Discharges

The main issue with consented discharges is the nutrient (phosphorus) loading to the Bedford Ouse from STWs. The WRc report commissioned by AWS suggest that some SO% of phosphate loading is sourced from these treatment works, though there is some controversy as to whether these figure are correct. High concentrations give rise to a eutrophic river which extends down into the Hundred Foot River and on to the tidal Great Ouse. These eutrophic waters affect the Washes component to the site 'continuously' and the Counter Drain seasonally. Full

74 implementation of the UWWTD is imminent and major reductions of phosphorus loadings to the river are anticipated. However, these reductions are not expected to allow favourable water quality conditions to return to the Washes although the situation for the Counter Drain may prove more marginal and could be significant. The present risk to the European features on site is assessed as high for the Washes and medium for the Counter Drain.

Local small scale STWs discharges within the Counter Drain catchment are thought to have contributed to past RE3 class failmes concerning a variety of sanitary indicators. This situation may also be influenced by landfills present in the catchment although the Agency discount this possibility. The present risk to the European features on site is assessed as low for the both the Washes and the Counter Drain.

9. Recommendations

9.1.1 Water Resources Management

It is considered that the site would benefit from improved strategic water resources management for the Bedford Ouse catchment extending down into the Hundred Foot River and the tidal Great Ouse. However before such possible action can be properly implemented improved outline knowledge of the catchment system is considered desirable as outlined below:

 The summer water resource requirements for the Lower Bedford Ouse (below Offord) extending down into the Hundred Foot River and the tidal Great Ouse should be investigated and quantified;  Within the Middle Level fen catchment draining to the Counter Drain the areas served seasonally by slacker transfers should be investigated to see if any parts can be serviced by possible alternative transfers made via Salters Lode and the Middle Level drainage system. This would reduce the need to supplement the Counter Drain, via Old Bedford Sluice, from the Tidal Great Ouse.  The significance of reduced phosphorus loading to the Bedford Ouse to the site should be reviewed subsequent to the full (or substantial) implementation of the UWWTD.

The above investigations can then be used to inform decision making for improved strategic water resources management and planning, possibly integrated into the CAMS process, to include various points, particularly:

 If, as suspected, implementation of the UWWTD was not to bring about the necessary reduction to phosphorus loading in the Bedford Ouse so as to significantly benefit the site then feasibility assessment of the following possible measures may be worthy of consideration: . Expansion of the programme by AWS to further reduce phosphorus loadings from STWs; . Possible circulation of summer flows in the Bedford Ouse through major reed beds may alleviate the high nutrient loading in the summer months. Such a scheme may be possible in conjunction with the proposed reed bed creation scheme at

Needingworth/Over and other possible sites which may become available through widespread mineral extractions in the Bedford Ouse floodplain; . Possible incorporation of local scale reed beds within the main soak dyke receptor of the Ouse Washes before subsequent distribution of water into the internal ditches of the Washes.

9.1.2 Flood Management of the Washes

The Environment Agency and interested parties continue to investigate and consider a range of possible measures aimed at reducing the flooding problem of excessive and unseasonal flooding to the Washes. As an extension to this initiative it may be worthwhile considering possible schemes which may also improve water resource and quality issues. Tentative ideas, which could possibly be allied to options already under consideration include:

 Potential re-profiling of the Hundred Foot River could incorporate a deeper main channel (for improved flood conveyance and maintenance of navigation) plus berms planted with reeds which may help improve river water quality.  A new tidal exclusion (or control) barrier on either the Hundred Foot River or the tidal Great Ouse which may also help with the management of saline ingress.

As per the Overview of Various Measures to alleviate Summer Flooding ·Posford Duvivier Report, October 2000.

9.1.3 Ecology and Water Quality Target Investigations

The Environment Agency currently monitors water quality and flow conditions in the river system and so can provide information on the conditions that spined loach currently experiences. However, there is a degree of uncertainty over the optimum conditions required for spined loach. There are two on-going research projects (one funded by the Agency with a contribution by English Nature and one by English Nature) which aim to further refine the habitat requirements in relation to appropriate habitat management prescriptions. However, neither is considered likely to directly explain the current large variation in spined loach density within the cSAC, although they should provide further information on the operational impacts linked to habitat, and other preferences of the species. In the meantime, the basis of monitoring spined loach in the cSAC has been provided by the recent English Nature contract and this should be continued at a frequency of between 1-3 years. Population trends can then be interpreted in the light of changes in water levels, management practice and nutrient concentrations experienced by the cSAC.

It is noted that a study, promoted by English Nature, of the existing condition of the site is currently nearing completion. This should provide a good indication of the current status of the habitats on site.

Flood water depths and water quality also need to be monitored to assess favourable condition. These activities should be promoted by the Agency's flood defence and water quality functions respectively.

RJK Summary, February 2015.

8. ENVIRONMENT AGENCY, OUSE AND NENE STRATEGIC STUDIES. OUSE WASHES: WATER AND NUTRIENT LEVEL ANALYSIS. DECEMBER 2003 (c), ENTEC UK LTD. 1.2 Background to the Ouse Washes

The Washes are currently felt to be out of condition, with a predominance of swamp vegetation communities rather than grassland, and are not currently ideal to provide the important conservation role that they have adopted. Specifically, the issues that are felt to need addressing are:

 Occurrence of spring flooding, which affects ground nesting bird species;  Average duration and depth of flooding during different periods of the year;  Excessive nutrients during summer periods causing eutrophication in the ditches which dissect the Washes;  Excessive nutrients during the first flood of winter affecting field communities.

This report attempts to explain the current condition of the Washes and to offer suggestions for the reassertion of more favourable vegetation communities.

1.3 Study Objectives

The objectives of this study are:

 To investigate the water and nutrient budgets of the Ouse Washes under a number of different artificial influence and naturalised scenarios;  To define the current condition of the Ouse Washes, in terms of water table depths and nutrient levels, against prescribed targets;  To investigate the impact on water table depths and nutrient levels, of the different artificial influence and naturalisation scenarios;  To investigate the source of nutrients affecting the Ouse Washes and  To recommend alterations to the management routine of the Washes in order to re•establish target vegetation communities.

The last of these objectives will be taken into a later stage of the overall study, probably occurring after the completion of the Appropriate Assessment, and will be based upon solving any issues or problems that this assessment identifies.

1.4 Approach to Study

The approach to the study is wholly analytical, utilising a water quality and flow model of the Great Ouse catchment and Washes system, which derives water and nutrient level data across the Washes. Five scenarios of varying artificial abstractions and discharges, diffuse pollution (related to landuse) and sluice gate configuration were undertaken. The five scenarios are:

1. Current abstraction and discharge values (after a recent flow naturalisation exercise on the catchment) and an estimate of current landuse and diffuse pollution loadings;

2. Current abstraction and discharge values, with an altered representation of Welmore Lake Sluice (outflow control from the washes) after its reconfiguration in 1999); 3. Maximum licensed abstraction and discharge values and an estimate of current landuse and diffuse pollution loadings; 4. Naturalised flows (with all point source abstraction and discharge removed), with an estimate of current landuse and diffuse pollution loadings; 5. Naturalised flows (with all point source abstraction and discharge removed), with an estimate of landuse and diffuse pollution loadings from the 1960s;

The results from this model are then compared to prescribed targets for water table depths and nutrient concentrations to determine the condition of the Washes. The Washes are delineated into 34 individual field units (see Section 3), two per slacker (see Figure 1.1), with an overall ground level elevation associated with each field. Each field is fed by a proportion of the flow from a slacker from the Hundred Foot River and by flood waters entering the Washes through Earith Sluice (should this occur). For the various analyses detailed in later sections, each field is assigned a target NVC community that English Nature would like to see re-established on that area of the site, against which it is tested and towards the re-establishment of which the management recommendations are aimed. The target vegetation communities are defined from an analysis of the vegetation survey data from 1972, held by English Nature. The targets are based upon the assumption that vegetation communities during the 1960s were approximately similar to those that need to be re• established and that there is a lag time between water level regime changes and vegetation community changes.

Regarding the various targets used by ENTEC to guide this work:

 The prescribed water table depth target information comes from a series of ecohydrological prescriptions produced as part of the 'Selected Sites' projects undertaken by the Environment Agency (see Section 2). These prescriptions are currently in draft format only, and the results produced should be treated within this context.  The prescribed acceptable total phosphorus thresholds are derived from a set of acceptable ortho-phosphate threshold guidelines produced by the Agency for sites affected under the Urban Wastewater Treatment Directive (UWWTD)2 The acceptable threshold defined in this document is 0.1 mg/1 ortho-phosphate (ortho• P). This value has been amended slightly for the purposes of this study (due to model output constraints) to 0.2 mg/1 total phosphorus, excluding sediment deposited P, (Total-P)3  The 0.1 mg/1 ortho-phosphate target is also found in the favourable condition table for the cSAC in relation to spined loach, which is directly relevant to the cSAC. The FCT for spined loach refers to an annual average target, and therefore, the targets for the various areas of the Washes should also be considered as annual average values. This factor is vital deciding whether ditches and other watercourses are in or out of regime.  The prescribed acceptable total nitrogen and TIN thresholds are taken from a previous study undertaken by WRc, on behalf of Anglian Water3. The thresholds used for the purposes of this study are 1.6 mg/1 total nitrogen and 0.8 mg/1 TIN.

The approach to this work is set out to show the level of detail that was applied in the model, with parameters being set for 34 individual field units, two per inflow slacker. Amongst other things it also gives a brief description of how the Washes function.

SECTION 2. ECOHYDROLOGICAL PRESCRIPTIONS

The ecohydrological prescriptions used in this study have been derived during a national study undertaken for the Environment Agency by Entec UK Ltd4. A focus of the guidelines is on plant communities (wet grassland and certain swamp communities in particular) which support breeding or wintering birds of European importance'. Where birds are the feature of importance, conservation objectives relate to the habitats that support those features. Therefore in this case guidelines have been drawn together primarily for those communities upon which the birds are themselves dependent (e.g. MG9, MG13, S4 and S5).

2.2 NVC Community: Agrostis stolonifera-Alopecurus geniculatus grassland (MG13). Note - this detail is presented here as an example of the information that is included in the report for all the main plant communities of ecological significance present.

The community is widely distributed throughout lowland England with the largest expanses being found in washland alongside the large rivers of Eastern England (e.g. Ouse, Nene). It is found on both peat and mineral soils and often occurs as narrow strips along old drainage features within other grassland types. Its total UK extent has been estimated at 2000 ha.

The preferred water table depth ranges for this community on the three soil types found are illustrated.

2.2.3 Nutrient Level Guidelines

There is available information relating to phosphorus (P) availability on MG13 sites. The community can tolerate Olsen available P values between 6 and 35 mg kg-1. Nitrogen availability is less well understood, but is likely to be limiting in grasslands so well supplied with phosphorus, especially as legumes are usually absent from the sward.

Many stands of MG 13 receive silt from river water spilling out of channel. Indeed silt is preferentially dropped in the floodplain depressions where this community typically occurs. No attempt has been made to construct a nutrient budget for this grassland type, therefore it is difficult to estimate quantitative tolerances in terms of nutrient delivery rates, but it is likely that the community can tolerate higher rates of nutrient input than more species-rich grasslands.

A Figure is provided which illustrates the perceived reaction of MG13 stands to various environmental pressures and changes, whilst a further figure shows those specific NVC community shifts that may occur in response to change in the water or nutrient regimes. Where flooding is prolonged then the community will tend toward swamp communities (e.g. S5). Where soil drying is prolonged, then one of several alternative grasslands may establish (e.g. MG9 or MG6).

There is an in-depth analysis of the ecological conditions and requirements of the main NVC communities present on the washes on which the wintering birds are dependent (e.g. MG9, MG13, S4 and S5). The preferred water table depth ranges for the communities are shown on relevant soil types. These water-table depth ranges are used in subsequent sections to define the condition and regime of different areas of the Washes.

SECTION 3. OUSE WASHES MODEL.

The model used to simulate water and nutrient levels across the Washes was developed by WRc, on behalf of Anglian Water as part of the Ouse and Nene strategic studies, to investigate the impact of the effects of AWS operations (abstractions and discharges) on the Washes. Following discussions with WRc, the model was amended for this study and a set of new model scenarios were generated. The model components and modifications are described and full details are shown in Appendix B.

Model Background

A major element of the Ouse and Nene Strategic Studies (ONSS), commissioned by Anglian Water in September 1999, was the development of a strategic modelling framework that can be used to aid water resource decision making within the Great Ouse and Nene catchments. The important characteristics of this model framework were defined as:

 Ability to simulate realistically the water quality and water level variations at key priority wildlife sites in the catchments for long (multi-year) periods;  Ability to represent a wide range of water management scenarios, in particular, different water abstraction regimes and wastewater treatment options;  A flexible post-processing module which provides statistical analysis and comparison of results in a way which is relevant for ecological risk assessment.

The final modelling framework – referred to here as the ONSS model - comprises separate models for the Ouse and Nene catchments. The ONSS Ouse model incorporates the QUESTS 1D model of the Ouse estuary (built for the Environment Agency in 1995) as an integrated component together with a water balance model of the Ouse Washes.

3.4.3. Ouse Washes Model – Counter Drain Level Calibration Error! Reference source not found. shows observed and modelled water levels in the Counter rain 1993 to 2002. The observed data are the daily mean levels from the Environment Agency, measured at Welches Dam. The model predicts water levels fairly well picking up most of the periods of lower water levels – in particular 1994, 1995, 1996.

3.4.4. Ouse Washes Model –Ditch and Field Water Level Calibration The Ouse ditch/field modules were calibrated using the dipwell and ditch water level monitoring data from the 2002/2003 monitoring work and using monitoring flow through the slackers from the summer of 2003.

3.4.5. Ouse Catchment Model – Water Quality Calibration

The predictions of water quality at Offord were compared with observed data and the results are shown in Error! Reference source not found. to Error! Reference source not found.. The sults for TP (Total Phosphate) are similar to those reported previously during Phase 1 of the study (WRc 2001). However, the results for TIN have been improved by making some adjustments to the calibration parameters, particularly the flushing rates.

SECTION 4. NUTRIENT SOURCE APPORTIONMENT.

4.2 General Seasonal Trends

Several general key trends may be seen from the graphs presented:

 Total P contributions are quite constant through the year, but point sources are relatively more important during summer months, when diffuse runoff decreases.  Nitrate contributions decrease during summer months, but the contribution of point sources to overall load increases. This is also attributable to decreased runoff and diffuse pollution.  Ammonia contributions and the importance of point and diffuse sources remain fairly constant during the year.  The area of the catchment supplying the highest point source nutrient load to the Washes is between Buckingham and Bedford, with the catchment between Bedford and Offord supplying the lowest point source nutrient loadings.

4.3.3 Nitrates

It is evident from the analysis of nitrates in each of the four rainfall runoff sub catchments that the main source of nitrates is from diffuse sources. Similar to ammonia, although far more pronounced, there appears to be a very strong seasonal trend in nitrate loading. Nitrate from diffuse sources is at its peak in November and December, whilst it is at its lowest in July. The reason for this trend is related to surface runoff rates. In the winter, surface runoff and erosion of nutrient rich soils is high and, hence, the runoff of diffuse nitrates is high relative to the point source contribution. This pattern reverses into the summer, as surface runoff decreases and diffuse sources become relatively less important than point.

It is noted that even with the 1960s landuse scenario, diffuse nitrate loadings still remain high, with an average daily loading from each sub-catchment during January being estimated at between 2000 and 6000 kg/day. P63

Diffuse Sources

The same general trends are seen for nitrates as were seen for ammonia, with the relative contribution of different areas varying as abstraction amounts vary. As with ammonia, the area contributing the lowest amounts of nitrates is between Bedford and Offord, with the remaining three sub-catchments all contributing approximately 30% of the total each. The relative contributions of the different areas does not significantly vary between the four scenarios.

The maximum licensed scenario produces lower loadings than the current scenario, since abstraction of nitrate rich water is increased, whilst the naturalised scenario produces higher loadings as abstractions are removed completely and dilution rates are altered.

4.3.4 Total Phosphorus

An examination of nutrient sources under the current scenario, at each of the four rainfall runoff sub catchments, reveals that the main source of phosphorus is point sources. Point sources at Brownshill account for 78.1% in January to 94.6% in July, compared to 5.4% in January to 21.8% in July from diffuse sources.

As is evident in the total phosphorus nutrient budget analysis, the monthly availability of phosphorus in each of the four catchments, due to point sources, gradually increases from its lowest point in January until it reaches a peak in July, after which it decreases. This is due to the decreased surface runoff during the summer, and therefore decreased diffuse pollution runoff, and hence a decreased relative contribution.

The trend in terms of actual loading is relatively constant throughout the year, with a small decrease in loading seen during the summer months. This is because sewage treatment work discharges, which are the main source of phosphorus, have quite a constant value throughout the year. The decreases seen during the summer may be due to decreased surface runoff and baseflow or decreased wastewater production, which slightly lower average STW discharge values and hence loadings.

Diffuse contribution to total phosphorus loadings remains low throughout the year. There is a seasonal trend, as with all other diffuse pollution, of higher values during the winter in response to increased runoff rates. As with ammonia and nitrates, the lowest point source contributions, and hence highest relative contribution of diffuse sources, is in the sub- catchment with the lowest numbers of treatment works (Bedford to Offord).

Average Contribution to Washes

The contribution of the various areas to the weight of phosphorus reaching Brownshill is set out in the report. These are assumed approximately equal to the loadings affecting the Washes.

Diffuse Sources

The same general trends arc seen for phosphates as discussed above for ammonia and nitrates. The relative contributions of the different areas of the catchment vary little between the four scenarios.

Point Sources

The general outcome of the maximum licensed scenario is to decrease total phosphorus loadings to the Washes. This is because, although the scenario increase discharge rates, this is counter balanced by a much higher increase in abstractions and hence a lower average total phosphorus loading.

The only area of the catchment that shows an increase in loading under this scenario is between Offord and Brownshill, due to a large number of sewage treatment works in this sub-catchment.

SECTION 5. WATER AND NUTRIENT BUDGETS.

Current Scenario

 Excess water is seen primarily in November- January, due to the operation of the Washes as flood storage, when Earith sluices open to allow the inflow of floodwaters from the upper catchment.  A deficit (outputs of water from Washes exceed inputs) of water is seen between February and May. This is due to a combination of the opening of Welmore sluices to allow the spring drainage of the Washes and the fact that the slackers are generally not opened during this period since irrigation water is not yet required.  Deficits are also seen through the summer due to high temperature and low effective rainfall, but the values of deficit are generally very low due to the intensive operation of irrigation slackers across the Washes to maintain ditch water levels.  Some excess water (inputs exceed outputs) is generally seen in September and October, probably associated with early winter floods during certain years or increased effective rainfall volumes.

There is a useful figure that shows this scenario (5.1).

Current Scenario with Altered Welmore Sluice

The general trend is the same as for the previous current scenario, although the deficits and excesses are slightly smaller for all months. This is because the new configuration of the Welmore Sluice allows a greater throughflow of water in the Washes, thus reducing both excesses and deficits.

Maximum Licensed Scenario

The general trend is the same as for the current scenario. There are slight differences due to the altered abstraction and discharge regimes, but no really significant differences

 The reason for this is that the difference between the current and maximum licensed scenarios is of the greatest significance during low flow periods. However, during low flow periods, the fluvial Great Ouse does not form the major influence on inflows into the Washes, but rather the tidal Hundred Foot river is the major control on inflow volumes. The majority of flow through the slackers is derived from the Hundred Foot and controlled primarily by tidal levels. The exception to this may be at the southern end of the Washes, where the influence of fluvial flows is greater.  During flood flows, when water from the fluvial Ouse is flowing in large volumes into the Washes, the artificial influences are a relatively negligible influence on total flows in the river and the water budget remains relatively unaltered.

5.3 Entire Washes Total Phosphorus Budgets

5.3.2 Current Scenario

• The total phosphorus budget generally follows the trend of the water budget, with highest excesses (inputs of total P exceed outputs) during flood periods (November- January) and highest deficits (outputs exceed inputs) during periods of flood discharge (February- May).

• The first flood of the autumn each year is expected to contain high levels of total-P since it is often associated with Combined Sewer Overflow (CSO) spills or flushing of stored waste products within a sewage treatment works storm overflow system. This is supported by this analysis. However, this nutrient flush will be short lived, since total-P concentrations tend to peak early in a flood event than tail off through the event.

The excesses of nutrients seen during the summer (June - September) are thought to be due to the high levels of irrigation feeding during this period, combined with the high concentrations of total-P in the Hundred Foot River.

5.3.4 Naturalised Scenarios

The two naturalised scenarios produce similar results for total-P budgets, although these vary from the current situation. These two scenarios have no point source pollution modelled in them.

The patterns seen during winter flooding are similar to those seen for the current scenario, although the amount of available total-P is generally half of that available under the current scenario.

• The only major exception to this occurs during January, where the excess phosphorus seen in the Current and Maximum Licensed scenarios becomes a deficit in the naturalised scenarios.

• The excesses and deficits of total phosphorus during the summer months (June - October) are very small, suggesting that there is very little phosphorus in the Washes system during this part of the year. This is because very little surface runoff occurs during the summer months and thus there is very little diffuse pollution loading from the Ouse catchment. Since point sources of P have been removed in the naturalised scenarios, this means that there is very little P entering the Washes system from the Ouse catchment during this period.

5.4 Entire Washes Total Inorganic Nitrogen (TIN) Budgets

5.4.2 Current Scenario

As with total phosphorus, the TIN budget approximately follows the water budget trend for the entire Washes.

• The majority of TIN is generated from surface runoff across agricultural areas, causing the loss of fertilisers into watercourses. This is supported by the trends seen for November to January, with high excesses of TIN associated with high winter runoff following fertiliser application in the autumn.

• The large TIN deficits seen during February and March are due to the high outflows of nitrogen-rich floodwaters through the Welmore sluice during these months, as the Washes drain down from the winter flood levels. In addition, there are decreased inflows through Earith during this period, as winter runoff decreases.

• The low values (either deficit or excess) seen in the late spring and summer are due to a combination of the decreased TIN loading into the washes resulting from decreased surface runoff rates and therefore less diffuse pollution.

5.4.5 Naturalised (existing landuse) Scenario

As discussed above, the general trends in the TIN budgets for this scenario are very similar to those for the current scenario.

The majority of TIN in the catchment is derived from diffuse sources, as discussed in Section 8, and therefore TIN budgets remain relatively unaffected by changes to point source pollution.

5.4.6 Naturalised (1960s landuse) Scenario

This altered landuse scenario illustrates the impact of decreased fertiliser usage and less intensive farming practices on nutrient loadings for the Washes. The general pattern is the same as for the other scenarios, although there has been a significant decrease in TIN excesses, since fertiliser usage has been reduced under this scenario.

This pattern clearly identifies the impact of decreased fertiliser usage and less intensive agricultural practices in the Ouse catchment, which is to decrease the amount of TIN within the washes by approximately 50%.

5.5 Field Water Budgets

Current Scenario

The results under the current scenario for the water budget analysis are very similar across all 34 of the model field cells. The only geographical difference is seen in the budgets for the four field cells closest to Welmore Sluice (Hagen Smart and Charity), which have significantly larger water excesses and deficits.

 These higher excesses and deficits of water are witnessed in the field cells fed by the 2 slackers closest to Welmore sluice. These higher excesses are thought to be due to the prolonged duration and high depth of flooding in this area of the Washes, as flood waters flow through the Washes to discharge at Welmore.  The larger deficits seen in these four fields during the winter are due to the invert of the slackers relative to the tidal level. Although Hagen Smarts and Charity are at the northern end of the Washes and hence the most influenced by the tidal Hundred Foot River, the inverts of the two slackers are the highest of all those along the Cradge Bank" and therefore only receive inflow during very high tides. The remainder of the slackers can receive inflow throughout the summer period and are, therefore, less vulnerable to tidal variations, and have a more reliable source of summer irrigation water.

 As shown by the water budgets for the entire washes, excess water is primarily seen in August to January due the use of the washes as flood storage. The highest excesses are evident between November and January when flows and water levels in the Ouse are generally highest. Under the current flood management routine for the Washes, this pattern results in an increased frequency in the operation of the sluices at Earith and greater occurrence of flooding in the Washes.

A deficit of water (outputs exceed inputs) is generally seen in the field cells between February and July. However, the deficit is generally low. These deficits are generated by the difference between the water demand in the ditches/fields and either the capacity of the slackers or the invert level. Often, tidal levels are insufficiently high or the slackers are too small to allow the required amount of water to flow into the Washes, and hence a deficit is seen for many of the fields.

Maximum Licensed Scenario

• The general trend is the same as for the current scenario. There are slight differences due to the altered abstraction and discharge regimes, but no really significant differences.

• The reason for this is that the difference between the current and maximum licensed scenarios is of the greatest significance during low fluvial flow periods. However, during low flow periods, the fluvial Great Ouse does not form the major influence on inflows into the Washes, but rather the tidal Hundred Foot river is the major control on inflow volumes. The majority of flow through the slackers is derived from the Hundred Foot and controlled primarily by tidal levels. The exception to this may be at the southern end of the Washes, where the influence of fluvial flows is greater.

• During flood flows, when water from the fluvial Ouse is flowing in large volumes into the Washes, the artificial influences are a relatively negligible influence on total flows in the river and the water budget remains relatively unaltered.

5.6 Field Total Phosphorus Budgets

Current Scenario

Excess phosphorus is seen primarily in May to September. This due in part, to the high levels of irrigation during this period, using nutrient rich water from the Hundred Foot River. Highest values of excess in the 34 field cells are generally seen in July or August when the nutrient load out of the field cells is at a minimum and vegetation uptake is greatest. May and June show lower values of excess as there is a loss of nutrients due to the continued drainage of the washes after winter/spring flooding.

A deficit of phosphorus is generally seen between October and April as flow through the slackers does not occur due to the use of the washes as flood storage. The highest values of deficit in the 34 field cells are generally seen in January, with deficits decreasing in February, March and April.

This annual trend is due to the operation of the Washes:

 During the summer, slackers allow irrigation water into the fields, which generally has a high total-P concentration. During this period, flows out to the River Delph are at their lowest. Hence, the highest excesses of total-P are seen for each field.  During winter periods, slackers are closed and the fields are fed by intermittent flooding only. However, the model does not include P deposition from floodwater and hence, the model predicts large P deficits for winter periods. These large deficits may not exist in the actual situation, but are partly a product of the model limitations.  There is a slight trend that the excesses of total-P decrease along the Washes towards the north, which supports expected trends of decreased in total-P concentrations down the Hundred Foot River towards the Wash, as salinity of the water increases. This trend, however, is not significant and total-P is not seen to vary greatly throughout the Washes model.  It is suggested, although this is not explicitly represented by the model due to the limitations associated with a lack of a terrestrial nutrient model, that total-P accumulates primarily in the ditch system during summer, fed by the slacker system, and is then flushed out in winter, during flood conditions. The fields themselves may experience no such seasonal change and P availability to vegetation is actually regulated by sediment deposition from large flood events and by the internal cycling of nutrients within the soil.

5.6.4 Naturalised Scenarios The general trend is that excess total-P values are significantly reduced than under the current and maximum licensed scenarios, due to the removal of all point sources from the model. This means that the inputs of total-P are decreased and therefore excesses of inputs over outputs decrease. Any total-P identified is sourced from diffuse pollution.

The annual trend is for deficits (outputs exceed inputs) of total-P between January and July (lowest in February), and excesses (inputs exceed outputs) for the remainder of the year (peak in November). This pattern is derived from the concentrations of total-P expected from diffuse pollution. Phosphorus levels will be highest in autumn and early winter when high surface runoff rates occur following fertiliser application to agricultural areas, hence the loadings into the Washes is highest and excesses are seen. Throughout the remainder of the year, phosphorus levels in diffuse pollution tend to be low and more phosphorus is exported from each field (as seepage and flow into Delph) than is imported into it, and hence deficits are seen.

5.7 Field Total Inorganic Nitrogen Budgets 5.7.2 Current Scenario The TIN budget for the current scenario in all 34 field cells is seen to follow two distinct patterns, based upon the occurrence of flooding across the field: 1. In situations where flooding is rare or does not occur (e.g. summer periods or for most winter periods across Black Sluice 2) the TIN budget is driven by the water budget. Nutrient transport processes are controlled by water transport processes, notably the excess of effective rainfall over seepage and the net loss or gain of water between the field and the River Delph.

When rainfall causes a net gain of water, this induces outflow from the field to the Delph (winter periods when flooding is not occurring) and there is a net deficit of TIN (inflows< outflows). During drier summer periods, effective rainfall is negative, inducing water to flow in through slackers and also from the Delph to the field. This mass balance results in a net gain in TIN as inflows exceed outflows. The breakdown of the water budget for Ely Singers I is shown in Figure 5.14 to illustrate this concept.

2. During flooding periods, the TIN budget begins to be influenced by the interactions of the fields and the flood storage module. During periods of inundation (defined by flood storage levels greater than average field elevation), there is a net loss or gain of nutrients between the field cell and the flood storage module. This interaction offsets the overall simple pattern of the TIN budget set out in 1 above.

In this scenario it can been seen that during the months of November, December, January and March there is a net gain of TIN (i.e. TIN inflow exceeds outflow), but the water budget shows a net deficit of water. This is because the water budget does not include the operation of the Washes as a flood storage unit, but the nutrient budget does. During these periods, periodic flood events and the associated nutrient interactions influence the field nutrient budget and skew the simple pattern. These interactions imply that the Washes model is operating correctly and reasonably simulating the interaction of nutrients in floodwater and field ditches.

5.7.3. Current (Welmore Altered) Scenario The trend in the TIN budget under the altered Welmore Lake Sluice scenario is almost identical to the current scenario.

5.7.4. Maximum Licensed Scenario The general trends in TIN availability under the maximum licensed scenario are very similar to those seen under the current scenario.

5.7.5. Naturalised Scenario with Current Diffuse The results of the naturalised scenario with current levels of diffuse pollution are very similar to the current and fully licensed scenarios. The slight difference being that the values of excess and deficit are slightly lower, associated with decreased TIN values in the river due to the lack of point sources.

5.7.6. Naturalised Scenario with 1960s Diffuse This is associated with the removal of significant amounts of diffuse pollution in this scenario. This expected pattern is still offset, since diffuse loadings remain quite high (see section 8), but the general trends are now more towards deficits in winter periods (caused by a net loss of water from the fields) and excesses during summer periods (caused by the gain in water into fields through slackers).

SECTION 6. WATER TABLE THRESHOLDS

Presentation of Results The water table depths are presented in three ways:  Timeseries of water table depths (1970 – 2000) to introduce the current field regime;  Monthly average analysis of water table depths, relative to the prescriptions, in order to try to establish the seasonal pattern behind the percentage analysis;  Analysis of the percentage of time that each field is within each regime range.

6.6 Summary 6.6.1. Water table Depths The results for each field are summarised in Table 6.14. This shows the percentage of the growing season (March – August) that each field is within the various water table depth ranges. As identified before, these results are for the current scenario, but there is little difference between the results of the 4 scenarios.

The table identifies several key issues:  The S5 community fields are all within the ideal range for over 85% of the growing season. Of the remaining time, only a maximum of 3% is spent outside the amber acceptable range. The S5 fields are considered to be largely within regime in terms of water table depths.  The MG9 community fields are typically within the ideal range for less than 46% of the growing season. This comparatively low value is thought to be due to excessive spring inundation and summer water table depth that are too high. The fields are, however, only outside of the ideal and acceptable ranges for less than 10% of the growing season. Therefore, although the fields do not fall within the ideal range for much of the time, the water table depths are mostly within the amber range when outside the ideal range. This range is acceptable for short periods and the fields may therefore be considered to be potentially within regime, depending on the durations of the periods when water table depths extend into the amber range.

The high water table depths suggested by the analysis may simply be a feature of the global value of hydraulic conductivity selected during model calibration, which may be maintaining water table depths at an artificially high level.

The MG9 fields are considered to be out of regime as a result of water table depths that are maintained too high during the early part of the growing season (March – May). This is thought to be due to excessive winter and spring flood depths causing water tables to be maintained at an excessive level during these spring months.

 The MG13 community fields on Midelney soil are within the ideal range for less than 35% of the growing season. They are all, however, within the amber range for 50 - 55% of the growing season, suggesting that whilst these fields could probably not be considered to be within regime, they are fairly close to the ideal regime for much of the

time. The periods spent outside the ideal range are generally due to high water tables during the spring and summer periods.

As with the MG9 fields, the high water table depths suggested by the analysis may simply be a feature of the global value of hydraulic conductivity selected during model calibration. This may be maintaining water table depths at an artificially high level.

The MG13 (Midleney) fields are considered to be out of regime as a result of water table depths that are maintained too high during the majority of the growing season (March – August). This is thought to be due to excessive winter and spring flood depths causing water tables to be maintained at an excessive level during the spring months and the maintenance of high ditch levels across the site.

As before, the water table depth may be influenced by model calibration, but all analysis would suggest that these areas are more likely to support an MG13 community, since they require wetter conditions throughout spring and summer periods.

The MG13 (Adventurers) fields are considered to be generally within regime in terms of water table depths. Problems may be caused as a result of water table depths that are maintained too high during the early part of the growing season (March – April). This is thought to be due to excessive winter and spring flood depths causing water tables to be maintained at an excessive level during these spring months. These results may also be summarised for all four scenarios, as an average for each community type (Table 6.15). This gives the average number of days each field with a particular vegetation community target (MG13, MG9 or S5) spends in a particular regime range.  It is evident that the results for the five scenarios vary little between each regime. This is because changes in abstraction and discharge regimes, which have been built into the fully licensed and naturalised scenarios, are only significant at times of low flows when little water enters the washes from the Ouse. It is expected that differences between the scenarios will be more evident the nutrient threshold analysis.  Those field cells which support grassland community S5 are shown to have ideal water table levels for the highest percentage of the time for all five scenarios. On average, approximately 90% of days within the growing season may be classified as within the ideal regime. This implies that these fields may be considered to be currently within the required range for water table depths.  Fields with targets of the other vegetation communities are within the ideal range for much less of the time, with the MG13 on Adventurers soil within the ideal range for approximately 60% of the growing season, MG13 on Midelney soil within the ideal range for around 30% and MG9 fields in the ideal range for around 44% of the growing season. As such, it is not possible to clearly identify these fields as being within the required range for water table depths.

SECTION 7. TOTAL PHOSPHORUS THRESHOLDS

Introduction

The guidelines used for assessing and quantifying the condition of different sections of the Washes, in terms of total phosphorus, were estimated from those derived for ortho-phosphate by the Agency for the Urban Wastewater Treatment Directive (UWWTD) . The total-P concentration for the ditch system feeding each field is produced within the model and this is compared to the threshold value offered in this document.

The thresholds offered for phosphate are 0.1 mg/l ortho-phosphate and 0.2 mg/l total phosphorus. Both thresholds may be viewed in terms of annual average values. Only the total-P threshold is used in this analysis, since ortho-phosphate is not available as a model output.

It should be noted that the concentrations discussed in this section relate primarily to the concentrations within the ditches surrounding a particular field, and this may not always be a reliable indicator of nutrient conditions across open fields. This is an identified limitation within the current modelling approach, whereby phosphorus deposition onto floodplains from floodwater is not accounted for, primarily due to a lack of research into these types of processes.

It has been stated by David Gowing (pers. comm.) that TIN and P levels are important determinants on the vegetation community but it is their availability in the soil which will control vegetation type. The current model, with its integrated ditch and field as a single well-mixed unit, does not provide this soil availability data. The fate of nitrogen and phosphorus within the system will be very different and these differences are not accounted for within the model:

1. N will be very mobile and dynamic and would be likely to seep laterally into fields from the ditches. N will also be arriving at high rates from atmospheric deposition and being lost through de-nitrification, which is a function of soil wetness. 2. P will be much less mobile and more highly conserved. Lateral movement from ditches to fields will be limited as will atmospheric interactions. The major processes that will be influencing phosphorus availability within the soils across the Washes will, therefore, be the deposition of phosphorus rich sediment by silt in floodwater and the equilibrium between available and unavailable forms in the soil (also influenced through soil wetness).

Therefore, the modelling results presented below offer information on nutrient loading and concentrations with in the ditch systems across the Washes. However, they do not provide information about how this ditch nutrient level converts to a field nutrient availability or the impacts of this field nutrient availability on the vegetation type present. These types of issues will need to be addressed through future research and incorporated into the modelling approach at a later date.

However, David Gowing has stated that he does not feel that the lack of a terrestrial nutrient model poses a significant problem at this stage, because the more sensitive ecosystems, in terms of nutrient concentrations, will be the aquatic ones. These communities have more exacting needs and are likely to drive the review decisions, and the terrestrial communities are fairly resilient to nutrient loading. It is suggested that understanding the nutrient loading

91 will, in the long term, affect the balance of the plant communities, but does not have to be solved within Stage 3 of the Habitats Directive RoC.

7.2 Time Series Analysis

• There is virtually no difference between the current scenario runs with different configurations of the Welmore Sluice. This would indicate that the changes to the Welmore Sluice have had very little effect on nutrient concentrations in the Washes. These two scenarios will therefore be considered together, below. • The concentrations used in this nutrient analysis relate to the total phosphorus concentrations within the ditches surrounding a given field. No accurate indication is possible of the open field concentrations across the Washes due to the modelling approach used, the lack of a terrestrial nutrient model and the complex nutrient interactions between the ditches and the fields.

7.2.1. Current Scenario

• Under the current scenario, annual, monthly and daily average concentrations exceed the threshold of 0.2 mg/l for the majority of the modelling period. Monthly and daily average values do dip below the threshold in most years, although this is usually only by a small amount and for only a short time. • As noted above, there is very little difference between phosphorus concentration timeseries for the two configurations of the Welmore Sluice.

7.2.2. Maximum Licensed Scenario

• The concentration timeseries for the maximum licensed scenario is similar to that for the current scenario. The threshold is exceeded for the majority of the modelling period, although monthly and daily averages do dip within the threshold for short periods during most years. • Total phosphorus concentrations are consistently higher than the current scenario throughout the modelling period. The higher total phosphorus concentrations seen for the maximum licensed scenario are due to the increased point source inputs considered under this scenario. In this scenario, sewage treatment works discharges are modelled as maximum licensed dry weather flow (DWF), rather than the actual measured or estimated DWF used in the current scenario. Since sewage treatment works are the primary source of phosphorus in the systems, the increased total phosphorus concentrations seen under the maximum licensed scenario can be attributed to this increase in point source phosphorus inputs.

7.2.3. Naturalised Scenario with Current Diffuse Pollution Loadings

• The naturalised scenario results show a distinct difference from the current and maximum licensed scenarios. Monthly and annual average values are within the threshold for the entirety of the modelling period. Daily average values exceed the threshold on two occasions, once in 1988 and once in 1999. In general, however, values fall within the range 0.02 - 0.15 mg/l.

• This is due to the removal of all point sources of pollution from the model during the naturalised scenario and hence the significantly lowered total-P concentrations in the River Great Ouse and hence in the water that flows into the Washes.

7.2.4. Naturalised Scenario with 1960s Diffuse Pollution Loadings

• The results under the naturalised scenario with 1960s diffuse pollution are primarily the same as witnessed under the naturalised scenario with current diffuse. This is due to the relative insignificance of diffuse sources to total-P loadings at the Washes.

7.3 Concentration Duration Curve Analysis

The concentration duration curves for each of the five scenarios for the field cell Cambient 1 are shown in figure 7.6: this graph is typical of all 34 of the field cells.

As the table shows, it can be seen that total phosphorus levels are below the threshold for virtually all of the time under the two naturalised scenarios. There is very little difference between the two current scenarios, with total phosphorus levels below the threshold for around 30% of the time. Total Phosphorus levels are substantially elevated above the current scenarios under the maximum licensed, falling below the threshold for only around 20% of the time.

In order to facilitate the assessment of favourable conditions for Spined Loach, a concentration duration curve for the model’s flood storage module is produced. This represents the nutrient concentration conditions in the River Delph. This shows a very similar trend to the individual field concentration curves, with threshold concentrations reached at slightly higher percentiles. The effect of Welmore Lake Sluice reconfiguration seems to be higher concentrations of Total-P through the range of values modelled, except for the very low concentration values (< 0.15 mg/l). The concentrations values are generally slightly lower than those seen for the individual fields since the fields gain nutrients predominantly from slackers flows during summer periods when nutrient concentrations are high and the Delph obtains nutrients predominantly from floodwaters, which have more dilute and lower nutrient concentrations. However, the nutrient concentrations in the Delph appear to be maintained at slightly higher levels than those in the the individual field ditches due to less uptake by vegetation.

SECTION 8. TOTAL INORGANIC NITROGEN THRESHOLDS

The guidelines used for assessing and quantifying the condition of different sections of the Washes, in terms of TIN, were those derived by WRc for their environmental impact assessment studies of the impact of abstractions on the Rivers Ouse and Nene . The TIN concentration for each field is produced within the model and this is compared to the threshold value offered in this document.

The thresholds offered for nitrogen are 1.6 mg/l total nitrogen and 0.8 mg/l TIN. There are currently no guidelines as to whether these thresholds should be viewed as annual average values or based upon mean daily values. In the following analysis, the duration curve and

93 percentage exceedence values are derived from the mean daily concentration data. Only the TIN threshold is used in this analysis, since total nitrogen is not available as a model output.

The same arguments that were presented for the total-P analysis, relating to the interactions between ditch and field concentrations and the modelling limitations, may be extended to cover the TIN analysis. All analysis discussed below relates to the ditch TIN concentrations and not the open field values. However, due to the mobile and dynamic nature of nitrogen, it is much more likely that the TIN value in the ditch is similar to that across the open field, and the flood deposition of TIN is a smaller component of the overall system.

8.2 Time Series Analysis

Examination of the TIN concentration timeseries’ for all five scenarios indicates that there is very little difference between the scenarios, with the exception of the naturalised scenario under 1960s diffuse pollution loadings. This scenario has significantly lower TIN concentrations as a result of the lower input of TIN to the River Great Ouse in surface runoff from agricultural areas.

8.2.1. Current Scenarios

• Under the current scenario, annual, monthly and daily average concentrations of TIN exceed the threshold for virtually all of the modelling period. This is the case in all 34 field cells. The TIN concentration only dips below the threshold very briefly on two occasions. • There is very little difference between the timeseries for the two different configurations of the Welmore sluice. Under the post-2000 configuration of the sluice the threshold is also exceeded throughout the modelling period. • TIN concentrations follow a distinct annual cycle, peaking during the months of November and December at values between 15 and 25 mg/l. Lowest daily and monthly concentrations occur during the period May - July, with minimum values generally in the range 1 - 5 mg/l. This cycle is linked to the occurrence of surface runoff within the catchment, which is high in winter providing a substantial TIN load to the river and hence to the washes. During summer this loading is low, since surface runoff and erosion of fertiliser-rich soils are at a minimum. This correlates with the TIN nutrient budget analysis for the washes.

8.2.2. Fully licensed scenario

• There is very little difference between the maximum licensed and current scenarios. The general trend is for daily, monthly and annual average concentrations to exceed the threshold for the entire modelling period. Peak TIN concentrations are slightly higher than in the current scenario. This is most likely due to the increased TIN loadings from point sources (i.e. sewage treatment works) under this scenario. The differences are only slight, however, since the majority of TIN is derived from diffuse sources rather than point sources.

8.2.3. Naturalised Scenario with current diffuse pollution loadings

• Although the indicative timeseries graph for the naturalised scenario with current diffuse pollution loadings appears similar to that for the current scenario, TIN concentrations are generally slightly lower, and hence closer to the threshold. The threshold is, however, still exceeded for the vast majority of the modelling period. • Annual minimum values are generally slightly lower, although still above the threshold. This is due to the removal of all point sources of TIN from the model and a resulting general decrease in concentrations in the Great Ouse.

8.2.4. Naturalised Scenario with 1960s diffuse pollution loadings

• There is a significant reduction in the concentrations on TIN under the naturalised scenario with 1960s diffuse pollution loadings. The threshold is still, however, exceeded through virtually all of the modelling period. • The annual cycle of TIN concentrations is still seen, although the values are significantly reduced. Peak concentrations fall within the range 6 - 13 mg/l, with minimum values in the range 0.5 - 2.5 mg/l. • The substantial reduction in TIN concentrations under this scenario is a result of the reduction in the diffuse TIN loadings from the land surface. As noted above, diffuse sources account for the majority of the TIN load to the Great Ouse and hence to the Washes, so a reduction in this load will have a significant effect in reducing TIN concentrations in the Washes. The fact that the threshold is still exceeded for the majority of the modelling period indicates that even the ‘natural’ diffuse pollution loading from the catchment provides sufficient TIN to keep the washes above the threshold of 0.8 mg/l TIN.

8.3 Concentration Duration Curve Analysis

The table confirms that TIN concentrations fall within the threshold for very little of the modelling period. The percentage of time within regime does not exceed 1% for any of the fields under the two current scenarios and the fully licensed scenario. The naturalised scenario with current diffuse pollution loadings shows slightly increased values, although the maximum time under this scenario is still as low as 1.4%. Under the naturalised scenario with 1960s diffuse pollution loadings the percentage of time TIN concentrations are within the threshold is greater than for the other scenarios, although still very low. The maximum time within the threshold under this scenario is 4.8% for the field cell Pontoon Wash 1.

This data is borne out by the concentration duration curves. As shown in the timeseries graphs, there is very little difference between the two current scenarios, the maximum licensed scenario and the naturalised scenario with current diffuse pollution loadings. The naturalised scenario with 1960s diffuse pollution loadings shows a significant reduction in TIN concentrations, although the threshold is still exceeded for virtually all of the modelling period. This confirms that the dominant influence on TIN concentrations is the diffuse pollution loading. The input of TIN to the Great Ouse from diffuse pollution is the same for all scenarios with the exception of the naturalised scenario with 1960s diffuse pollution loadings. The reduced loading under this scenario results in substantially lower concentrations of TIN within the Washes, although even the ‘natural’ TIN loading is still sufficient to ensure that the threshold value is exceeded for the majority of the time.

In order to facilitate the assessment of favourable conditions for Spined Loach, a concentration duration curve for the model’s flood storage module is produced. This represents the nutrient concentration conditions in the River Delph. This shows a similar trend to the individual field concentration curves, but the relative concentrations of the different scenarios is changed. The two current and the naturalised (current landuse) scenarios show higher nutrient concentrations than the maximum licensed scenario and all four are significantly greater than the naturalised (1960s landuse) scenario. This is related to the dominant nutrient source mechanisms for the fields and the Delph. The Delph is fed by floodwaters through, Earith Sluice, which tend to have diluted TIN concentrations, whereas the fields are fed by slacker flows from the Hundred Foot River, during summer low flow periods, and the nutrient concentrations of these inflows tends to be high. The influence of naturalisation and alterations to abstractions amounts is easily discernible in the field durations curves, whereas this pattern of low flow impacts is lost in the Delph. Hence, the two current, the naturalised (current landuse) and the maximum licensed scenarios all show very similar concentrations values. The maximum licensed scenario shows lower TIN values than the other three scenarios due to dilution effects from altered abstraction patterns.

The naturalised (1960s diffuse) scenario shows much lower TIN concentrations than the other four scenarios, since diffuse pollution inputs are strongly related to storm runoff across agricultural areas. The removal of many diffuse sources is discernible in the Delph, since this affects storm runoff, nutrients in the river during high flows and hence flows through Earith into the Delph.

SECTION 9. CONCLUSIONS

9.2 Source apportionment

9.2.1. General Trends.

• Total P contributions are quite constant through the year, but point sources are relatively more important during summer months, when diffuse runoff decreases. • Nitrate contributions decrease during summer months, but the contribution of point sources to overall load increases. This is also attributable to decreased runoff and diffuse pollution. • Ammonia contributions and the importance of point and diffuse sources remain fairly constant during the year. • The area of the catchment supplying the highest point source nutrient load to the Washes is between Buckingham and Bedford, with the catchment between Bedford and Offord supplying the lowest point source nutrient loadings.

9.2.2. Ammonia

• The area of the catchment offering the highest point source ammonia loads is between Buckingham and Bedford, with Offord to Brownshill contributing significant amounts. • The highest diffuse loadings to the Washes are derived from the catchment between Offord and Brownshill, with the remaining three, upstream areas offering similar amounts.

• There is a trend in both the point and diffuse loading data, that ammonia loads are higher during the winter. This is thought to be due to higher incidence of storm runoff, removing ammonia in both diffuse runoff and storm water discharges from treatment works. • The maximum licensed scenario increases the point source loading from three of the four catchments, associated with increased STW effluent. A decrease is seen for the catchment between Bedford and Offord, thought to be due to a lack of treatment work discharges combined with a significant increase in surface water abstraction in this area.

9.2.3. Total-P • An examination of nutrient sources under the current scenario, at each of the four rainfall runoff sub catchments, reveals that the main source of phosphorus is point sources. Point sources at Brownshill account for 78.1% in January to 94.6% in July, compared to 5.4% in January to 21.8% in July from diffuse sources. • As is evident in the total phosphorus nutrient budget analysis, the monthly availability of phosphorus in each of the four catchments, due to point sources, gradually increases from its lowest point in January until it reaches a peak in July, after which it decreases. This is due to the decreased surface runoff during the summer, and therefore decreased diffuse pollution runoff, and hence a decreased relative contribution. • The trend in terms of actual loading is relatively constant throughout the year, with a small decrease in loading seen during the summer months. This is because sewage treatment work discharges, which are the main source of phosphorus, have quite a constant value throughout the year. The decreases seen during the summer may be due to decreased surface runoff and baseflow or decreased wastewater production, which slightly lower average STW discharge values and hence loadings. • The fully licensed scenario shows an increase in the average daily loading from point source phosphorus in the catchment between Offord and Brownshill, but a decrease in all other areas. As before this is due to increased phosphorus loads entering via the treatment works under this scenario, but also strongly increased abstractions in many areas. • Diffuse contribution to total phosphorus loadings remains low throughout the year. There is a seasonal trend, as with all other diffuse pollution, of higher values during the winter in response to increased runoff rates. As with ammonia and nitrates, the lowest point source contributions, and hence highest relative contribution of diffuse sources, is in the sub-catchment with the lowest numbers of treatment works (Bedford to Offord).

9.2.4. Nitrates

• The main source of nitrates is from diffuse sources. Similar to ammonia, although far more pronounced, there appears to be a very strong seasonal trend in nitrate loading. Nitrate from diffuse sources is at its peak in November and December, whilst it is at its lowest in July. • The reason for this trend is related to surface runoff rates. In the winter, surface runoff and erosion of nutrient rich soils is high and, hence, the runoff of diffuse nitrates is high relative to the point source contribution. This pattern reverses into the summer,

as surface runoff decreases and diffuse sources become relatively less important than point. • As with the current scenario the main source of nitrates under the maximum licensed scenario is from diffuse sources. However, the maximum licensed scenario does increase the nitrate loading from point sources. This is especially true in those areas with a concentration of treatment work discharges (such as Buckingham to Bedford). • The fully licensed scenario is seen to follow the same seasonal trend as the current scenario. The difference between the two scenarios being that there is a slightly increased contribution under the fully licensed scenario from point sources due to an increasing load of nitrates through the treatment works. As a result percentage contribution from diffuse sources is slightly less. • The impact of the naturalised (1960s landuse) scenario is to significantly lower diffuse nutrient loadings from all sub-catchments. This mirrors the pattern seen previously for ammonia and strengthens the conclusions that the majority of nitrates are from diffuse sources. However, even with the 1960s landuse scenario, diffuse nitrate loadings still remain high, with an average daily loading from each sub-catchment during January being estimated at between 2000 and 6000 kg/day. This suggests that there is a high natural level of nitrates in the catchment and management of artificial discharges or agricultural diffuse pollution within the catchment may be relatively ineffective at controlling nitrate levels.

9.3 Flooding Occurrence and Duration

This section considers the effect of flooding on each of the main plant communities present in turn (S5;MG9;MG13).

9.4 Water Table Depths

This section considers the effect of water table depth on each of the main plant communities present in turn (S5;MG9;MG13).

9.5 Total-P Thresholds

 Both of the naturalised scenarios produce a condition across the vast majority of the Washes that is within the threshold for virtually all of the time.  In general terms, all of the 34 fields show a very similar percentage value for each of the five scenarios. Under the current scenario the threshold is met for 30-33% of the time with the exception of the Black Sluice, Youngs Hold and Reads fields where values are slightly higher (34-37%). This pattern is reproduced for the revised configuration of the Welmore Sluice, although the threshold is met slightly less under this scenario (29-31%).  The fully licensed scenario shows total phosphorus concentrations in the Washes that are below the threshold for only 19% to 21% of the time.

Total-P concentrations in the River Delph are slightly lower than those seen across the Washes but there is no significant difference from the trends outlined above.

9.6 TIN Thresholds

 TIN concentrations fall within the threshold for very little of the modelling period. The percentage of time within regime does not exceed 1% for any of the fields under the two current scenarios and the fully licensed scenario.  The naturalised scenario with current diffuse pollution loadings shows slightly increased values, although the maximum time under this scenario is still as low as 1.4%.  Under the naturalised scenario, with 1960s diffuse pollution loadings, the percentage of time TIN concentrations are within the threshold is greater than for the other scenarios, although still very low. The maximum time within the threshold under this scenario is 4.8% for the field cell Pontoon Wash 1.

TIN concentrations in the River Delph are very similar to those seen across the Washes. The naturalised (1960s landuse) scenario shows the lowest concentration values, with the other four scenarios all showing similar curves. The lack of impact from altered point source pollution on the Delph is related to the dominant mechanisms for water to enter the channel (dilute flood water in winter rather than concentrated irrigation water in the summer).

These results confirm that the dominant influence on TIN concentrations in the Washes is the diffuse pollution loading. The input of TIN to the Great Ouse from diffuse pollution is the same for all scenarios with the exception of the naturalised scenario with 1960s diffuse pollution loadings. However, the ‘natural’ TIN loading from the catchment is still sufficient to ensure that the threshold value is exceeded for the majority of the time.

RK Summary, 16 March 2015.

9. BLACK & VEATCH, 2003. INVESTIGATIONS INTO SOLUTIONS TO WATER QUANTITY PROBLEMS AFFECTING THE SPECIAL NATURE CONSERVATION INTERESTS OF THE OUSE WASHES. ENGLISH NATURE. Summary

English Nature's most recent assessment of the Ouse Washes SSSI/SPA/cSAC and Ramsar site concludes that all the management units of the Ouse Washes are in unfavourable condition and that this failure of the site to meet the conservation objectives relates to external factors of water quantity (including control of management of water) and water quality (nutrient enrichment, notably Phosphorus). The aim of this study was to investigate solutions to the water quantity problems affecting the special nature conservation interests of the Ouse Washes.

A Working Group, comprising of nominated officers in English Nature, the Environment Agency, the Royal Society for the Protection of Birds (RSPB) and the Middle Level Commissioners, was set up to help define hydro-ecological objectives against which options could be tested. The Working Group agreed that the main period that was critical for breeding birds was April. This is because flooding in early April prevents birds from establishing territories and nests. Flooding between April and mid-May results in the flooding of nests, so avoiding high water levels between April and mid-May is also critical.

In the previous Posford study (October 2000), storage requirements were estimated from spring and summer periods combined. However, previous major flood events during the summer months have all tended to occur in mid to late October. In addition, it was agreed with the Working Group that October was not a critical month for birds, therefore combining the spring and summer periods to determine the storage volume is not necessary. This study has therefore focused on the problems of spring flooding, i.e. April to June.

Based on flooding patterns of the Ouse Washes, the impact of flooding on breeding birds and vegetation prescriptions, the Working Group agreed that a flood frequency of I in 4 years should be considered as the desired standard of protection.

An analysis of the hydrological characteristics in the period 1950-77 indicates that it is not possible to predict with any level of confidence what the equivalent flood frequency would be today (based on the period 1978-2002), in order to reproduce the flood conditions that occurred on the Ouse Washes in the period preceding the 1970s. This is mainly due to the fact that it is not possible to quantify with any confidence all the changes that have occurred since the 1950s.

The following hydro-ecological objectives were therefore agreed for the study:

Hydro-ecological objective 1: A flood frequency of I in 4 years for the spring period (April to June).

Hydro-ecological objective 2: A depth not greater than I.5m for longer than 3 consecutive days in the winter period (November to March).

As part of the hydrological analysis, the additional flood storage capacity or flood diversion capacity required to protect the Ouse Washes to a standard of I in 4 years was investigated, based on the flow records for 1978-2002. This analysis indicated that to achieve hydro- ecological objective I (HEOI), a storage volume (or equivalent flow diversion) of 37Mm3 of water would be required.

The Posford Duvivier report (October 2000) concluded that only larger schemes able to reduce the flow substantially should be considered further. As a review of previous studies indicated that none of the options considered previously were large enough to fulfil HEO I , this report focused on identifying 'larger' options of flood storage and flood diversion, using GJS methods to identify suitable locations.

The appraisal of flood storage and flood diversion channel options has indicated that there is no single solution that will achieve HEOI, i.e. a standard of protection of I in 4 years for the spring period April-June. However, a combination of these larger options - i.e. a flood storage option and flood diversion channel - could potentially achieve HEOI. Due to the reduction in storage volume required if the channel capacity in the system were increased, a combination option would also minimise the storage volume, and thus landtake for the storage area, required.

To reduce the land take associated with a combination solution, we recommend that conversion of the Old West River into a flood conveyance channel should be examined. However, as there are currently no details of the potential capacity of this river, this would need to be investigated in further detail. Such an examination should consider the potential capacity of the Old West river and of its receiving waters. It also needs to address the potential impact of diversion on siltation within the Tidal River. The outcome of this detailed study could then provide the basis for identifying the overall solution to water quantity problems in the Ouse Washes, for example the volume of storage required to provide a standard of protection of I in 4 years for the period April• June.

In addition to the landtake benefits achieved through the combination of flood storage with flood diversion, the combination of these two options is likely to be cheaper than using storage areas only to achieve HEOI. For example, to achieve HEOI would require both storage area site D and site A or B, at a cost of about £63M. In comparison, the cost of diversion to the Old West River with a storage area of approximately IO Mm3 is estimated at £47M.

To provide an integrated solution, the combination of flood storage areas and flood diversion channels with other solutions identified in previous reports as contributing positively to the problem of spring and winter flooding were also considered.

The Ramsar report (Ramsar Advisory Mission, November 2001) drew attention to the potential contribution of drainage from the Middle Level to flooding of the Washes, with a reduction in the inflows at Welches Dam recommended as part of an integrated solution. Although this option would not be sufficient on its own to achieve the hydro-ecological objectives, and would therefore need to be considered in combination with the larger options, it could contribute to an integrated solution. This option would only be worth pursuing if the water entering the

Washes from Welches Darn was identified as a cause of significant flooding once Bedford Ouse flows have been diverted. This would need to be investigated in further detail.

The storage areas and flood diversion channels will only provide a solution to spring flooding if they are empty and available for use on I April. The hydrological analysis indicated that a storage capacity of 79Mm3 would be required if these areas were to store March floods, thus requiring significant more volume than that provided by the storage areas identified, and therefore significant more land take.

The only option identified to address the problem of winter flooding (HE02) was that of Reprofiling the Tidal River. Although this option will not prevent flooding of the Washes, lowering of the bed levels will help remove flood waters off the Washes more rapidly. This would reduce the duration and depth of flooding in spring and winter. As each flood would drain more rapidly, water levels at the start of the next flood would also be lower, thereby reducing the depth of flooding and the maximum flood volume of subsequent floods. This option was costed at £7M in the Posford Duvivier report (October 2000).

In conclusion, the options in this report have been assessed against hydro-ecological objectives. These hydro-ecological objectives have been agreed by the Working Group, on the basis of the hydrology review, the hydro-ecological prescriptions and a review of the flooding patterns of the Ouse Washes. It is recommended that to identify a preferred solution further study on the capacity of the Old West River should be undertaken. From this, the storage capacity required to fulfil HEOI can be determined. In addition to this study, the effect of water entering the Washes from Welches Dam needs to be investigated.

Further work is also required to evaluate the options (and their resulting standard of protection) against ecological criteria to confirm that they provide for the favourable conditions identified for the interest features of the Ouse Washes.

RK, 28 April 2015.

10. GRAHAM, J. 2003.OUSE WASHES – HYDRO-ECOLOGICAL PRESCRIPTIONS FOR FAVOURABLE CONDITION. ENGLISH NATURE. The following account is an attempt to define, with justification and based on the FCT, the ecological management prescriptions for the Ouse Washes in terms of managing the water quantity and quality required to secure favourable condition. Important attributes within the FCT which do not relate to water quantity and quality have not been included in this account: for many positive management can be secured relatively easily and the principles are well known and documented.

2. Changes to open wash vegetation (1972-2001)

Figures 1-4 show the distribution of the main plant communities for the years 1972, 1988, 1992 and 2001 and the map keys broadly correspond with the following National Vegetation Class (NVC) communities:

Agrostis (light green) = MG13

Deschampsia (orange / brown) = MG9

Glyceria (yellow) = S5

Phalaris (darker green) = S28

Inundation (pink) = OV30/32

Dry ruderal (brown) = OV28/29

Phragmites (blue) = S4

Woodland / open water (white) = Woodland / open water

Table 1 summarises changes to washland vegetation during the period 1972-2001 (Prosser and Wallace, 2002). The additional communities (not recorded in significant stands by Prosser and Wallace) probably still occur on the site: MG4 and MG5/6 recorded from the slopes of the Bulwark, Earith and MG5/6 recorded from higher ground elsewhere on the washes (NCC, 1983).

The period 1972-2001 has seen major change to plant communities from a ‘closed grassland’ system dominated by fine-leaved grass (MG11/13), Deschampsia caespitosa (MG9) and swamp (S5/28) communities to an ‘open weedy’ system of species-poor swamp (S4/5) and open (OV28/29/30/32) communities. Although MG11/13 have not been separated consistently during the period 1972-2001, MG13 (now scarce) was regarded by early surveys as the major, if not sole, community of the low growing inundation swards of the washes and Rodwell, writing in the early 1980s, draws attention to the tight sheep-grazed swards of MG13 on the Ouse Washes (Rodwell, 1992).

There are some important notes to Table 1, particularly Note 1:

 Based on bird data alone as an indication of the favourable condition of the vegetation, it is likely that the Ouse Washes were in a favourable condition at the time of SSSI

notification in 1955 and during the 1960s. The vegetation communities then began to change through the 1970s and showed an accelerated rate of decline during the late 1980s through to the present day. During this period, a number of key bird species, such as black-tailed godwit, have also declined.

2.2 Relationship between vegetation change and inundation

Table 2 (data courtesy of RSPB Reserve, Welches Dam) shows the percentage of years in which the Ouse Washes experienced partial flood months (ODN [Ordnance Datum Newlyn]>0.91m for at least one day) and full flood months (ODN>1.75m). An attempt was made to demonstrate the relationship between the extent of flooding and the distribution of broad vegetation types across the washes in 2001.

A snapshot of a partial flood event was obtained on 24 November 2001 when a set of oblique aerial photographs was obtained by C. Carson (RSPB) during a low level flight. The flood level recorded at Welches Dam at the time was 1.11m ODN. A series of ‘ponding’ maps were produced from these photographs by RSPB staff and these were overlaid onto the vegetation map produced for 2001. The outline of ponded areas was digitised and flood areas derived. When the extent of flooding on 24 November 2001 is related to the vegetation pattern, it can be demonstrated that it is the Glyceria-dominated areas and those supporting inundation communities of the Bidention which are most affected (see Table 3).

2.3 Likely vegetation succession with increasing inundation

This is illustrated in a diagram. The most recent comprehensive vegetation survey (2001) showed that the vegetation of the Ouse Washes lies to the far right of centre of this schematic for vegetation succession.

The known vegetation succession from other sites with increasing ‘prolonged water logging during the growing season’ and ‘nutrient enrichment’ is presented from a draft paper (Gowing, 2003 in draft) as part of a joint EA/EN contract.

2.5 Relationship between vegetation change and nutrient enrichment

Prosser and Wallace (2001) noted that increasing concentrations of available nutrients, especially soluble N, may be contributing to the changes in species composition and species dominance across the washes. Suggestion of such an effect is provided through a comparison of the Ellenberg ‘N’ values of those species perceived to be increasing in the swards of the washes with those taxa which are apparently in decline.

3. Vegetation of ditches and pools

Table 5 shows the plant communities as defined under the National Vegetation Classification (NVC) for the Ouse Washes. Cathcart (2001) studied the ditch communities of the Ouse Washes placing them into eight main groups. The table shows how these groups relate to NVC communities. Key Nationally Scarce (NS), Regionally Scarce (RS) and Red Data Book (RDB) species and their most recent record are included in the last column.

3.2 Relationship between aquatic communities and water nutrient enrichment

Table 6 indicates the change in aquatic vegetation communities with increasing nutrient enrichment of the water.

Table 6. Relationship between NVC (aquatic) ditch communities and mean water chemistry (adapted from Cathcart, 2001)

Group NVC No. Total P Total N Chlorophyll a pH Turbidity Dissolved (Cathcart ) community ditches (mg/l) (mg/l) (μg/l) (NTU) oxygen (%)

1 A5b 6 0.54 1.73 25.34 7.84 4.89 86.16

2 A15 12 0.58 2.99 49.60 8.09 9.39 90.50

3 A1/A2b/A3 15 1.08 2.69 43.79 7.72 9.47 47.94

4 A16a 14 1.05 3.63 90.29 7.50 17.57 53.25

There are some important Notes to this Table:

1. There is the following successional trend with increasing nutrient status: Charophyte ssp. to Elodea to Ceratophyllum demersum - Lemna minor - Lemnaceae, and this succession loosely follows a pattern from species-rich Cathcart community groups 1 (NVC A5b) and 2 (A15) to species-poor Cathcart community groups 3 (A1/A2b/A3) and 4 (A16a). 2. Further analysis of this relationship and the relationship between the nutrient status of the Bedford Ouse and the internal ditches of the Ouse Washes is currently being undertaken as part of a joint EN/EA water quality project which includes additional water sampling undertaken in 2002 and 2003. 3. Currently, the average total P concentration for internal ditches is approx. 0.7mg/l (seven times the conservation objective targets). The average total N (oxidised) concentration is 0.4mg/l (within the conservation objective target of 1.5 mg/l) but there is a large range (0.2 - 8.0 mg/l). Further work is required as highlighted above in note 2.

I have unusually included this Table as this Section 3.2 is fundamental to the objectives of the review and sets out the relationship between water chemistry and plant communities, drawing on the work of Cathcart, 2002, the most detailed piece of research carried out on the Washes themselves looking at these factors. The trend in the relationship is clear as is the succession in communities associated with it.

Table 5 sets out the plant communities of ditches and pools. Again there are Notes:

1. True Aquatic communities (NVC ‘A’) are the most important communities in terms of rare plants. Cathcart community groups 1 (NVC A5b) and 2 (A15) are more important

than the species-poor community groups 3 (A1/A2b/A3) and 4 (A16a). Group 4 (A16b) includes all the most species- poor ditches. 2. Of 47 ditches sampled by Cathcart, 29 (62%) comprised species-poor community groups 3 and 4 with group 4 (very species-poor communities) comprising 30% of samples.

4. Invertebrates

Insufficient data exists to provide comprehensive hydroecological prescriptions for invertebrates, the most notable component of which is associated with internal ditches.

5. Birds

5.1 Ideal water regime required to enable nesting, feeding and roosting

Figure 5 of this paper, referring to the ‘new ideal’, is important as it shows the required physical water regime for birds using the Ouse Washes (ie nests of spring waders not flooded, correct water levels for different species to feed in summer and winter). Again it has Notes:

1. The ideal water regime is based on over 30 years of bird recording by RSPB. 2. To further provide the range of different water levels required by different bird species, water levels should fluctuate widely (often naturally as ‘pulses’ in relation to the tide cycle) between the upper and lower limits. 3. Water levels should be maintained within the limits of the ‘new ideal’ regime three years in every four years.

5.2 Food preferences

Table 7 is a large Table that summarises bird food preferences for the Ouse Washes. Numbers in brackets under the species refer to Thomas (1978) and denote frequency of plant/animal food items per bird species sample. For example, shoveler (16+/101) means that plant/animal species were recorded in at least 16 of the 101 shoveler guts examined. The NVC community that the different species are using for feeding are also given in this Table. Again there are Notes:

1) Important plant communities for feeding birds include MG11/13, S5, S6 and S19, species rich aquatic communities. 2) MG9, although grazed notably by wigeon, is less important than MG11/13 in terms of plant food for birds but will likely harbour important invertebrate food. It also has a ‘tussocky’ structure important for nesting waders due to the presence of the grass Deschampsia caespitosa. 3) In addition, S28 is enormously variable but of general value to birds.

6. The spined loach and its associated habitat - Counter (Old Bedford) and Old Bedford

(Delph) Drains

To be written following guidance outlined in the completed final reports of the joint EN/EA spined loach habitat manipulation study being undertaken by APEM aquatic scientists at Moretons Leam Drain (Nene Washes).

Summary, RK February 2015.

11. ENVIRONMENT AGENCY – ANGLIAN REGION. OUSE WASHES HABITAT CREATION: BUSINESS CASE FOR THE NEXT 5 YEARS OF INVESTIGATION, LAND PURCHASE AND PERMISSIONS. MARCH 2007. Noted - Ouse Washes Habitat Creation (First 5 Years of Land Purchase, Permissions and Consents) = £31,305,912 (incl. contingency).

1.1 INTRODUCTION AND BACKGROUND 1.2 The Ouse Washes Special Protection Area (SPA) in Cambridgeshire is an internationally important wildlife site (see Figure A). Its condition has deteriorated since the 1970's as a result of summer flooding and, to a lesser extent, nutrient enrichment. There is a legal obligation on the UK, arising from Article 6(2) of the EU Habitats Directive and associated articles of the EU Birds Directive to address this deterioration. A range of studies have been undertaken in the last 20 years to find a solution with this information reviewed in 2004 by a high level Steering Group set up by Detra. Having considered the recommendations of this Steering Group Detra announced, on 24th March 2005, that money would be made available to fund the creation of additional habitat to off-set the damage to the existing Ouse Washes. The Environment Agency was tasked with delivering 1008 ha of new wet grassland habitat.

1.3 An overarching Implementation Strategy has been prepared with its principal objective being 'to provide new wet grassland habitat to meet the ecological requirements for those species negatively affected by deterioration of the Ouse Washes (namely Black-tailed Godwit, Snipe, Wigeon and Ruff)'. This business case seeks approval to fund the first five years of securing suitable land and obtaining the relevant permissions and consents to implement the Strategy.

2.1 The Problem 2.2 An overarching Implementation Strategy has been prepared with its principal objective being 'to provide new wet grassland habitat to meet the ecological requirements for those species negatively affected by deterioration of the Ouse Washes (namely Black- tailed Godwit, Snipe, Wigeon and Ruff)'. This business case seeks approval to fund the first five years of securing suitable land and obtaining the relevant permissions and consents to implement the Strategy. 2.3 In liaison with an Ecological Consultation Group three potentially suitable target areas within 5km of the existing Ouse Washes SPA were chosen for further work in November 2005. During 2006 the landowners in these areas have been identified and approached, with sensitivity, to introduce them to the project and to gauge their interest in selling land. In addition, some fieldwork has been undertaken to confirm the soils and hydrological conditions. 2.4 We are now in a position where approval is needed to be able to fund land purchases and land swaps, and to progress obtaining the necessary permissions and consents to enable habitat creation to take place.

3.1.1. Options

3.1.2. A range of habitat delivery options have been considered in both the Implementation Strategy and in this business case. The options revolve around whether to strive for one site of just over 1OOOha, for two sites or up to 5 smaller sites. The do nothing and do minimum options were rejected as they both fail to meet the legal requirement to address deterioration of the Ouse Washes SPA.

4.1 PREFERRED OPTION

4.2 The preferred Strategic option is to aim to secure and develop two separate sites of 550ha each (approximately 500ha of habitat plus 50 ha of infrastructure). 500ha is the minimum desirable site area criteria set out by Natural England. Whilst this option is not the ideal situation in terms of site size (a 1000ha habitat site would have fewer edge effects and would be slightly cheaper to manage) achieving it is considered to be more realistic and would mean that some new habitat is likely to be delivered and functioning more quickly.

5.1 ECONOMIC CASE AND PRIORITY SCORE

5.2 A typical benefit:cost analysis and the calculation of a priority score are not appropriate to this project as it is required to meet a UK legal requirement. Table X presents PV costs for the preferred option, subject to this business case and for the full 100 years of the Implementation Strategy. The costs for the preferred option have been developed in close consultation with both conservation organisations and land agents.

Present value costs: £22,635,9055 5 years (land purchase, permissions and consents).

100 years {all costs) £43,915,222.

6.1 ENVIRONMENTAL CONSIDERATIONS

6.2 By its very nature this project has been developed in a manner sensitive to the environment. The criteria for selection of land areas to pursue are environmentally and ecologically based. A non-statutory SEA Environmental Report has been prepared to accompany the Implementation Strategy. It sets out the strategic environmental objectives relevant to this project, identifies key environmental opportunities, constraints and impacts.

6.3 Once suitable land parcels have been assembled they will be subject to an EIA and an Environmental Statement prepared to accompany a planning application. An Appropriate Assessment has been prepared at the Strategy level. In addition, scheme level Appropriate Assessments are likely to be required for suitable land parcels as they are progressed through the planning system.

6.4 Consultation has been undertaken with a wide range of organisations. The overwhelming response to the proposals has been positive. In addition, we have approached landowners near the Ouse Washes to ensure that they hear about the project from us and to gauge their interest in participating.

7 RISKS

8 IMPLEMENTATION

8.1 Approval for the overarching Implementation Strategy which covers the 100 years is being sought separately. This Business Case seeks approval for the first five years of work in securing land and gaining the appropriate permissions and consents to allow habitat creation to proceed. It does not cover habitat creation and management costs and it is anticipated that approval for these will be sought regionally.

9.0 Contributions and Funding.

No contributions are anticipated.

10.0 Status

The work detailed in this business case is in accord with Defra's instruction to deliver habitat to address the deterioration of the Ouse Washes SPA. It is also in accord with the Ouse Washes Implementation Strategy. It seeks approval for the work associated with securing land, permissions and consents as part of the first five years of the Implementation Strategy. Costs associated with subsequent habitat creation works and site management are covered in the Strategy but are out with this business case. Approval will be sought for them on a site by site basis.

11.0 Recommendations

Approval is sought to progress land purchase, detailed design, EIA and to obtain the necessary permissions and consents to enable habitat creation to proceed. The approval sum is £26,983,346 without contingencies and £31,305,912 with contingencies (95%ile).

A summary of the costs is provided.

Part of this Report is a detailed Director’s briefing paper.

Background

Detailed studies of the 'summer flooding' issues were undertaken in the 1990s, to understand the problem and identify solutions. In October 2000 the site was entered onto the Montreux Record, a list of failing Ramsar sites.

In 2004, Detra set up a high-level Steering Group for the Ouse Washes, with the membership made up of Directors from Defra, English Nature (now Natural England), the Royal Society for the Protection of Birds and the Environment Agency. The purpose of this group is to ensure the improvements to the Ouse Washes that are required to remove the site from the Montreux record. The first element that this group has addressed is the solution to the flooding issues.

Through the Ouse Washes Steering Group, there was an increased effort to finding a solution, reaching a decision and obtaining funding. This included a multi• organisation discussion (over a period of 6 months) on the legal nature conservation requirements, particularly those relating to the European designations for the Ouse Washes. From the Environment Agency

the discussions involved National Flood Risk Management policy and national legal advisors to ensure that the outcome for the Ouse Washes does not present unacceptable precedents for elsewhere in England and Wales.

Creating new wet grassland habitat outside the existing Ouse Washes is an alternative solution for the degraded nature conservation interest and within the Steering Group much effort was concentrated on calculating the area needed and detailing the requirements e.g. soil type and water availability.

By March 2005, Detra had concluded that there was a legal obligation on Government to take action on the degraded habitat under Article 6(2) of the EU Habitats Directive, and associated articles of the EU Birds Directive, and that habitat creation was the most appropriate solution.

On 24th March 2005, Elliot Morley MP held a press conference on 'Making way for water' and within it he referred to the Ouse Washes:

"The Government is committed to ensuring that the flood risk management programme takes proper account of the environmental impacts of our interventions. As a practical example of this I am pleased to announce that we shall be taking measures to offset damage occurring to the Ouse Washes Natura 2000 site. This will allow the site to continue to protect people and property from flooding at the same time as addressing the environmental value it provides for birds."

At the Steering Group meeting on 5th April 2005 the details of the Minister's approval were outlined and the implementation discussed. In summary the details are:

 1008 hectares of wet grassland to be created to support the deteriorated species of bird.  Criteria for the site selection to be produced by English Nature (now Natural England).  Environment Agency to be asked to implement the creation of the area.  Environment Agency would not be the operator of the area, but would be expecting a consortium of RSPB, WWT and the Wildlife Trust to operate the site.  Funding will be provided from Detra FM budget and this will be organised through the Environment Agency's FRM funding. A provisional sum is already in the Long Term Plan that went to Detra in October 2004.  Financial phasing of the project will be required [over 4-5 years].

In Summer 2005 the Ouse Washes Habitat Creation Project was set up to implement the above decisions and to deliver the replacement habitat.

The Project Executive is responsible for the delivery of the project. The Project Board members provide support and expertise to the Project Executive, who chairs the Project Board meetings. The Project Manager, under the management of the Project Executive, is responsible for the successful planning, development and delivery of the project. The Project

Manager manages the Project Team. The Business User's role is to ensure that the product(s) delivered by the project are fit for purpose.

An Ecological Consultation group was set up to advise and make recommendations to the Project Board on a range of ecological issues within the project. A similar group has been used to explore Land Acquisition issues.

Approach to Approvals

It is recognised that the creation of such a large total area of replacement habitat (over 1OOOha) will take several years to achieve; will involve a number of partner organisations; and is likely to involve habitat creation work at a number of distinct geographical locations around the Ouse Washes . Therefore an overarching 'Implementation Strategy' has been prepared which sets out how the project as a whole will be managed and implemented. This document was submitted to the National Review Group (NRG) in May 2007 together with an accompanying non• statutory Strategic Environmental Assessment report.

2.2 Problem

The background to this project and the decision to proceed with habitat creation is summarised above and is described further in the Implementation Strategy. The challenge now facing the project revolves around acquiring land that meets the site suitability criteria and then securing the permissions and consents necessary to enable habitat creation to commence.

Confirmation of Suitable Areas at Sutton

All the above information was presented to the Ecological Consultation Group in July 2006 and the Project Board in August 2006. Agreement was reached that habitat creation at Sutton was a viable proposition and that work should proceed to develop this business case (i.e. to seek approval to proceed with land purchase, detailed design, Environmental Impact Assessment, and securing the various permissions and consents).

2.3 Options Considered.

A range of alternative solutions to the ecological problems of the Ouse Washes have been examined over the last 20 years. These are summarised in the Ouse Washes Solutions Report and are referred to in the Implementation Strategy. Following Defra's instruction in 2005 to proceed with replacement habitat creation as the preferred solution an overarching Implementation Strategy has been prepared and presented to the National Review Group in May 2007. The Implementation Strategy examines options for the delivery of replacement habitat. It identifies the preferred strategic option to be the creation of two new 550ha habitat sites. In light of this the options discussed below are limited to Do Nothing, Do Minimum and progressing with the preferred option in the Implementation Strategy.

Progress with Creating Replacement Habitat

Having secured agreement from the Project Board and the Ecological Consultation Group that a viable site could be created within 5km of the Ouse Washes this option involves the

progression of work to acquire land and thereafter create replacement habitat. It will fulfil Defra's instruction to the Environment Agency to undertake this work and will ensure the government meets its legislative obligations. This is the preferred option and is in accordance with the Implementation Strategy.

We know from work to date that there are sufficient suitable areas for habitat creation available within 5km of the Ouse Washes to meet the needs of this project. However, at this stage landowner negotiations have not reached a point where we can have certainty over their success.

A section of the report then looks at the costs of options.

2.8 Other Considerations In addition to the costs of purchasing land, obtaining permissions and consents and creating the required habitat there is an ongoing longer term cost associated with the project resulting from work to manage and monitor the habitat sites. These costs, which are approximately £440k per annum have been calculated based on experience of managing similar sites elsewhere and are presented in the Implementation Strategy and in this business case.  An allowance to account for future climate change has been incorporated into the whole life costs in the Implementation Strategy (i.e. through the provision of a sum to allow for a second storage reservoir to be constructed in 2040).

I have not reviewed the Project Plan which is included in this document as it repeats much of what is set out above.

RK Summary, 18 March 2015.

12. A SUMMARY OF THE WATER QUALITY INFORMATION AVAILABLE IN THE NATURAL ENGLAND OUSE WASHES FILES. BAYLISS, S. 2008. Most of the reports relating to water quality were produced for the Environment Agency to inform the Review of Consents work and the various AMP programmes. These data and reports therefore focus mainly on point sources of phosphates. However, an analytical assessment of the apportionment of diffuse and point sources, from different parts of the Great Ouse catchment, for both phosphates and nitrates is available.

1. Ouse and Nene Strategic Studies, Ouse Washes: Water and Nutrient Level Analysis. December 2003, Entec UK Ltd for the Environment Agency.

The approach to this study was wholly analytical, using water quality and flows models of the Great Ouse catchment and the OW system to derive data and make predictions. Caution should therefore be applied to the interpretation of these derived data, as any modelling approach carries some inherent risks and uncertainties.

Acceptable Thresholds (phosphates and nitrates,page 3)

The prescribed acceptable total phosphorus thresholds are derived from a set of acceptable ortho-phosphate threshold guidelines produced by the Agency for sites affected under the Urban Wastewater Treatment Directive (UWWTD). The acceptable threshold defined in this document is 0. 1 mg/I ortho-phosphate (ortho• P). This value has been amended slightly for the purposes of this study (due to model output constraints) to 0.2 mg/l total phosphorus, excluding sediment deposited P, (Total-P). This value has been used in the absence of any better value, and has been discussed and agreed fully by the Environment Agency.

The 0. 1 mg/l ortho-phosphate target is also found in the favourable condition table for the cSAC in relation to spined /oach, which is directly relevant to the cSAC. The FCT for spined loach refers to an annual average target, and therefore, the targets for the various areas of the Washes should also be considered as annual average values. This factor is vital deciding whether ditches and other watercourses are in or out of regime.

The prescribed acceptable total nitrogen and TIN thresholds are taken from a previous study undertaken by WRc, on behalf of Anglian Water. The thresholds used for the purposes of this study are 1.6 mg/I total nitrogen and 0.8 mg/l TIN. These values have also been used in the absence of any better value, and have been discussed and agreed fully by the Environment Agency.

Although we do not have specific targets relating to nitrates in our Favourable Condition Tables (FCTs) (also referred to as 'Conservation Objectives') for the OW, we do know the 'tolerances' of various grassland and aquatic plant communities to nitrates, published in various reference sources. This is discussed further below under 'Aquatic plants'.

When discussing diffuse inputs, it is important to understand that the OW SAC and SSSI ditch feature consists of the two parallel main 'rivers' (very large drainage ditches) running along the north-western side of the OW. The 'outer river' (Counter Drain/Old Bedford) derives its water from the pump-drained Middle Level and is virtually hydrologically separate from the

'the inner river' (Old Bedford/River Delph) which derives its water from Earith and higher up the Great Ouse catchment. This is illustrated and discussed further below in the section relating to Table 5.1.

Chapter 4 Nutrient source apportionment Nitrates page 63

The impact of scenario 4 {decreased diffuse pollution) is to significantly lower diffuse nutrient loadings from all sub-catchments. This mirrors the pattern seen previously for ammonia and strengthens the conclusions that the majority of nitrates are from diffuse sources. However, even with the 1960s landuse scenario, diffuse nitrate loadings still remain high, with an average daily loading from each sub-catchment during January being estimated at between 2000 and 6000 kg/day. This suggests that there is a high natural level of nitrates in the catchment and management of artificial discharges or agricultural diffuse pollution within the catchment may be relatively ineffective at controlling nitrate levels.

This paragraph is not worded very clearly, but looking at Figure 4.9, page 63, there is little difference between the current licensed scenario (current abstractions and discharges) and the naturalised scenario (no abstractions and discharges) that included an estimate of current diffuse inputs. This does indicate that the majority of nitrate inputs are diffuse.

However, I don't completely follow the argument that there is a high natural level of nitrates in the catchment. Figure 4.9, page 63, shows a reduction of approaching 6000 kg per day (average daily load) between the naturalised scenario that included an estimate of current land use and the naturalised scenario that estimated 1960s land use.

Note that the 1960s naturalised scenario produces the lowest nitrate loadings, which is assumed to be due to decreased fertiliser applications rates and less intensive farming practices. Note also that the naturalised scenarios also remove the abstraction licences, which will affect dilution factors.

Note that there is very little difference between the current land use naturalised scenario and the 1960s naturalised scenario and there is a predicted increase in diffuse inputs of phosphates under both naturalised scenarios (removal of abstraction licences and discharge consents) from the current scenario. Interpretation of this Table is not straightforward as it suggests dilution (from reduced abstraction) makes the loading from diffuse inputs worse. One interpretation is that some of the phosphates are being taken out of the system via water abstraction. Entec echoes this and considered that: the third scenario (naturalised, but with current landuse) offers the highest nutrient loading, since diffuse pollution continues at a high level, but abstractions (and hence removal of phosphorus rich waters) are removed completely (Page 72).

Currently, therefore, there is approximately 75kg phosphorus on average, per day, entering the system from these parts of the catchment from diffuse sources. During the year, as for nitrates, this is heavily weighted towards the winter months, presumed to be due to agricultural run-off under increased rainfall conditions. Although the relative contribution of phosphates from diffuse sources is small as compared to point sources (circa 22% in winter and 5% in summer), this modelling work does identify its presence and it cannot therefore be

ignored. Furthermore, as the planned improvements to Sewage Treatment Works (STWs) are implemented in the catchment (via AMP4), the relative significance of these diffuse phosphorus inputs will increase.

As a comparison Bayliss presents a Table 4.6 which shows that the point source contribution is predictably much higher than diffuse sources at 325kg per day compared to 75kg per day.

2. Monitoring of the Wash and Ouse Washes in 2007 for the National Environment Programme, Fifth Annual Report. Black and Veatch, August 2008, report for Essex and Suffolk Water.

The following table is extracted from the above report; work that was required for the monitoring of the Denver Licence variation. It is presented in a clear format but note that there are also long• running water quality data available from the Environment Agency, and Natural England hold some of this information on file.

Table 5.1 Tributary and Ouse Washes water quality in 2007.

Tributary Site Total oxidized N Ortho-phosphate Mg/l N Mg/l P Bedford Ouse Brownshill 7.9 0.23 Middle Level main Mullicourt Priory Sluice 7.8 0.08 drain Counter Drain/Old Old Bedford Sluice 7.5 0.04 Bedford Counter Drain/Old Welney Bridge 9.6 0.02 Bedford Counter Drain/Old Welches Dam 9.7 0.02 Bedford Old Bedford/Delph Welmore Lake Sluice 4.1 0.18 Old Bedford/Delph Welney Bridge 4.4 0.19 Old Bedford/Delph Welches Dam 4.5 0.06

This gives just a snapshot of water quality for the 'outer river' (Counter Drain/Old Bedford) river and the 'inner river' (Old Bedford/Delph). Ouse Washes site features that require direct water quality monitoring for a CSM compliant Condition Assessment are the Spined Loach feature and the ditch feature. In addition, the Favourable status of the vascular plant assemblage (mainly aquatic macrophytes) is affected by water quality (both nitrates and phosphates).

The Table shows the difference in water quality between the two 'rivers' that derive their water from different sources. In general, phosphate concentrations are higher in the Old Bedford/Delph and upstream at Brownshill, as compared to those readings in the Counter Drain/Old Bedford.

Interestingly, the converse seems to be true for N, where levels are higher in the 'outer river' fed from the pump-drained Middle Level catchment as compared to the inner river. This may be due to dilution, which is far greater in the waters entering the Old Bedford/Delph from higher up the Great Ouse catchment than that occurring in the Middle Level.

It is unclear whether 2007 was a typical year and there are further data available for other years via these reports and other sources, which can be sought and supplied if necessary.

3. Targets for N and P for the Ouse Washes SSSI and SAC features

Spined Loach - SAC feature

The target in the FCT for this SAC feature is 0.1mg per I of 'soluble reactive phosphorus' expressed as an annual mean. This target is CSM compliant. The rationale behind this target is that: excessive enrichment with phosphorus increases the risk of impacts on the submerged plant community, which the spined loach uses for cover.

There is no specific target for nitrates in the FCT for Spined Loach. However, there is also an attribute to achieve ditch water quality targets of: equivalent quality to Chemical GQA Class 'C' (for dissolved oxygen, total ammonia and Biological Oxygen Demand).

Ditch system - SSSI feature (specifically the 'outer river' and 'inner river')

A target of 0.1mg per I of 'total phosphorus' applies for this SSSI feature and this is also CSM compliant.

There is no specific target for N for this feature. Again, there is an attribute to measure water chemistry and the target here is: Chemical GQA Class 'B'. In addition, no drop in class from existing situation.

Aquatic plants

The Ouse Washes SSSI is also notified for a 'vascular plant assemblage' as a number of nationally scare and rare plants occur in the drainage ditches (and the wet grassland). Although there is no specific target for N or P attached to this feature, they do have known tolerances of levels of nutrients as indeed do the various wet grassland communities.

The previous Responsible Officer for the Ouse Washes drew up the Hydro-ecological prescriptions for Favourable Condition (Jonathan Graham, May 2003). This document considered the tolerances of key aquatic plant species to nutrient enrichment and drew upon work done by Rob Cathcart in 2001 ( Effects of Nutrient Loading on the Ditch Flora of the Ouse Washes: Current Impacts and Potential Mitigation) and the then emerging Ecohydrologica/ Guidelines for Lowland Wetland Plant Communities (since published by the Environment Agency, Final report, December 2004). In summary, Graham considered that; the majority of the internal ditches support NVC A5 and A 15 aquatic plant communities (Cathcart groups 1 and 2). These communities require concentrations of total phosphorus to remain consistently below 0.11 mg per I and total nitrogen below 1.5 mg per l.

4. What do we need to know?

What we don't know is the exact mechanism by which the diffuse nutrient inputs enter the Ouse Washes system. We just know they are there and highly likely to be from agricultural sources, given the nature of the catchment. Routes of entry are, in general terms, well known and consist of leaching and percolation of drainage water through the soil into the drainage

ditch or river system, run-off from inorganic and organic fertilisers applied to the land, erosion of nutrient-laden surface soils into watercourses and movement of fine soil particles into subsoil drainage systems. Whether it is feasible, necessary or cost-effective to get a better understanding of these processes for this catchment or a sub-catchment is unclear and would require specialist input to determine.

5. Summary

There is a body of research and evidence to support the inclusion of diffuse water pollution as an 'adverse reason' for Unfavourable condition for this site. Ouse Washes specific sources of evidence, especially that relating to apportionment of diffuse and point sources are derived from the Environment Agency and rely on analytical modelling. Long-running water quality data are also available from the Agency. There are also published sources of information and guidance relating to botanical communities and their tolerances to nutrient levels, which can be applied to both the Ouse Washes and other designated sites. We do not know the relative importance of the likely routes of entry of diffuse nutrients and it is unclear as to whether it is necessary to improve this understanding to successfully progress the Catchment Sensitive Farming project and the Strategic Partnership Catchment for the Great Ouse.

RK Summary, 23 February 2015.

13. A REPEAT TRANSECT VEGETATION SURVEY OF THE OUSE WASHES – A REPORT FOR THE ENVIRONMENT AGENCY. JONATHAN GRAHAM, FENLAND BOTANICAL SURVEYS, 2008. Introduction

The vegetation of the Ouse Washes (excluding field ditches) was surveyed by MV Prosser and HL Wallace in 2001 (Vegetation Change on the Ouse Washes, Prosser & Wallace, January 2002). A major part of this piece of work included surveying the vegetation using quadrats along 8 transects and assigning vegetation types based on the National Vegetation Classification (NVC).

The Environment Agency has commissioned Fenland Botanical Surveys to repeat these vegetation transects in 2008 but with no interpretation of the data beyond assigning the vegetation of individual quadrats to NVC.

Methodology

Following the Prosser & Wallace methodology, both 50cm x 50cm quadrats estimating rooting frequency and 100 x 100m quadrats estimating percentage cover were undertaken at 20m intervals along each transect line. Survey work was undertaken on the 18, 19, 26, 27 August and 01, 02, September 2008. In the field, transects were located by reference to location maps from the Prosser & Wallace report and by using a compass and hand held GPS unit. For reference, the Prosser & Wallace original location maps are included in this report as Appendix 6.

Results

The Prosser & Wallace original quadrat data (per transect) has been copied into Microsoft Excel. The purpose of this is to allow greater statistical manipulation of the data in the future by third parties. The format of the data has also been lightly modified so that in most cases, quadrat data for each transect can be printed on a single side of A4 landscape. Species nomenclature has also been updated to reflect changes in taxonomy during the period between the two surveys (2001-2008).

All quadrat data is contained in 32 Excel files. These are:

1) Prosser & Wallace original 2001 quadrat data for rooting frequency at the 8 transects (8 Excel files)

2) Prosser & Wallace original 2001 quadrat data for percentage cover at the 8 transects (8 Excel files)

3) Repeat quadrat data (J Graham, 2008) for rooting frequency at the 8 transects (8 Excel files)

4) Repeat quadrat data (J Graham, 2008) for percentage cover at the 8 transects (8 Excel files)

All 32 files (printed mostly on a single side of A4 landscape) comprise Appendices 2-5 of this report.

NVC communities

Based on the quadrat data in Appendices 2-5 (J Graham, 2008), 11 NVC communities were recorded. In addition, following Prosser & Wallace (2002), stands of Glyceria maxima (S5) with greater than 2% cover of Reed canary-grass Phalaris arundinacea have been recorded as S5(P) and stands of Phalaris arundinacea (S28) with greater than 2% cover of Reed sweet-grass Glyceria maxima gave been recorded as S28(G).

Considerations in interpreting change in NVC communities (2001 - 2008)

When comparing distribution of NVC communities between Prosser & Wallace (2002) and J Graham (2008), there are clear changes, most notably a sharp reduction in the number of quadrats with NVC OV communities in contrast to a sharp increase in the number of quadrats with Glyceria maxima type vegetation - S5a/b and S5(G). 2008 was a flood year with water staying on the site as late as May 2008 and with several flood events during the summer months, and heavy rain in August resulting in flooding of the site by early September. This has had two related effects on the vegetation: a.Extended period of flooding during the growing season

Water (greater than 10cm depth) stayed on lower lying washes for such a length of time during the growing season that plant species of drains, including true aquatics such as duckweeds Lemna species and rigid hornwort Ceratophyllum demersum became establishes within the open wash vegetation. The result of this is that many of the quadrats have a small number of aquatics which are of a transitory nature and need to be partly ignored when interpreting quadrat data. b.Reduced grazing pressure as a result of flooding during the growing season

The long flood season of 2008 meant that grazing was late and consequently, at the time of survey, many of the washes had rank swards that were either ungrazed or were just starting to be grazed. As a result, Glyceria areas were rank and species-poor. The same was true of many of the other transects which were cattle grazed but also had rank areas of species-poor Glyceria. When Glyceria is under-grazed, it becomes rank (50-60cm height) and shades out other species. As a result of this, common associated herbs, such as Marsh bedstraw Galium palustre and Water mint Mentha aquatica, were present at a cover of less than 2% and quadrats with 100% cover of Glyceria were recorded a good number of times. In addition, swards of Glyceria maxima with frequent Phalaris [S5(P)] are more likely to revert to a denser cover of Glyceria with reduced grazing pressure.

RK Summary, May 2015.

14. GREAT OUSE AND OUSE WASHES: CATCHMENT APPRAISAL REFRESH PROFORMA, 2009. DJL AGRONOMICS, FULSTOW, LOUTH, LINCLONSHIRE LN11 OXR. It is unfortunate that there is no introduction to this report so that the context is difficult to pick up. It is also written in an informal style that does not help understanding, however the report does have a summary. The distance yet to be travelled in addressing issues relating to diffuse pollution is perhaps indicated by the fact that a number of the recommendations are quite broad and perhaps lack specificity.

KEY DISCUSSION POINTS

1. With the improvement of Sewage Treatment Works discharges, the general assumption follows that the diffuse component now needs to be addressed more comprehensively. It is not clear however, what the breakdown of phosphorus loadings is between agricultural runoff and remnant levels remaining in the rivers and floodplain sediments. In other words a legacy from the STW and other uses is likely to remain and contribute to the loadings for some time in the future. Could give consideration to targeting floodplains for more detailed soil analysis, perhaps also including some heavy metal assessments in addition to the normal range? 2. High intensity rainfall events are often cited as the reason for erosion and runoff occurring. Encouragement should be given to treat such events as becoming more common and appropriate measures and cropping treated as good management. 3. No sediment management plan appears to be in place for the catchment. Such a plan would highlight the range of contributing issues leading to sediment loading and the joined up approach necessary to reduce the problems on a catchment wide basis involving all users. It would be essential to include in this flood management policy and the use of floodplains as increases in use and changes in approach will impact on floodplain management of the land. 4. As part of the Catchment management process clear measures of success or milestones need to be agreed and set with all members of the partnership. Such measures are important for achieving the objectives of the programme and also to build customer and partner confidence in the work being promoted. 5. Management objectives in terms of catchment priorities would be a useful step in targeting improvements, especially for oilseed rape and temporary grassland. 6. It is important that some clarity is brought to the data and objectives so the Strategic Partnership programme and priorities can be focussed on specific issues where a clear link between agricultural practice and pollution problem can be attributed. Additional work is required working with all partners to better identify the issues of concern. The proper working of the Strategic Partnership should allow for example raised levels of a pesticide in water to be traced back to users using the increased range of data sources available through the partnership. 7. Soil management especially the use of minimal cultivations and direct drilling may have an influence on runoff levels from the clay areas of the catchment. The management

and implications of these cultivations will be a priority, especially targeting higher risk areas and fields. 8. To meet the requirements of the Water Framework Directive, Habitats Directive, Drinking Water Directive, and other Regulations multiple pressures have been identified in this report, which require an integrated catchment wide management approach from a range of partners. These pressures which are identified as sediments, nitrates, phosphates and pesticides. These are often interrelated and hence the need for integration both to meet partners interest and resources as well as appropriate corrective measures. 9. Water Framework Directive classifications do not closely match the General Quality Assessment classifications for the target sub catchments. The extent of the chemical problems (N and P) therefore may not be fully represented.

CATCHMENT APPRAISAL REFRESH - SUMMARY DETAILS General description The catchment covers an area in excess of 3300km2 dominated by the River Great Ouse from its source north of Brackley. The Grand union canal bisects the upper catchment and there are also a number of feeder rivers including the Rivers Tove, Ouzel and Ivel. In the lower reaches the Middle Level catchment interlinks with the river system and interlinks with the Ouse Washes and Middle level River systems. Land use is mainly agricultural with the major urban areas of Milton Keynes, Leyton Buzzard, Bedford, Hitchin and Huntingdon within the catchment. The catchment is bisected by the M1, A 1 and A 14 major trunk routes. Soils reflect the geology and topography and are predominantly clay based glacial tills with sandy soils of the Qreensand ridge and chalk based derived from the Chiltern hills. A range of agriculture is practised within the catchment with arable, including high value vegetable crops and also extensive areas of grassland particularly associated with the river valleys and floodplains. The catchment has several waterbodies classified at high risk of diffuse pollution within the Water Framework Directive criteria1. This is particularly in evidence around the Bedford Ouse through to the Lower Ouse at Earith. The entire length of the Great Ouse from the headwaters has recorded high levels of nitrates and phosphates . Whilst sediment loads are recorded as moderate within the river systems there are significant issues with sediment deposition around Denver Sluice. Whilst some progress is predicted to improve the quality status of the river systems there are classified at present as predominantly moderate. This gives a strong focus for a strategic partnership approach to achieve wider objectives of the diverse users and dependencies both within and outside the catchment.

PROTECTED AREAS AT RISK OF DIFFUSE POLLUTION FROM AGRICULTURE - NO ALTERNATIVE OBJECTIVE ALLOWED 3.2 DRINKING WATER PROTECTED AREAS List or map of individual abstractions that are failing to meet Article 7.3 because of diffuse pollution from agriculture with a high degree of confidence and it is judged that existing measures will not be sufficient to reverse the situation or have insufficient legal force to be

relied upon. A map illustrating surface and ground water sources within the catchment is included at Appendix 11. 3.3 GROUNDWATER PROTECTION ZONES Three zones are within the catchment boundary and are illustrated. 4. PROTECTED AREAS AT RISK OF DIFFUSE POLLUTION FROM AGRICULTURE - EXTENDED DEADLINE ALLOWED

4.1 N2K Protected Areas that are failing conservation objectives N2K Protected Sites failing conservation objectives due to diffuse pollution from agriculture. See plan at Appendix 4 for an overview of sites within the catchment area.

4.2 SSSls in unfavourable condition due to DWPA Flitwick Moor.

5. SOILS Soils are very important element of the land use, farming and catchment characteristics and a table of the main soil types their location and description has been included for reference.

6. EXTENDED DEADLINE AND/OR LESS STRINGENT OBJECTIVES

6.1 SEDIMENT Local and anecdotal information - Sedimentation - there is a Table that shows this information.

6.2 PHOSPHORUS The map provided shows the following information: • WFD risk map for phosphorus • WFD compliance map for phosphorus • PSYCHIC map for diffuse phosphorus Notes on the data; see Appendix 2 There is a Table of - Local and anecdotal information – Phosphorus. This Table includes the Comment: GQA data indicates high levels of P in all river sections. Levels of 5 on a 1-6 scale with 6 being the highest and 1 the lowest are recorded at monitor ing points located in all river and tributary sections. Although there are some lower recorded figures the general trend is of high levels which are a significant issue to be taken forward to the targeting process. Whilst point source contributions continue to be high, inputs from diffuse sources within the catchment are significant. Total P entering the river systems from diffuse sources are currently in the order of 75kg/day. This is we ighted towards the winter months and the general assumption is that a high proportion of this is from agricultural sources. Surface wash is likely to be the main contributor. Review of consents data for Sewage treatment works indicates that point sources contribute above 60% of the P loadings and diffuse sources 40% and below. Of the 40% all is not from agricultural sources but a significant proportion is likely to be so and in the order of 20% based on Entec data for the Environment Agency .8.

6.3 NITRATE There is a Table of Local and anecdotal information – Nitrate. This has the following issues:  Abstraction points failing Article 7.3 resulting from Agricultural diffuse pollution. The areas concerned are between Huntingdon and Earith; to south and west of Bedford; West and south of Milton Keynes. Source reported failing because of diffuse pollution from agriculture with a high degree of confidence and it is judged that existing measures will not be sufficient to reverse the situation or have insufficient legal force to be relied upon.  Diffuse N - Impacts on SAC and SSSI features including aquatic plants, indicator species and ditch systems. Describes large geographical areas affected including the internationally designated sites. The main sources of Nitrates in the catchment are reported to be from diffuse sources, with a strong seasonal trend identified in nitrate loading. Peaks in November and December with a low in July have been identified. 9 This trend is attributed in the main to surface runoff rates with an assumption that this relates in the main to arable cropping. Whilst arable cropping (including vegetables) is the main land use, grassland represents a significant proportion and therefore both must be factored into the scenarios. Further assessment needs to be made through NVZ and the Strategic Partnership Programme to encourage landowners to better assess nitrogen inputs and improve soil management to minimise runoff.  Outdoor Pigs – mainly lighter soils to the South and west of the catchment, Extent and management requires further analysis but likely to be located on lighter sandier soils to the South and west of the catchment.

6.5 Pesticide There is a Table of local and anecdotal information:  Metaldehyde - peaks recorded in winter with very high levels recorded in 2008. Look to VI measures and catchment initiatives to reduce. High levels in exported water also so an issue for adjoining catchments (applies also to Clorpyralid)  Mecoprop - use on cereals and grassland (particularly for rushes on wet grassland indicating a priority to target flood grassland in the lower reaches of the Bedford Ouse may be appropriate. Also review use in terms of recreational land uses especially golf courses and domestic use for lawns etc  Clopyralid - increasing evidence that this chemical is becoming more evident in the water sources. Evidence from water company monitoring that peaks occur in late summer/autumn in both surface and groundwater sources. Catchment management is considered an important part of the toolbox for water quality improvements. Total pesticides and high levels of mecoprop (at a range of dates) are immediate issues which are relevant to catchment management. These need greater analysis as there is no particular conclusions that can be drawn except a peak of mecoprop in a number, but not all years, in the autumn. Cropping, rainfall, soil condition or tillage operations could be link but none are definitive.

6.6 SUMMARY OF RISKS AND IMPACTS IN THE CATCHMENT Local summary of risks and impacts in the catchment: 1. Drinking Water failing to meet Article 7.3

2. Impacts on Ouse washes and Portholme Natura 2000 sites 3. High to very high levels of P and N within the majority of the rivers and tributaries within the catchment 4. Water Framework objectives to be delivered through River Basin Management Plan 5. Changes in farming practise.

7.0 OTHER RELEVANT ACTIVITIES IN THE CATCHMENT A Table summarises these.

8.0 RANKING OF PROBLEMS - INCLUDING PRACTICES OF CONCERN Has a useful Table that looks at the issues by Subcatcment.

9.0 TARGET AREAS FOR 2009/10 AND 2010/11 Not really very informative and appears to lack clear specific actions.

10.0 Issues to be targeted within sub-catchments Useful summary but again fairly general.

11.0 General Issues within the catchment and also targeted areas Activities should therefore be focussed around reducing diffuse source losses from agriculture. Assuming that the farming community are following NVZ, CoGAP and Good Agricultural and Environment Condition (GAEC) requirements, a set of 7 recommendations for reducing the runoff of nutrients are recommended. Table 4 – has a weighting of issues within the catchment.

Table 5. Typical Agricultural Land use of some Risky crops and trends within the Catchment Key Facts from data relevant to catchment • Potato area in Bedfordshire increased 17% from 2006-07 • Permanent grass in Bedfordshire increased 3% 06-07 and 13% from 2000 • Oil seed rape increased significantly in both counties 06-07 • Temporary Grass increased significantly in both counties 06-07 • Rough grazing saw a sharp fall in Cambridgeshire but remained relatively constant in Bedfordshire

Appendices 1-6 inclusive missing from the version that I have, as well as 11 & 12.

Summary, RK 1 March 2015.

15. COMMON STANDARDS MONITORING CONDITION ASSESSMENTS OF THE OUSE WASHES SSSI, CSM SURVEY REPORT, OCTOBER 2009. WWT CONSULTING. 1.1 In July 2009, Natural England commissioned WWT Consulting to undertake Common Standards Monitoring surveys of MG11, MG13 and related wet grassland habitat within 12 management units of the Ouse Washes SSSI. The work was undertaken using the standard ‘structured walk’ protocol as described in Robertson and Jefferson, 2000. The remit was to provide data to enable Natural England to produce up to date condition assessments of the SSSI units as part of their ongoing monitoring programme. The original brief set out in Natural England’s tender document specified additional survey work to establish presence/absence of nationally rare and scarce vascular plants on the Ouse Washes. Following discussion prior to appointment, it was agreed with the Client that this element of the work was beyond the scope of the current survey in terms of cost. Therefore it was agreed that such plant species would only be recorded if encountered within the context of the general condition assessment work.

2. Aims and Objectives.

2.1 The aim of the project was to provide the Client with the necessary survey information, in an accessible form, to enable the Client to undertake a CSM compliant Condition Assessment of the current condition of the MG11 and MG13 grasslands of the Ouse Washes SSSI.

2 2.2 The objectives of the project were as follows:

 To undertake a Common Standards Monitoring compliant survey of the areas of remaining neutral grassland on the Ouse Washes SSSI;  To provide a map of the approximate extent and locations of the remaining areas of MG11/MG13 lowland neutral grassland communities (Rodwell,1998) and S28 Phalaris arundinacea swamp (Rodwell, 1997), where this occurs in a mosaic with the MG11/MG13 communities;  To provide a short report on the findings, to include a brief summary of the methodology, maps showing the approximate route of the ‘structured walk’ and ‘stop’ locations, dates of the visits, photographs and a summary of the results and botanical species lists recorded for all stops. All survey data would be appendicised; and  To incidentally record the presence/absence of nationally scarce vascular plants; Narrow-leaved Water-dropwort Oenanthe silaifolia, Greater Water-parsnip Sium latifolium and Marsh Sow-Thistle Sonchus palustris during the context of the CSM monitoring survey work.

3.1 All work was carried out by four WWT Consulting staff operating in two teams over a three day period between 4th and 6th August, 2009.

3.7 Data was recorded on photocopies of the rapid assessment forms for MG11 and MG13 Agrostis related grasslands from Robertson and Jefferson, 2000. Additional pages were included as required. Maps for each habitat unit provided by Natural England were used as field maps during the survey.

3.8 Nationally rare and scarce vascular plants

During the undertaking of CSM monitoring, surveyors looked for the following Nationally Scarce vascular plant species (Narrow-leaved Water-dropwort, Greater Water Parsnip and Marsh Sow- thistle). Detailed survey of these species was however, conducted only within the context of this work and no survey of additional habitat was conducted.

3.11 The remit of the current report was to provide the required data to enable Natural England to assess the condition of the survey sites. The discussion element of this report, therefore seeks to provide a broad overview of the findings rather than to undertake condition assessments based on CSM guidelines. The element of habitat ‘extent’ has been considered and discussed in terms of conformity to the target habitat and in relation to encroachment of swamp habitats S5 and S28 in particular.

4. Results

4.1 Maps detailing the extent of areas surveyed, approximate stop locations and direction of structured walks for each unit are shown. The maps also show extent of stands of habitat within each unit which were excluded from the survey due to being non-target habitat. In particular, the maps show the approximate extent of continuous patches of Glyceria maxima S5 and Phalaris arundinacea S28 swamp habitat within the habitat patches surveyed.

4.3 Extent data for MG11/13 habitats across the units are included in Appendix II, Table 2. I calculated the following totals from their table: Total Unit Area (Ha) 1178.94 Total Area of Glyceria/Phalaris (Ha) 319.92 Total Area Not Surveyed (Ha) 431.15 Total Area MG11 + MG13 351.61 Habitat (Ha) Other excluded habitat (Ha) 75.67

4.4 Nationally rare and scarce vascular plants

None of the specified Nationally Scarce or Rare species were recorded during the survey.

5. Discussion

5.1 General

In Natural England’s tender brief (2009) it was stated that ‘The grassland communities on the Ouse Washes have most recently been surveyed via a transect-based NVC methodology with aerial photography in 2001 (Prosser and Wallace, 2002) with these transects being repeated in 2008 (Graham, 2008). However, although these surveys will contribute to the SSSI Condition Assessment, the transects did not cover all the SSSI Units.’ The purpose of the current survey was, therefore to provide data to augment the existing survey data; Specifically to provide Natural England with appropriate CSM survey data to inform Condition Assessments of the MG11/MG13 and related grasslands of the Ouse Washes SSSI.

5.2 As such the following discussion does not seek to evaluate the current condition of the assessed habitat, more to provide an accessible dataset which may be used as a baseline for future CSM compliant survey.

5.8 12 of a possible 19 positive indicator species were recorded during the structured walks with species such as Water Mint Mentha aquatica and Marsh Bedstraw Galium ulignosum comprising the two most frequently recorded positive indicator species with Autumn Hawksbit Leontodon autumnnalis, Creeping Jenny Lysimachia nummularia and Amphibious Bistort Persicaria amphibium also being recorded relatively frequently.

5.10 Negative indicators

The frequency and abundance of negative indicator species including Creeping Thistle Cirsium arvense, Spear Thistle Cirsium vulgare, Curled Dock Rumex crispus, Broad-leaved Dock Rumex obtusifolius and Common Nettle Urtica dioica varied across the site. Of the negative indicators recorded, Rumex crispus was by far the most frequent negative indicator recorded with Cirsium arvense also being frequent. Cirsium vulgare and Urtica dioica occurred only rarely within the sward for the most part.

Current Condition

5.16 Robertson and Jefferson, 2000 state that ‘Seasonally flooded types of grassland are particularly sensitive to water tables remaining high from late March onwards’. This can result in a shift to inundation grasslands and swamp communities. In WWT (2008) the wet grassland habitat of the Ouse Washes are said to have declined in quantity and quality since the 1970s; furthermore, this has been attributed to an increase in the frequency of spring and summer flooding events of increased depth and duration. Nutrient enrichment from water entering the site is also considered to have contributed to the decline of the habitat.

5.17 The majority of MG11 and MG13 grasslands, within the SSSI units surveyed, were subject to encroachment by swamp communities. Glyceria maxima was by far the most abundant swamp habitat encountered both as stand alone habitat and in a tight mosaic with MG11 and MG13 grassland. Phalaris arundinacea occurred to a lesser extent, but was frequently abundant alongside Glyceria within the stands.

5.18 Much of the grassland habitat across all units surveyed was stock grazed (usually by cattle, occasionally by ponies and sheep), there was evidence of topping in some fields and very occasionally hay cuts had occurred just prior to survey, making adequate assessment unfeasible. It was not clear from the survey to what extent grazing affected colonisation by waterlogging indicators such as Glyceria maxima and Phalaris arundinaecea, however, in certain areas these species had evidently been grazed short.

Limitations

5.19 Due to time constraints, it was not possible to ground truth the aerial mapping in great detail. For the most part, it was possible to verify the nature of excluded habitat in fields adjoining the Agrostis spp. mapped target areas, but it was rarely possible to walk over the excluded areas. Frequently, the boundaries between continuous stands of Glyceria maxima

swamp (S5) and Phalaris arundinacea (S28) habitats in relation to the Agrostis grasslands (MG11 and MG13) were clear and as such it was mostly possible to verify that adjacent, excluded fields did in fact conform to the aerial mapping.

RK Summary, 17 March 17, 2015.

16. BLACK & VEATCH, 2005. MONITORING OF THE WASH AND OUSE WASHES IN 2004 FOR THE NATURAL ENVIRONMENT PROGRAMME. SECOND ANNUAL REPORT. ESSEX AND SUFFOLK WATER. The temporary Denver Licence Variation was granted to the Environment Agency for a period of five years, which commenced on the 21 November 1997 and expired on the 20 November 2002. Within the Licence Variation application the Environment Agency, supported by Essex & Suffolk Water, proposed an extensive monitoring programme of the Great Ouse estuary and The Wash. A monitoring group was established to review the effects of the licence variation and advise the Environment Agency on the monitoring programme, interpretation of results and mitigation measures.

The temporary Licence Variation:

 Allowed the release of the Ely Ouse Minimum Residual Flow (MRF) through any of the sluices at Denver.

 Allowed a reduction in the MRF in October, November and December each year.

 Required an increase in the MRF in March and April each year.

 Allowed a 13% increase in the volume of water that may be transferred to Essex.

When the Licence Variation expired, the licence reverted to the original conditions in place prior to 1998. A slight variation on the original licence conditions is that discharge of the MRF is now permitted through any sluice; this means that Denver Sluice can be used in preference to the Residual Flow Sluice. Essex & Suffolk Water agreed to continue monitoring of the Great Ouse estuary and The Wash in order to review the environmental effects of the Denver Licence upon these areas to inform stakeholders prior to the permanent variation proposed as part of the Abberton Scheme.

Freshwater flows

Monthly river flows in the Ely Ouse were 12% higher than the 1972-1996 average overall. The Bedford Ouse flows during 2004 were lower than average for much of the year. Flows downstream of Denver were low for the first four months of the year, average during the summer, but low again at the end of the year.

Conditions in the upper Estuary

The water quality during 2004 was similar to that reported in previous years, though the total oxidized nitrogen and conductivity were generally higher and the turbidity and ortho- phosphate were lower.

Saline intrusion was recorded at Downham on 15 days in June, July and August. The monitor did not work for most of the remainder of the year. Records from the Salter/'s Lode salinity moni tor are awaited from the Environment Agency.

The recorded bed levels in the tidal Ouse estuary during 2004 were around O.5m higher than those recorded during 2003.

The high spring flows in the Bedford Ouse caused the Ouse Washes to be flooded during spring and did not drain to their summer level until mid June.

3. Flow conditions

3.1 Ely Ouse Flows

The current Environment Agency operating policy, which was reinstated as a result. of the Denver Sluice Operational Review (Ref I ), is designed to optimise the discharge through Denver Sluice, but gives priority to the evacuation of floodwater from the Ouse Washes through Welmore Lake Sluice. The volume discharged through Denver Sluice in 2004 was 45.9 Mm3, which is only a little less than in 2003 but considerably less than the release in 2002 (l53.9Mm3). The release through Denver Sluice in 2004 was the smallest release in any year when the sluice was fully operational appart from 1996, a year of low river flows when the release was 43.7 Mm3

3.3 Water levels in the estuary at Denver

Discharges through Denver Sluice can only take place when water levels in the Tidal Ouse Estuary are lower than the level upstream of the sluice. Low water levels in the Tidal River meant that gravitational discharges could occur through Denver Sluice throughout 2004. Only in January and February, and short periods in the middle of May and also at the end of November and the beginning of December were water levels in the Tidal Ouse Estuary too high to allow gravitational discharge from the Ely Ouse at Denver.

Low water levels in the Tidal River at Denver only occasionally dropped below l.OmOD during 2004, unlike 2003 when levels were around 0.5mOD for around six months. This meant that i n 2004 gravity drainage of the Ouse Washes to the Tidal Ouse Estuary via Denver Sluice could only occur at times of flood when water levels in the Ouse Washes were higher than those downstream.

3.5 Ouse Washes water levels

Water levels on the Ouse Washes during 2004 are shown on Figure 3.9. The Ouse Washes were flooded from the beginning of January to the 16th June when the target su mmer water level of 0.5mOD was reached. The target water level of 0.8mOD by the 8th April was almost

reached but continuing flood flows during May prevented the 0.5mOD target being reached until 15th June. Water levels in early summer of 2004 were the highest since 2000.

There was a small rise in Old Bedford water levels between 22nd August and 9 September which probably flooded some of the lowest washes. Winter flooding of the Washes commenced on 17th October and persisted to the end of December.

The failure to reach the target water level before mid June would have seriously disrupted the bird breeding season . The persistence of flooding of the washes during the summer of 2004 would also have seriously limited the amount of grazing of the Washes that could be carried out.

5. WATER QUALITY

The water quality of the Great Ouse estuary, its tributaries and the Wash is monitored at a large nu mber of sites. The principal sites on each watercourse are listed in Tables 5.1 and 5.6. The sites upstream of Denver are marked on Figure 5.1 and those downstream of Denver on Figure 5.1

5.1 Tributary and Ouse Washes Water quality

Table 5.1 presents the mean values of some key water quality parameters in 2004 to aid comparison of the water quality of the main tributaries of the Great Ouse estuary and the rivers of the Ouse Washes.

The water quality of most tributaries and the Ouse Washes rivers are fairly similar reflecti ng the rural intensively farmed catchments that they all drain. Tables 5.2 and 5.3 repeat the tributary water quality data for 2003 and 2002 to aid comparison with the 2004 water quality in Table 5.1.

In general, the water quality in 2004 reflects that of 2003 and 2002. There was a decrease in chloride and orthophoshate at most sites as a consequence of the greater summer freshwater flows compared to 2003. The higher oxidized nitrogen in the Bedford Ouse at Brownshill and the Ely Ouse at Denver were because the concentrations recorded in January (twice) and in March at Brownshill and in September and October at Denver were the highest for these months for more than seven years.

Table 5.1 lists 15 sites where water quality was monitored.

RK Summary, 7 April 2015.

17. BLACK & VEATCH, 2010. MONITORING OF THE WASH AND OUSE WASHES IN 2008 FOR THE NATURAL ENVIRONMENT PROGRAMME. SIXTH ANNUAL REPORT. ESSEX AND SUFFOLK WATER. The temporary Denver Licence Variation was granted to the Environment Agency for a period of five years, which commenced on the 21 November 1997 and expired on the 20 November 2002. Within the Licence Variation application the Environment Agency, supported by Essex & Suffolk Water, proposed an extensive monitoring programme of the Great Ouse estuary and The Wash. A monitoring group was established to review the effects of the licence variation and advise the Environment Agency on the monitoring programme, interpretation of results and mitigation measures.

The temporary Licence Variation:

 Allowed the release of the Ely Ouse Minimum Residual Flow (MRF) through any of the sluices at Denver.  Allowed a reduction in the MRF in October, November and December each year.  Required an increase in the MRF in March and April each year.  Allowed a 13% increase in the volume of water that may be transferred to Essex.

The Ouse Washes were flooded from the beginning of January to the 11th May when the target summer water level of 0.5m0D was reached, but was only maintained until 27th May. Following this, severe flooding of the Ouse Washes occurred and lasted until mid-July when 0.5m OD was again achieved. After this flood event, water levels were maintained close to the target summer water level until 7th September when the Ouse Washes was flooded until the end of October.

Water quality in the upper estuary was comparable with that of 2007, and reflects the relatively high freshwater flows experienced during both years. It should be noted, however, that as with 2007 the number of samples collected was notably reduced in comparison with the number collected in the previous years. This is a result of the Environment Agency's methodology for water quality sampling being modified to tie in with the requirements of the Water Framework Directive.

2. ESTUARY SALINITY

The Environment Agency has an automatic monitor for measuring conductivity at a site in the Tidal Ouse estuary: namely Salter's Lode, which can be regarded as part of the Denver sluice. Two other monitoring sites at Welney Bridge and Downham Bridge are no longer operational. The Salter's Lode monitor is used to monitor the occurrence of saline intrusion to prevent

saline water being abstracted from the Tidal River and taken into the Counter Drain on spring tides when freshwater flows are low. Due to various problems, especially siltation, the Environment Agency is currently reviewing this monitoring station to determine whether there is a solution, or whether it discontinues using this site.

5. WATER QUALITY

The water quality of the Great Ouse estuary, its tributaries and The Wash is monitored by the Environment Agency at a large number of sites. The principal sites on each watercourse that effect the Ouse Washes are shown below:

Tributary Site Total oxidized Ortho-phosphate mg/l P Nitrogen mg/l N 2008 2008 Middle Level Main Mullicourt Priory Sluice 12.0 0.06 Drain Bedford Ouse Brownshill 7.1 0.21 Counter Drain, Old Old Bedford Sluice 3.8 0.10 Bedford Welney Bridge 2.8 0.03 Welches Dam 5.3 0.02 Old Bedford Delph Welmore Lake Sluice 3.1 0.30 Welney Bridge 3.5 0.33 Welches Dam 3.1 0.24 Ely Ouse Denver 8.8 0.30

Appendix A is the Terms of Reference For the Monitoring Group.

Summary, RK 3 March 3, 2015.

18. BLACK & VEATCH, 2010. MONITORING OF THE WASH AND OUSE WASHES IN 2009 FOR THE NATURAL ENVIRONMENT PROGRAMME. SEVENTH ANNUAL REPORT. ESSEX AND SUFFOLK WATER. Executive Summary for the Upper Estuary

Conditions in the upper Estuary

 The sluice at Denver has been used intensively since it was reopened. The proportion of Ely Ouse Flow discharged through Denver Sluice in 2009 was 35.7% of the total Ely Ouse flow, the highest percentage since 1999.  The flow in the Bedford Ouse at Offord of 487.0 Mm3 was 12% higher than the 1972- 1996 average of 436.7Mm3.  Water levels on the Ouse Washes were close to their optimum level for effective bird breeding during the summer period from mid April to late October, apart from a short period of low level flooding in mid August.  Operational difficulties have stopped monitoring of conductivity in the Ouse estuary and it 1s unlikely to be resumed.  The concentration of water quality parameters such as chloride and conductivity increased in the tributaries in 2009 in comparison with 2008 and 2007. This is a result of lower flows in 2009 than the two previous years providing less dilution to water quality determinands. In the Old Bedford Delph, the annual mean ammonia concentrations were unusually high, however, the annual average concentration of orthophosphate in the Ely Ouse at Denver was lower than in recent years.  Collection of water quality data are being rationalised to fit in with the requirements of the Water Framework Directive and are likely to be reduced overall especially in the saline and brackish tidal waters of the Ouse estuary and The Wash.  The maximum bed levels in the Tidal River varied between +0,20mOD in and -0.19mOD, a lower level than that recorded in 2008. These bed levels were the lowest since 2004/5 and reflect the larger volume of discharges through Denver Sluice as a result of the effmts by the Environment Agency to use Denver Sluice whenever practical.

3.5 Ouse Washes water levels

Water levels on the Ouse Washes during 2009 (and partially 2010) are compared against those of 2008 in Figure 3.9. The Ouse Washes were flooded from the beginning of January in 2009 with water levels ranging from lm AOD to 3.52m AOD until 11th April when the water level dropped below 0.9m AOD (the level at which the Ouse Washes start to flood).

The flooding peaked at 3.54m 0D on 16'h February 2009, the flood levels had been above 3mAOD for three days previously and remaining above 3.0mAOD for a further five days. Flooding in the Ouse Washes ceased on 11'h April, and there were no further flood events twtil November l 61h. This flooding continued to the end of 2009, peaking at 2.56mAOD on 31" December.

The target water level of O.SmAOD (for effective bird breeding) was reached on 13th April 2009, it remained close to this target level until 6th August when the water level rose (peaking

at l .22mAOD), but returned to the target water level on 23"' August. The water level remained close to the target (with a range of 0.48mAOD - 0.53mAOD) until 21" October when it rose to 0.6m AOD until the end of the month, before gradually rising to reach 1.0mAOD on 16th November.

4. ESTUARY SALINITY

The Environment Agency has an automatic monitor for measuring conductivity at Salter's Lode in the Tidal Ouse Estuary as shown on Figure 4.1. Two other monitoring sites at Welney Bridge and Downham Bridge are no longer operational.

The Salter's Lode monitor is used to monitor the occurrence of saline intrusion to prevent saline water being abstracted from the Tidal River and taken into the Counter Drain on spring tides when freshwater flows are low. The water quality monitoring station at Salters Lode has not been functioning or recording since 2007. This is due to siltation problems. Any instrumentation installed here soon becomes buried. This station is next to the lock, which is a busy navigable section of the river. This therefore restricts the type of monitoring methods which could be used or installed at this location. The Environment Agency is currently reviewing this monitoring station to determine whether there is a solution, or whether it discontinues using this site.

5. WATER QUALITY

The water quality of the Great Ouse estuary, its tributaries and The Wash is monitored by the Environment Agency at several sites. The number of sampling points and the frequency of sampling have gradually declined over the years. This is part of a transition in the monitoring programme to bring it in line with the requirements of the Water Framework Directive. Following changes to the way the Environment Agency will be required to collect water quality data, next year's study will only be able to report from five of the water quality sample points monitored in 2009 (as noted in Table 5.1). This is because the Environment Agency is in a transitional phase is response the requirements of the new Water Framework Directive methodologies set out for assessing river quality.

Tributary Old Monitoring Site New Monitoring Site Middle Level Main Drain Mullicourt Priory Sluice Yes Bedford Ouse Brownshill No Counter Drain, Old Bedford Old Bedford Sluice No Welney Bridge No Welches Dam No Old Bedford Delph Welmore Lake Sluice No Welney Bridge No Welches Dam No Ely Ouse Denver Denver Ten Mile River? Hundred Foot River Earith Road bridge Hundred Foot River Mepal Road bridge

The Bedford Ouse at Earith is likely to have similar water quality to the Bedford Ouse at Brown shill so will allow continued assessment of water quality of the Bedford Ouse. There are no plans to continue monitoring sites on the Cut Off Channel, Old Bedford Delph, Counter Drain Old Bedford and Flood Relief Channel watercourses nor in the saline and brackish waters of the Great Ouse estuary and The Wash.

5.1 Tributary and Ouse Washes Water Quality

Table 5.2 presents the mean values of some key water quality parameters in 2009 to aid comparison of the water quality of the main tributaries of the Great Ouse estuary and the rivers of the Ouse Washes. The water quality of most tributaries and the Ouse Washes drains and rivers are fairly similar reflecting the rural intensively farmed catchments that they all drain.

The concentration of water quality parameters such as chloride and conductivity increased in the tributaries in 2009 in comparison with 2008 and 2007. This is a result of lower flows in 2009 than the two previous years providing less dilution for water quality determinands.

The reported levels of ammonia in the tributaries were generally similar to those recorded in 2008 and 2007. However, in the Old Bedford Delph, the annual mean ammonia concentrations were unusually high. At both Welches Dam and Welney on this river, one or two samples during the winter months reported concentrations in the range 1.45 - 2.0 mg/I.

The annual average concentration of orthophosphate in the Ely Ouse at Denver has been above 0.3mg/l since 2005 and was higher in earlier years. In 2009 the annual average concentration fell to 0.17mg/1 with only two samples during the year at this site containing 0.3mg/l or more orthophosphate; this is possibly as a result of increased phosphate stripping in recent years at water treatment works that discharge into the Ely Ouse system.

Tributary Site Total oxidized Nitrogen Ortho-phosphate mg/l mg/l N 2009 P 2009 Middle Level Main Mullicourt Priory Sluice 7.2 0.09 Drain Bedford Ouse Brownshill 7.3 0.22 Counter Drain, Old Old Bedford Sluice 5.0 0.11 Bedford Welney Bridge 1.0 0.19 Welches Dam 2.8 0.04 Old Bedford Delph Welmore Lake Sluice 1.4 0.11 Welney Bridge 2.2 0.31 Welches Dam 3.6 0.11 Ely Ouse Denver 9.1 0.17

Summary, RK 4 March 2015.

19. OUSE WASHES AND PORTHOLME DIFFUSE WATER POLLUTION PLAN, NATURAL ENGLAND AND THE ENVIRONMENT AGENCY, 2010. NOTE THIS DOCUMENT IS STILL LIVE AND ON AT LEAST VERSION 11, 31 MARCH 2014. This is set out as a Tabular document in landscape format, so it is helpful to be able to see the contents. The documents I have seen have no introduction, so it is difficult to get the context for it or to gauge the level of commitment to it by participating organisations.

Contents

1. Plan coverage and contacts. 2. Characteristics of the catchment 3. Monitoring attributes and compliance status 4. Pressures and Impacts: evaluation of evidence 5. Additional available evidence 6. Catchment modelling 7. Measures and mechanisms already in place 8. Additional measures required 9. New evidence required to secure future mechanisms 10. Prioritised DWP action list 11. Actions required on non-DWP sources 12. Monitoring 13. Sign Off Annex 1 Extract from regional meeting held on 17 August 2010: Resource Protection - Delivery through HLS ELS CSF CFE Annex 2 Catchment boundary map Annex 3 Map showing STW in the catchment. Taken from Great Ouse and Ouse Washes catchment appraisal. Annex 4 Measures listed in WFD Programme of Measures for the Ouse Washes Annex 5 STWs with P removal included in the River Great Ouse SIMCAT model Annex 6 Actions to tackle diffuse sources of phosphorus in the River Ouse catchment upstream of the Ouse Washes SAC, as identified in the Ouse Washes and Portholme Environment Agency Review of Consents Site Action Plans

1. Plan coverage and contacts. This section notes:  the large catchments in relation to the small Natura 2000 sites  that no comprehensive analysis of agri-environment and other measures which may help to address diffuse water pollution has been conducted in the catchment in relation to improvements that may result for the SSSIs.  that there is no targeted CSF work for these SSSIs. This means that this DWP plan necessarily operates at a more generic level than those produced for SSSIs which benefit from more detailed catchment data.

 the need for a ‘local geographical owner’, identified at a regional meeting held on 17 August 2010, who would have the responsibility of overseeing the delivery of resource protection options within the catchment. There has been significant staff turnover in both organisations since that time and this requirement still stands.

2. Characteristics of the catchment

Sources of sewage

The Environment Agency Review of Consents project identified a large number of STW in the catchment, the two largest being Bedford with a consented discharge of 35,000m3/d and Cotton Valley (78,000m3/d). There were 274 consents for small private discharges of sewage effluent between 10 and 50 km from the site. Annexes map the STWs and list STWs in the catchment used for the EA RoC SIMCAT model.

Entec reported in 2003 that the main source of phosphorus is point sources, accounting for 78.1% total-P in January and 94.6% in July. However, at that time, only four STWs had phosphate removal installed. Since then P-removal has been introduced, and in some cases improved, at all of the largest STWs in the River Ouse catchment, and at all STWs immediately upstream of the two SSSIs.

3. Monitoring attributes and compliance status Natural England’s Conservation Objectives attributes:

Phosphate, Include all of the following which are relevant: 1) 2005 English interpretation of Common Standards Monitoring attributes. Note that CSM is to be reviewed which is likely to lead to a significant tightening of P attributes over existing levels; 2) Interim phosphate guidance from Chris Mainstone developed for ROC; 3) Attributes proposed for Common Standards Review Ouse Washes  Phosphate attribute for ditches: 0.1 mg L-1 annual mean. This is also the target for the SAC feature spined loach (although EA disagree).

Compliance: FAILING – due to P (2005)

 Concentrations of around 0.3 and 0.4 mg/l TP in the Old Bedford/Delph and Counterdrain/Old Bedford, respectively (The Ouse Washes strategic model studies results for the cSAC part of the Ouse Washes)

Macrophytes and Negative Indicators: Ouse Washes

 Mean cover of filamentous macro-algae and Enteromorpha not more than 10% (mid June to end August)

Other relevant conservation objective attributes: Nitrates There are no conservation objective attributes for nitrates for either site, although both are considered to be affected by significant diffuse inputs of nitrates.

Work undertaken by Jonathan Graham in 2003 provides hydro-ecological prescriptions and nitrate tolerances for ditch aquatic macrophyte communities. This work points to a shift in botanical communities.

Water Framework Directive targets For both sites the target is Good Ecological Potential by 2027 for the waterbodies in which the SSSIs sit. The reason for the target being GEP is that the waterbodies are considered to be ‘Heavily modified’. 2027 could be due to the fact that this is a very large catchment and there will be difficulty in tackling all the sources.

WFD introduces formal in-river phosphate targets for the first time for all waterbodies.

For all appropriate waterbodies adjacent to the SSSIs, the WFD target is 0.12 mg/l orthophosphate as an annual average.

See Annex 4 for a table showing the two measures for nitrate identified in relation to the Ouse Washes.

4. Pressures and Impacts: evaluation of evidence

Pressure  Elevated phosphate levels/loading in the rivers/ditches. Entec report (2003)The main source of phosphorus is point sources, accounting for 78.1% total-P in January and 94.6% in July. P levels in the Great Ouse have been examined at a range of different flow levels, before and after sewage treatment improvements (Entec 2006). Reductions in total-P are much lower at high flows, suggesting that diffuse pollution may be a major source of P during floods and / or there is lots of P from agricultural and non- agricultural sources locked up in river sediments.  Deposition of phosphate onto lowland wet grassland. Prosser and Wallace(2002) Vegetation Change on the Ouse Washes 1972-2001. English Nature, RSPB, WWT commissioned report. Provides documented evidence, plus there is visual and observational evidence.  Sediment loading upstream delivering nutrients to the SSSIs Anecdotal evidence (see catchment appraisal) PSYCHIC maps WFD sediment risk maps

 Increased nitrate loading NB: Included here as context only, as nitrate is not a CSM conservation objective attribute. It would however be possible to set site specific targets using the tolerances identified in the hydro-ecological prescriptions report. The main source of nitrates is from diffuse sources. There appears to be a strong seasonal trend in nitrate loading, with a peak in November and December whilst at its lowest in July. EA report - Ouse and Nene Strategic Studies Ouse Washes: Water and Nutrient level Analysis March 2004

5. Additional available evidence NE has various ditch surveys and monitoring reports. EA has water quality monitoring. One sample per month is the standard regime so data is constantly being updated. Some monitoring points are directly relevant to the SSSIs, but there are many others in the upstream catchment. (Further detail can be found in the RoC appropriate assessment report)

6. Catchment modelling To be included later.

7. Measures and mechanisms already in place Only a few picked out:  Upper Ouse Catchment Partnership (CSF funded strategic partnership) – The catchment partnership is funded by ECSFDI and is also linked to WFD. Simon Bateman is the catchment officer. Also links to 2009 report by Alicia Cortes: Diffuse Water Pollution from Agriculture (Upper Great Ouse catchment). The focus is on fish impacts and sediment.  Great Ouse Wetland Vision This EA / NE vision for wetland rehabilitation in the River Great Ouse involves working in partnership to identify appropriate projects within the catchment – identifying threats and prioritising opportunities for habitat protection and restoration. Schemes to restore river and floodplain links could result in wider-ranging water quality benefits. The aim is to co-ordinate projects to deliver maximum benefit for the catchment.

8. Additional measures required Measure and pressure  Reduce nutrient input from the wider upstream catchment  Gather additional evidence of the impacts of nutrient enrichment on site: Soil sampling for nutrients in wetland areas of Ouse Washes.  Continue to collect / gather additional evidence of DWP sources in the upstream catchment: i) extension of water quality monitoring (see section 12 below, monitoring); ii) nutrient source sampling e.g. soil sampling in potential ‘hotspot’ locations, slurry sampling

 Analyse all available evidence from SSSIs and upstream catchment, to develop nutrient budget to identify main DWP sources, to facilitate targeting of future measures: . A key element of this work will be source apportionment modelling work to be done by EA Regional Water Quality Team as part of WFD investigations. The aim is to identify and quantify the different sources of phosphates in the Great Ouse catchment by the end of 2012. . For Ouse Washes use survey data to ground-truth modelled nutrient budget from EA report - Ouse and Nene Strategic Studies Ouse Washes: Water and Nutrient level Analysis March 2004  Water quality communication campaigns targeting farmers to take ownership of the issues  Farmer-led water quality surveys to gather additional evidence of impact  A catchment wide review of actions already being implemented and those needed. To provide evidence for future targeting etc.  Creation of flood storage elsewhere in the catchment thereby helping to reduce sediment / nutrient loading to the SSSIs.  Reduce nutrient input to catchment through educating agronomists, suppliers (of fertilizers, pesticides and livestock feeds) and livestock nutritionists about DWP so that they can advocate effectively on behalf of NE with farmers. NE to be clearer with external stakeholders about what is needed in the catchment.  Reduce nutrient input to catchment by influencing interest groups who can share peer advice to promote DWP friendly practices  Reduce nutrient input to catchment through promotion of best farm practice to help reduce DWP  Reduce nutrient input to catchment by NE / EA staff who engage with the farming community tailoring advice to benefit the Ouse Washes and Portholme SSSIs by encouraging DWP reductions.  Reduce nutrient input to catchment through a reduction in nitrate loadings and best farm practice re manure loadings etc  Reduce nutrient input to catchment via phosphate planning – P plans linked to manure loadings (whether compliant with NVZ or not)  Reduce sediment & nutrient input to catchment from roads

9. New evidence required to secure future mechanisms

What evidence is needed and why?

Strong evidence to link land use change in the upper catchment with impacts on the Ouse Washes and Portholme SSSIs. As the upstream catchment is large there are potentially many other contributing factors, despite the largely agricultural nature of the catchment. Evidence is needed for whether changing farming practice would make much difference or not to the SSSIs.

10. Prioritised DWP action list

There are 24 Actions listed in the Table therefore I have not reproduced them all. Those with a High category for implementation are: i a) Reduce nutrient input from wider catchment via extension of ECSFDI post-2011 strategy i b) Reduce nutrient input from wider catchment via RB209 ix a) Educate / clarify with external stakeholders (e.g. agronomists, suppliers and livestock nutritionists) what is needed to address DWP in the catchment via NE advocacy work x) Influence interest groups to share peer advice to promote DWP friendly practices via NE / EA partnership working with River Trusts, FWAG groups etc xii c) Ensure NE/EA staff in wider catchment tailor farm advice to benefit the Ouse Washes & Portholme via implementation of appropriate training for DWP vii) Catchment wide review of actions already implemented to provide evidence for future targeting, via special project (NE Genesis team or region?) iv) Analyse evidence to develop nutrient budget to facilitate future targeting – key element is EA source apportionment modelling to be completed by 2012. iii a) Continue to collect / gather additional evidence of DWP sources in upstream catchment i) WQ routine monitoring, ii) nutrient source sampling via EA routine monitoring xii a) Ensure NE/EA staff in wider catchment tailor farm advice to benefit the Ouse Washes & Portholme via research to identify training needs xii b) Ensure NE/EA staff in wider catchment tailor farm advice to benefit the Ouse Washes & Portholme via provision of information to enable promotion of suitable RP options

11. Actions required on non-DWP sources

Issue/Remedy:  Future flooding regime on the Ouse Washes

The exact methods by which the Ouse Washes will be managed as a flood storage structure over the medium-long term is currently unclear. This is due to uncertainties relating to how climate change scenarios will affect the catchment as a whole and, in particular, the management of siltation in the tidal river, which will affect the ability of the OW to gravity discharge water. Some measures and mechanisms are in place and planned through the Great Ouse Tidal River Strategy and the Great Ouse Catchment Flood Management Plan. Flooding will continue at the site as it is a flood storage structure, with the quantity and frequency of inundation continuing to be unpredictable.

The frequency and quantity of water entering the site, the ability of the structure to gravity discharge sufficiently quickly and the extent by which pumping water off will be considered reasonable are key questions for the future management of the Ouse Washes as a flood storage structure. These issues may have serious implications for the SSSI, SPA, SAC, Ramsar interest features and, as a result, we are currently unclear as to the future prognosis for the designated site features. We cannot rule out that additional legislative drivers may be used to secure future off-setting or compensation.

 Off-setting documented deterioration caused by changes in annual flooding patterns, with nutrient loading considered a contributory factor.

The off-site Ouse Washes Habitat Creation project (OWHCP) (Project Manager – Peter Doktor) is a project provided via a Habitats/Birds Directive driven legal mechanism to off-set the deterioration of the Ouse Washes for some SPA/Ramsar bird features and associated grassland habitat, between a baseline in the 1970s and up to 2002. It is likely to provide some opportunities for other SSSI/SPA/Ramsar features as well e.g. ditch flora and fauna and other bird species. There are currently no specific mechanisms in place with regard to water quality, but this will be considered at detailed design stage and when land is under management.

This project can be seen as a ‘partial remedy’ with regard to the adverse reason ‘inappropriate water levels’ and future remedies with regard to this adverse reason will depend on whether there is future deterioration over and above the level that has already been documented and addressed.

The OWHCP is not a measure/project/’remedy’ that will off-set or address the elevated nutrient levels in Counter Drain/Old Bedford and Old Bedford/River Delph (part of SSSI ditch, vascular plant assemblage features and SAC Spined Loach habitat).

 Nutrient contribution from sewage treatment works

Due to the requirements of Urban Wastewater Treatment Directive and Habitats Directive phosphate removal is already in place at all of the largest STWs in the upstream catchment. Actions to date have addressed the proportional inputs of phosphate from these point source discharges, meaning that the current emphasis is on reducing contributions from diffuse sources.

WFD has, however, introduced formal river phosphate targets for the first time. Evaluation of current and planned river status will determine whether any further P- removal schemes are necessary. Detailed requirements and delivery of any additional schemes will be determined through the formal AMP planning process.

12. Monitoring

Monitoring required:

 Routine water quality monitoring for Water Framework Directive to enable tracking of progress in reducing phosphate concentrations / efficacy of actions taken in relation to the rivers adjacent to both SSSIs  Farm / field level monitoring of agri- environment measures. Integrated monitoring to show how actions are making a difference Field level indicators of success on farms (agri env schemes)  Common Standards Monitoring of bird & vegetation features

General recommendations The plans should be reviewed every three years during first two WFD cycles, thereafter every six years following SSSI condition assessment.

Triggers for early review These include:  New data providing robust evidence of contribution from diffuse sources.

 Evidence indicating improvements are not being delivered as anticipated.

 Evidence from EA CSF / PSA modelling (see section 6) – especially if validated

Signed off: Sarah Fendley, Natural England, 27 October 2010. Helen Smith, Environment Agency, 8 November 2010.

RK Summary, May 2015.

20. NATURAL ENGLAND. IMPROVEMENT PROGRAMME FOR ENGLAND’S NATURA 2000 SITES (IPENS). 18 DECEMBER 2012 & DIFFUSE WATER POLLUTION THEME WORKSHOP NOTE, NATURAL ENGLAND, 5 SEPTEMBER 2013. Overview

Special Areas of Conservation (SAC) and Special Protection Areas (SPA) are collectively known as Natura 2000 sites and are protected under European legislation for their important wildlife and habitats. In England there are 337 sites covering 2,077,276 hectares.

Working with partners to improve Europe’s most important wildlife areas

The improvement programme for England’s Natura 2000 sites (IPENS) is working with these partners, and other stakeholders to develop a strategic approach to achieving favourable condition on these sites by reviewing:

 the risks and issues that are impacting on and/or threatening the condition of the site

 which actions and measures could be used to address them

 how much it will cost and where the money could come from

This will be the first time that this information will have been drawn together for all of England’s Natura 2000 sites. It will provide Natural England and our partners with:

• an improved understanding of the issues affecting the sites and how to address them

• a clear plan of action for improving their condition and how much it may cost

• recommendations to improve gaps in funding and evidence

Timetable

The following will be available by June 2015:

 a site improvement plan for each Natura 2000 site in England

 theme plans to address common issues across multiple sites

 an overall programme plan outlining the future management of all sites

 a directory of actions, measures and funding options to achieve favourable condition

Site improvement plans

The site improvement plans will outline the priority measures needed to achieve and maintain the European species and habitats within a site in favourable condition. They:

 provide a high level overview of the issues affecting the condition of the site

 identify the priority actions to address the issues

 identify the potential funding sources available

Significantly a SIP has been produced for the Ouse Washes (SIP160, 2014/12/19).

Theme Plans

IPENS is developing a suite of eleven Theme Plans. These Plans will address the issues that impact on, and affect the condition of, multiple Natura 2000 sites and which are difficult to resolve on a site-by-site basis. The project has identified the need for a Theme Plan on Diffuse Water Pollution.

As a high percentage of Special Areas of Conservation (SAC) and Special Protection Area (SPA) sites are affected by diffuse pollution it has been identified as a priority for the IPENS project to address. A technical workshop was held on 5 September 2013 to discuss the delivery mechanisms for diffuse pollution for Natura 2000 sites, the barriers to implementation of solutions on the ground and how these might be resolved.

Diffuse Water Pollution – Theme workshop Note – 5 September 2013.

As a high percentage of Special Areas of Conservation (SAC) and Special Protection Area (SPA) sites are affected by diffuse pollution it has been identified as a priority for the IPENS project to address. Often sites are affected by multiple sources of pollution, many of which have proved difficult to tackle in the past. However the inclusion in River Basin Management Plans (RBMP) of Natura 2000 sites as ‘Protected Areas’ under the Water Framework Directive (WFD) provides an added driver for understanding the sources of diffuse pollution and progressively addressing these using a range of measures. Whilst some mechanisms are available and actions are underway or planned, implementation often involves complex and costly measures with habitat responses uncertain, and the timescales for recovery often lengthy or unknown.

A technical workshop was held on 5 September 2013, attended by eight experts from Natural England and other organisations. The workshop attendees discussed the delivery mechanisms for diffuse pollution for Natura 2000 sites (such as Diffuse Water Pollution Plans, New Environmental Land Management Scheme (NELMS), Catchment Sensitive Farming (CSF), and WFD etc), the barriers to implementation of solutions on the ground and how these might be resolved.

Key messages from the Workshop

 43 Natura 2000 sites were identified as requiring a Diffuse Water Pollution Plan in August 2013. Approximately two thirds of these have a Catchment Sensitive Farming initiative in place.  As a core principle, we should recognise the need to set the direction of travel towards achieving often challenging water quality targets for individual Natura 2000 sites, whilst recognising the uncertainties involved and acknowledging the need to adopt an adaptive management approach in practice.

 Tackling diffuse pollution in Natura 2000 catchments involves a sequential approach with a good quality Diffuse Water Pollution plan (DWPP) as a starting point. That is, apply the advice and incentive approach, driven as appropriate, by awareness raising, and enforcement of, existing underpinning regulation. If this is not effective seek to apply tougher regulation e.g. Water Protection Zones (WPZ) (supported by advice and incentives) and as a last resort consider land use change (supported by advice and incentives and compensation).  Diffuse Water Pollution Plans need to set out and confirm what the priorities are in a particular catchment; they need to become spatially explicit (new data will help); and take account of local information e.g. from walk-over surveys and knowledge from partners. The importance of a collaborative approach and integration within the Catchment based Approach(CaBA) was emphasised.  There is a desire from some NGOs to see targets adopted so that progress at reducing diffuse pollution can clearly be tracked. Appropriate levers and legislation need to be in place to support the process of managing invasive species. The will and resource to take regulatory or enforcement action are also required.

Envisaged next steps

 Secure wider engagement with the results of the workshop through the development of a Theme Plan.  Agree an approach and develop guidance on how to deal with Diffuse Water Pollution Plans (DWPP) and the need to link this with the next round of RBMP as part of the development of Site Improvement Plans (SIPs) by IPENS.  Scope out the evidence gap related to our understanding of the impacts of urban diffuse pollution and available solutions.  Consider current regulatory mechanisms and their effectiveness in practice; identify Natura 2000 test cases where diffuse pollution problems exist and standard approaches have been tried without satisfactorily addressing the problem.

RK May, 2015.

21. IMPROVEMENT PROGRAMME FOR ENGLAND’S NATURA 2000 SITES (IPENS). SITE IMPROVEMENT PLAN – OUSE WASHES. NATURAL ENGLAND, 19 DECEMBER 2014. Introduction

Site Improvement Plans (SIPs) have been developed for each Natura 2000 site in England as part of the Improvement Programme for England's Natura 2000 sites (IPENS). This work has been financially supported by LIFE, a financial instrument of the European Community.

The plan provides a high level overview of the issues (both current and predicted) affecting the condition of the Natura 2000 features on the site(s) and outlines the priority measures required to improve the condition of the features. It does not cover issues where remedial actions are already in place or ongoing management activities which are required for maintenance.

The SIP consists of three parts: a Summary table, which sets out the priority Issues and Measures; a detailed Actions table, which sets out who needs to do what, when and how much it is estimated to cost; and a set of tables containing contextual information and links.

Once this current programme ends, it is anticipated that Natural England and others, working with landowners and managers, will all play a role in delivering the priority measures to improve the condition of the features on these sites.

The SIPs are based on Natural England's current evidence and knowledge. The SIPs are not legal documents, they are live documents that will be updated to reflect changes in our evidence/knowledge and as actions get underway. The information in the SIPs will be used to update England's contribution to the UK's Prioritised Action Framework (PAF).

The SIPs are not formal consultation documents, but if you have any comments about the SIP or would like more information then there is the opportunity to get in touch with Naturel England.

SIPs and River Basin Management Plans

The Water Framework Directive (WFD) provides the main framework for managing the water environment throughout Europe. Under the WFD a management plan must be developed for each river basin district. The River Basin Management Plans (RBMP) include a summary of the measures needed for water dependent Natura 2000 sites to meet their conservation objectives.

For the Second Round of RBMPs Second Round of RBMPs, SIPs are being used to capture the priorities and new measures required for water dependent habitats on Natura 2000 sites. SIP actions for non-water dependent sites/habitats do not form part of the RBMPs and associated consultation.

Site Improvement Plan for the Ouse Washes

Plan Summary

This table shows the prioritised issues for the site(s), the features they affect, the proposed measures to address the issues and the delivery bodies whose involvement is required to deliver the measures. The list of delivery bodies will include those who have agreed to the actions as well as those where discussions over their role in delivering the actions is on-going.

Priority and Issue Pressure or Threat Measure Delivery Bodies

Inappropriate water Pressure Habitat creation to Defra, Environment levels offset historical Agency, Natural decline of wintering England and breeding birds and other strategies to alleviate flooding

Water pollution Threat Implementation of Environment Agency, Diffuse Water Natural England Pollution plan to tackle inappropriate levels of nutrients from flooding

Issues and Actions

This table outlines the prioritised issues that are currently impacting or threatening the condition of the features, and the outstanding actions required to address them. It also shows, where possible, the estimated cost of the action and the delivery bodies whose involvement will be required to implement the action. Lead delivery bodies will be responsible for coordinating the implementation of the action, but not necessarily funding it. Delivery partners will need to support the lead delivery body in implementing the action. In the process of developing the SIPs Natural England has approached the delivery bodies to seek agreement on the actions and their roles in delivering them, although in some cases these discussions have not yet been concluded. Other interested parties, including landowners and managers, will be involved as the detailed actions are agreed and delivered. Funding options are indicated as potential (but not necessarily agreed or secured) sources to fund the actions.

Action Action description Cost estimate Timescale Delivery lead body

1A Creation of a 500 ha of wetland Not yet 2017/18 Environment grassland habitat creation at the determined Agency Ouse Washes Habitat Creation Project adjacent to the Ouse

Washes to offset a historical decline of breeding and wintering species on the ouse Washes. Currently 92 ha of habitat creation at Coveney is underway.

1B Creation of a further area of 500 ha Not yet 2020 Not yet of wetland grassland habitat determined determined creation, as part of the originally allocated 1008 ha, at Coveney and Sutton sites on the Ouse Washes to offset a historical decline of breeding and wintering bird species on the Ouse Washes.

1C Further measures to address the £2.27 million 2009 Environment effect of inappropriate water levels per year onwards Agency on populations of breeding and wintering birds on the Ouse Washes. The increased flooding harms habitat suitable many of the birds which visit the site. Implementation of the Great Ouse Tidal River Strategy which looks at flood risk management over the next 100 years for the New Bedford and Great Ouse Tidal Rivers, will focus on flood risk to the areas protected by the South Level Barrier Bank and Tidal River East and West Embankments. 1D Deliver a new Water Level Not yet 2015-16 Natural England Management Plan for 2015 and determined beyond.

2. Water Pollution.

Inappropriate levels of nutrients from diffuse pollution in combination with inappropriate water levels from flooding have adversely affected the extent/composition of vegetation communities on the washes. Resulting changes to the grassland mosaic has potential to affect the notified bird interests by destroying habitat suitable for many of the birds that visit or breed at the site. Occasional incidences of low oxygen levels on River Delph and Counter Drain have potential to impact spined loach populations.

Action Action description Cost estimate Timescale Delivery Lead Body 2A Implement the current Diffuse £4,732,000 2015 Natural England Water pollution Plan (DWP) to onwards

tackle inappropriate levels of nutrients from flooding on the Ouse Washes. 2B Implement the Ouse Washes From incident Reviewed Environment Incident Management Plan to response annaully Agency improve the management of water budget retained on the Washes and to manage dissolved oxygen levels.

The rest of the SIP is a presentation of designation details for the two Natura 2000 sites present.

RK, May 2015.