Investigating and managing water quality in saline lagoons based on a case study of nutrients in the Chesil and the Fleet European marine site September 2000 Charlotte M. Johnston (Entec UK Ltd) & Paul M. Gilliland (English Nature) Prepared for the UK Marine SACs Project, Task Manager: Paul Gilliland, English Nature The work on which this report is based involved collaboration between English Nature, the Environment Agency and Cardiff University This report is produced as part of the UK Marine SACs Project - a joint venture involving English Nature, Scottish Natural Heritage, Countryside Council for Wales, Joint Nature Conservation Committee, Environment and Heritage Service Northern Ireland and Scottish Association of Marine Science and the financial support of the European Commission's LIFE-Nature Programme. ISSN 0967-876X © Copyright English Nature 2000 Citation: Johnston, C.M and Gilliland, P.M. 2000. Investigating and managing water quality in saline lagoons based on a case study of nutrients in the Chesil and the Fleet European marine site. English Nature. (UK Marine SACs Project). Contents Page Preface ...................................................................5 Summary ..................................................................7 1. Introduction .........................................................13 1.1 UK Marine SACs Project ........................................13 1.2 Scope and objectives of the study ...................................13 1.3 Audience .....................................................14 1.4 Report structure ................................................14 2. Background .........................................................17 2.1 Background to European marine sites ................................17 2.2 Background to saline lagoons in the UK ..............................19 3. Guidance on potential water quality impacts in saline lagoons ....................23 3.1 Introduction ...................................................23 3.2 Sensitivity of different lagoons ......................................23 3.3 Sensitivity of lagoonal communities and species .........................24 3.4 Summary of water quality issues ....................................29 4. Case Study - The Fleet ................................................35 4.1 Background and objectives to case study .............................35 4.2 Introduction to the Fleet ..........................................36 4.3 Review of historical data and interpretation ............................41 4.4 Water quality monitoring and investigations ............................42 4.5 Nutrient load analysis and modelling .................................55 4.6 Modelling tidal currents and solute distributions .........................57 4.7 Relevant studies of parameters other than nutrients ......................59 4.8 Summary and interpretation of nutrient budget, distribution and fate ..........62 4.9 Assessment of change in conservation interests in response to nutrient levels ........................................................65 4.10 Implications for management of the Fleet ..............................68 4.11 Further work recommended for the Fleet .............................70 5. Guidance on investigating and managing water quality in saline lagoons ..............76 5.1 Introduction ...................................................76 5.2 Relevance of the Fleet to other lagoons ...............................76 5.3 Guidance on investigating water quality impacts in saline lagoons ............78 5.4 Guidance on managing water quality impacts in saline lagoons ..............88 5.5 Further research required on water quality in saline lagoons ...............92 Acknowledgements .........................................................94 References ...............................................................95 Figures Figure 2.1 Location of Special Areas of Conservation for marine interests. .............22 Figure 4.1 Fleet lagoon - Location map including EA sampling points and known discharges 37 Figure 4.2 Ecological divisions within the Fleet lagoon ............................38 Figure 4.3 Annual nitrogen loads to the Fleet ...................................56 Figure 4.4 Annual phosphorus loads to the Fleet ................................57 Figure 4.5 Distribution of tracer released to mimic inputs from the Abbotsbury swannery after 10 tidal cycles ......................................60 Figure 4.6 Distribution of tracer released to mimic stream inputs after 10 tidal cycles .....61 Figure 5.1 Steps in investigating the impact of nutrients in the Fleet. ..................80 Tables Table 2.1 Annex I habitats and Annex II species in UK candidate marine SACs ........19 Table 2.2 Summary of UK lagoon SACs and component individual lagoons. ...........21 Table 3.1 Size of different lagoon types in the UK ..............................24 Table 4.1 Inventory of inputs to the Fleet lagoon ................................43 Table 4.2 Summary nutrient data for the Fleet, April 1996-August 1997 ..............48 Table 4.3 Summary data for chlorophyll-a for the Fleet, April 1996-August 1997 .......48 Table 4.4 Sediment nutrient data for Fleet samples, 15th October 1998 ...............51 Table 4.5 Summary of estimated annual nutrient loads to the Fleet ...................54 Table 4.6 Estimated nitrogen contribution of sources entering the Fleet ...............63 Table 4.7 Estimated phosphorus contribution of sources entering the Fleet ............63 Table 4.8 Estimated N:P ratios at sites within the Fleet.. ..........................64 Table 5.1 Saline lagoons in which the foxtail stonewort Lamprothamnium papulosum is known to occur .....................................78 Annexes Annex A. List of saline lagoon Special Areas of Conservation in the UK .............101 Annex B. Summary from Davison and Hughes (1998) ..........................103 Annex C. Extract from favourable condition table for Chesil and the Fleet European marine site (from English Nature 1999) ...................................109 Annex D. List and summaries of relevant references from Fleet Study Group archive ...114 Preface The 1990s saw a “call to action” for marine biodiversity conservation. The global Convention on Biodiversity, the European Union’s Habitats Directive and recent developments to the Oslo and Paris Convention have each provided a significant step forward. In each case marine protected areas are identified as having a key role in sustaining marine biodiversity. The Habitats Directive requires the maintenance or restoration of natural habitats and species of European interest at favourable conservation status, with the management of a network of Special Areas of Conservation (SACs) being one of the main vehicles to achieving this. Among the habitats and species specified in the Annexes I and II of the Directive, several are marine features and SACs have already been selected for many of these in the UK. But to manage specific habitats and species effectively there needs to be clear understanding of their distribution, their biology and ecology and their sensitivity to change. From such a foundation, realistic guidance on management and monitoring can be derived and applied. One initiative now underway to help implement the Habitats Directive is the UK Marine SACs LIFE Project, involving a four year partnership (1996-2001) between English Nature, Scottish Natural Heritage, Countryside Council for Wales, Environment and Heritage Service, Department of the Environment for Northern Ireland, Joint Nature Conservation Committee, and Scottish Association of Marine Science. The overall goal of the Project is to establish management schemes on 12 of the candidate marine SAC sites. A key component of the Project is to assess the interactions that can take place between human activities and the Annex I and II interest features on these sites. This understanding will provide for better management of these features by defining those activities that may have a beneficial, neutral or harmful impact and by giving examples of management measures that will prevent or minimise adverse effects. Seven areas where human activity may impact on marine features were identified for study, ranging from specific categories of activity to broad potential impacts. They are: ! port and harbour operations ! recreational user interactions ! collecting bait and shoreline animals ! water quality in lagoons ! water quality in coastal areas ! aggregate extraction ! fisheries. These seven were selected on the grounds that each includes issues that need to be considered by relevant authorities in managing many of the marine SACs. In most cases, the existing knowledge is extensive but widely dispersed and there is therefore a requirement to collate it together. In the case of water quality in lagoons, it is apparent that there have been few site specific studies and therefore little material that can be reviewed. Accordingly, the first step has been to trial an approach on a demonstration site and use this to inform broader guidance for other sites as to the assessment and 7 management of water quality in saline lagoons. Through a review undertaken by the Environment Agency, the site selected for this study was Chesil and the Fleet European marine site. Here there is a perceived water quality issue, a site of considerable nature conservation interest and some data on which to build. The reports from all these studies are the result of specialist input and