Poole Harbour Consent Order Technical Document Recommendations to deliver Favourable Status across Poole Harbour Catchment DRAFT for consultation 18 May 2018 1 Prepared by: Giles Bryan: Environment Agency Alun James: Environment Agency Rosanne Broome: Environment Agency Contributions from Karen Edwards Environment Agency Douglas Kite Natural England Andrew Nicholson: Natural England Sarah Sanders Natural England Supporting information Richard Gooday, Paul Newell Price: ADAS Ruth Barden: Wessex Water 3 Contents Executive Summary .............................................................................................................. 7 1.0 Introduction. .................................................................................................................... 9 2.0 Background ..................................................................................................................... 9 2.1 Conservation objectives ............................................................................................... 9 2.2 Conservation Status of Poole Harbour Catchment ..................................................... 10 2.3 Measures put under Nutrient Management Plan to achieve conservation objectives. 10 3.0 Measures put in Place Since 2013 & Review of catchment Targets for the Purpose of the Consent Order .................................................................................................................... 11 3.1 Conservation Objective Targets ................................................................................. 11 3.2 Measures implemented or proposed to be implemented since 2013 .......................... 12 3.3 NMP reduction strategy ........................................................................................ 13 4.0 Mechanisms in place to deliver catchment objectives & Effectiveness of these measures. ....................................................................................................................... 13 4.1 Mechanisms and measures put in place to deliver catchment objectives ................... 13 5.0 Updated Evidence & Catchment Objectives .................................................................. 15 5.1 Source Apportionment & Nutrient reduction from the current strategy ................... 15 6.0 Macroalgae Modelling: Current and Future Scenarios ................................................... 19 6.1 Macro-algae densities modelled from 2010-11, 2013-17 and NMP Scenarios. .......... 19 6.2: Future Water Quality Targets required to meet model macroalgae density and threshold density targets.................................................................................................. 22 6.3 Modelled nutrient loading required to achieve macroalgae targets............................. 25 6.4 Point Source Measures to deliver macroalgae targets ............................................... 27 6.5: Diffuse Measures to deliver macroalgae targets ....................................................... 28 6.5 Alternative Measures to Deliver Diffuse Pollution Reduction: Wetland Creation......... 32 6.6 Recommended in combination Measures to Deliver Water Quality Improvements .... 33 7.0 Mechanisms and timescales to Deliver Favourable Conservation Targets. ................... 35 7.1 Point Source Mechanisms to Implement Measures ................................................... 35 7.2: Mechanisms to deliver diffuse pollution reductions and measures. ........................... 36 7.2:1 Current legal powers to prevent pollution ............................................................ 36 7.2.2: Recommended diffuse pollution mechanism & measures .................................. 36 8.0 Stakeholders & Engagement ......................................................................................... 39 9.0 Cost effectiveness ......................................................................................................... 40 10.0 Recommendations ...................................................................................................... 40 Appendix 1 : Summary of Poole Harbour dynamic Combined Phytoplankton and Macroalgae (CPM) Modelling- Calibration Study. Edwards 2018 ........................................................... 45 Appendix 2: Water Quality and Macroalgae Modelling of Poole Harbour: Estimated the required reduction in nutrient to achieve acceptable densities of Macroalgae; James, Edward & Bryan 2018. ..................................................................................................................... 47 5 Appendix 3: Background information for understanding the catchment situation on nitrogen nutrient enrichment in the Poole Harbour Natura 2000 site: Kite & Nicholson 2018 ............ 49 Appendix 4: Phosphorus Sources Across the Poole Harbour Catchment & Apportionment; Total Inorganic Phosphorus (TP) & Orthopho-phosphorus Bryan 2018. .............................. 51 Appendix 5; Trends in total oxidised nitrogen (TON) in surface waters in the Poole Harbour catchment, 1976 to 2016; Environment Agency Wessex Area Analysis and Reporting Team. Draft October 2016 ................................................................................................. 53 6 Executive Summary In 2015 the World Wildlife Fund UK, the Angling Trust and Fish Legal undertook a Judicial Review (JR) against the Secretary of State for the Environment, Food and Rural Affairs and the Environment Agency (EA). It was based on the perceived non-consideration of Water Protection Zones (WPZs), to deliver measures to tackle diffuse water pollution impacting on water-dependent Natura 2000 (N2K) sites. As a result of the JR the EA, working with Natural England (NE), undertook to evaluate whether the existing measures and mechanisms to tackle pollution will lead to the improvements in water quality necessary to meet the conservation objectives for each N2K site. This document, represents this review for the Poole Harbour catchment. Since publishing the Nutrient Management Plan (NMP) “Strategy for Managing Nitrogen across the Poole Harbour Catchment to 2035” in 2013, advice on our interpretation of conservation objectives and standards used for the macroalgae abundance, have been updated. These have been based on emerging scientific evidence. The primary conclusions from this are that: - a lower average modelled biomass of <c500g/m2 is required across the available intertidal habitat, to ensure there are no adverse effect from opportunistic macroalgae. - a wet weight macroalgae biomass of 1.0 kg/m2 on suitable intertidal habitat should be used as a threshold value in, for example, assessing field data, as the point at or above which significant harmful effects on habitat biota are likely to occur. This is a reduction from the value used in the NMP to describe when partial success of the NMP will be observed (NMP Section 1.2). Macroalgae modelling now suggests that to achieve these targets, Nitrate loads need to be reduced to the target set in the NMP (c1730 tonnes/N/yr) and Orthophosphorus reduced to 20 -21.5 tonnes OP/yr from their current levels of c2300 tonnes N/yr & c51 tonnes OP/yr or 71 tonnes TP/yr. To achieve this, additional measures are needed to reduce both diffuse and point-source pollution. Based on current trends, the voluntary uptake of agricultural mitigation measures will not meet the required reduction in pollution. Since the publication of the NMP the farming community has worked hard to start to implement the findings of the NMP. However evidence now indicates that because of the scale of N & P reduction required, to increase the confidence in delivery measures fundamental to delivering diffuse pollution reduction and maximum leaching targets for nitrate and phosphorus should be given regulatory backing through a Water Protection Zone or other mechanisms. Details regarding these measures should be developed in partnership with the appropriate stakeholders and or their representatives and where appropriate, further support and incentives should be made available to assist farmers in delivering any obligations above those that might be expected in other parts of the country. Since publication the NMP, Wessex Water have also implemented measures to reduce the impact of their discharges on the water environment, including their innovative NTrade system, offsetting 40 tonnes N/yr to mitigate for projected growth. Modelling now however, indicates that they will need to go further. Recommendations made in this report outline the need for them to reduce point source phosphorus loads entering the Wareham Channel by c30% (c3 tonnes OP/yr). In addition to this, all of the macroalgae-modelling scenarios show the discharge from Poole STW is having a significant impact on Holes Bay and the wider 7 catchment, as a result of the proportionately high nutrient load during spring and summer. To meet the conservation objectives it will be necessary for effluent from Poole STW to be discharged out of the catchment (to a location that would not cause harm to the environment or humans) or treatment levels on the site should be increased to c50% BAT for N and c10% BAT for P. The final permit conditions should be determined through further refined modelling and investigations proposed in PR19. Option appraisal also indicate that it will also be necessary to implement alterative diffuse mitigation options, such as wetland systems to remove sufficient N & P to meet conservation objectives. Currently c50 ha of wetland are currently