Nutrient modelling and a nutrient budget for Llangorse Lake L. May, B. Dudley, B. M. Spears and T.W. Hatton-Ellis CCW Contract Science Report No. 831 © CCGC/CCW date You may reproduce this document free of charge for non-commercial and internal business purposes in any format or medium, provided that you do so accurately, acknowledging both the source and Countryside Council for Wales' copyright, and do not use it in a misleading context. This is a report of research commissioned by the Countryside Council for Wales. However, the views and recommendations presented in this report are not necessarily those of the Council and should, therefore, not be attributed to the Countryside Council for Wales. Report series: CCW Contract Science Reports Report number: 831 Publication date: April 2008 Contract number: FC 73-02-336 Contractor: Centre for Ecology and Hydrology Contract Manager: T.W Hatton-Ellis Title: Nutrient modelling and a nutrient budget for Llangorse Lake Author(s): L. May, B. Dudley, B. M. Spears and T.W. Hatton-Ellis Series editor(s): Restrictions: None Distribution list (core): CCW HQ Library, Bangor National Library of Wales CCW North Region Library, Mold British Library CCW North Region Library, Bangor Welsh Assembly Government Library CCW S&E Region Library, Cardiff Joint Nature Conservation Committee Library CCW S&E Region Library, Llandrindod Scottish Natural Heritage Library CCW West Region Library, Aberystwyth Natural England Library CCW Abergavenny Office Distribution list (others): Llangorse Lake Advisory Group, Llangorse Environment Agency Wales, St Mellons Graham Motley, CCW Abergavenny Geoff Phillips, Environment Agency Jo-Ann Pitt, Environment Agency Simon Leaf, Environment Agency Havard Prosser, Welsh Assembly Government Peter Samuel, Welsh Assembly Government Stewart Clarke, Natural England Mary Hennessy, Scottish Natural Heritage Tony Waterman, EHS (Northern Ireland) Jim Ryan, Wildlife and Heritage Service (Ireland) John Lucey, Environmental Protection Agency (Ireland) Recommended citation for this volume: L. May, B. Dudley, B. M. Spears and T.W. Hatton-Ellis 2008. Nutrient modelling and a nutrient budget for Llangorse Lake. CCW Contract Science Report No: 831, 75 pp, Countryside Council for Wales, Bangor. CONTENTS EXECUTIVE SUMMARY............................................................................................................i CRYNODEB GWEITHREDOL.................................................................................................iii 1 Introduction................................................................................................................................1 2 The study site..............................................................................................................................3 3 Literature Review........................................................................................................................4 3.1 Water quality.......................................................................................................................4 3.2 Sedimentation rate...............................................................................................................5 3.3 Land use................................................................................................................................5 3.4 Macrophyte species diversity..............................................................................................6 4 Methodology...............................................................................................................................7 4.1 Estimating the nutrient load to the lake by field survey..................................................7 4.1.1 Sampling regime and exceptions...................................................................................7 4.1.2 Hydraulic load to the lake..............................................................................................7 4.1.3 Nutrient concentration in the lake inflows....................................................................9 4.1.4 Phosphorus concentrations in the sediments...............................................................10 4.2 Historical variations in nutrient concentrations in the inflow and outflow ...............10 4.2.1 Inflow data provided by the Environment Agency.....................................................10 4.2.2 Outflow data provided by the Environment Agency...................................................10 5 Results.......................................................................................................................................11 5.1 Hydrology...........................................................................................................................11 5.2 Nutrient concentrations in inflowing streams.................................................................12 5.2.1 Phosphorus concentrations..........................................................................................12 5.2.2 Nitrate concentrations..................................................................................................18 5.3 Nutrient loads.....................................................................................................................20 5.4 Nutrients in sediments.......................................................................................................25 5.5 Nutrient concentrations in the lake..................................................................................27 5.6 Historical variations in nutrient concentrations in the inflow and outflow ................29 5.6.1 Inflow data provided by the Environment Agency....................................................29 5.6.2 Outflow data provided by the Environment Agency...................................................32 6 Discussion.................................................................................................................................36 7 Implications for Catchment management...............................................................................38 7.1 Identifying the problem.....................................................................................................39 7.2 Developing numerical targets...........................................................................................40 7.2.1 Water quality targets for the lake................................................................................40 7.2.2 Water quality targets for the catchment.......................................................................41 7.3 Assessing the sources of N and P......................................................................................42 7.4 Linking targets to sources.................................................................................................44 7.5 Reducing loads...................................................................................................................45 7.5.1 Catchment sensitive farming.......................................................................................45 7.5.2 Nitrate vulnerable zone................................................................................................45 7.5.3 Sustainable tourism......................................................................................................45 7.5.4 Better management of domestic waste........................................................................46 7.6 Developing a monitoring evaluation/plan........................................................................46 8 Possible in-lake Restoration Measures to accelerate recovery processes..............................46 8.1 Vertical Mixing..................................................................................................................47 8.2 Flushing..............................................................................................................................47 8.3 Bio-manipulation...............................................................................................................47 8.4 Sediment removal..............................................................................................................48 8.5 Nutrient inactivation by precipitation or bottom sealing..............................................48 8.6 Biomass harvesting............................................................................................................48 9 Conclusions ..............................................................................................................................49 10 Management Recommendations..........................................................................................49 11 Acknowledgements...............................................................................................................50 12 References...............................................................................................................................50 Appendix 1: Llyn Safaddan Parish Profile...............................................................................54 Appendix 2: INTENTIONALLY LEFT BLANK......................................................................56 Appendix 3: Summary Data.......................................................................................................58 LIST OF FIGURES Figure 3.1 Variation in annual mean in-lake TP concentration in Llangorse Lake. Figure 3.2 Variation in within lake