Evidence Review of Lake Eutrophication in Wales Dr Tristan Hatton-Ellis NRW Evidence Report No 135 Date www.naturalresourceswales.gov.uk About Natural Resources Wales Natural Resources Wales is the organisation responsible for the work carried out by the three former organisations, the Countryside Council for Wales, Environment Agency Wales and Forestry Commission Wales. It is also responsible for some functions previously undertaken by Welsh Government. Our purpose is to ensure that the natural resources of Wales are sustainably maintained, used and enhanced, now and in the future. We work for the communities of Wales to protect people and their homes as much as possible from environmental incidents like flooding and pollution. We provide opportunities for people to learn, use and benefit from Wales' natural resources. We work to support Wales' economy by enabling the sustainable use of natural resources to support jobs and enterprise. We help businesses and developers to understand and consider environmental limits when they make important decisions. We work to maintain and improve the quality of the environment for everyone and we work towards making the environment and our natural resources more resilient to climate change and other pressures. www.naturalresourceswales.gov.uk Page 1 Evidence at Natural Resources Wales Natural Resources Wales is an evidence based organisation. We seek to ensure that our strategy, decisions, operations and advice to Welsh Government and others are underpinned by sound and quality-assured evidence. We recognise that it is critically important to have a good understanding of our changing environment. We will realise this vision by: Maintaining and developing the technical specialist skills of our staff; Securing our data and information; Having a well-resourced proactive programme of evidence work; Continuing to review and add to our evidence to ensure it is fit for the challenges facing us; and Communicating our evidence in an open and transparent way. This Evidence Report series serves as a record of work carried out or commissioned by Natural Resources Wales. It also helps us to share and promote use of our evidence by others and develop future collaborations. www.naturalresourceswales.gov.uk Page 2 Report series: NRW Evidence Reports Report number: 135 Publication date: September 2016 Title: Evidence Review of Lake Eutrophication in Wales Author(s): Hatton-Ellis TW. NRW Peer Reviewer(s) Jones PS, Duigan CA. Independent Expert Review: Bennion H (University College London). Approved By: Evans, M. Restrictions: None Distribution List (core) NRW Library, Bangor 2 National Library of Wales 1 British Library 1 Welsh Government Library 1 Scottish Natural Heritage Library 1 Natural England Library (Electronic Only) 1 Distribution List (others) James Dowling, Welsh Government Rachel Lewis-Davies, NFU Cymru Andrew Sherlock, Welsh Government Peter Howells, NFU Cymru Natalie Hall, NRW Karen Anthony, CLA Mark Squire, NRW Paul Henderson, DC / WW Brian Pawson, NRW Environment Agency, Bristol Andrea Winterton, NRW Katie-Jo Luxton, RSPB Cymru Ged Davies, NRW Stewart Clarke, National Trust Robert Edwards, NRW Sean McHugh, Wales Biodiversity Helen Millband, NRW Partnership Hazel Wright, FUW Jo-Anne Pitt, Environment Agency Rhianne Jones, FUW Recommended citation for this volume: Hatton-Ellis, T.W. 2016. Evidence Review of Lake Nitrate Vulnerable Zones in Wales. NRW Evidence Report No: 135, 163pp, Natural Resources Wales, Bangor. www.naturalresourceswales.gov.uk Page 3 Contents 1. Crynodeb Gweithredol .................................................................................................... 9 2. Executive Summary ...................................................................................................... 11 3. Introduction ................................................................................................................... 13 3.1. The Nitrates Directive Evidence Review Process .............................................................13 3.2. The Eutrophic Waters NVZ Criteria ..................................................................................15 4. Methods ........................................................................................................................ 17 4.1. Nitrogen Thresholds ..........................................................................................................17 4.2. Updates to the WFD monitoring methods .........................................................................18 4.3. Impact of the classification tool updates ...........................................................................20 4.4. Interpretation of other evidence ........................................................................................20 4.5. Update to the Environment Agency Weight of Evidence (WoE) Tool ..............................20 4.6. Combination of nitrogen and WoE results ........................................................................22 4.7. Nitrogen Limitation ............................................................................................................23 4.8. Data used in the Assessment ...........................................................................................24 4.9. Catchment Land Use ........................................................................................................24 4.10. Source Apportionment ......................................................................................................25 4.11. Pumped Storage Reservoirs .............................................................................................26 4.12. Managing Uncertainty .......................................................................................................26 4.13. Independent Expert Review ..............................................................................................27 5. Results ......................................................................................................................... 28 5.1. Nitrogen concentrations ....................................................................................................28 5.2. Ecological Evidence using the WoE Tool .........................................................................30 6. Summary Information for Individual Lakes .................................................................... 33 6.1. Bosherston Lakes .............................................................................................................33 6.2. Plas Uchaf and Dolwen Reservoirs ..................................................................................38 6.3. Llyn Coron .........................................................................................................................42 6.4. Llyn Maelog .......................................................................................................................46 6.5. Cefni Reservoir .................................................................................................................50 6.6. Valley Lakes ......................................................................................................................53 6.7. Llyn Alaw ...........................................................................................................................61 6.8. Llyn yr Wyth Eidion ...........................................................................................................64 6.9. Llangorse Lake .................................................................................................................68 6.10. Hanmer Mere ....................................................................................................................72 6.11. Llyn Pencarreg ..................................................................................................................77 6.12. Llandegfedd Reservoir ......................................................................................................81 6.13. Llyn Tegid..........................................................................................................................83 6.14. Witchett Pool .....................................................................................................................90 6.15. Eglwys Nunnydd Reservoir ...............................................................................................94 6.16. Llwyn-On Reservoir ..........................................................................................................98 6.17. Llyn Elsi Reservoir ..........................................................................................................101 www.naturalresourceswales.gov.uk Page 2 6.18. Llyn Padarn .....................................................................................................................103 6.19. Llyn Tryweryn ..................................................................................................................107 6.20. Pant-yr-Eos Reservoir .....................................................................................................110 6.21. Ty Mawr Reservoir ..........................................................................................................112 6.22. Wentwood Reservoir .......................................................................................................115 6.23. Ynysyfro Reservoirs ........................................................................................................117