University of Plymouth PEARL https://pearl.plymouth.ac.uk 04 University of Plymouth Research Theses 01 Research Theses Main Collection 1995 AN EVALUATION OF ALTERNATIVE MANAGEMENT STRATEGIES FOR SHALLOW EUTROPHICATED LAKES AND RESERVOIRS WILSON, HELEN M. http://hdl.handle.net/10026.1/1870 University of Plymouth All content in PEARL is protected by copyright law. Author manuscripts are made available in accordance with publisher policies. Please cite only the published version using the details provided on the item record or document. In the absence of an open licence (e.g. Creative Commons), permissions for further reuse of content should be sought from the publisher or author. AN EVALUATION OF ALTERNATIVE MANAGEMENT STRATEGIES FOR SHALLOW EUTROPHICATED LAKES AND RESERVOIRS by HELEN M. WILSON A thesis submitted to the University of Plymouth in partial fulfilment for the degree of DOCTOR OF PHILOSOPHY Department of Environmental Sciences Faculty of Science In collaboration with the Nature Conservancy Council for England (English Nature) [ May 1995 UNiV JTHI ttemNo. Date 1 ] Q ti07 \m 0889Wsili-' S'i't»32X Cont).No (XTo3.1^0•=im- 90 0245657 5 REFERENCE ONLY This copy of the thesis has been supplied on condition that anyone who consults it is understood to recognise that its copyright rests with the author and that no quotation from the thesis and no information derivedfrom it may be published without the author's prior written consent. "In the first place, we have to face that any observed phenomenon can in theory be explained from many different mechanisms. Trivial as it is, this appears hard to keep in mind in every day scientific life. The well known problem associated with it is that one tends to become attached quickly to ones own tentative hypothesis causing an inevitable bias in further research... There is then the imminent danger of an unconscious selection and of a magnifying of phenomena that fall into harmony with the theory and support it and an unconscious neglect of phenomena that fail of coincidence." Scheffer and Beets, 1994 p.ll9 THE P SONG Cycle me, cycle me, you know where Into the oceans and through the air And if you don't cycle me in the right place ril weed up your rivers and eutroph your lakes. Professor Bob Garrels [Cited in Helgeson, 1992] IV An Assessment of Alternative Management Strategies for Shallow Eutrophicated Lakes and Reservoirs Helen M. Wilson Abstract External phosphorus loadings on a range of freshwater Sites of Special Scientific Interest (SSSIs) thought to be affected by eutrophication were predicted utilising export coefficients. The effect of such loadings on lake trophic status was evaluated using the Vollenweider-OECD eutrophication model. Estimates of the relative contribution of phosphorus from various sources enabled the selection of possible reduction strategies on a site specific basis. The effect of reduction strategies on trophic status was predicted with the aid of the model. It was established that diffuse agricultural losses of phosphorus are the most common source of enrichment. However, consented discharges of sewage efHuent appear to affect a significant number of sites. Phosphorus in urban runoff is a notable source for lakes situated in less rural areas. Agricultural point sources significantly influence a small number of lakes. A critique of the methodology concluded that the use of separate export coefficients for organic and inorganic sources may be useful for identifying appropriate management strategies, but that the scientific basis for such an approach is dubious. In addition, the employment of agricultural returns for data on livestock levels may introduce an unacceptable degree of error into the calculations. The Vollenweider-OECD model appears to predict the trophic status of the lakes under assessment reasonably well, but there is a need for a reliable method of ascertaining loading reduction objectives. A review of current legislation and policy applicable to the alleviation of eutrophication of freshwater SSSIs encompassed laws relating to nature conservation, to water quality, and to agricultural extensiflcation. It confirmed that legislation which directly addresses the problem is nonexistent, but that certain laws may be applied in a piecemeal manner. In general, the form of nature conser\'ation protection adopted in this country is not designed to prevent deterioration of water quality. An aspect of eutrophication control which may prove to be the most problematical in legislative teniis is the regulation of diffuse agricultural sources of phosphorus. Proposals for changes in law and policy on this issue included the establishment of a catchment-wide scheme, specifically designed to reduce diffuse agricultural lossesof phosphorus, and targeted at eutrophicated SSSIs. List of Contents List of Tables xii List of Figures xv List of Abbreviations xvii Acknowledgemenls xix Author's Declaration xxi Chapter 1: Introduction 1 LI Background 1 1.2 Aims and Outline of the Study 1 1.3 The Lake-Watershed Ecosystem Concept 3 1.4 The Process of Eutrophication 5 1.5 The Need for Conservation and Restoration 10 Chapter 2: Means of Achieving Reductions in External Phosphorus Loadings 20 2.1 Domestic and Industrial Sources of Phosphorus 22 2. LI Tertiary Treatment of Wastewater 22 2.1.2 Constructed Wetlands for Tertiary Treatment 26 2.1.3 The Use of Non-Phosphate Detergents 28 2.1.4 Diversion of Sewage Effluent 31 2.1.5 Stormwater Management 32 2.2 Agricultural Sources of Phosphorus 39 2.2.1 Adherence to Good Agricultural Practice 44 2.2.2 Agricultural Land Diversion 47 2.2.3 Agricultural Extensification 53 2.3 Summary 59 Chapter 3: Prediction and Evaluation of External Phosphorus Loadings 61 3.1 The Determination and Use of Export Coefficients 61 3.2 Application of Export Coefficients in the U.K. 66 3.3 The Vollenweider-OECD Model 75 Chapter 4: Legislative Framework for Conservation and Restoration 81 4.1 Sources of Legislation 81 4.1.1 British Legislation 82 4.1.2 EC Legislation 82 4.1.3 International Legislation 84 VI List of Contents (Continued) 4.2 Nature Conservation 84 4.2.1 The Development of Legislation for Nature Conservation 85 4.2.1.1 The Post War Era 85 4.2.1.2 Developmenis During the 1960s and 1970s 86 4.2.1.3 The Wildlife and Countryside Act 1981 88 4.2.1.4 The Present System 90 4.2.2 EC Directives 99 4.2.2.1 The Birds Directive 100 4.2.2.2 The Habitats Directive 101 4.2.3 International Conventions 104 4.2.3.1 The Ramsar Convention 104 4.2.3.2 The Bern Convention 105 4.3 Agriculture 106 4.3.1 Agricultural Support in the Post War Era 106 4.3.2 The Common Agricultural Policy 107 4.3.3 Agricultural Extensification 110 4.3.3.1 Environmentally Sensitive Areas 110 4.3.3.2 Options under the Set-Aside Scheme 112 4.3.3.3 Organic Aid Scheme 116 4.4 Water Quality 117 4.4.1 The Development of Water Quality Legislation 117 4.4.2 Water Resources Act 1991 120 4.4.2.1 The Role of the National Rivers Authority 121 4.4.2.2 Water Protection Zones 126 4.4.2.3 Nitrate Sensitive Areas 128 4.4.2.4 Statutory Water Quality Objectives 130 4.4.3 EC Directives 132 4.4.3.1 Directive on Nitrates 134 4.4.3.2 Directive on Urban Waste Water Treatment 135 4.4.3.3 Proposed Directive on the Ecological Quality of Surface Waters 138 4.5 Synthesis 139 Chapter 5: Methods 142 5.1 Selection of Sites for Evaluation 142 5.2 Data Collection 144 5.2.1 Catchment Defmition 145 5.2.2 Land Use 145 5.2.3 Livestock Levels 146 5.2.4 Consented Discharges 149 5.2.5 Morphometric Data 149 5.2.6 Export Coefficients 149 VII List of Contents (Continued) 5.3 Prediction and Evaluation 154 5.3.1 Computing the Data 154 5.3.2 Phosphorus Loading Reduction Strategies 155 5.3.3 Evaluation of Results 157 Chapter 6: Site Descriptions 158 6.1 Coastal Lakes of South West England 158 6.1.1 LoePool 158 6.1.1.1 Lake and Catchment Characteristics 158 6.1.1.2 Current Status 161 6.1.2 Slapton Ley 161 6.1.2.1 Lake and Catchment Characteristics 161 6.1.2.2 Current Status 163 6.2 Surrey Ponds 164 6.2.1 Bay Pond 165 6.2.1.1 Lake and Catchment Characteristics 165 6.2.1.2 Current Status 166 6.2.2 Hedgecourt Lake 166 6.2.2.1 Lake and Catchment Characteristics 166 6.2.2.2 Current Status 167 6.3 Norfolk Broads 168 6.3.1 Barton Broad 169 6.3.1.1 Lake and Catchment Characteristics 169 6.3.1.2 Current Status 170 6.4 Reservoirs of Eastern England 171 6.4.1 Grafham Water 172 6.4.1.1 Lake and Catchment Characteristics 172 6.4.2 Pitsford Reservoir 173 6.4.2.1 Lake and Catchment Characteristics 173 6.4.3 Rutland Water 174 6.4.3.1 Lake and Catchment Characteristics 174 6.4.4 Current Status 176 6.5 West Midlands Lakes 178 6.5.1 Sutton Park Pools 178 6.5.1.1 Lake and Catchment Characteristics 178 6.5.1.2 Current Status 179 6.6 North West Midlands Meres 180 6.6.1 Aqualate Mere 180 6.6.1.1 Lake and Catchment Characteristics 180 6.6.1.2 Current Status 182 vin List of Contents (Continued) 6.6.2 Chapel Mere 182 6.6.2.1 Lake and Catchment Characteristics 182 6.6.2.2 Current StaUJs 183 6.6.3 Comber Mere 184 6.6.3.1 Lake and Catchment Characteristics 184 6.6.3.2 Current Status 185 6.6.4 Norbury Meres 186 6.6.4.1 Lake and Catchment Characteristics 186 6.6.4.2 Current Status 187 6.6.5 Petty Pool 188 6.6.5.1 Lake and Catchment Characteristics 188 6.6.5.2 Current Status 189 6.6.6 Quoisley Meres 190 6.6.6.1 Lake and Catchment Characteristics 190 6.6.6.2 Current Status 191 6.6.7 TableyMere 192 6.6.7.1 Lake and Catchment Characteristics 192 6.6.7.2 Current Status 193 6.6.8 Tatton Mere 194 6.6.8.1 Lake and Catchment Characteristics 194 6.6.8.2 Current Status