EUTROPHICATION IN CONTROLLED WATERS IN THE WARWICKSHIRE AVON CATCHMENT (Final Report) Volume 1 March 1998 En v ir o n m e n t A g e n c y C O V K NT ItY UNIVERSITY E n v ir o n m e n t Ag e n c y NATIONAL LIBRARY & INFORMATION SERVICE HEAD OFFICE Rio House. Waterside Drive, Aziec West. Almondsbury. Bristol BS32 4UD 2 EUTROPHICATION IN CONTROLLED WATERS IN THE WARWICKSHIRE AVON CATCHMENT (Final Report) A Research Report Commissioned by the Environment Agency Volume 1 Report and Executive Summary Environment Agency Project Manager: Peter Buckland September 1994 - November 1996 Diane Mcllroy November 1996 - March 1998 Project Executive: Keith WagstafT September 1994 - November 1997 Roger Wade December 1997 - March 1998 Coventry University Centre for Environmental Research and Consultancy:- Project co-ordinator: Ian D.L. Foster Research Team: Janice Sheasby, Steven Wade & Sarah Harrison Management team: Serwan Baban, Sue Charlesworth & Roz Jackson March 1998 For further information contact Roger Wade or Diane Mcllroy at Environment Agency, Riversmeet House, Newtown Industrial Estate, Northway Lane, Tewkesbury, Glos GL20 8JG. 3 Contents Page EXECUTIVE SUMMARY 7 1. INTRODUCTION 12 2. STUDY BACKGROUND 13 2.1 Phosphorus and nitrogen in natural waters 17 3. PROJECT TECHNICAL PLAN 19 3 .1 Sampling Programme 19 3.2 Analytical Schedule 22 4. PROJECT REVIEW 23 4.1 Sampling Programme 23 4.2 Sampling Performance 23 4.3 Laboratory Analysis 24 4.4 Flow Gauging 25 4.5 Data Analysis 26 4.6 Background and definitions 27 5. NUTRIENT CONCENTRATIONS 28 5.1 STW Data 28 5.2 River Data 30 5.3 Seasonal trends in water quality 35 5.4 Downstream trends in concentration 73 6. THE IMPACT OF THE URBAN WASTE WATER TREATMENT DIRECTIVE ON STW DISCHARGES AND RIVER CONCENTRATIONS 83 1. CALCULATION OF NUTRIENT LOADS 90 7.1 Background 90 7.2 Load Calculation procedures 90 7.3 The magnitude of nutrient loads in the Avon Catchment 92 8. NUTRIENT BUDGETS 94 8.1 Calculating Budgets 94 8.2 Sewage Treatment Works 94 8.3 Rivers 95 8.4 Local impacts of STWs 98 4 8.5 Downstream trends in river loads 103 8.6 Seasonal trends in river loads and the contribution of STWs to N and P loads at Evesham 104 8.7 The impact of the Urban Waste Water Treatment Directive on River Loads. 117 9. EFFECTS OF FIELD FILTERING ON ORTHOPHOSPHATE ANALYSIS 120 10. FUTURE INVESTIGATIONS 10.1 Investigate the Impact of P Removal in the Avon Catchment 127 10.2 Calculating nutrient loads 127 10.3 Subcatchments generating high P loads from diffuse and unaccountable sources 127 10.4 Export coefficient modelling and testing 127 10.5 The role of Wetlands (Brandon Marsh) as sediment and nutrient sinks and as phytoplankton re-seeding areas 129 10.6 Phytoplankton and eutrophication 129 10.7 Rural sewage pollution 130 10.8 Climate change and eutrophication 131 11. ACKNOWLEDGEMENTS 134 12. REFERENCES 135 Tables Table 1. Summary of sampling compliance 23 T able 2. Analytical errors for laboratory determinands 25 Table 3. Summary N (a), P (b) and BOD and COD (c) concentration data from qualifying and minor STWs 29 Table 4. Summary concentration data for river monitoring sites 32 Table 5. Nutrient loads for selected river Avon sites (kg/d) 92 Table 6. Nutrient loads for selected river Avon sites (a) and other recent estimates for UK rivers (b) 92 Table 7. Estimated P loads from catchments 93 Table 8. Estimated N and P loads for qualifying and minor STWs 95 Table 9. Total P and N budgets for major sub-catchments (a-e) and the Avon at Evesham (f) 97 Table 10. Downstream trends in river P and N loads 103 Table 11 Comparison between filtered and unfiltered orthophosphate determinations on paired samples from 18 weekly monitoring sites in the Avon catchment. 120 Table 12. The quality of streams receiving sewage effluent in rural areas 131 5 Table 13. Summary Statistics for the Coventry and the England and Wales Annual Rainfall Series 132 Illustrations Figure 1 The river Avon and its sub-catchments 14 Figure 2 Land use in the Avon catchment 15 Figure 3 Schematic catchment diagram showing the location of sampling stations 21 Figure 4 Location of STW monitoring sites 37 Figure 5 Seasonal trends in water quality at Rugby (Newbold) STW 38 Figure 6 Seasonal trends in water quality at Coventry (Finham) STW 40 Figure 7 Seasonal trends in water quality at Leamington (Heathcote) STW 42 Figure 8 Seasonal trends in water quality at Warwick (Longbridge) STW 44 Figure 9 Seasonal trends in water quality at Red ditch (Spemal) STW 46 Figure 10 Seasonal trends in water quality at Braunston STW 48 Figure 11 Seasonal trends in water quality at Harbury STW 50 Figure 12 Seasonal trends in water quality at Wootton Wawen STW 52 Figure 13 Location of the main Avon quality monitoring stations 56 Figure 14 Seasonal trends in water quality at Kilworth 57 Figure 15 Seasonal trends in water quality at Clifton 59 Figure 16 Seasonal trends in water quality at Little Lawford 61 Figure 17 Seasonal trends in water quality at Stare Bridge 63 Figure 18 Seasonal trends in water quality at Stoneleigh 65 Figure 19 Seasonal trends in water quality at Barford 67 Figure 20 Seasonal trends in water quality at Stratford 69 Figure 21 Seasonal trends in water quality at Evesham 71 Figure 22 Downstream trends in TON concentration (log scale) 76 Figure 23 Downstream trends in P 04 concentration (log scale) 76 Figure 24 Downstream trends in NH3 concentration (log scale) 77 Figure 25 Downstream trends in Kjeldahl Nitrogen (KN) concentration (log scale) 77 Figure 26 Downstream trends in total N concentration (log scale) 78 Figure 27 Downstream trends in total P concentration (log scale) 78 Figure 28 Downstream trends in redox potential (log scale) 79 Figure 29 Downstream trends in electrical conductivity (log scale) 79 Figure 30 Downstream trends in BOD (log scale) 80 Figure 31 Downstream trends in COD (log scale) 80 Figure 32 Downstream trends in suspended solids concentration (log scale) 81 Figure 33 Downstream trends in chlorophyll a concentration (log scale) 81 Figure 34 Particulate-P concentrations in selected rivers (log scale) 82 6 Figure 35 Regrouped data of Figure 34 (log scale) 82 Figure 36 Phosphorus concentrations at Stare Bridge under various scenarios of concentration at Rugby STW 85 Figure 37 Phosphorus concentrations at Stoneleigh under various scenarios of concentration at Finham STW 86 Figure 38 Phosphorus concentrations at Stratford under various scenarios of concentration at Stratford (Milcote) STW 87 Figure 39 Phosphorus concentrations at Broom under various scenarios of concentration at Redditch STW 88 Figure 40 Phosphorus concentrations at Evesham under various scenarios of concentration at all qualifying STWs 89 Figure 41 Local impact of qualifying STWs on flow and nitrogen loads 100 Figure 42 Local impact of qualifying STWs on flow and phosphorus loads including an estimate of the impact of P removal at qualifying STWs 101 Figure 43 Monthly TN loads at all weekly monitoring sites 106 Figure 44 Monthly TP loads at all weekly monitoring sites 111 Figure 45 Seasonal contribution of STW effluent loads to P transport at Evesham 116 Figure 46 Seasonal contribution of STW effluent loads to N transport at Evesham 116 Figure 47 The potential impact of meeting the UWWT Directive on N and P loads at Evesham 118 Figure 48 The potential impact of further reductions in P concentrations from STW discharges on P loads at Evesham. 119 Figure 49 The relationship between orthophosphate concentrations determined on filtered and unfiltered samples for sites where weekly sampling was undertaken. 122 Figure 50 A nitrogen export coefficient model for the Bourne Brook, North Warwickshire 1965-1991. 128 Figure 51 Boxplots of chlorophyll a concentrations for all sites (log scale) 130 Figure 52 Coventry monthly rainfall 1900-1996 133 Appendices Appendix 1 Sampling compliance for individual sites 139 Appendix 2 Analytical compliance for water Quality data 141 Appendix 3 Methods used for infilling ‘missing* water quality data for load calculations 144 Appendix 4 Additional Hydrometric Data supplied by EA Hydrometric Section, Solihull 147 7 EXECUTIVE SUMMARY Introduction The River Avon was designated a Sensitive Area (Eutrophic) under the UWWT Directive in 1994. A major advance in dealing with the problems of eutrophication (increased phytoplanton blooms, excess macrophyte growth etc.) is the removal of significant levels of phosphate from the major sewage works in the Catchment. Following on from designation as a SA(E) this project was initially designed to: • Identify the present levels of phosphate and nitrate in the Avon catchment. • Estimate the likely effect of phosphate removal at the major sewage works • Estimate the possible further improvements possible by extending phosphate treatment to smaller sewage works • Identify the other major sources of phosphate and nitrate in the catchment. The project also provides a baseline for assessing the improvements that shall result from phosphate treatment at the major STWs commencing at the end o f 1998. It has also identified a number of areas where additional investigative work may be required to improve the understanding of nutrients in the Avon catchment. This will allow targeting of resources to reduce the input of diffuse phosphate and nitrate to the river. The following points highlight the major issues addressed within this report: 1. The Avon has shown signs of accelerated eutrophication in recent years by the presence of attached and planktonic algae and as a result of the presence of nuisance blue-green algal blooms. Such characteristics are undesirable from both a water quality management and recreation/resource perspective.