Overview. Impact of UWWTD on nutrient levels and biological responses in river systems. Rachael Dils Environment Agency

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1 Impact of UWWTD on nutrient levels and biological responses in river systems Rachael Dils Environment Agency Overview Background SA(e) identification and designation Case studies: River Nene,, River Test and River Eden

2 EU UWWTD - Background 91/271/EEC adopted in 1991 Most important policy initiative to address nutrient discharges from sewage treatment works Requires P and N removal (tertiary treatment) wherever discharges (>1, pe) ) are into sensitive areas, defined as being eutrophic or which in the near future may become eutrophic if protective action is not taken Discharge limits: 1,-1, 1, - limit value of 2 mg TP/l (annual av.) >1, - limit value of 1 mg TP/l (annual av.) Sensitive Area (eutrophic( eutrophic) ) identification Assessed using indicative chemical, biological and use-related criteria (demonstration of an undesirable disturbance) Parameters include phosphate, nitrate, DO, chlorophyll a, macrophytes,, diatoms, occurrence of algal blooms, retention time, water clarity Separate criteria for standing f/w, running f/w and saline waters

3 UWWTD SA(e) designation Currently: 62 rivers/canals (2,54 km) 13 lakes/reservoirs 5 estuaries + NI: Lough Neagh & Lough Erne + Scotland: Ythan Impact of designation Date of designation Number of SA(e) designated Number of s affected p.e million million 21 review c.32 potential candidates tbd tbd

4 River Nene Corby (154, pe) Wilton (22, pe) Broadholmes (191, pe) Great Billing (339, pe) 5km Phosphate (SRP) trends SRP Concentration (mg/l) Whilton (indirect) Great Billing DETR criterion Broadholme (pre-p removal) 99- (post-p removal) Corby (indirect) 11 Distance downstream (km)

5 Chlorophyll-a a trends 4 Chlorophyll-a (µg/l) DETR criteria (-stripping) (-stripping) 11 Distance downstream (km) Macrophyte trends - % cover Corby Broadholmes Great Billing Upstream of Downstream of

6 Corby - summer 2 Upstream Downstream Macrophyte trends - MTR MTR Zones >65 Unlikely to be eutrophic Likely to be eutrophic/at risk of becoming eutrophic <25 Badly damaged by eutrophication Corby Broadholmes Great Billing Upstream of Downstream of

7 Slow rate of recovery High nutrient concentrations throughout designated stretch - small s and diffuse sources Macrophytes obtain P from sediment so relationship with SRP concentrations is weak - epiphytic diatoms are sensitive to nutrient concentrations in water (and distinguish organis pollution) Difficult for nutrient-sensitive species to displace nutrient tolerant species P concs and biological response strongly influenced by other factors eg flow River Test Classic chalk river, SSSI, fen meadow, flood pasture and swamp habitats Andover (52, 35 pe) u/s annual mean <.1 mg P/l d/s annual mean mg P/l 36 km designated in 1993 as SA(e) P-stripping installed in March 1998

8 Impact of P stripping Orthophosphate (mg P/l) Paper mill Andover P-removal P-removal Romsey Distance from source (km) Impact of P stripping - Biology Minimal biological response mean chlorophyll a concs decreased by 1.44 µg/l (from 4.99 µg/l to 3.55 µg/l) No significant reduction in MTR values due to high u/s values (minor s,, paper mill, diffuse agricultural sources) low DQI values u/s and d/s

9 % contribution from point source discharges to River Test 8 % contribution P stripping P stripping 1 Andover Paper mill King Sombourne Romsey Cress farms East Grinstead Stockbridge Fish farms River Eden (Lake District) MTR Score Success: Fast-flowing river Low annual average P concentrations throughout stretch 15 µg P/l u/s of Appleby 14 µg P/l pre P-stripping, P 25 µg P/l post P-strippingP u/s d/s Low risk Eutrophic or at risk Badly damaged

10 Conclusions Targeting large s (>1, pe) ) under UWWTD does not always produce desired environmental improvements Other drivers: Habitats Directive - review of discharge consents to ensure SACs are protected Water Framework Directive - need to achieve good ecological status Ecological improvements lag behind chemical improvements