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University of Brighton Pilot Area Report: The Pevensey Levels, UK

University of Brighton Pilot Area Report: The Pevensey Levels, UK. Dave Diston, School of Environment and Technology, University of Brighton. Assessment of the current trophic status of the Pevensey Levels SSSI/Ramsar site Soluble Reactive Phosphorus (SRP) Identification of chemical trends

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University of Brighton Pilot Area Report: The Pevensey Levels, UK

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  1. University of Brighton Pilot Area Report: The Pevensey Levels, UK Dave Diston, School of Environment and Technology, University of Brighton

  2. Assessment of the current trophic status of the Pevensey Levels SSSI/Ramsar site Soluble Reactive Phosphorus (SRP) Identification of chemical trends long-term temporal/spatial To conduct a nutrient source apportionment study (1) examination of seasonal determinand fluctuations (2) employing boron as a chemically conservative tracer of STW effluent, (3) relationship of determinand with flow and (4) mass balances Pilot study objectives OECD trophic status (1982) Decreasing water quality 2

  3. Q P N C and T A O R HNSTW D HSSTW B W L F K S G H E and U I and V M J Pevensey Haven (PH) 23 sites - 16 on PH; 7 on WH Wallers Haven (WH)

  4. Pevensey Levels hydrology • 9 sub-catchments • Little freshwater input • PH • Numerous retention • structures

  5. Methodology • Two data sets utilised in the study: • Data set A (Environment Agency) • 19 sites (A-S) • Weekly from January 1994 to March 2007 • Wide spectrum of chemical determinands • Spectrophotometry and ICP-MS used for analysis • Data set B (University of Brighton) • 4 sites (T-W) • Bi -monthly monitoring from April 2005 – August 2006 • SRP and B analysis (as borate) • Spectrophotometer (Model: Hach DR/2400) used for analysis 5

  6. Results: Trophic status (SRP only) Median SRP at sites T-W Classification of sites by SRP concentrations (WH in bold) 1000μg • Majority of sites on PH hyper eutrophic; WH tends to be eutrophic • Significant difference between Pevensey and Wallers Haven (663 µg-P l-1 (n = 1442) and 122 µg-P l-1 (n = 858) respectively • Large within catchment variance 6

  7. G O H C E R S P B K L M I F N Q D A J Results: Spatial variance (SRP only) Pevensey Haven Wallers Haven WHSTW • SRP concentrations rise significantly downstream of both Hailsham STW and WHSTW (also with N compounds – NH4, NO2 and NO3), generally diluting towards the mouth • Manxey Levels have unique chemical signature – very low nutrient levels and elevated BOD levels

  8. Results: Spatial variance – correlation of sites - All sites appear to be chemically unrelated, the exception being sites E&H and H&J; this is most likely due to close proximity of the sites (<1km). - Influence of water retention structures?

  9. Results: Long term trends Nutrient stripping Median concs increased – Increased nitrification? Less variance, median concs decreased slightly HNSTW HSSTW Less variance, median concs significantly decreased Less variance, median concs decreased Little change within Wallers Haven – no change in background loads

  10. Results: Source apportionment (seasonal analysis) Sites that experience summer determinand peaks Only sites on Wallers Haven are O and R (13 and 11km d/s of small STW Few sites have seasonal patterns -Only site on Pevensey Haven is site E (11.5km d/s of STW) Characteristic of point source pollution

  11. Results: Source apportionment (seasonal analysis) Sites that experience winter determinand peaks Characteristic of diffuse source pollution • - Inversion of pattern at site C in post stripping period • This may indicate that diffuse contributions are being delivered during the winter period, or that P is being abiotically/biotically stripped from the water column during summer • The majority of sites display no discernable relationship (18/23)

  12. Results: Source apportionment (B analysis) THEORY Release 9.5:1 Uptake SRP/B relationship in 7 STW effluents (Neal et al., 1998) SRP/B relationship in STW affected waterbodies (Jarvie et al., 2005) Both determinands are primarily derived from cleaning and bleaching agents BUT vary in bioavailability

  13. A B Results: Source apportionment (B analysis) 9.5:1 1.9:1 High B, low SRP Uptake 1.9:1 • Sites located directly downstream of major STW (T and U) have the strongest correlations (lower than found in other studies; >0.90) suggesting presence of point source pollution • All SRP:B ratios are relatively stable (exception is site T) and significantly below 1.9:1 gradient suggesting significant instream SRP loss

  14. Results: Source apportionment (flow analysis) Sites displaying point source signals • Only two sites (WH data only) showed negative relationships between flow and SRP – these were weak compared to other studies • Indicative of point source pollution (sites O and R are d/s of WHSTW)

  15. Results: Source apportionment (flow analysis) Sites displaying diffuse source signals Only site Q shows a positive relationship between SRP and flow. Possibly representing mobilisation of septic tank/small STW discharges during rainfall events OR diffuse Various other sites in the Wallers Haven catchment display positive relationships between N and flow

  16. Results: Source apportionment (mass balances) Point source pollution is major contributor of SRP Diffuse source pollution is major contributor of NO3

  17. Influence of water retention structures • Encourages SRP assimilation • Distorts SRP:B ratio • Distorts seasonal patterns Conceptual model of Pevensey Levels drainage system 12

  18. Summer Influence of water retention structures Water retained Pevensey Levels ditch management 13

  19. Conclusions • The two catchments exhibit significantly different levels of eutrophication; the PH catchment has higher nutrient/BOD concentrations, whilst having lower DO levels; • Results from source apportionment studies indicate that the cause of elevated nutrient levels is likely to be Hailsham STW; WHSTW has a limited effect in the WH catchment; • Water retention gates appear to disrupt seasonal nutrient patterns, inhibit connectivity between sites and retard SRP-B relationship; • Boron appears to act a suitable tracer of STW effluent within wet grasslands; • Further work is required to fully understand nutrient patterns (i.e. boron isotope study). 14

  20. Thank you for your attention! Selected references JARVIE, H.P., NEAL, C., and WITHERS, P.J.A., 2005. Sewage-effluent phosphorus: A greater risk to river eutrophication than agricultural phosphorus? The Science of the Total Environment, vol 360, issues 1-3, pp. 246-253. NEAL, C., FOX, K.K., HARROW, M., and NEAL, M., 1998. Boron in the major UK rivers entering the North Sea. The Science of the Total Environment, vol 210 211, pp. 41-51

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