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Impact of phosphorus control measures on in-river phosphorus retention associated with point source pollution
1The Macaulay Institute, Craigiebuckler, Aberdeen AB15 8QH, UK
2Department of Biology, University of Leicester, Leicester LE1 7RH, UK
3Environment Agency, Station Road, Haddiscoe, Gt Yarmouth, Norfolk, NR31 9JA, UK
4Anglian Water, Henderson House, Lancaster Way, Huntingdon, Cambs. PE29 6XQ, UK
Abstract. In-river phosphorus retention alters the quantity and timings of phosphorus delivery to downstream aquatic systems. Many intensive studies of in-river phosphorus retention have been carried out but generally on a short time scale (2-4 years). In this paper, monthly water quality data, collected by the Environment Agency of England and Wales over 12 years (1990-2001), were used to model daily phosphorus fluxes and monthly in-river phosphorus retention in the lowland calcareous River Wensum, Norfolk, UK. The calibrated model explained 79% and 89% of the observed variance before and after phosphorus control, respectively. A split test revealed that predicted TP loads were in good agreement with observed TP loads (r2=0.85), although TP loads were underestimated under high flow conditions. During relatively dry years, there was no net export of phosphorus from the catchment. High retention of phosphorus occurred, particularly during the summer months, which was not compensated for, by subsequent higher flow events. This was despite a relatively modest critical discharge (Q) above which net remobilisation occur. Phosphorus removal from the effluent at two major STWs (Sewage Treatment Works) reduced phosphorus retention but not the remobilisation. This may indicate that the presence of impoundments and weirs, or overbank flows may have more control on the phosphorus dynamics under high flow conditions. Further phosphorus remedial strategies will be necessary to prevent downstream risks of eutrophication occurring independently of the unpredictable variability in weather conditions. More research is also needed to quantify the impact of the weir and overbank flows on phosphorus dynamics.
Final Revised Paper (PDF, 1025 KB) Discussion Paper (HESSD)
Citation: Demars, B. O. L., Harper, D. M., Pitt, J.-A., and Slaughter, R.: Impact of phosphorus control measures on in-river phosphorus retention associated with point source pollution, Hydrol. Earth Syst. Sci., 9, 43-55, 2005. Bibtex EndNote Reference Manager
