In-river phosphorus retention alters the quantity and timings of phosphorusdelivery to downstream aquatic systems. Many intensive studies of in-riverphosphorus retention have been carried out but generally on a short timescale (2-4 years). In this paper, monthly water quality data, collected bythe Environment Agency of England and Wales over 12 years (1990-2001), wereused to model daily phosphorus fluxes and monthly in-river phosphorusretention in the lowland calcareous River Wensum, Norfolk, UK. The calibratedmodel explained 79% and 89% of the observed variance before and afterphosphorus control, respectively. A split test revealed that predicted TPloads were in good agreement with observed TP loads (r2=0.85),although TP loads were underestimated under high flow conditions. Duringrelatively dry years, there was no net export of phosphorus from thecatchment. High retention of phosphorus occurred, particularly during thesummer months, which was not compensated for, by subsequent higher flowevents. This was despite a relatively modest critical discharge (Q) abovewhich net remobilisation occur. Phosphorus removal from the effluent at twomajor STWs (Sewage Treatment Works) reduced phosphorus retention but not theremobilisation. This may indicate that the presence of impoundments andweirs, or overbank flows may have more control on the phosphorus dynamicsunder high flow conditions. Further phosphorus remedial strategies will benecessary to prevent downstream risks of eutrophication occurringindependently of the unpredictable variability in weather conditions. Moreresearch is also needed to quantify the impact of the weir and overbank flowson phosphorus dynamics.
展开▼
