PHOSPHORUS LOADS IN A SMALL GROUNDWATER-FED RIVER DURING THE 1989-1992 EAST ANGLIAN DROUGHT

Gains and losses in the phosphorus load in a small groundwater-fed river, the River Nar in East Anglia, have been estimated over four drought years. Annual phosphorus balances between downstream sites imply that dissolved inorganic phosphorus (DIP) was retained increasingly over the drought. The external DIP loading to the River did not change over the 4 years although phosphorus retention increased from 30% of the gain in 1989 to 70% during 1992. Over the different years, between about 5% and 15% (which was about 100-400 kg year(-1)) of the DIP in the River was washed out to its estuary. Biological uptake by higher plants probably accounted for most of the DIP which was retained. Data used for this work have been taken from existing monitoring programmes. The resolution of the desk study has none the less been sufficient to show that increases in phosphorus retention have been large enough for undesirable effects on the biological community of the River.