Phosphorus and its biological effect in lowland rivers

Eastern England is mostly rural with extensive arable farming. It is one of the driest areas of the UK, receiving approximately two thirds of the national rainfall average. The rivers in this region are generally considered sluggish with high nutrient content.;This study examined the sources and seasonal pattern of phosphorus concentrations in these lowland rivers. Biological effect of phosphorus (measured as soluble reactive phosphorus, SRP) was investigated in algae; specifically the response of diatom species and periphyton biomass to elevated levels of phosphorus.;The rivers in this part of the UK are routinely monitored by the Anglian Region of the Environment Agency. Routine monitoring data for SRP were used to identify high and low phosphorus rivers. Overall, concentrations ranged between <10 g 1-1 to over 10,000 g 1-1 SRP with values significantly skewed towards the lower end of this range. For 1991-5, 215 of sampled river stretches had 100 g 1-1 SRP or below, 49% between 100-500 g l-1 and 30% between 500-1000 g l-1. The ratio of nitrogen to phosphorus (total oxidised nitrogen to soluble reactive phosphorus by mass) for the upper reaches of eight rivers indicated that 83 % of sites on these rivers during summer months were potentially phosphorus-limited when the boundary ratio of 10:1 was applied.;Effluent and geology were found to influence instream SRP concentrations. Rivers on chalk geologies had significantly lower phosphorus concentrations than those on other geologies. A significant relationship between effluent load and instream load was found in the small headwater streams of the River Welland and eight other rivers within the Region.