Nutrient budget for a hypertrophic reservoir

A nutrient budget for the shallow, hypertrophic Ardleigh Reservoir, a pumped storage scheme in eastern England, is described for the period 1979–1982. Algal succession in the reservoir was typical of eutrophic waters, with maximum chlorophyll-a of 98 mg m⁻³. Although the reservoir did not stratify thermally, the concentrations of SRP, Mn and Fe increased in bottom waters during summer. The weight ratio of inorganic N to inorganic P ranged from 720 to 5. On average, SRP represented 72% of the total P content of the reservoir.Some 44% of water input was of pumped river water, 48% being of direct catchment flow. The specific loading of SRP was 5.014 g m⁻² yr⁻¹.Ninety per cent of the annual SRP load was derived from pumped water and 60% of the SRP load was retained in the reservoir. Nitrate input was more diffuse, with approx. 33% from pumped water and 66% from catchment flow. A net release of P from the sediment of 23 mg P m⁻² day⁻¹ was recorded in summer, equivalent to 33% of annual mean external SRP loading. Strategies of P control are discussed in relation to loading models.