Experiments with Large Enclosures in a Fertile, Shallow, Brackish Lake, Hickling Broad, Norfolk, United Kingdom

Abstract

AbstractEvents in the plankton community of a 120 ha, shallow (1.2 m), brackish lake have been studied with the help of two watertight enclosures, each of which isolated about 300 m3 of water and its underlying sediment. Analyses of soluble reactive phosphorus, total phosphorus, ammonia‐N, nitrate‐N, silicate‐Si, chloride, photosynthetic pigments, phytoplankton and zooplankton counts are reported and are related to inputs of nitrogen and phosphorus into the lake from adjoining basins and the catchment, and to the hydrologic regime. The inputs of phosphorus are budgeted and a very large roost of black‐headed gulls appears to provide most of the phosphorus supply. The results are discussed with reference to the eutrophication of the lake and decline of aquatic macrophytes which have occurred in the past ten years.