The relation between phosphorus and eutrophication in the Thames catchment, UK

Phosphorus trends in the Thames Catchment have been investigated, and the relation between phosphorus, flow and phytoplankton blooms evaluated. Temporal and spatial trends in phosphorus concentrations were examined in three rivers, the Thames, Blackwater and Kennet, which have a diverse range of surrounding land use. Phosphorus levels were generally found to be high, averaging 0.99 mg/l PO4-P with a maximum of 6.70 mg/l PO4-P, particularly in relation to urban areas where effluent discharge was a significant source. A strong seasonal component relating to flow was evident. The relation between phosphorus, flow and chlorophyll-a (used as the measure of algal abundance) was analysed by regression analysis. Neither phosphorus nor flow appeared to be limiting phytoplankton growth, probably because phosphorus concentrations were much greater than levels likely to be limiting. There was a clear relation between phosphorus and phytoplankton growth, with peak values of phosphorus occurring after the phytoplankton maxima. Cycles of algal assimilation and decomposition readily explain this relationship.