In May 1994 an artificial destratification system was installed at the eutrophic 27,200ML Hanningfield raw water reservoir in Essex U.K. The main objective of this installation was to prevent poor raw water quality, which can result from hypolimnetic isolation in the Summer months when thermal stratification often occurs. By adopting an intermittent destratification strategy to constantly change reservoir conditions thus promoting competition amongst algae, it is hoped that an overall decrease in annual phytoplankton biomass at the reservoir will result. This in turn will reduce the pressure on the raw water treatment processes required to produce a potable water supply. This paper evaluates algal, meteorological, and other monitored variables to assess the effect of destratification on Hanningfield Reservoirs phytoplankton community from 1994 to 1996. Although noting the limited data period the results show little dominant phytoplankton type changes, but notes a fall of 66% in mean total biomass in 1996 compared to 1994 values.

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