Further studies on the palaeolimnology and changes in the phosphorus budget of Barton Broad, Norfolk

SUMMARY. Patterns of sedimentation have been studied in Barton Broad, Norfolk, a man‐made lake created by peat excavation prior to the fifteenth century. Sedimentation rates since before 1800 have increased by as much as 50‐fold owing to the effects of hypereutrophication and sediment movement downriver into the lake. A striking horizontal pattern has been found; a long black tongue of sulphide‐rich sediment extends into the broad from the inflow river. This dates (210Pb method) back to 1920–30 and is associated with enrichment from sewage effluent and a change from a macrophyte‐dominated to a plankton‐dominated lake. Past phosphorus concentrations (1800, 1900, 1920, 1940) and budgets have been predicted from sediment core analyses by use of a model previously validated by contemporary measurements on the lake. The analyses and calculations provide a perspective for plans to restore the lake to a less fertile state capable of supporting aquatic macrophytes.