A DIATOM-PHOSPHORUS TRANSFER-FUNCTION FOR SHALLOW, EUTROPHIC PONDS INSOUTHEAST ENGLAND

Shallow ponds in southeast England are often eutrophic with high phosp horus concentrations. The aim of this study was to develop a diatom-ph osphorus 'transfer function' to enable past phosphorus levels in such waters to be inferred from the sediment record. A water chemistry surv ey of 123 randomly chosen, shallow, artificial ponds in southeast Engl and was carried out. Principal components analysis (PCA) revealed that phosphorus was an important environmental variable. A subset of 31 si tes was selected along a total phosphorus (TP) gradient (winter TP ran ge 7-1123 mug l-1), in order to explore the relationship between the s urface-sediment diatom assemblages and the contemporary water chemistr y using canonical correspondence analysis (CCA). Annual mean TP was th e most significant variable in explaining the variance in the diatom s pecies data. Weighted averaging (WA) regression and calibration techni ques were used to generate a transfer function, enabling annual mean T P (range 25-646 mug l-1) to be inferred from the diatom species TP opt ima of 102 common taxa in the dataset (r2 = 0.79; RMSE = 0.161; RMSE(b oot) = 0.279; n = 30). The model was applied to fossil diatom assembla ges in a sediment core from Marsworth Reservoir, Hertfordshire, a Site of Special Scientific Interest (SSSI), with currently high TP levels of 476 mug l-1 to reconstruct past epilimnetic annual mean TP concentr ations. The study shows that artificial, shallow waters can be suitabl e for palaeolimnological research and that it is possible to reliably infer lake water TP using the WA technique, across a large range of ph osphorus concentrations. This method has the potential to provide limn ologists, conservationists and water quality managers with an estimate of pre-enrichment phosphorus concentrations and an indication of the onset and development of eutrophication at a site. This information is essential for lake management strategies and restoration programmes.