ACCURACY OF DIATOM-INFERRED TOTAL PHOSPHORUS CONCENTRATIONS AND THE ACCELERATED EUTROPHICATION OF A LAKE DUE TO REDUCED FLUSHING AND INCREASED INTERNAL LOADING

The sedimentary record in a small eutrophic lake (White Lough, Norther n Ireland) is used to check the accuracy of reconstructing lake total phosphorus concentrations using diatoms and to propose a mechanism for the accelerated eutrophication of certain lakes. The diatom-inferred total phosphorus and sedimentary calcium, magnesium, potassium, iron, manganese, and phosphorus concentrations were measured in a dated sedi ment core and compared with lake monitoring results for 1978-1983. The values of and trends in diatom-inferred total phosphorus concentratio n closely follow the monitored concentrations. There was a period of a ccelerated eutrophication between 1973 and 1979 and the evidence indic ates that this was due to reduced hydraulic flushing of the lake durin g a dry period and a sudden increase in the sediment phosphorus releas e rate. The results indicate that meso- to eutrophic lakes with hydrau lic residence time around a year may be susceptible to this type of ac celerated eutrophication.