Description:
<jats:p>1. A weighted averaging (WA) regression and calibration model for diatoms and total phosphorus (TP) was developed from a dataset of 45 surface‐sediment samples from Swedish lakes. Jack‐knifed error statistics were comparable with those for similar diatom–TP datasets: <jats:italic>r</jats:italic><jats:sup>2</jats:sup><jats:sub>jack</jats:sub>=0.47, root mean squared error of prediction (RMSEP)=0.24 log<jats:sub>10</jats:sub>μg TP L<jats:sup>–1</jats:sup> and mean bias=–0.002 log<jats:sub>10</jats:sub> μg TP L<jats:sup>–1</jats:sup> for the simple WA model; <jats:italic>r</jats:italic><jats:sup>2</jats:sup><jats:sub>jack</jats:sub>=0.36, RMSEP=0.27 log<jats:sub>10</jats:sub> μg TP L<jats:sup>–1</jats:sup> and mean bias=0.017 log<jats:sub>10</jats:sub> μg TP L<jats:sup>–1</jats:sup> for WA with tolerance downweighting.</jats:p><jats:p>2. The model was used to estimate TP concentrations for the Ekoln basin of Lake Mälaren using a <jats:sup>210</jats:sup>Pb‐dated sediment core record. Highly eutrophic conditions developed in the basin in the 1960s as a result of nutrient inputs from cultivated land and the city of Uppsala. A reduction in the supply of phosphorus from sewage outlets in the late 1960s resulted in less eutrophic conditions.</jats:p><jats:p>3. The model results indicated levels of 50–60 μg TP L<jats:sup>–1</jats:sup> prior to 1900. The rapid eutrophication of the lake basin after the 1950s and the subsequent recovery were evident from the diatom data.</jats:p><jats:p>4. Diatom‐inferred TP (DI–TP) values were validated by comparison with monitored data for the period 1966–95. The diatom model tended to underestimate TP at high levels (> 80 μg L<jats:sup>–1</jats:sup>) but overestimate at lower concentrations.</jats:p><jats:p>5. A good agreement was observed between the trends in TP concentration and the DI–TP concentration and the timing of the maximum was well reflected by the diatom‐based reconstruction. A significant correlation (<jats:italic>r</jats:italic><jats:sup>2</jats:sup>=0.69, <jats:italic>P</jats:italic> < 0.01) was found between DI–TP and measured TP at this site.</jats:p>