Ecosystem changes in large and shallow Võrtsjärv, a lake in Estonia : evidence from sediment pigments and phosphorus fractions

Palaeopigments, organic matter dissolved in sediment porewater (pDOM) and phosphorus fractions were analysed in a sediment core from large shallow Vortsjarv with the aim to assess whether the trends of climate-driven and anthropogenic changes in lake trophy within the 20th century are reflected in its sediment record. In the first half of the last century, the lake was naturally slightly eutrophic as the accumulation of palaeopigments was low and the load of nutrients stable; investigated variations in palaeoparameters were induced by the regular natural water level fluctuations. Since the mid-1950s eutrophication of Vortsjarv has accelerated — content of fossil pigments, CaCO 3 and nutrients increased, while pDOM revealed high autochthonous matter input. The increase of palaeopigment's concentrations during the last decade may be consistent with regional climate warming. Investigated palaeoindicators and water level changes had a stronger relationship in the second half of the 20th century.