Storm-triggered, increased supply of sediment-derived phosphorus to the epilimnion in a small freshwater lake

Abstract

This study investigated internal loading of sediment-derived phosphorus (P) in a small, meso-eutrophic lake (surface area 0.2 km2, catchment area 2.7 km2, mean depth 6 m, maximum depth 14 m) on the Atlantic seaboard of western Europe. High resolution data collected over 2.5 years (1 Mar 2011 to 30 Sep 2013) revealed inconsistent patterns in (1) the timing and magnitude of lake turnover and (2) the relative importance of the transfer of hypolimnetic sediment-derived P to the epilimnion when compared with external catchment loading. Lake turnover events during spring and summer had the effect of increasing the internal loading of epilimnetic P during the main growing season, thus adding to eutrophication pressure and contributing to algal blooms in the lake. Abrupt pre-fall (autumnal) turnover events and associated increases in eutrophication pressure such as those reported here may become more frequent occurrences in western Europe because of warming-induced increases in Atlantic summer storm frequency and magnitude, and they could counter the apparent effectiveness of measures aimed at reducing eutrophication impacts through limiting external loadings of nutrients from the catchment.