Spatial and seasonal changes of phosphorus internal loading in two lakes with different trophy

Abstract

Two lakes with different trophy, Strzeszyńskie Lake and Uzarzewskie Lake (Western Poland), were studied in ex situ experiments with the aid of intact bottom sediment cores in order to analyse the internal loading as well as the spatial and seasonal changes of total phosphorus (TP) release from bottom sediments. It was stated that the TP release from a hypereutrophic Lake Uzarzewskie, despite its earlier restoration using iron treatment, was over 6 times higher than in a mesotrophic one. The observed values in both lakes were higher in the deepest part of the lake than in the littoral zone. TP release in Strzeszyńskie Lake was very similar in all four seasons of the year with the maximum value of 2.8mgPm−2d−1 in winter. TP release did not exceed 1.3mgPm−2d−1 in the littoral zone and in winter its accumulation prevailed over release from bottom sediments. TP release in Uzarzewskie Lake was 44.7mgPm−2d−1 in autumn in the profundal zone and 6.8mgPm−2d−1 in the littoral zone. A domination of P accumulation in sediments over release was observed at both stations in winter (0.33mgPm−2d−1 in the deepest place and 0.62mgPm−2d−1 in the littoral). Knowledge of the internal loading of P in lakes allows managers to compare changes in human impact on the ecosystem and to design practical treatments for limiting their trophy and approaches to the management of restoration measures.