Internal nutrient loading in a eutrophic lake, reflected in seasonal variations of some sediment parameters

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Abstract
Summary The external P loading to Lake Vallentunasjön was decreased by 92% when sewage effluents were diverted from the lake in 1970. The trophic level still remains very high due to internal loading of nutrients from the sediments. In 1982, N and P were recycled from the sediments in proportions similar to sediment contents and to the contents of algae, indicating the participation of bacterial mineralization in the release process. Furthermore, a sudden release of P from the sediments, primarily PO4, occurred in late July. This process was associated with a high temperature and a low oxygen concentration in the bottom waters and with a high microbial activity in the surface sediments. This release of P could also be detected as a substantial loss of organic P from the surface sediments (50% of the pool in the upper 2 cm of accumulation sediments).