Interactions Between Benthic Phosphorus Release and Sulfur Cycling in Lake Scharmützelsee (Germany)

Sulfur (S) conversions were determined during summer stratification in 1995/96 to assess the extent to which benthic release of phosphorus (P) is influenced by the S cycling in eutrophic, dimictic, sulfate-rich (61.33 ± 10.41 mg SO₄2− l−1) freshwater Lake Scharmützelsee. Hypolimnetic SO₄2− reduction (4.56 ± 0.73 g (S) m−2 d−1) fomiing ΣH₂S (44.71 ± 17.57 mg ΣH₂S m−2 d−1), leading to iron sulfide precipitation (5.62 ± 1.72 mg FeS m−2 d−1) and dissolved iron depletion in the hypolimnion has a major influence on benthic P mobilization and release. The most important inorganic S pool is the CRS (FeS₂ + S° + H₂S; 15.1% total S), being 1.3 to 6.6 times higher than the AVS (FeS + H₂S) in the uppermost 0 – 8 cm sediment This diminishes the ability of the sediment to bind P (indicated by 14.6 % loosely bound P (NH₄CI-P) and an exhaustion of the redox-sensitive P (BD-P)), leading to interstitial water P concentrations up to 10.8 mg l− and P release rates of 2.64 ± 0.56 mg P m−2 d−1. As a consequence the P content of the lake increased fourfold within 58 days.