Interactions between benthic phosphorus release and sulfur cycling in lake scharmützelsee (Germany)

Abstract

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 SO₄ ²⁻1⁻¹) freshwater Lake Schammützelsee. Hypolimnetic SO₄ ²⁻ reduction (4.56 ± 0.73 g (S) M⁻² d⁻¹) forming ΣH₂S (44.71 ± 17.57 mg ΣH₂S m⁻² d⁻¹), leading to iron sulfide precipitation (5.62 ± 1.72 mg FeS m² 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 urn sediment. This diminishes the ability of the sediment to bind P (indicated by 14.6 % loosely bound P (NH₄CI-P) and an exhaustion ofthe redox-sensitive P (BD-P)), leading to interstitial water P concentrations up to 10.8 mg 1⁻¹ and P release rates of 2.64 t 0.56 mg P m⁻² d⁻¹. As a consequence the P content ofthe lake increased fourtfold within 58 days.