Interstitial water concentrations of phosphorus, iron and manganese in a shallow, eutrophic swedish lake—Implications for phosphorus cycling

Abstract

Abstract The seasonal variation of ferrous iron, manganese and phosphate concentrations in the interstitial water (0–30 cm), ETS activities in the surface sediments (0–10 cm) and water quality properties were studied in 1983, in the polymictic, eutrophic Lake Vallentunasjon, Sweden. In addition, phosphorus release experiments using intact sediment cores were performed in the laboratory. Ferrous iron was generated to the interstitial water in two layers, namely in the surface sediments and at ≈ 10–30 cm down in the sediment. Manganese in a reduced form was mobilized in a single layer close to the sediment-water interface, while phosphate was generated at a sediment depth of 3–8 cm in shallow areas (2 m) and in deeper sediment layers ( > 25 cm ) at a water depth of 4m. A mobilization of both ferrous iron and phosphate in the interstitial water mainly during periods of high water temperature and ETS activity in the surface sediments, suggests that microbial processes were involved in the liberation. Reduction of ferric iron-phosphorus complexes could account for only a minor proportion of the phosphate mobilization in the interstitial water as demonstrated by the P/Fe molar ratios. In accordance, ferric iron formation, caused by ferrous iron diffusion from deeper sediment layers and oxidation at the sediment surface, could only partially retain the diffusive phosphate flux towards the sediment-water interface. The phosphorus retention capacity appears to be low in Lake Vallentunasjon sediments, even at high bottom water oxygen concentrations.