The role of sediments in the phosphorus cycle in Lake Lugano. II. Seasonal and spatial variability of microbiological processes at the sediment-water interface |
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| Authors: | Maja A Lazzaretti Kurt W Hanselmann Helmut Brandl Daniel Span Reinhard Bachofen |
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| Institution: | (1) Institute F.-A. Forel, University of Geneva, 10 route de Suisse, CH-1290 Versoix, Switzerland;(2) Institute of Plant Biology/Microbiology, University of Zürich, Zollikerstr. 107, CH-8008 Zürich, Switzerland |
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| Abstract: | P, Fe, Mn, and S species were analyzed in water samples from the sediment-water interface collected at four seasonally different times during the course of a year at two sampling sites in the southern basin of Lake Lugano (Lago di Lugano). The results reveal the strong influence of the biogeochemical processes in the sediment on the chemical composition of the lake water above. Consumption of oxygen and nitrate under oxic to microoxic conditions in the water column as well as sequential release of reduced manganese and iron under anoxic conditions was observed as a direct or indirect consequence of microbially mediated degradation of organic matter. The seasonal pattern observed for the release and the retainment of dissolved reduced iron and manganese correlates well with the one for dissolved phosphate. Iron, manganese and phosphorus cycling are coupled tightly in these sediments. Both sediment types act as sinks for hydrogen sulfide and sulfate. An inner-sedimentary sulfur cycle is proposed to couple iron, manganese and phosphorus cycling with the degradation of organic matter. Nutrient cycling at the sediment-water interface might thus be driven by a microbially regulated  electron pumping mechanism. The results contribute to a better understanding of the role of sediment processes in the lake's internal phosphorus cycle and its seasonal dynamics. |
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| Keywords: | Phosphorus cycling iron and manganese reduction sedimentary sulfur cycling sediment microbiology pore water concentration gradients electron driven nutrient cycles Lake Lugano (Lago di Lugano) |
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