Phosphorus (P) releases from lake sediments are controlled in the long term by P burial into the deep sediment and on shorter time scales by the redox conditions at the sediment-water interface. In Lake Sempach (Switzerland), hypolimnetic oxygen concentration was increased by artificial aeration after two decades of nearly anoxic conditions. Using diagenetic reaction-transport modeling and sediment core analysis, we investigated the effects that this change, as well as variations in the organic carbon loadings, had on the long-term mobility of sediment P. During low-oxygen conditions, the reducible iron pool in the sediment was depleted, resulting in the release of previously accumulated P. The remobilization of iron-bound P affected phosphate effluxes from the sediment on the time scale of the sediment iron cycle (several years). On longer time scales, P effluxes followed the sedimentation fluxes of organic matter. Mass balance calculations indicate that, despite the dominance of internal P loading in Lake Sempach, over the long-term phosphorus content in the water column was controlled by the external P inputs. The results suggest that, whereas short-term decreases in sediment P releases may be achieved by preventing sediment anoxia, long-term solutions should involve reductions in the external P inputs.
Bibliographical noteFunding Information:
We acknowledge financial support from the Swiss National Science Foundation (SNF Nr 200021-107985/1 ). S.K. was supported by the postdoctoral fellowship from the Natural Science and Engineering Research Council of Canada (NSERC) and by the University of Minnesota Duluth start-up funds. M.D. was supported by the Connaught Fund ( University of Toronto ). We thank Sabine Sibler for her help with chemical extractions, Michael Schulter for the sampling, Doris Hohmann for enumeration of benthic community, Beat Müller and René Gächter for sharing data.
- Early diagenesis
- Hypolimnion aeration
- Lake sediment
- Reaction-transport modeling