Lakes and reservoirs are hot spots of biogeochemical activity in the landscape and, as such, are important regulators of environmental quality. Within the lake system, intense biogeochemical cycling occurs at the sediment-water interface (SWI), where the mineralization of organic matter (OM), coming from catchment inputs and primary production, stimulates hypolimnetic oxygen consumption and the recycling of phosphorus (P). To study the role of the SWI in controlling lake water quality we have expanded the lake system model MyLake, which comprises a detailed representation of water column processes, to include sediment diagenesis. The updated model now represents hydrodynamics, primary production, as well as metabolic activities involving the oxidation of OM. Forcing data input for the model include the observed weather and the outputs of hydrological and biogeochemical catchment models. We simulated the response of sediment-bound P and of water-column phytoplankton biomass in two hypothetical lakes from two catchments with the following contrasting sulfur (S) dynamics representative of Northern Europe: 1) an S-poor, acid-sensitive catchment with shallow soil cover and poorly weathering granitic bedrock, and 2) a S-rich catchment with thick soil cover and alkaline marine deposits. With similar inputs of catchment OM, fertilizer P and atmospheric S to both lakes, the lake in the S-poor catchment is predicted to remain oligotrophic until peaking atmospheric S deposition trigger a regime shift towards frequent summer algal blooms and bottom water anoxia. The lake in the S-rich catchment is predicted to reach higher algal biomass than the lake in the S-poor catchment. Under the future wetter and warmer climate projected by the HADRM3 model for Northern Europe, it is expected that lakes in both catchment types will become more sensitive to changing P loads.

Modeling the biogeochemical response of lakes to catchment-scale changes in nutrient dynamics: the case of sulfur-controlled eutrophication

247th National Meeting (2014)

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