Water Resources of North Dakota

Importance of Bottom-Sediment Diffusive Fluxes to Chemical Budget of Devils Lake, North Dakota

By R. M. Lent and J. D. Wald

Abstract: North Dakota Water Quality Symposium, Bismarck, North Dakota, March 25-26 1992

Devils Lake is a brackish-water lake located in a large (about 10,000-km2 ) closed-drainage basin in northeastern North Dakota. Sediment cores were collected in Main Bay of Devils Lake four times between May and October 1991 to assess the effect of biogeochemical processes occurring in the bottom sediments on the water quality of the lake. The bottom-sediment processes that are important in Main Bay include microbially-mediated oxidation of organic matter by sulfate reduction, dissolution of evaporite minerals, and dissolution and precipitation of carbonate minerals. The processes have created well-defined major ion and nutrient pore-water gradients that, in turn, drive molecular diffusion of the major ions and nutrients from bottom sediments to Devils Lake. The contribution of major ions and nutrients from bottom sediments to Devils Lake during May to October 1991 as a result of molecular diffusion was modeled using Fick's first law. Important bottom-sediment contributions of salinity to the lake include sodium (2.7 to 12 mmol/m2 /d) and total sulfur (2.3 to 9.5 mmol/m2 /d). Bottom sediments also were important sources of nutrients during the study period, including orthophosphate (0.0053 to 0.040 mmol/m2 /d) and ammonia (0.53 to 0.77 mmol/m2 /d). The bottom-sediment contributions of major ions and nutrients dominated potential inputs to major ion and nutrient chemical budgets of Devils Lake during the study period.

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