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Denitrification and Nitrate Reduction in Wisconsin Lake Sediments¹

ABSTRACT

The fate of ¹⁵N-labelled NO₃-N in Wisconsin lake sediment-water systems was investigated in laboratory and field experiments. In the laboratory, approximately 90% of the added NO₃-N disappeared from a calcareous sediment (Lake Mendota) compared to about 40% from a noncalcareous sediment (Trout Lake) after 48 hours when incubated under He. About 10% (Mendota) and 5% (Trout) of the added NO₃-N was recovered as organic-N and NH₄-N. The presence of significant amounts of ¹⁵NH₄-N, particularly in Lake Mendota sediment, indicated that immobilized N was subject to rapid mineralization. Nitrate-¹⁵N not accounted for was assumed lost through denitrification. Under aerobic conditions 10% (Mendota) and 2% (Trout) of the ¹⁵N was recovered as organic N but little ¹⁵N appeared in the NH₄-N fraction.

In a field investigation, ¹⁵NO₃-N, added to Lake Mendota sediment samples and returned to the lake bottom in wide-mouth plastic bottles, disappeared within 4 days. After 4 days about 37% of the added NO₃-N was in the organic and NH₄-N fractions, while the remaining 63% was likely lost through denitrification. These data illustrate that denitrification and NO₃-N reduction in sediments receiving NO₃-N in ground waters must be evaluated in calculating nitrogen budgets of seepage lakes.

Key Words: Lake Mendota • Trout Lake • nitrogen transformations • eutrophication

¹ Research supported by the College of Agricultural and Life Sciences, University of Wisconsin, Madison, and by a research grant from the Federal Water Quality Administration no. 16010 EHR. Presented in part before Div. S-2, S-3, and S-4, Soil Science Society of America, Tucson, Airzona, Aug. 26, 1970.

² Research Assistant, Associate Professor, Project Associate, Department of Soil Science 53706, and Visiting Professor, Department of Bacteriology. The third and fourth authors are currently Assistant Professor, Department of Soils, Univeristy of Florida, Gainesville, and Senior Lecturer, Department of General Bacteriology, University of Edinburgh, Scotland, respectively.

Received for publication May 21, 1971.