Microelectrode Measurements of Nitrate Gradients in the Littoral and Profundal Sediments of a Meso-Eutrophic Lake (Lake Vechten, The Netherlands)

NO₃⁻ concentration profiles were measured in the sediments of a meso-eutrophic lake with a newly developed microelectrode. The depth of penetration of NO₃⁻ varied from only 1.3 mm in organic-rich profundal silty sediments to 5 mm in organic-poor littoral sandy sediments. The thickness of the zone of denitrification in the organic-rich sediments was <500 μm. Oxygen profiles measured simultaneously revealed that the zone of denitrification was directly adjacent to the aerobic zone. The results demonstrate high denitrification rates (0.26 to 1.31 mmol m⁻² day⁻¹) at in situ nitrate concentrations in the overlying water (0.030 mmol liter⁻¹) and limitation of denitrification by nitrate availability.