Microelectrode measurements of nitrate gradients in the littoral and profundal sediments of a meso-eutrophic lake (lake vechten, the Netherlands).

NO(3) concentration profiles were measured in the sediments of a meso-eutrophic lake with a newly developed microelectrode. The depth of penetration of NO(3) 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 mum. 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 day) at in situ nitrate concentrations in the overlying water (0.030 mmol liter) and limitation of denitrification by nitrate availability.