Datensatz

Zusammenfassung

The spatial distribution of interstitial NO2- concentrations was studied in NO3--exposed freshwater sediment microcosms, using pore water extractions as well as ion-selective microsensors. Porewater extractions revealed ecotoxicologically critical NO2- concentrations in hypoxic and anoxic sediment layers in which significant NO3- consumption took place. In contrast, the use of ion-selective microsensors demonstrated the high capacity of the thin oxic surface layer of the sediments to consume NO2- and to produce NO3-. Two modes of NO3-. Supply to the sediments were compared: In treatments with NO3- supply to the overlying water, a subsurface maximum of NO2- concentration was observed, coinciding with the site of maximum NO3- consumption. When NO3- was perfused up through the sediment cores, however, NO2- accumulated throughout the entire sediment column. Such spatially extensive NO2- accumulations were only observed in sediments poor in organic matter with a relatively high permeability. By manipulating the O-2 content of the overlying water, the release of NO2- from the sediments could be influenced: In treatments with air-saturated overlying water, the sediments did not release detectable amounts of NO2- into the water phase. When kept hypoxic (25% air saturation) instead, significant NO2- accumulations were recorded in the overlying water. These findings suggest that in treatments with air-saturated overlying water, NO2- that was produced in deeper sediment layers (denitrifying conditions) was completely consumed at the oxic sediment surface (nitrifying conditions) before it could reach the overlying water.