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Small-scale distribution of interstitial nitrite in freshwater sediment microcosms: The role of nitrate and oxygen availability, and sediment permeability

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Stief,  P.
Permanent Research Group Microsensor, Max Planck Institute for Marine Microbiology, Max Planck Society;

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De Beer,  D.
Permanent Research Group Microsensor, Max Planck Institute for Marine Microbiology, Max Planck Society;

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Citation

Stief, P., De Beer, D., & Neumann, D. (2002). Small-scale distribution of interstitial nitrite in freshwater sediment microcosms: The role of nitrate and oxygen availability, and sediment permeability. Microbial Ecology, 43(3), 367-378.


Cite as: http://hdl.handle.net/21.11116/0000-0001-D325-7
Abstract
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.