Nitrogen dynamics in the shallow groundwater of a riparianwetland zone of the Garonne, SW France: nitrate inputs, bacterialdensities, organic matter supply and denitrification measurements
2003
Sanchez-Pérez, José-Miguel | Vervier, Philippe | Garabétian, Frédéric | Sauvage, Sabine | Loubet, M. | Rols, Jean-Luc | Bariac, Thierry | Weng, P.
This study highlights the role of interactions between surface and sub-surface water of the riparian zone of a large river (the Garonne, SWFrance). Information is given about the role of surface water in supplying Dissolved Organic Carbon (DOC ) to the riparian zone for nitrateremoval processes. The densities of bacteria (up to 3.3106 cell m L-1) in groundwater are strongly conditioned by the water moving duringflood events. Total bacterial densities in groundwater were related to surface water bacterial densities. In sediment, total bacteria are attachedmainly to fine particles (90 % in the fraction < 1 mm). Spatial variations in organic carbon and nitrate content in groundwater at the sitestudied are correlated with exchanges between the groundwater and the river, from the upstream to the downstream part of the meander. Totalbacterial densities, nitrate and decressing organic carbon concentrations follow the same pattern. These results suggest that, in this kind ofriparian wetland, nitrate from alluvial groundwater influenced by agricultural practices may be denitrified by bacteria in the presence oforganic carbon from river surface water.
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