Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
5743892 | Ecological Engineering | 2017 | 13 Pages |
Abstract
Nitrate (NO3â) contamination of freshwater systems is a global concern. In alluvial floodplains, riparian areas have been proven to be efficient in nitrate removal. In this study, a large spatio-temporal dataset collected during one year at monthly time steps within a meander area of the Garonne floodplain (France) was analysed in order to improve the understanding of nitrate dynamic and denitrification process in floodplain areas. The results showed that groundwater NO3â concentrations (mean 50 mg NO3â Lâ1) were primarily controlled by groundwater dilution with river water (explaining 54% of NO3â variance), but also by nitrate removal process identified as denitrification (explaining 14% of NO3â variance). Dilution was controlled by hydrological flow paths and residence time linked to river-aquifer exchanges and flood occurrence, while potential denitrification (DEA) was controlled by oxygen, high dissolved organic carbon (DOC) and organic matter content in the sediment (31% of DEA variance). DOC can originate both from the river input and the degradation of organic matter (OM) located in topsoil and sediments of the alluvial plain. In addition, river bank geomorphology appeared to be a key element explaining potential denitrification hot spot locations. Low bankfull height (LBH) areas corresponding to wetlands exhibited higher denitrification rates than high bankfull height (HBH) areas less often flooded. Hydrology determined the timing of denitrification hot moments occurring after flood events. These findings underline the importance of integrating dynamic water interactions between river and aquifer, geomorphology, and dual carbon source (river and sediment) when assessing nitrate dynamics and denitrification patterns in floodplain environments.
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Authors
Léonard Bernard-Jannin, Xiaoling Sun, Samuel Teissier, Sabine Sauvage, José-Miguel Sánchez-Pérez,