Nitrogen dynamics in complex Danube River floodplain systems: effects of restoration

We used a hydromorphological model to assess areas of potential high denitrification rates and nitrous oxide release in a frequently and an infrequently connected floodplain system of the Danube River under different river discharge conditions. Based on the model's projections, the decoupled floodplain was predicted to have more areas of high potential denitrification during mean and elevated discharge, but with more sites dominated by incomplete denitrification, resulting in higher N2O emission. In the restored floodplain, frequently inundated, the model predicted that lower rates of denitrification would occur at lower river discharge levels, dominated by complete denitrification, resulting in N2 rather than N2O production. During an annual flood (5300 m3s-1), flooding both floodplains, the restored floodplain was predicted to have more areas of high potential denitrification activity than the decoupled floodplain. The model outputs suggest that floodplains subject to frequent inundations can effectively and efficiently use nitrate input from the main river channel, resulting in complete denitrification. Restoration measures should attempt to promotefrequent inundation periods in order to fully realize the high denitrification potential of floodplain systems.