Upscaling nitrogen removal processes in fluvial wetlands and irrigation canals in a patchy agricultural watershed

Abstract The evaluation of nitrogen (N) removal in aquatic ecosystems within human exploited watersheds may allow the setting of upper limits of N use in agriculture. However, such an evaluation is complex owing to the small scale heterogeneity of aquatic ecosystems, including dominant vegetation an...
Ausführliche Beschreibung

Abstract The evaluation of nitrogen (N) removal in aquatic ecosystems within human exploited watersheds may allow the setting of upper limits of N use in agriculture. However, such an evaluation is complex owing to the small scale heterogeneity of aquatic ecosystems, including dominant vegetation and inherent N-related processes. In this work, microbial denitrification and primary producer assimilation were estimated in fluvial wetlands and irrigation canals of the Mincio River watershed (~ 850 $ km^{2} $, Italy), and scaled-up to the whole watershed using GIS and remote-sensing techniques. Denitrification in the fluvial wetland area which covered only ~ 3% of the watershed was estimated to permanently remove 80% of the excess N, defined as N soil surplus (~ 5500 t N $ y^{−1} $) minus N river export (~ 1300 t N $ y^{−1} $). Adding the estimated N uptake by primary producers in the wetland system, approximately all the N excess produced in adjacent agricultural land of the Mincio watershed can be retained or removed by internal processes. In contrast, the canal network had a linear extent of over 1770 km but its estimated denitrification capacity was comparatively much smaller (up to 7% of the excess N). Combinations of N-budgeting at the whole basin scale, experimental data, GIS and remote sensing techniques offer the possibility to analyze N retention capacity in heterogeneous aquatic environments. The application of such approach to the Mincio watershed stresses the functional relevance of even small wetland areas in agricultural settings. Ausführliche Beschreibung