Nitrogen sources, processes, and associated impacts of climate and land-use changes in a coastal China watershed: Insights from the INCA-N model.

The Integrated Nitrogen CAtchments (INCA-N) model was applied to identify the sources and processes controlling riverine nitrogen (N) export in the Jiulong River watershed, coastal China. Future riverine N exports were simulated under various scenarios of climate and land-use changes. The modeling results showed good agreement between the observed and simulated values of streamflow, N concentrations, and loads. It was revealed that fertilizer application, atmospheric N deposition, and sewage discharges were the main N sources, while the primary N cycling processes included soil nitrification, soil denitrification, and N leaching. Nitrate-N exports were predominantly impacted by climate change, whereas ammonium-N exports were more affected by land-use change. The coupled effects of climate and land-use changes were projected to amplify nitrogen export by 30%, 36%, and 36% for nitrate-N and 32%, 48%, and 71% for ammonium-N during the years for 2030s, 2050s, and 2080s, respectively.