Rivers worldwide are under stress from eutrophication and nitrate pollution, but the ecological consequences overlap with climate change and the resulting interactions may be complex, unexpected, and as yet unexplored. Understanding how climate change impacts on thermal and hydrological regimes may affect nutrient dynamics and transport to coastal areas is crucial for implementing effective management strategies to mitigate eutrophication in human-impacted watersheds, such as the Po River basin (northern Italy). The present work addresses the long-term trends (1992-2020) of nitrogen export to the Adriatic Sea by investigating its relationship with water temperature and discharge trajectories. Despite the constant nitrogen surplus on arable land, a marked decrease in nitrogen export, mainly as nitrate, was recorded in the last decade compared to the 1990s. The reduction of nitrogen loads in all seasons was probably related to an increased metabolic capacity of the river, triggered by warming water temperatures. An extended seasonal window of warm temperatures and the persistence of low-flow conditions are likely to stimulate denitrification and create favourable conditions for permanent nitrate removal, resulting in reduced delivery to the sea from spring to early autumn, when the risk of eutrophication is higher. The present outcomes suggest that temperature warming due to climate change would unexpectedly increase nitrogen processing efficiency, thereby reducing export from catchments and partially buffering eutrophication.

Primary Presenter: Elisa Soana, University of Ferrara (elisa.soana@unife.it)

Authors:

Elisa Soana, ​​Department of Environmental and Prevention Sciences ​, University of Ferrara  (elisa.soana@unife.it)

Maria Pia Gervasio, ​​Department of Environmental and Prevention Sciences , University of Ferrara  (mariapia.gervasio@unife.it)

Tommaso Granata, CESI - Italian Electrical and Technical Experimental Center  (tommaso.granata@cesi.it)

Giuseppe Castaldelli, ​​Department of Environmental and Prevention Sciences , University of Ferrara  (ctg@unife.it)