The role of salinity in shaping dissolved inorganic nitrogen and N2O dynamics in estuarine sediment–water interface

We investigated the influence of salinity on sediment inorganic nitrogen dynamics in three Portuguese estuaries (Cلvado, Ave and Douro). Anaerobic slurry experiments were run at different salinity treatments (0, 10, and 25) and net changes in concentration of nitrate, nitrite, ammonium, and nitrous oxide were monitored. Salinity-induced NH 4 + sediment desorption was observed at all sites. No significant salinity driven changes in NO 3 - concentrations were observed, except for Ave estuarine sediments, where NO 3 - consumption increased 10 times as the salinity rose from 0 to 10. In the upper stretches of the three estuaries, N2O production increased sharply as salinity rose. Although no stimulation of N2O production was observed in higher salinity areas, the salinity-driven changes in N2O production are of major concern given the greenhouse characteristics of the gas. The global trend of decreasing freshwater discharge, and therefore increase in salinity, to estuarine systems could thereby exacerbate N2O production and global warming.