Effects of Aquatic Acidification on Microbially Mediated NitrogenRemoval in Estuarine and Coastal Environments

Acidification of estuarine and coastal waters isanticipated to influence nitrogen (N) removal processes, which arecritical pathways for eliminating excess N from these ecosystems.We found that denitrification rates decreased significantly underacidified conditions (P< 0.05), which reduced by 41-53% inestuarine and coastal sediments under an approximately 0.3 pHreduction of the overlying water. However, the N removal ratesthrough the anaerobic ammonium oxidation (anammox) processwere concomitantly promoted under the same acidificationconditions (increased by 47-109%,P< 0.05), whereas the totalrates of N loss were significantly inhibited by aquatic acidification(P< 0.05), as denitrification remained the dominant N removalpathway. More importantly, the emission of nitrous oxide (N2O)from estuarine and coastal sediments was greatly stimulated byaquatic acidification (P< 0.05). Molecular analyses further demonstrated that aquatic acidification also altered the functionalmicrobial communities in estuarine and coastal sediments; and the abundance of denitrifiers was significantly reduced (P< 0.05),while the abundance of anammox bacteria remained relatively stable. Collectively, this study reveals the effects of acidification on Nremoval processes and the underlying mechanisms and suggests that the intensifying acidification in estuarine and coastal watersmight reduce the N removal function of these ecosystems, exacerbate eutrophication, and accelerate global climate change.

Automated summary

This study reveals the effects of acidification on nitrogen removal processes in estuarine and coastal waters. It shows that denitrification rates decrease while anammox process rates increase under acidified conditions. The study also finds that acidic conditions lead to increased nitrous oxide emissions and altered microbial communities in sediment.