Ocean Deoxygenation Conference | Kiel 2018

Estuaries received eroded sediments from catchment with heavy anthropogenic nutrient and organic loadings serving as a bioreactor favoring intensive cycling of elements, such as nitrogen and organics. Increasing evidences showed the importance of active particle mediated aerobic-anaerobic metabolisms in estuary and coastal waters, however, little is known about the production of N2O, a strong greenhouse gas, in such environment due to technological difficulty. By using multiple isotope labeling technique, we investigated potential nitrogen transformation pathways contributing to N2O production in two estuaries in Southeast of China along a wide DO gradient. We found nitrogen oxidation and reduction processes co-existed and both actively contributed to N2O production. Particle mediated aerobic-anaerobic metabolisms accounted for such co-existence. Moreover, the bulk production N2O and the fractional contribution of reduction pathway to N2O were negatively correlated with DO and nutrient concentrations. Our results demonstrated that eutrophication and deoxygenation synergistically promote N2O production in turbid and eutrophic estuarine systems that might induce enhancing feedback to global warming.