Nitrous Oxide from Abiotic Processes of Hydroxylamine and Nitrite in Estuarine and Coastal Ecosystems: A Review

Abiotic processes of nitrogen (N) are suggested to contribute to nitrous oxide (N2O) production; however, the important role of these processes in N2O emissions is invariably ignored. This review synthesized the main abiotic processes of hydroxylamine and nitrite and associated biogeochemical controls in estuarine and coastal ecosystems. Abiotic processes of hydroxylamine and nitrite are availably detected in estuarine and coastal environments. The abiotic processes of hydroxylamine contribute more to N2O production than the abiotic processes of nitrite in estuarine and coastal environments, suggesting that hydroxylamine plays an important role in N2O production. The isotopic fractionation effects of N can occur during the abiotic processes of hydroxylamine and nitrite and are enriched with the increasing rates of N reactions. In addition, abiotic processes of hydroxylamine and nitrite are highly dependent on pH, oxygen, Fe2+, Fe3+, and Mn4+ and are also triggered by the increasing substrate contents. These results suggest that abiotic processes of hydroxylamine and nitrite have been greatly concerned for the estuarine and coastal environments, whereas the dynamics of these processes are still sparse for projecting N fates and dynamics in response to environmental factors changes. This review highlights the importance of abiotic processes of N and associated environmental implications and presents the future trend of N cycling in estuarine and coastal environments.