1172 / 2019-08-05 09:52:39

Benthic and water column nitrous oxide production in the Changjiang River plume, China

2、地球化学 > 专题4：河口海岸带生物地球化学

Coastal oceans, one of the major contributors of nitrous oxide (N2O) to the atmosphere, have received tremendous amounts of anthropogenic nitrogen from land, cumulatively resulting in an exacerbation of surface eutrophication and near-bottom hypoxia. The pristine nitrogen cycle in coastal oceans has thus been altered obviously, however, the origin and processes of associated N2O production responsible for subsequent atmospheric emission remain unclear due to the lack of rate measurements for specific processes in the field. Here, we conducted N2O production measurements for both water-column and sediments in the hypoxia zone along the Changjiang River plume where has been found as a hot-spot of N2O release to the atmosphere. Our results indicate that sediments host the predominant pathways (e.g. the coupled nitrification-denitrification, canonical sedimentary denitrification) responsible for approximately 90% of N2O accumulated in the bottom-water, consequently, the efflux to the atmosphere. Whereas the water-column nitrification and denitrification contribute <10% within the time of water residence in the system. Such high benthic N2O contribution is mainly driven by active sedimentary nitrification accompanied with denitrification in sediments, which is likely related to rapid supply of labile organic matters to the sediment surface. Our study has strong implications in promoting the role of coastal sediments in contributing to the global N2O budget to feedback on future climate as the human-induced eutrophication and hypoxia in coastal oceans are expanding.