We found a match
Your institution may have access to this item. Find your institution then sign in to continue.
- Title
High Incidence Hypoxia Increases Benthic Nitrogen Retention but Decreases Nitrogen Removal in Seasonally Hypoxic Areas off the Changjiang Estuary.
- Authors
Li, Xiaofei; Qian, Wei; Qi, Mengting; Gao, Dengzhou; Liu, Cheng; Liu, Min; Hou, Lijun
- Abstract
How the partitioning between dissimilatory nitrate reduction to ammonium (DNRA) and N2 production responds to hypoxia in seasonally hypoxic estuaries has not been well understood. In this study, 15N tracer incubations were used to investigate benthic denitrification, anammox and DNRA rates for three years (2016–2018) across seasonally hypoxic areas off the Changjiang Estuary. Dissolved oxygen contents in bottom water were significantly lower in July than in February/March. Concentrations of NH4+ and NOx– in bottom water throughout the sampling sites did not vary between seasons. Rates of benthic denitrification (0.45–6.55 nmol N g−1 h−1), anammox (0.02–0.30 nmol N g−1 h−1) and DNRA (0.06–0.59 nmol N g−1 h−1) varied largely along the estuary. Denitrification, anammox and DNRA rates did not vary significantly between inshore and offshore sites. However, denitrification rates were significantly lower and DNRA rates were significantly higher in consistently than transiently hypoxic sites. Anammox rates were slightly lower in consistently than transiently hypoxic sites. Ratios of DNRA to N2 production were in a range of 0.015–0.53, and were significantly higher in consistently than transiently hypoxic sites, but did not vary significantly between inshore and offshore sites. The lower temperature sensitivity of denitrification and anammox compared to their Q10 values further indicated that hypoxia may inhibit N2 production. These results suggest that high incidence hypoxia can decrease denitrification and anammox rates but increase DNRA rates with important implications on N retention versus removal, thereby exacerbating eutrophication and hypoxia in estuarine and coastal environments. Plain Language Summary: This study investigated benthic denitrification, anammox and dissimilatory nitrate reduction to ammonium (DNRA) rates for three years (2016–2018) across the consistently and transiently hypoxic areas off the Changjiang Estuary. Denitrification rates were significantly lower, whereas DNRA rates were significantly higher in consistently than transiently hypoxic sites. Anammox rates were slightly lower in consistently than transiently hypoxic sites. The ratios of DNRA to N2 production (including denitrification and anammox) were significantly higher in consistently than transiently hypoxic sites, but did not vary significantly between inshore and offshore sites. Therefore, it is concluded that high incidence hypoxia can decrease N2 production but facilitate nitrogen retention, which may further exacerbate eutrophication and hypoxia in estuarine and coastal environments. Key Points: Denitrification dominated over anammox and dissimilatory nitrate reduction to ammonium (DNRA) throughout the sampling seasons and sitesDenitrification and anammox rates were lower, whereas DNRA rates were higher in consistently than transiently hypoxic sitesHigh incidence hypoxia favored N recycling rather than N removal off the Changjiang Estuary
- Subjects
HYPOXIA (Water); DISSOLVED oxygen in water; NITROGEN content of seawater; ESTUARY management; ESTUARINE restoration
- Publication
Journal of Geophysical Research. Biogeosciences, 2021, Vol 126, Issue 7, p1
- ISSN
2169-8953
- Publication type
Article
- DOI
10.1029/2021JG006419