第五届氮素生物地球化学循环学术论坛

21 / 2024-07-08 19:16:48

Spatial and Seasonal Variability of Hydroxylamine Concentrations in a Human-Impacted Estuary Off Southeast China

Hydroxylamine (NH₂OH) is an important intermediate of nitrification and can contribute to nitrous oxide (N₂O) production through abiotic and biotic processes. NH₂OH concentrations and associated biogeochemical controls in estuarine environments remain poorly understood. Here, we investigated spatial and seasonal variability of NH₂OH concentrations in water and sediments, and determined the correlation between NH₂OH concentration and N₂O flux in Min River Estuary off southeast China. NH₂OH concentrations in water and sediments varied from 0.22 to 140 nmol N L^‒1 and from 0.17 to 9.22 μmol N kg^‒1, respectively. NH₂OH concentrations were significantly higher in warm than in cold seasons, suggesting that NH₂OH production highly depends on temperature. Upper estuary (urban section) had higher NH₂OH concentrations in water and sediments, followed by lower and middle estuary. Temperature, dissolved oxygen, and pH were the major drivers of spatial and seasonal variability in NH₂OH concentrations. Water dissolved N₂O concentrations and water-air N₂O fluxes varied between 1.52 and 55.9 nmol N L^‒1 and between ‒57.7 and 78.7 nmol N m^‒2 h^‒1, respectively, with switches from net sinks in spring season to net sources of N₂O emissions in other seasons. N₂O concentration and flux were observed to significantly correlate with NH₂OH concentration, suggesting that NH₂OH is an important contributor to N₂O emissions. Although N₂O concentrations and fluxes were linearly correlated with water NH₂OH concentrations, the contribution of NH₂OH to N₂O production could not be addressed. Therefore, the dynamics of NH₂OH concentrations are a useful tool to assess potential production and consumption pathways of N₂O in estuarine and coastal ecosystems.