Anaerobic oxidation of methane with denitrification in sediments of a subtropical estuary: Rates, controlling factors and environmental implications.

ABSTRACT

Anaerobic oxidation of methane with denitrification (DAMO), as an important microbial process regulating methane emission, has been widely reported in freshwater ecosystems. However, the DAMO process and associated biogeochemical controls in estuaries remain poorly understood. Here, we used 13C- and 15N-labelling experiments to quantify the potential rates of DAMO and determined the crucial factors controlling the DAMO rates in the sediment of Yangtze Estuary. Potential rates of DAMO varied greatly across the estuary, ranging from 0.07 to 0.28 nmol CO2 g-1 d-1. Salinity negatively affected the DAMO and also showed an indirectly negative influence on DAMO process by high salinity inhibition on NO3- availability and denitrification. Nitrate concentrations were significantly correlated with the DAMO rates. Denitrification rates showed positive correlation with DAMO rates, implying that nitrate reduction drives the DAMO process. Sediment total organic carbon and NH4+ had important effects on DAMO rates. These results together indicate that DAMO process can occur and the DAMO rates were mainly controlled by sediment NO3- and denitrification in estuary. We further conclude that increasing NO3- load can drive the DAMO process with more important implications on methane sink in estuarine ecosystems.