The effects of salinity on coupled nitrification and aerobic denitrification in an estuarine system

Salinity has significant effects on nitrification and denitrification processes, particularly in estuarine systems. A dissolved oxygen-enriched river and its estuary in northern China were selected to investigate the impact of salinity gradients (0.6, 4, 7.6, 11.4 and 14.7%) obtained from the mixing of river samples and estuarine samples with different proportions on coupled nitrification and aerobic denitrification via incubation experiments (35 and 10 degrees C). Results indicated that: (a) nitrification and coupled nitrification-aerobic denitrification occurred for all treatments, which resulted in NO3- being either accumulated or removed at the end of the incubation; (b) a suitable range of salinity is 4.0-11.4% for nitrification and 4.0-7.6% for coupled nitrification-aerobic denitrification; and (c) the relatively higher temperature (35 degrees C) can effectively stimulate N transformation processes compared to the lower temperature (10 degrees C) in the incubation experiment.