Summer-time denitrification and nitrous oxide exchange in the intertidal zone of the Yangtze Estuary

摘要

Sediment denitrification rates and nitrous oxide (N_2O) exchange fluxes in the Yangtze estuary intertidal zone (mudflats and salt marshes) were measured in summer-time using an acetylene inhibition technique and an in situ static closed chamber method. N_2O natural production rates ranged between 0.10 μmol N m~(-2) h~(-1) and 8.50 μmol N m~(-2) h~(-1), and the denitrification rates ranged from 18.71 μmol N m~(-2) h~(-1) to 35.87 μmol N m~(-2) h~(-1). The N_2O natural production rates in overlying water were low, with intertidal sediment being the source of overlying water N_2O during the submerged period. Data analysis indicated that most sediment N_2O was not derived from denitrification, but from several other nitrogen-cycling processes. During the low tide, the middle tidal marsh was the source of atmosphere N_2O (exchange fluxes changed between -11.03 μmol N m~(-2) h~(-1) and 13.17 μmol N m~(-2) h~(-1)). 5 cm and 10 cm depth ground temperatures were significant factors controlling the emission flux. At the low tidal flat, N_2O emission flux rates ranged from -5.75 μmol N m~(-2) h~(-1) to 0.49 μmol N m~(-2) h~(-1) at the sediment-atmosphere interface. Overall, the middle tidal marsh was the source of atmospheric N_2O, while the low tidal flat was a sink for atmospheric N_2O. Plants of the intertidal zone (Scirpus mariqueter and benthic algae) were significant factors controlling N_2O exchange flux. Photosynthesis of intertidal zone plants inhibited the emission of N_2O and induced consumption, while plant respiration may enhance N_2O emission from the intertidal zone. N_2O emission and consumption at the intertidal zone-atmosphere interface correlated positively with the emission and consumption of CO_2.