Program
 
General Session 2: Marine & estuarine biogeochemistry
 
 
 
Poster
Comparison nitrous oxide production between water column and sediments in the early stage of hypoxia in the inner shelf off Changjiang Estuary
GS2-12
Ting-Chang Hsu* , Department of Geography, National Taiwan University, Taiwan
Sung-Yun Hsiao, Institute of Earth Science, Academia Sinica, Taiwan
Yu-Fen Tseng, Flow cytometry Core Facility of the Scientific Instrument Center Academia Sinica in IPMB-AS, Taiwan
Fuh-Kwo Shiah, Research Center for Environmental Changes, Academia Sinica, Taiwan
Minhan Dai, State Key Laboratory of Marine Environmental Science, Xiamen University, Xiamen, China
Shuh-Ji Kao, State Key Laboratory of Marine Environmental Science, Xiamen University, Xiamen, China
Presenter Email: leontj@gmail.com
The inner shelf off Changjiang River is one of the largest coastal hypoxia areas in the world and an important region of nitrous oxide (N2O) flux to the atmosphere. This study measured the rates of N2O production directly using 15N tracer in water column and their spatial distributions in the early stage of hypoxia. The higher rates observed at low dissolved oxygen waters (60~120 microM) via nitrification. Detectable but very low denitrification activity (< 0.005 nmol N2O l-1 d-1) in oxic water suggested that the particle surface might provide suboxic-anoxic microenvironments beneficial to denitrifiers and perhaps nitrifiers. Spatial coupled N2O production rates and N2O accumulation in water were found; however, the rates were insufficient to support the sea-to-air flux (8.9 ± 4.1 micromol N2O m-2 d-1) and to regenerate water column N2O within water resident time (16 days) in the hypoxia region. The average rate of water column integrated production was 0.48 ± 0.64 micromol N2O m-2 d-1 which accounted for only 5.4% of the sea-to-air flux and replaced only 4.4% of water column N2O in 16 days. In contrast, the reported sedimentary N2O production rates (8.1 ± 3.3 micromol N2O m-2 d-1) in the same cruise accounted for 91% of the sea-to-air flux and could regenerate water column N2O in 21 days. Therefore, we concluded that sedimentary N2O production was the dominate source to emit N2O to water column. To our knowledge, this is the first study determining N2O production from both water and sediment simultaneously with 15N-lebaled technique which give a clear evidence to identify N2O sources and pathways comprehensively in coastal and estuary ecosystems.