长江口潮间带湿地涨退潮期N2O的排放通量研究

随着河口区接收上游人为氮排放量的增加，为这一区域氧化亚氮（N2O）的排放增加了很大不确定性。选择长江河口潮间带湿地为研究对象，分别采用原位静态箱法和静态顶空法，从2011年1月至12月对长江口沉积物 大气界面以及涨潮水 大气界面的N2O排放通量进行了为期一年的现场观测和研究。研究结果表明，沉积物 大气界面N2O通量有着显著的时空差异。N2O排放通量在日变化以及季节变化上都表现出明显的源汇转变，就年平均排放通量，光滩带沉积物 大气界面达到了599 μgN2O/(m2〖DK〗·h)，而海三棱藨草盐沼带与大气间N2O交换则十分微弱，为060 μgN2O/(m2〖DK〗·h)。对长江口涨退潮期光滩和草滩上覆水体 大气界面N2O排放通量的研究表明，长江口涨退潮期在夏季和秋季，无论是光滩还是草滩均表现为大气N2O的稳定排放源，其中夏季平均253 μgN2O/(m2〖DK〗·h)，秋季平均排放通量为207 μgN2O/(m2〖DK〗·h)。作为河口区上游排放氮素的直接接收者，和沉积物 大气界面N2O排放相比，长江口涨潮水 大气界面N2O排放稳定而又显著，是长江口N2O排放的主要贡献者，应成为这一区域N2O排放的关注热点

EXCHANGE FLUXES OF N2O BETWEEN INTERTIDAL WETLANDS AND ATMOSPHERE DURING THE LOW AND HIGH TIDES IN YANGTZE ESTUARY

As one of the most important greenhouse gases, nitrous oxide (N2O) has been recognized to contribute global warming by 25%. The Global nitrogen enrichment has resulted in increased N2O emission that greatly contributes to global warming and stratospheric ozone destruction. With the increase of upstream nitrogen importation, the uncertainties of N2O emissions also increased due to the complex nitrogen cycles in estuary area. Although some studies have already been carried out to identify the N2O emission fluxes in the Yangtze estuary, the N2O emission flux of water body during the tide movement remains unknown. From February to December 2011, we chose Yangtze estuary intertidal zone (Scripus mariqueter salt marshes and bare tidal flat) as research area to study the natural N2O fluxes between the sediment and atmosphere and also between the tide water and atmosphere during the tide movement. The sediment air and water air N2O fluxes were respectively measured using the static closed chamber and static headspace techniques. The study results indicated that both Scripus mariqueter salt marshes and bare tidal flat acted as net sources of atmospheric N2O at the low tide when the sediments were exposed to the air. Considering both N2O emission and absorption, the annual average N2O fluxes of sediment air interface in Scripus mariqueter salt marshes and bare tidal flat were 060 and 599 μg N2O/(m2〖DK〗·h), respectively. N2O fluxes between the sediment and atmosphere showed large temporal variations. The transformation of N2O sink and source in both Scripus mariqueter salt marshes and bare flat appeared in different time scales including daily and monthly time scale. The fluctuation of N2O emission and absorption was probably caused by the low concentration of active inorganic nitrogen in the sediment, which brought many uncertainties to the N2O production ratio during the denitrification process. The N2O fluxes between the water air interfaces during the processes of tide rising and ebbing showed that both Scripus mariqueter salt marshes and the bare tidal flat acted as the steady and significant emission sources of the atmospheric N2O. The average air sea fluxes of N2O in summer and autumn were 253 and 207 μgN2O/(m2〖DK〗·h), respectively. The water air N2O fluxes didnt exhibit significant seasonal change and were also not influenced much by the ambient temperature. In terms of spatial variation, water air N2O fluxes in Scripus mariqueter salt marshes were lower than that in bare tidal flat and the N2O fluxes were 1966 and 2588 μg N2O/(m2〖DK〗·h), respectively. In addition, the differences of water air N2O fluxes between the diurnal tide and night tide were also not obvious, which indicated that light condition exerted little impact on water air N2O emission. The concrete water air N2O fluxes of the diurnal tide and night tide were 2169 and 2459 μg N2O/(m2〖DK〗·h), respectively. As the main receiver of upstream imported nitrogen, the water body in the Yangtze estuary during the tide movement acted as the more significant emission source of atmospheric N2O, thus the tide water should be paid more attention from the terms of the greenhouse gas emissions compared with the N2O fluxes from the sediment and atmosphere.〖