Study On Greenhouse Gas Flux From Newly Created Marshes And Carbon Sink In The Three Gorges Reservoir

From early July to late September2008, we studied CO₂, CH₄, N₂O emissionsfrom4different stands in Newly Created Marshes of the Three Gorges Reservoir （TGR）at10-day intervals, using the static opaque chamber-GC techniques. From February toDecember2009, take measurements of CH₄emissions from the surface of the TGR. Onthe basis of this study, we analyzed the spatial patterns of carbon storage based on GISand the natural environments in drawdown area of TGR, and proposed to optimize themanagement of drawdown area of TGR.The results showed highly spatial variations of CO₂emissions among the fourstands. The greatest CO₂emission (627.8±335.9mg m^-2h^-1) was observed in Scirpustriqueter stand. The smallest CO₂emission (450.4±271.5mg m^-2h^-1) was observed inJuncus amuricus stand. Standing water depths and aboveground biomass wereimportant factors to explain such spatial variations in CO₂emissions. We also found atypical seasonal variation of CO₂emissions in this area, i.e., maximal emissions rangingfrom mid-July to mid-August. The seasonality of CO₂emissions in the newly createdmarshes was found closely related to water temperature and soil temperatures （r=0.577,0.557（5cm）, P<0.001）.The results showed highly spatial variations of methane emissions among the fourstands, with the smallest emission (0.25±0.65mg CH₄m^-2h^-1)in the Juncus amuricusstand, and the greatest (14.9±10.9mg CH₄m^-2h^-1) in the Scirpus triqueter stand. Wefound that the spatial variations of CH₄emissions are caused by difference in standingwater depth and dissolved organic carbon （DOC）. Results also showed a specialseasonal variation of CH₄emissions in this area, i.e., maximal emissions in early Julyfollowed by a low and steady value before the winter flooding. The seasonality of CH₄emissions was found closely related to temperature and standing water depth.The results showed great spatial variations of N₂O emissions among the fourstands.The greatest N₂O emissions (0.052±0.063mg N₂O m^-2h^-1) were from Scirpus triqueterstand, while the lowest N₂O emissions (0.020±0.020mg N₂O m^-2h^-1) were from Typhaangustifolia stand. To suchspatial variations in N₂O emissions, standing water depthsand soil water content may be important explaining factors. Besides spatial variations,we also found significant temporal variations of N₂O emissions in this area. Thetemporal variation of N₂O emissionsin the growing season was not found significantly related to any measured factor in the study. However, based on principal componentanalysis, we consider it partly caused by thermal conditions and the marked temporalvariation of the standing water depth in thegrowing season, which to some degreeinfluenced the process of denitrification and N₂O emissions.The results showed: Carbon storage in drawdown area was514862.3tC, it wasgradually playing a role as regional carbon sink. Carbon storage changed along theelevational grade, which160m¹70m had the biggest carbon storage,229367.46tC,following with the order160m¹70m>150m¹60m>170m¹75m>145m¹50m.The carbon storage was zero in the area with greater land slopes （>25°）, due to watererosion and bedrock exposed vegetation growth scarce. In different slopes zone, thecarbon storage was in sequence of7°¹5°>7°以下>15°²5°.