| Due to anthropogenic activities and climate change, wetland ecosystems in China keep degrading, which significantly threaten the ecological security of China. After an estimate of the soil organic carbon (SOC) stock and spatial distribution for the national palustrine wetlands, this study chose Zoige alpine wetland (Ruoergai County and Hongyuan County) as study area, and focused on wetland SOC stock to analyze spatial-temporal changes under the context of global change. Field investigation, laboratory analysis, model simulation, and statistical analysis were carried out to estimate spatial-temporal changes of SOC stock in the Zoige alpine wetland, based on which the spatial distribution of SOC stock in the area of Zoige alpine wetland was revealed. This study also quantified changes in the SOC stock in these two counties between 1980 and 2010 in response to progressive drainage of the wetlands and increased grazing intensity. Meanwhile, the trends of wetland SOC stock change under different scenarios were predicted. According to a systematic study, the main results and conclusions are as follows:(1) In the uppermost 1 m of wetland soil, the average SOC density of wetland in Ruoergai County and Hongyuan County was 69.5 kg C m-3, which were triple larger than the average of the wetland SOC density in China and six times larger than the national average. The SOC content and SOC density decreased with increasing soil depth, which was highest in the topmost 0.3 m soil layer and was significant higher than the 0.3-1 m soil layer. The horizontal distribution of SOC was heterogeneous. The SOC stock in the uppermost 1 m of wetland soils totaled 514 Tg C, accounting for 8.3% to 10.2% of the total SOC stock in the topmost 1 m of wetland soils in China, playing an important role in carbon cycle of China.(2) The Zoige wetland showed a net carbon sink during the period of 1980-2010. The results indicated that wetland soils in the uppermost 1 m sequestered ～0.25 t C ha-1 yr-1 despite the degradation that has occurred due to drainage and grazing. However, the potetial capacity of carbon sink decreased with the intensifying wetland degradation. Conversion of wetlands to grassland via drainage since 1980 had resulted in a potential loss of approximately 0.49-4.05 t C ha-1 from the SOC stock in the uppermost 1 m of wetland soils. In the short term, more intensive grazing might have positive impact on root biomass accumulation, thus enhancing the SOC stock. However, grazing was also a reason why wetlands were drained with all the negative effects on the SOC pool. The potential SOC sequestration of intensive grazing was offseted by the negative effect of drainage.(3) Reasonable wetland conservation, management and restoration could significantly enhance wetland carbon sink. The results indicated that SOC stocks presented increasing trends under different scenarios. Compared with 2010, the wetland SOC pool will be increased by 15.80 (±7.43) Tg C in the uppermost 1 m of wetland soils by the end of this century. Compared with no wetland restoration, the carbon sequestration potential of wetland could be increased by 0.19 (±0.01) t C ha-1 yr-1 under wetland restoration. Considering the huge potential of wetland carbon sequestration, the wetland restoration should be further strengthened under the context of global change to enhance the role of wetland in the mitigation of climate change. For instance, implement the wetland restoration projects and take reasonably measures to control grazing to graually restore wetland area and wetland fuctions to effectively improve carbon sequestration protential of wetland. |
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