| Zoige wetland is the world's largest alpine wetland and highland swamp concentrated area, and its huge carbon stock plays an important role in the global carbon cycle. However, human activities and climate change have broken the ecological balance of Zoige wetland and subsequently affected the distribution and change of soil organic carbon (SOC) stock in recent decades. We use the RS and GIS technology, combined with field investigations, laboratory analysis and related statistical data to estimate SOC stock depletion in 100 cm depth and its determinants across the study area in 1981,2006 and 2011. To understand the SOC stock change characteristics with wetland degradation, the process of wetland degradation, and its response mechanism to natural and human factors interference, as well as provide a scientific basic data for Zoige wetland rational utilization, restoration and protection. The main research conclusions were as follows:(1) The study area suffered severe wetland degradation from 1981 to 2011. In the past 30 years, the wetland distribution areas decreased by 34.8% (annual reduction of 198.39 hm~2). Among them, the swamp area decreased by 78.8% (annual reduction of 87.80 hm~2), the areas of seasonal swamp and meadow decreased by 32.7% (annual reduction of 54.08 hm~2) and 19.6% (annual reduction of 53.05 hm~2), respectively. On the other hand, among non-wetland types, the pasture and desert land areas increased by 21.3% (annual increase of 53.05 hm~2)and 45.0% (annual increase of 19.91 hm~2), respectively, while the area of shrub land decreased by 15.4%(annual reduction of 20.24 hm~2). The areas of lake, river, ditch, building land and road changed little.(2) The SOC concentrations of different landscapes showed significant difference, and the SOC concentrations of wetland landscapes were significantly higher than that of non-wetland types (P<0.01). In the past 30 years, the average SOC concentrations of different landscape showed different change trends. Among them, the SOC concentrations of seasonal swamp, meadow, shrub land and pasture decreased by 3.8%,15.8%,10.1% and 21.6%, respectively. In contrast, the SOC concentrations of swamp and desert land increased by 5.7% and 185.9%, respectively. The SOC concentrations of other landscapes changed little.(3) The SOC densities of different landscapes showed significant difference, the SOC densities of wetland landscapes were significantly higher than that of non-wetland types(P<0.01). The SOC densities of swamp, seasonal swamp, meadow, pasture and shrub land decreased by 4.4%,9.3%,10.2%,17.7%and 7.5%from 1981 to 2011, respectively, while the SOC density of desert land increased by 125.7%, the SOC densities of other landscapes changed little.(4) The SOC stocks across the landscapes showed a decreasing trend from 1981 to 2011. The regional SOC stock was depleted from 20.61 Tg in 1981 to 16.29 Tg in 2006 and 15.38 Tg in 2011, respectively, and led to a total of 5.23 Tg depletion in the past 30 years. Among them, swamp, seasonal swamp and meadow were the main SOC stock depletion landscapes, and accounted for about 42.3%,29.4% and 23.5% of the total carbon depletion.(5) Wetland severe degradation and SOC stock depletion were the results of artificial drainage, overgrazing, climate change and plant community successions. Artificial drainage and climate warming led to wetland landscape evolution and SOC density decrease and overgrazing decreased litter input to soils. These key factors were also strong drivers of plant community successions. The successions from hydrophytes or helophytes to mesophytes or psammophytes, mesophytes to forbs or psammophytes caused SOC stock depletion, while the psammophytes replaced with restoration communities would increase SOC stock. |
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