Spatial extent and per cent of total area covered by each class within the study area

Table 2. 
Spatial extent and per cent of total area covered by each class within the study area.
Abstract Climate-induced changes to permafrost are altering high latitude landscapes in ways that could increase the vulnerability of the vast soil carbon pools of the region. Permafrost thaw is temporally dynamic and spatially heterogeneous because, in addition to the thickening of the active layer, localized thermokarst features form when ice-rich permafrost thaws and the ground subsides. Thermokarst produces a diversity of landforms and alters the physical environment in dynamic ways. To estimate potential changes to the carbon cycle it is imperative to quantify the size and distribution of thermokarst landforms. By performing a supervised classification on a high resolution IKONOS image, we detected and mapped small, irregular thermokarst features occurring within an upland watershed in discontinuous permafrost of Interior Alaska. We found that 12% of the Eight Mile Lake (EML) watershed has undergone thermokarst, predominantly in valleys where tussock tundra resides. About 35% of the 3.7 km2 tussock tundra class has likely transitioned to thermokarst. These landscape level changes created by permafrost thaw at EML have important implications for ecosystem carbon cycling because thermokarst features are forming in carbon-rich areas and are altering the hydrology in ways that increase seasonal thawing of the soil.

表 2. 研究区域内各等级空间范围及其占总面积百分比。摘要：气候引起的永久冻土变化正在以可能增加该地区广阔土壤碳库脆弱性的方式改变高纬度景观。永久冻土的融化在时间上具有动态性，在空间上具有异质性，因为除了活动层增厚外，当地热喀斯特特征的形成还发生在富含冰的永久冻土融化并引起地面沉降时。热喀斯特形成了多样化的地表形态，并以动态的方式改变物理环境。为了估计碳循环的潜在变化，量化热喀斯特地表形态的大小和分布至关重要。通过对高分辨率 IKONOS 影像进行监督分类，我们在阿拉斯加内陆不连续永久冻土的上游流域中检测并绘制了小而不规则的热喀斯特特征。我们发现，八英里湖（EML）流域有 12% 的面积经历了热喀斯特作用，主要发生在苔原山谷中。大约 35% 的 3.7 平方公里苔原类可能已经转变为热喀斯特。由 EML 永久冻土融化引起的这些景观级变化对生态系统碳循环具有重要影响，因为热喀斯特特征正在碳富集区域形成，并以增加土壤季节性融化的方式改变水文条件。