Ecological classification of Herschel Island based on supervised classification of multispectral satellite imagery@en

Permafrost landscapes experience different disturbances and store large amounts of organic matter, which may become a source of greenhouse gases upon permafrost degradation. We analysed the influence of terrain and geomorphic disturbances (e.g. soil creep, active-layer detachment, gullying, thaw slumping, accumulation of fluvial deposits) on soil organic carbon (SOC) and total nitrogen (TN) storage using 11 permafrost cores from Herschel Island, western Canadian Arctic. Our results indicate a strong correlation between SOC storage and the topographic wetness index. Undisturbed sites stored the majority of SOC and TN in the upper 70 cm of soil. Sites characterised by mass wasting showed significant SOC depletion and soil compaction, whereas sites characterised by the accumulation of peat and fluvial deposits store SOC and TN along the whole core. We upscaled SOC and TN to estimate total stocks using the ecological units determined from vegetation composition, slope angle and the geomorphic disturbance regime. The ecological units were delineated with a supervised classification based on RapidEye multispectral satellite imagery and slope angle. Mean SOC and TN storage for the uppermost 1 m of soil on Herschel Island are 34.8 kg C/m**2 and 3.4 kg N/m**2, respectively.多年冻土（permafrost）景观会遭受不同类型的扰动，且储存着大量有机质，在多年冻土退化后，这些有机质可能成为温室气体的来源。本研究基于加拿大北极西部赫歇尔岛（Herschel Island）的11根冻土岩芯，分析了地形与地貌扰动（如土壤蠕变、活动层滑脱、沟壑侵蚀、热融滑塌、河流沉积物堆积）对土壤有机碳（soil organic carbon, SOC）和总氮（total nitrogen, TN）储量的影响。研究结果表明，土壤有机碳储量与地形湿度指数（topographic wetness index）存在显著相关性。未受扰动的样点，其土壤有机碳和总氮主要储存在表层0~70 cm的土壤中。以块体运动（mass wasting）为特征的样点，表现出显著的土壤有机碳亏缺与土壤压实现象；而以泥炭和河流沉积物堆积为特征的样点，其土壤有机碳和总氮在整个岩芯剖面中均有储存。本研究基于由植被组成、坡度角及地貌扰动类型划定的生态单元，对土壤有机碳和总氮储量进行尺度上推以估算总储量。上述生态单元通过基于RapidEye多光谱卫星影像与坡度角的监督分类完成勾绘。赫歇尔岛表层1 m土壤的平均土壤有机碳储量为34.8 kg C/m²，平均总氮储量为3.4 kg N/m²。