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

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）景观会遭受各类扰动，并储存巨量有机质，当冻土发生退化时，这些有机质可能转化为温室气体排放源。本研究利用加拿大北极西部赫歇尔岛的11根冻土岩芯，分析了地形与地貌扰动（包括土壤蠕变（soil creep）、活动层脱离（active-layer detachment）、沟壑侵蚀（gullying）、融滑塌（thaw slumping）、河流沉积物堆积（accumulation of fluvial deposits））对土壤有机碳（soil organic carbon, SOC）与总氮（total nitrogen, TN）储量的影响。研究结果表明，SOC储量与地形湿度指数（topographic wetness index）存在显著相关性。未受扰动样地的绝大部分SOC与TN储存在0~70 cm的上层土壤中。以块体搬运作用（mass wasting）为特征的样地出现了显著的SOC损耗与土壤压实现象，而以泥炭与河流沉积物堆积为特征的样地，其SOC与TN储量贯穿整个岩芯。本研究基于由植被组成、坡度与地貌扰动类型确定的生态单元，对SOC与TN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的监督分类（supervised classification）方法完成划定。赫歇尔岛表层1米土壤的平均SOC储量为34.8 kg C/m²，平均TN储量为3.4 kg N/m²。