Eight Mile Lake Research Watershed, Thaw Gradient: Seasonal thaw depth

In this larger study, we are asking the question: Is old carbon that comprises the bulk of the soil organic matter pool released in response to thawing of permafrost? We are answering this question by using a combination of field and laboratory experiments to measure net carbon exchange, radiocarbon isotope ratios in soil organic matter, soil respiration, and dissolved organic carbon, in tundra ecosystems. The objective of these proposed measurements is to develop a mechanistic understanding of the SOM sources contributing to C losses following permafrost thawing. We are making these measurements at an established tundra field site near Healy, Alaska in the foothills of the Alaska Range. Field measurements center on a natural experiment where permafrost has been observed to warm and thaw over the past several decades. This area represents a gradient of sites, each with a different degree of change due to permafrost thawing. In this area, we eatablished three sites with different degrees of disturbance from the permafrost thaw: 1) a relatively undisturbed tussock tundra (Minimal Thaw site), 2) a site adjacent to to the borehole which is monitoring permafrost thaw since 1985 with intermediate degree of disturbance (Moderate thaw site) and 3) a site where permafrost thaw apeared to have started more than three decades ago (Extensive thaw site) As such, this area is unique for addressing questions at the time and spatial scales relevant for change in arctic ecosystems.

在本大型研究中，我们提出核心科学问题：占土壤有机质（Soil Organic Matter）库主体的古老碳，是否会因永久冻土解冻而被释放？为解答此问题，本研究结合野外与室内实验，在苔原生态系统中测定碳净交换量、土壤有机质的放射性碳同位素比值、土壤呼吸速率与溶解性有机碳含量。本次拟开展的测定工作旨在从机制层面解析永久冻土解冻后碳流失所涉及的SOM来源。本研究将在阿拉斯加山脉山麓、阿拉斯加州希利附近一处已建成的苔原野外监测站点开展上述测定工作。野外实验以一项天然观测实验为核心：该区域内永久冻土在过去数十年间持续增温并解冻。该区域布设了一系列梯度样地，各样地因永久冻土解冻所经历的变化程度各不相同。在此区域内，我们设置了3处受永久冻土解冻干扰程度各异的样地：1）相对未受干扰的草丘苔原样地（轻度解冻样地）；2）毗邻自1985年起监测永久冻土解冻的钻孔、受干扰程度中等的样地（中度解冻样地）；3）永久冻土解冻于三十余年前便已启动的样地（重度解冻样地）。因此，该区域具备独特的研究条件，可在与北极生态系统变化相匹配的时间与空间尺度上解答相关科学问题。