Supra-permafrost aquifers within the active layer are present in the Arctic during summer. Permafrost thawing due to Arctic warming can liberate previously frozen particulate organic matter (POM) in soils to leach into groundwater as dissolved organic carbon (DOC). DOC transport from groundwater to surface water is poorly understood because of the unquantified variability in subsurface properties and hydrological environments. These dynamics must be better characterized because DOC transport to surface waters is critical to predict the long-term fate of recently thawed carbon in permafrost environments. Here, we used distributed Darcy’s Law calculations to quantify groundwater and DOC fluxes into Imnavait Creek, Alaska, a representative headwater stream in a continuous permafrost watershed. We developed a statistical ensemble approach to model the parameter variability and range of potential contributions of steady-state groundwater flow to the creek. We quantified the model prediction uncertainty using statistical sampling of in-situ, active-layer soil hydro-stratigraphy (water table, ice table, and soil stratigraphy), high-resolution topography data, and DOC data. Moreover, the predicted groundwater discharge values representing all possible hydrologic conditions towards the end of the thawing season were also considered given the potential variability in saturation. The model predictions were similar to and span most of the observed range of Imnavait Creek streamflow, especially during recession periods, and also during saturation excess overland flow. As the Arctic warms and supra-permafrost aquifers deepen, groundwater flow is expected to increase. This increase is expected to impact stream, river, and lake biogeochemical processes by dissolving and mobilizing more soil constituents in continuous permafrost regions. This study highlights how quantifying the uncertainty of hydro-stratigraphical input parameters helps understand and predict supra-permafrost aquifer dynamics and connectivity to aquatic systems using a simple, but scalable, modeling approach.

中文翻译：

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从超永久冻土含水层到跨水文状态的溪流的水和碳通量


活动层内的永久冻土层上含水层在夏季出现在北极。北极变暖导致的永久冻土融化可以释放土壤中先前冻结的颗粒有机物 （POM），以溶解有机碳 （DOC） 的形式渗入地下水。由于地下特性和水文环境的不可量化的变化，人们对从地下水到地表水的 DOC 迁移知之甚少。必须更好地描述这些动态，因为 DOC 向地表水的迁移对于预测永久冻土环境中最近融化的碳的长期归宿至关重要。在这里，我们使用分布式达西定律计算来量化进入阿拉斯加 Imnavait Creek 的地下水和 DOC 通量，这是连续永久冻土流域中具有代表性的源头溪流。我们开发了一种统计集成方法来模拟稳态地下水流对小溪的参数可变性和潜在贡献范围。我们使用原位活性层土壤水文地层学（地下水位、冰位和土壤地层学）、高分辨率地形数据和 DOC 数据的统计采样来量化模型预测的不确定性。此外，考虑到饱和度的潜在变化，还考虑了代表解冻季节结束时所有可能水文条件的预测地下水流量值。模型预测与 Imnavait Creek 溪流的大部分观测范围相似并跨越，尤其是在衰退时期，以及饱和过剩的陆上流量期间。随着北极变暖和超永久冻土含水层加深，预计地下水流量将增加。 预计这种增加将通过溶解和移动连续永久冻土区域中的更多土壤成分来影响溪流、河流和湖泊的生物地球化学过程。本研究强调了量化水文地层输入参数的不确定性如何利用简单但可扩展的建模方法帮助理解和预测永久冻土层上含水层动力学以及与水生系统的连通性。