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首页> 外文期刊>Hydrological Processes >Tracer-based evidence of heterogeneity in subsurface flow and storage within a boreal hillslope
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Tracer-based evidence of heterogeneity in subsurface flow and storage within a boreal hillslope

机译：基于示踪剂的寒山坡地表地下流体和储层非均质性证据

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Runoff from boreal hillslopes is often affected by distinct soil boundaries, including the frozen boundary and the organic-mineral boundary (OMB), where highly porous and hydraulically conductive organic material overlies fine-grained mineral soils. Viewed from the surface, ground cover appears as a patchwork on sub-meter scales, with thick, moss mats interspersed with lichen-covered, silty soils with gravel inclusions. We conducted a decameter-scale subsurface tracer test on a boreal forest hillslope in interior Alaska to quantify locations and mechanisms of transport and storage in these soils, focusing on the OMB. A sodium bromide tracer was added as a slug addition to a pit and sampled at 40 down-gradient wells, screened primarily at the OMB and within a 7x12 m well field. We maintained an elevated head in the injection pit for 8.5 hr to simulate a storm. Tracer breakthrough velocities ranged from <0.12 to 0.93 mhr(-1), with the highest velocities in lichen-covered soils. After 12 hr and cessation of the elevated head, the tracer coalesced and was only detected in thick mosses at a trough in the OMB. By 24 hr, approximately 17% of the tracer mass could be accounted for. The majority of the mass loss occurred between 4 and 12 hr, while the tracer was in contact with lichen-covered soils, which is consistent with tracer transport into deeper flow paths via preferential flow through discrete gravelly areas. Slow breakthroughs suggest that storage and exchange also occurred in shallow soils, likely related to saturation and drainage in fine-grained mineral soils caused by the elevated hydraulic head. These findings highlight the complex nature of storage and transmission of water and solutes from boreal hillslopes to streams and are particularly relevant given rapid changes to boreal environments related to climate change, thawing permafrost and increasing fire severity.
机译：北方山坡的径流经常受到不同的土壤边界的影响，包括冻结边界和有机矿物质边界（OMB），其中高度多孔且具有水力传导性的有机材料覆盖在细颗粒的矿物土壤上。从表面上看，地表覆盖物看起来像是亚米级的拼布，厚厚的苔藓垫子上散布着地衣覆盖的粉质土壤，里面夹杂着砾石。我们在阿拉斯加内部的一个北方森林山坡上进行了十米规模的地下示踪剂测试，以OMB为重点量化这些土壤中的位置和运输与存储的机理。将溴化钠示踪剂作为矿渣添加到矿井中，并在40个向下倾斜的井中取样，主要在OMB处和7x12 m井场内进行筛查。我们在注入坑中保持高扬程8.5小时，以模拟风暴。示踪剂突破速度范围从<0.12到0.93 mhr（-1），在地衣覆盖的土壤中具有最高的速度。停止抬头12小时后，示踪剂合并，仅在OMB的一个槽中的厚苔藓中检测到。到24小时，约占示踪剂质量的17％。大部分质量损失发生在4到12小时之间，而示踪剂则与地衣覆盖的土壤接触，这与示踪剂通过优先流经离散的砾石区进入更深的流路是一致的。缓慢的突破表明，储存和交换也发生在浅层土壤中，这可能与水力压头升高引起的细粒矿质土壤的饱和和排水有关。这些发现突显了水和溶质从北方山坡到溪流的存储和传输的复杂性，鉴于与气候变化有关的北方环境的快速变化，永久冻土的融化以及火灾严重性的增加，这些结果尤为重要。

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