Perennial flow through convergent hillslopes explains chemodynamic solute behavior in a shale headwater catchment
Perennial flow through convergent hillslopes explains chemodynamic solute behavior in a shale headwater catchment
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通过收敛山坡的常年流动解释了页岩源头集水区的化学动力学溶质行为
DOI：
10.1016/j.chemgeo.2018.06.019
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发表时间：
2018
期刊：
影响因子：
3.9
通讯作者：
Sullivan, Pamela L.
中科院分区：
文献类型：
--
作者：
Herndon, Elizabeth M.;Steinhoefel, Grit;Dere, Ashlee L.D.;Sullivan, Pamela L.
河流化学反映了流域内复杂的生物地球化学反应的混合物，这些反应在空间和时间上各不相同。例如，在不同的水流状态下，河流与异质水源的水文连通性不断变化;然而，目前仍不清楚季节性水流路径如何将这些不同的水源联系起来，并调节浓度-排放行为，即，作为排放函数的水流溶质浓度的变化。在美国宾夕法尼亚州中部的萨斯奎汉纳页岩山临界区观测站（SHCZO），化学稳定溶质（K，Mg，Na，Si，Cl）的浓度在很宽的放电值范围内变化不大，而化学动力溶质（Fe，Mn，Ca）的浓度随着流量的增加而急剧下降。为了阐明化学动力学溶质行为的控制，我们调查了地表水和浅层地下水的化学在SHCZO在初秋时，排放量可以忽略不计，化学动力学溶质的浓度很高。溶解离子，胶体和微米级颗粒提取的山坡土壤和流沉积物，以评估如何元素被动员到孔隙沃茨和运输从山坡上的流。在研究期间，当流动是间歇性的，流由孤立的水坑，化学变量沿着的长度的通道。地下水的输入流被限制在一个地区的上升流附近的河流源头，和地下水位保持超过一米以下的河床沿着其余的渠道。化学动力学元素Fe和Mn优先动员从有机丰富的土壤作为溶解的离子，胶体和微米级颗粒的混合物，因此，地下水排水有机丰富的土壤在上游集水区富集铁和锰。相反，钙增加对集水区出口，主要是动员从流沉积物中的Ca 2+。恒化溶质的浓度是相对不变的整个cathets.We的结论，在SHCZO的化学动力学行为是由季节性变化的流和山坡土壤之间的连接。在旱季，溪流水来自浅栖息的地下水位（interflow），上升产生富含金属的溪流源头。高浓度的可溶性铁和锰在低流量时发生富含金属的源头被冲到集水出口在定期降雨事件。在旱季的Interflow源于水渗透通过有机丰富的沼泽，因此，在低流量的流中的金属最终来自收敛的山坡上的生物过程集中和/或动员这些化学动力学元素。相反，高浓度的Ca 2+在低排放可能动员从流沉积物中含有次生方解石沉淀。我们推断，化学动力学溶质稀释在高排放主要是由于通过平面山坡流量增加。这项研究突出了如何空间异质性土壤地球化学和季节性变化的流动路径调节集水区内的浓度排放行为。
Stream chemistry reflects the mixture of complex biogeochemical reactions that vary across space and time within watersheds. For example, streams experience changing hydrologic connectivity to heterogeneous water sources under different flow regimes; however, it remains unclear how seasonal flow paths link these different sources and regulate concentration-discharge behavior, i.e., changes in stream solute concentration as a function of discharge. At the Susquehanna Shale Hills Critical Zone Observatory (SSHCZO) in central Pennsylvania, USA, concentrations of chemostatic solutes (K, Mg, Na, Si, Cl) vary little across a wide range of discharge values while concentrations of chemodynamic solutes (Fe, Mn, Ca) decrease sharply with increasing stream discharge. To elucidate controls on chemodynamic solute behavior, we investigated the chemistry of surface water and shallow subsurface water at the SSHCZO in early autumn when discharge was negligible and concentrations of chemodynamic solutes were high. Dissolved ions, colloids, and micron-sized particles were extracted from hillslope soils and stream sediments to evaluate how elements were mobilized into pore waters and transported from hillslopes to the stream.During the study period when flow was intermittent, the stream consisted of isolated puddles that were chemically variable along the length of the channel. Inputs of subsurface water to the stream were limited to an area of upwelling near the stream headwaters, and the water table remained over a meter below the stream bed along the rest of the channel. Chemodynamic elements Fe and Mn were preferentially mobilized from organic-rich soils as a mixture of dissolved ions, colloids, and micron-sized particles; consequently, subsurface water draining organic-rich soils in the upper catchment was enriched in Fe and Mn. Conversely, Ca increased towards the catchment outlet and was primarily mobilized from stream sediments as Ca2+. Concentrations of chemostatic solutes were relatively invariable throughout the catchment.We conclude that chemodynamic behavior at SSHCZO is driven by seasonally variable connectivity between the stream and hillslope soils. During the dry season, stream water derives from a shallow perched water table (interflow) that upwells to generate metal-rich stream headwaters. High concentrations of soluble Fe and Mn at low discharge occur when metal-rich headwaters are flushed to the catchment outlet during periodic rain events. Interflow during the dry season originates from water that infiltrates through organic-rich swales; thus, metals in the stream at low flow are ultimately derived from convergent hillslopes where biological processes have concentrated and/or mobilized these chemodynamic elements. In contrast, high concentrations of Ca2+at low discharge are likely mobilized from stream sediments that contain secondary calcite precipitates. We infer that chemodynamic solutes are diluted at high discharge primarily due to increased flow through planar hillslopes. This study highlights how spatially heterogeneous biogeochemistry and seasonally variable flow paths regulate concentration-discharge behavior within catchments.
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