Using chemical, hydrologic, and age dating analysis to delineate redox processes and flow paths in the riparian zone of a glacial outwash aquifer‐stream system
Using chemical, hydrologic, and age dating analysis to delineate redox processes and flow paths in the riparian zone of a glacial outwash aquifer‐stream system
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DOI：
10.1029/2001wr000396
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发表时间：
2002-08
影响因子：
5.4
通讯作者：
L. Puckett;T. Cowdery;P. McMahon;L. H. Tornes;J. D. Stoner
中科院分区：
文献类型：
--
作者：
L. Puckett;T. Cowdery;P. McMahon;L. H. Tornes;J. D. Stoner
化学和溶解气体分析，氯氟烃年龄测定和水文测量相结合，用于确定在何种程度上，在河岸湿地的地球化学过程负责从地下水中去除NO3-排放到水的水獭尾河在中西部明尼苏达州。对河流化学和流量数据的分析表明，由于地下水排放到河流中，在8.3 km研究河段的下半部分，河流中的NO3−浓度增加。地下水水头测量沿着一个研究样带通过河岸湿地揭示了地下水排放区延伸到河流。根据综合化学、溶解气体、年龄数据和水文结果，确定了河岸湿地下的水化学主要受地下水的控制，这些地下水遵循16米深的流动路径，并在湿地下排放，从而形成了一种逐渐老化、化学还原程度更高的低NO3−水的模式，从湿地边缘向河流方向发展。这些发现对研究河岸缓冲区生物地球化学过程的研究人员提出了挑战，因为逐渐老化的地下水在早些年进入含水层时，使用较少的NO3-肥料。由于反硝化作用和逐渐增强的还原条件，原本存在于地下水中的NO3−浓度在逆时针含水层中也有所下降。由此产生的整个河岸带NO3−浓度下降的模式可能被错误地解释为反硝化损失的证据，而不是在顺向含水层。因此，重要的是要了解水文地质背景和年龄结构的地下水取样，以避免误解河岸带的地球化学过程。
A combination of chemical and dissolved gas analyses, chlorofluorocarbon age dating, and hydrologic measurements were used to determine the degree to which biogeochemical processes in a riparian wetland were responsible for removing NO3− from groundwaters discharging to the Otter Tail River in west central Minnesota. An analysis of river chemistry and flow data revealed that NO3− concentrations in the river increased in the lower half of the 8.3 km study reach as the result of groundwater discharge to the river. Groundwater head measurements along a study transect through the riparian wetland revealed a zone of groundwater discharge extending out under the river. On the basis of combined chemical, dissolved gas, age date, and hydrologic results, it was determined that water chemistry under the riparian wetland was controlled largely by upgradient groundwaters that followed flow paths up to 16 m deep and discharged under the wetland, creating a pattern of progressively older, more chemically reduced, low NO3− water the farther one progressed from the edge of the wetland toward the river. These findings pose challenges for researchers investigating biogeochemical processes in riparian buffer zones because the progressively older groundwaters entered the aquifer in earlier years when less NO3− fertilizer was being used. NO3− concentrations originally present in the groundwater had also decreased in the upgradient aquifer as a result of denitrification and progressively stronger reducing conditions there. The resulting pattern of decreasing NO3− concentrations across the riparian zone may be incorrectly interpreted as evidence of denitrification losses there instead of in the upgradient aquifer. Consequently, it is important to understand the hydrogeologic setting and age structure of the groundwaters being sampled in order to avoid misinterpreting biogeochemical processes in riparian zones.