Nitrate reduction potential of a fractured Middle Triassic carbonate aquifer in Southwest Germany
Nitrate reduction potential of a fractured Middle Triassic carbonate aquifer in Southwest Germany
复制标题
DOI：
10.1007/s10040-021-02418-9
复制
发表时间：
2021-12
影响因子：
2.8
通讯作者：
K. Osenbrück;Eva Blendinger;C. Leven;H. Rügner;M. Finkel;N. Jakus;H. Schulz;P. Grathwohl
中科院分区：
文献类型：
--
作者：
K. Osenbrück;Eva Blendinger;C. Leven;H. Rügner;M. Finkel;N. Jakus;H. Schulz;P. Grathwohl
硝酸盐还原是缓解地下水资源广泛和持续的硝酸盐污染的重要自然机制。然而，在裂隙含水层中，电子供体的丰度和可及性及其与地下水流动路径的空间相关性往往知之甚少。在这项研究中，研究了德国西南部上Muschelkalk的裂缝碳酸盐含水层的硝酸盐还原潜力，其中的反硝化是由于亚铁和还原硫的氧化。岩石样品的岩石学分析显示，同沉积和成岩形成的黄铁矿的浓度在1%至4%之间，不同相类型之间只有很小的差异。鞍状白云岩中还含有亚铁（高达2.6 wt.%），可能是由构造诱导的低温热液渗流形成的。地下水井的井眼测井（流量计、视频、伽马）表明，大部分地下水沿岩溶层理面流动，部分位于浅滩和后滩相白云岩内。这些相的高孔隙度（15-30%）有利于溶质在裂缝流动路径和孔隙基质中的活性矿物之间进行分子扩散交换。高孔隙相与以黄铁矿或鞍状白云岩沉积为特征的水力活动裂缝构成了含水层内硝酸盐还原潜力最大的区域。基于模型的电子受体/供体平衡估计表明，保护供水井的硝酸盐还原潜力随着岩石基质孔隙度的增加而增加，而随着水力导度（或有效裂缝孔径）和裂缝网络间距的增加而降低。
Nitrate reduction constitutes an important natural mechanism to mitigate the widespread and persistent nitrate contamination of groundwater resources. In fractured aquifers, however, the abundance and accessibility of electron donors and their spatial correlation with groundwater flow paths are often poorly understood. In this study, the nitrate reduction potential of a fractured carbonate aquifer in the Upper Muschelkalk of SW Germany was investigated, where denitrification is due to the oxidation of ferrous iron and reduced sulfur. Petrographical analyses of rock samples revealed concentrations of syn-sedimentary and diagenetically formed pyrite ranging from 1 to 4 wt.% with only small differences between different facies types. Additional ferrous iron is available in saddle dolomites (up to 2.6 wt.%), which probably were formed by tectonically induced percolation of low-temperature hydrothermal fluids. Borehole logging at groundwater wells (flowmeter, video, gamma) indicates that most groundwater flow occurs along karstified bedding planes partly located within dolomites of the shoal and backshoal facies. The high porosity (15–30%) of these facies facilitates molecular diffusive exchange of solutes between flow paths in the fractures and the reactive minerals in the pore matrix. The high-porosity facies together with hydraulically active fractures featuring pyrite or saddle dolomite precipitates constitute the zones of highest nitrate reduction potential within the aquifer. Model-based estimates of electron acceptor/donor balances indicate that the nitrate reduction potential protecting water supply wells increases with increasing porosity of the rock matrix and decreases with increasing hydraulic conductivity (or effective fracture aperture) and spacing of the fracture network.