Long-term solute transport and geochemical equilibria in seepage water and groundwater in a catchment cross section
Long-term solute transport and geochemical equilibria in seepage water and groundwater in a catchment cross section
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流域断面渗流水和地下水的长期溶质迁移和地球化学平衡
DOI：
10.1007/s12665-013-2393-0
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发表时间：
2013
影响因子：
2.8
通讯作者：
P. Grathwohl
中科院分区：
文献类型：
--
作者：
U. Maier;Matthias Flegr;H. Rügner;P. Grathwohl
弥漫污染、农用土地利用和气候变化对地下水水质长期反应的影响尚未得到很好的了解，但这是评估水资源管理备选办法的先决条件。这项研究的目的是模拟水化学的演化，从土壤入渗到非饱和带，通过基岩和颗粒含水层运移到河流，以确定瞬变水流条件下的浓度梯度和高动态区。建立了一个由典型沉积岩建造的1,500米×1,150米的二维垂直剖面、山谷中的冰川-河流第四系砾石含水层和土层组成的数值模型。该模型耦合了稳态和非饱和条件下的饱和/非饱和渗流和反应性运移。地球化学相互作用，包括氧与溶解有机物在水中的动力学反应，以及碳酸盐溶解/沉淀的动力学。选择这一模型部分是为了深入了解不同流动路径上影响水化学的主要过程和时间尺度。采用数值模拟软件MIN3P，这是一个计算变饱和潜流和多组分反应输运的有限体积程序。结果表明，地下水的停留时间约为2至2,000年。对于矿物平衡的发展，预计会有不同的区域；即，纯粹受大气影响，以及开放和封闭体系的碳酸盐溶解。然而，对日平均降水量变化的短期响应仅在流动系统和溶质负荷的较浅和靠近河流的部分有一定程度的可见。这很可能是因为水流路径的方向性变化，表明在山坡尺度上，平衡的地球化学条件占主导地位，即水质取决于输送路径，而不是动力效应。还原条件的程度受富含有机层(即泥炭沉积)的存在、含水层有机质的溶解动力学以及随后通过水动力分散与含氧水的混合所控制。
The impact of diffuse pollution, agricultural land use and climate change on the long-term response of subsurface–surface water quality is not well understood, but is a prerequisite for evaluation of water management options. The goal of this study is to model geochemical evolution of water chemistry from the infiltration through soil into the unsaturated zone, transport through bedrocks and granular aquifers to a river in order to identify zones of steep concentration gradients and high dynamics under transient flow conditions. A numerical model was constructed comprising a 2-D 1,500 m × 150 m vertical cross-section of typical sedimentary rock formations, a glacio-fluvial quaternary gravel aquifer in the valley and soil layers. The model coupled saturated/un-saturated flow and reactive transport under steady state and transient conditions. Geochemical interactions, include intra-aqueous kinetic reactions of oxygen with dissolved organic matter, as well as kinetics of carbonate dissolution/precipitation. This model section was chosen to provide insight in to the principal processes and time scales affecting water chemistry along different flow paths. The numerical simulator MIN3P was used, a finite volume program for variably saturated subsurface flow and multi-component reactive transport. The results show that subsurface water residence times range from approximately 2 to 2,000 years. Different zones are to be expected with respect to the development of mineral equilibria; namely, purely atmospherically influenced, as well as open and closed system carbonate dissolution. Short-term responses to daily averaged changes in precipitation, however, are only visible to some extent in the shallower and near-river parts of flow system and solute loads. This can most likely be explained by directional changes in flow paths, indicating that equilibrium geochemical condition predominate at the hillslope scale, i.e. water quality depends on transport pathways rather than on kinetic effects. The extent of reducing conditions is controlled by the presence of organic-rich layers (i.e. peat deposits), the dissolution kinetics of aquifer organic matter and the subsequent mixing with oxygenated water by hydrodynamic dispersion.