Modeling CO2 degassing and pH in a stream-aquifer system
Modeling CO2 degassing and pH in a stream-aquifer system
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DOI：
10.1016/s0022-1694(98)00093-6
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发表时间：
1998-08-01
影响因子：
6.4
通讯作者：
Harvey, JW
中科院分区：
文献类型：
--
作者：
Choi, J;Hulseapple, SM;Harvey, JW
亚利桑那州Final Creek接收了高溶解无机碳（57-75 mg/l）和低pH值（5.8-6.3）的地下水流入。在地下水流入点下游3 km处，观察到河流pH值从约6.0增加到7.8。我们推测，CO2气体交换是最重要的因素，导致pH值的增加，在这个河流含水层系统。现有的传输模型，耦合地下水-地表水系统（奥蒂斯），进行了修改，包括碳酸盐平衡和CO2脱气，用于模拟碱度，总溶解无机碳（C-T），和pH值在皮纳尔溪。由于pH与Cn之间存在非线性关系，修正的迁移模型采用数值迭代法求解非线性。输运模型参数由注入溴和丙烷两种示踪剂确定。由此产生的碱度、C-T和pH值模拟再现了下游浓度的总体趋势，但没有拟合。使用多参数敏感性分析（MPSA）来确定预测对传输模型中使用的六个物理和化学参数的相对敏感性。MPSA结果表明，地下水与河流水的混合和CO2脱气控制了河流水的C-T和pH。这两个过程的相对重要性在空间上的变化取决于水文条件，如流流速和是否达到获得或失去与地下水的相互作用所造成的流水。本研究提出的CO2脱气耦合模型和广义敏感性分析可用于其他河流-地下水耦合系统的碳输运和pH值计算。(C)1998 Elsevier Science B. V.保留所有权利。
Final Creek, Arizona receives an inflow of ground water with high dissolved inorganic carbon (57-75 mg/l) and low pH (5.8-6.3). There is an observed increase of in-stream pH from approximately 6.0-7.8 over the 3 km downstream of the point of groundwater inflow. We hypothesized that CO2 gas-exchange was the most important factor causing the pH increase in this stream-aquifer system. An existing transport model, for coupled ground water-surface water systems (OTIS), was modified to include carbonate equilibria and CO2 degassing, used to simulate alkalinity, total dissolved inorganic carbon (C-T), and pH in Pinal Creek. Because of the non-linear relation between pH and Cn the modified transport model used the numerical iteration method to solve the non-linearity. The transport model parameters were determined by the injection of two tracers, bromide and propane. The resulting simulations of alkalinity, C-T and pH reproduced, without fitting, the overall trends in downstream concentrations. A multi-parametric sensitivity analysis (MPSA) was used to identify the relative sensitivities of the predictions to six of the physical and chemical parameters used in the transport model. MPSA results implied that C-T and pH in stream water were controlled by the mixing of ground water with stream water and CO2 degassing. The relative importance of these two processes varied spatially depending on the hydrologic conditions, such as stream flow velocity and whether a reach gained or lost stream water caused by the interaction with the ground water. The coupled transport model with CO2 degassing and generalized sensitivity analysis presented in this study can be applied to evaluate carbon transport and pH in other coupled stream-ground water systems. (C) 1998 Elsevier Science B.V. All rights reserved.