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Local and Global Sensitivity Analysis of a Reactive Transport Model Simulating Floodplain Redox Cycling
Water Resources Research ( IF 5.4 ) Pub Date : 2021-11-12 , DOI: 10.1029/2021wr029723
Z. Perzan 1 , T. Babey 1 , J. Caers 2 , J. R. Bargar 3 , K. Maher 1
Affiliation  

Reactive transport models (RTMs) are essential tools that simulate the coupling of advective, diffusive, and reactive processes in the subsurface, but their complexity makes them difficult to understand, develop and improve without accompanying statistical analyses. Although global sensitivity analysis (SA) can address these issues, the computational cost associated with most global SA techniques limits their use with RTMs. In this study, we apply distance-based generalized sensitivity analysis (DGSA), a novel and computationally efficient method of global SA, to a floodplain-scale RTM and compare DGSA results to those from local SA. Our test case focuses on the impact of 17 uncertain environmental parameters on spatially and temporally variable redox conditions within a floodplain aquifer. The input parameters considered include flow and diffusion rates, geochemical reaction rates, and the spatial distribution of sediment facies. Sensitivity was evaluated for three distinct components of the model response, encompassing both multidimensional and categorical output. Parameter rankings differ between local SA and DGSA, due to nonlinear effects of individual parameters and interaction effects between parameters. DGSA results show that fluid residence time, which is controlled by aquifer permeability, generally exerts a stronger control on redox conditions than do geochemical reaction rates. Sensitivity indices also demonstrate that sulfate reduction is key for establishing and maintaining reducing conditions throughout the aquifer. These results provide insights into the key drivers of heterogeneous redox processes within floodplain aquifers, as well as the main sources of uncertainty when modeling complex subsurface systems.

中文翻译:

模拟洪泛区氧化还原循环的反应性传输模型的局部和全局敏感性分析

反应输运模型 (RTM) 是模拟地下对流、扩散和反应过程耦合的重要工具,但它们的复杂性使它们在没有伴随的统计分析的情况下难以理解、开发和改进。尽管全局敏感性分析 (SA) 可以解决这些问题,但与大多数全局 SA 技术相关的计算成本限制了它们与 RTM 的使用。在这项研究中,我们将基于距离的广义敏感性分析 (DGSA),一种新颖且计算效率高的全局 SA 方法应用于洪泛区尺度 RTM,并将 DGSA 结果与局部 SA 的结果进行比较。我们的测试案例侧重于 17 个不确定的环境参数对漫滩含水层内时空变化的氧化还原条件的影响。考虑的输入参数包括流动和扩散速率、地球化学反应速率和沉积相的空间分布。对模型响应的三个不同组成部分的敏感性进行了评估,包括多维和分类输出。由于单个参数的非线性效应和参数之间的交互效应,局部 SA 和 DGSA 之间的参数排名不同。DGSA 结果表明,受含水层渗透率控制的流体停留时间通常比地球化学反应速率对氧化还原条件施加更强的控制。敏感性指数还表明硫酸盐还原是整个含水层建立和维持还原条件的关键。
更新日期:2021-12-03
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