School of Engineering and Sierra Nevada Research Institute, University of California, Merced, California 95343, United States.
Environ Sci Technol. 2015 Apr 21;49(8):4842-50. doi: 10.1021/es504483q. Epub 2015 Apr 13.
Quantifying distributed lateral groundwater contributions to surface water (GW-SW discharges) is a key aspect of tracking nonpoint-source pollution (NPSP) within a watershed. In this study, we characterized distributed GW-SW discharges and associated salt loading using elevated GW specific conductance (SC) as a tracer along a 38 km reach of the Lower Merced River in Central California. High resolution longitudinal surveys for multiple flows (1.3-150 m(3) s(-1)) revealed river SC gradients that mainly decreased with increasing flow, suggesting a dilution effect and/or reduced GW-SW discharges due to hydraulic gradient reductions. However, exceptions occurred (gradients increasing with increasing flow), pointing to complex spatiotemporal influences on GW-SW dynamics. The surveys revealed detailed variability in salinity gradients, from which we estimated distributed GW-SW discharge and salt loading using a simple mixing model. Modeled cumulative GW discharges for two surveys unaffected by ungauged SW discharges were comparable in magnitude to differential gauging-based discharge estimates and prior GW-SW studies along the same river reach. Ungauged lateral inlets and sparse GW data limited the study, and argue for enhancing monitoring efforts. Our approach provides a rapid and economical method for characterizing NPSP for gaining rivers in the context of integrated watershed modeling and management.
量化侧向地下水对地表水（GW-SW 排放）的分布式贡献是追踪流域内非点源污染（NPSP）的关键方面。在本研究中，我们使用升高的 GW 电导率（SC）作为示踪剂沿加利福尼亚州中部的下默塞德河 38 公里河段对分布式 GW-SW 排放和相关盐分负荷进行了特征描述。针对多种流量（1.3-150 m3 s-1）进行的高分辨率纵向调查显示，河流水 SC 梯度主要随流量增加而降低，表明存在稀释效应和/或由于水力梯度降低而减少 GW-SW 排放。然而，也存在例外情况（随着流量增加而增加的梯度），这表明 GW-SW 动态存在复杂的时空影响。这些调查揭示了盐度梯度的详细变化，我们使用简单的混合模型来估算分布式 GW-SW 排放和盐分负荷。两次调查中不受未测量 SW 排放影响的累积 GW 排放量模型与基于差动测量的排放估计值以及沿同一河流断面的先前 GW-SW 研究相当。未测量的侧向入口和稀疏的 GW 数据限制了这项研究，并呼吁加强监测工作。我们的方法为在综合流域模型和管理背景下对获得的河流进行 NPSP 特征描述提供了一种快速而经济的方法。
