U.S. Geological Survey, Earth System Processes Division, Hydrogeophysics Branch, 11 Sherman Place, Unit 5015, Storrs, CT 06269, USA.
U.S. Geological Survey, Leetown Science Center, Aquatic Ecology Branch, 11649 Leetown Road, Kearneysville, WV 25430, USA.
Sci Total Environ. 2018 Sep 15;636:1117-1127. doi: 10.1016/j.scitotenv.2018.04.344. Epub 2018 May 3.
Streams strongly influenced by groundwater discharge may serve as "climate refugia" for sensitive species in regions of increasingly marginal thermal conditions. The main goal of this study is to develop paired air and stream water annual temperature signal analysis techniques to elucidate the relative groundwater contribution to stream water and the effective groundwater flowpath depth. Groundwater discharge to streams attenuates surface water temperature signals, and this attenuation can be diagnostic of groundwater gaining systems. Additionally, discharge from shallow groundwater flowpaths can theoretically transfer lagged annual temperature signals from aquifer to stream water. Here we explore this concept using multi-year temperature records from 120 stream sites located across 18 mountain watersheds of Shenandoah National Park, VA, USA and a coastal watershed in Massachusetts, USA. Both areas constitute important cold-water habitat for native brook trout (Salvelinus fontinalis). Observed annual temperature signals indicate a dominance of shallow groundwater discharge to streams in the National Park, in contrast to the coastal watershed that has strong, apparently deeper, groundwater influence. The average phase lag from air to stream signals in Shenandoah National Park is 11 d; however, extended lags of approximately 1 month were observed in a subset of streams. In contrast, the coastal stream has pronounced attenuation of annual temperature signals without notable phase lag. To better understand these observed differences in signal characteristics, analytical and numerical models are used to quantify mixing of the annual temperature signals of surface and groundwater. Simulations using a total heat budget numerical model indicate groundwater-induced annual temperature signal phase lags are likely to show greater downstream propagation than the related signal amplitude attenuation. The measurement of multi-seasonal paired air and water temperatures offers great promise toward understanding catchment processes and informing current cold-water habitat management at ecologically-relevant scales.
受地下水排泄强烈影响的溪流可能成为在热条件日益边缘的地区中对敏感物种的“气候避难所”。本研究的主要目标是开发配对的空气和溪流水年度温度信号分析技术，以阐明地下水对溪流水的相对贡献和有效地下水流动路径深度。地下水排入溪流会削弱地表水温度信号，这种衰减可以作为地下水补给系统的诊断依据。此外，浅层地下水流动路径的排放理论上可以将含水层的滞后年度温度信号传递到溪流水中。在这里，我们使用来自美国弗吉尼亚州 Shenandoah 国家公园的 18 个山区流域和美国马萨诸塞州的一个沿海流域的 120 个溪流站点的多年温度记录来探索这一概念。这两个地区都构成了本地溪红点鲑（Salvelinus fontinalis）的重要冷水栖息地。观测到的年度温度信号表明，在国家公园中，浅层地下水对溪流的排泄占主导地位，而在沿海流域中，地下水的影响显然更深。Shenandoah 国家公园中空气到溪流信号的平均相位滞后为 11 天；然而，在一小部分溪流中观察到大约 1 个月的延长滞后。相比之下，沿海溪流具有明显的年度温度信号衰减，而没有明显的相位滞后。为了更好地理解这些观测到的信号特征差异，使用分析和数值模型来量化地表水和地下水的年度温度信号混合。使用总热预算数值模型进行的模拟表明，地下水引起的年度温度信号相位滞后可能比相关的信号幅度衰减具有更大的下游传播。多季节空气和水温的测量非常有希望用于了解集水区过程，并在生态相关尺度上为当前的冷水栖息地管理提供信息。
