Abstract Climate change is expected to reduce recharge to montane aquifers in the western United States, but it is unclear how this will impact groundwater resources in watersheds where intensive surface-water development has disrupted the natural hydrologic regime. To better understand sources of recharge and associated vulnerabilities of groundwater supply in this setting, we made a detailed geochemical survey of domestic wells finished in fractured bedrock throughout the Yuba and Bear River watersheds (Sierra Nevada foothills, northern California) during historic drought (2015–2016). Stable isotopes of water and noble gas recharge temperatures closely tracked atmospheric lapse rates across a broad elevation gradient (100–2000 m), indicating groundwater inputs are dominated by local precipitation that rapidly recharges fractured bedrock during the winter wet-season. However, nearly one-quarter of wells had water isotopes that were fractionated by evaporation and warm recharge temperatures, indicative of mixing with dry-season recharge by surface water. Monte Carlo mixing models suggest evaporation-impacted groundwater samples are mixtures of local rain with an average of 28% ± 13% from diverted surface water that can recharge bedrock aquifers during the dry-season by either irrigation return flow or seepage from extensive distribution infrastructure. Wells that received recharge subsidies from diverted surface water had elevated levels of nitrate and coliform bacteria compared to those replenished exclusively by local precipitation, which are more vulnerable to supply shortage during drought. It is important to consider the impacts of increased surface-water development on the quantity and quality of groundwater recharge in rapidly developing montane watersheds.

中文翻译：

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山区流域发展对干旱期生活地下水供应脆弱性的影响

摘要 气候变化预计将减少美国西部山地含水层的补给量，但尚不清楚这将如何影响集水区的地下水资源，在这些流域中，密集的地表水开发破坏了自然水文制度。为了更好地了解这种情况下地下水补给的补给来源和相关脆弱性，我们对在历史性干旱期间（2015 年至加利福尼亚北部）在整个尤巴河和贝尔河流域（加利福尼亚北部内华达山脉山麓）的断裂基岩中完成的国内井进行了详细的地球化学调查。 2016）。水和惰性气体补给温度的稳定同位素在宽阔的海拔梯度（100-2000 m）上密切跟踪大气递减率，表明地下水输入主要由当地降水主导，在冬季雨季期间，这些降水对裂隙基岩进行快速补给。然而，近四分之一的井具有通过蒸发和温暖补给温度分馏的水同位素，表明与地表水的旱季补给混合。Monte Carlo 混合模型表明，受蒸发影响的地下水样本是当地雨水的混合物，平均 28% ± 13% 来自转移的地表水，可以在旱季通过灌溉回流或广泛分布基础设施的渗漏来补给基岩含水层。与完全由当地降水补充的井相比，从改道地表水中获得补给补贴的井的硝酸盐和大肠菌水平较高，在干旱期间更容易受到供应短缺的影响。重要的是要考虑增加地表水开发对快速发展的山地流域地下水补给量和质量的影响。