Streamflow regimes that maintain vital functions and processes of aquatic ecosystems are critical to sustaining ecosystem health. In rivers with altered flow regimes, restoring components of the natural flow regime is predicted to conserve freshwater biodiversity by supporting ecological functions and geomorphological processes to which native communities are adapted. However, the effectiveness of environmental flow restoration is poorly understood because of inadequate monitoring and uncertainty in ecological responses to managed changes in specific, quantifiable aspects of the annual streamflow regime. Here, we used time series models to analyze 25 years of fish assemblage data collected before and after environmental flow implementation in a dammed river in California, USA. We examined the response of the fish community to changes in individual components of the flow regime known to support ecosystem functions. We found that as functional flow components shifted toward their predicted natural range, the quasi‐extinction risk (likelihood of population declines of >80%) decreased for the native fish assemblage. Following environmental flow implementation, observed changes toward natural ranges of dry season duration, fall pulse flow magnitude, and wet season timing each reduced quasi‐extinction risk by at least 40% for the native assemblage. However, functional flow components that shifted away from their predicted natural range, including lower spring recession flows and higher dry season baseflow, resulted in greater quasi‐extinction risk for native species. In contrast, non‐native species decreased in abundance when flow components shifted toward predicted natural ranges and increased when components shifted away from their natural range. Although most functional flow components remained outside of their natural range following environmental flow implementation, our results indicate that even moderate shifts toward a natural flow regime can benefit native and suppress non‐native fish species. Overall, this study provides the most compelling evidence to date of the effectiveness of functional environmental flows in supporting native fish recovery in a highly regulated river.

中文翻译：

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模仿自然水流状态的功能元素促进受监管河流中本地鱼类的恢复


维持水生生态系统重要功能和过程的水流状况对于维持生态系统健康至关重要。在流态改变的河流中，恢复自然流态的组成部分预计将通过支持当地社区适应的生态功能和地貌过程来保护淡水生物多样性。然而，由于对年度水流状况的具体、可量化方面的管理变化的监测不足和生态响应的不确定性，人们对环境流量恢复的有效性知之甚少。在这里，我们使用时间序列模型分析了美国加利福尼亚州一条筑坝河实施环境流量前后 25 年收集的鱼类组合数据。我们研究了鱼类群落对已知支持生态系统功能的流态各个组成部分变化的反应。我们发现，随着功能流成分向其预测的自然范围转移，本地鱼类组合的准灭绝风险（种群下降的可能性为 >80%）降低。实施环境流后，观察到旱季持续时间、秋季脉冲流强度和雨季时间自然范围的变化，使本地生物群落的准灭绝风险降低了至少 40%。然而，功能流量成分偏离了预测的自然范围，包括春季衰退流量较低和旱季基流较高，导致本地物种面临更大的准灭绝风险。相比之下，当流量成分转向预测的自然范围时，非本地物种的丰度减少；当成分偏离其自然范围时，非本地物种的丰度增加。 尽管大多数功能性水流成分在环境水流实施后仍然超出其自然范围，但我们的结果表明，即使适度转向自然水流状态也可以使本地鱼类受益并抑制非本地鱼类物种。总体而言，这项研究提供了迄今为止最令人信服的证据，证明功能性环境流在支持高度监管的河流中本地鱼类恢复方面的有效性。