Center for Watershed Sciences, University of California Davis, Davis, California, USA.
California Department of Fish and Wildlife, West Sacramento, California, USA.
Ecol Appl. 2024 Sep;34(6):e3013. doi: 10.1002/eap.3013. Epub 2024 Jul 14.
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.
维持水生生态系统重要功能和过程的水流状态对于维持生态系统健康至关重要。在水流状态发生改变的河流中，恢复自然水流状态的组成部分被预测可以通过支持生态功能和地貌过程来保护淡水生物多样性，这些生态功能和地貌过程是本地群落适应的。然而，由于对具体、可量化的年度水流状态方面的管理变化的生态响应监测不足和不确定性，环境水流恢复的效果仍不清楚。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座大坝河流在实施环境水流前后 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水流状态个别组成部分变化的响应。我们发现，随着功能水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（种群下降超过 80%的可能性）降低。在实施环境水流之后，观察到的旱季持续时间、秋季脉冲流量幅度和湿季时间向自然范围的变化，使本地组合的准灭绝风险至少降低了 40%。然而，向其自然范围偏离的功能水流成分，包括春季退水流量较低和旱季基流较高，导致本地物种的准灭绝风险增加。相比之下，当水流成分向其自然范围转移时，非本地物种的数量减少，而当水流成分偏离其自然范围时，非本地物种的数量增加。尽管在实施环境水流之后，大多数功能水流成分仍处于其自然范围之外，但我们的研究结果表明，即使是向自然水流状态的适度转变也可以有利于本地鱼类的恢复并抑制非本地鱼类的生长。总体而言，这项研究提供了迄今为止最有力的证据，证明功能环境水流在高度调节的河流中支持本地鱼类恢复的有效性。
