Department of Environmental Science, Policy, and Management, University of California, Berkeley, Berkeley, CA, USA.
National Socio-Environmental Synthesis Center (SESYNC), University of Maryland, Annapolis, MD, USA.
Glob Chang Biol. 2018 Aug;24(8):3749-3765. doi: 10.1111/gcb.14133. Epub 2018 Apr 17.
Novel flow regimes resulting from dam operations and overallocation of freshwater resources are an emerging consequence of global change. Yet, anticipating how freshwater biodiversity will respond to surging flow regime alteration requires overcoming two challenges in environmental flow science: shifting from local to riverscape-level understanding of biodiversity dynamics, and from static to time-varying characterizations of the flow regime. Here, we used time-series methods (wavelets and multivariate autoregressive models) to quantify flow-regime alteration and to link time-varying flow regimes to the dynamics of multiple local communities potentially connected by dispersal (i.e., a metacommunity). We studied the Chattahoochee River below Buford dam (Georgia, U.S.A.), and asked how flow regime alteration by a large hydropower dam may control the long-term functional trajectory of the downstream invertebrate metacommunity. We found that seasonal variation in hydropeaking synchronized temporal fluctuations in trait abundance among the flow-altered sites. Three biological trait states describing adaptation to fast flows benefitted from flow management for hydropower, but did not compensate for declines in 16 "loser" traits. Accordingly, metacommunity-wide functional diversity responded negatively to hydropeaking intensity, and stochastic simulations showed that the risk of functional diversity collapse within the next 4 years would decrease by 17% if hydropeaking was ameliorated, or by 9% if it was applied every other season. Finally, an analysis of 97 reference and 23 dam-affected river sites across the U.S. Southeast suggested that flow variation at extraneous, human-relevant scales (12-hr, 24-hr, 1-week) is relatively common in rivers affected by hydropower dams. This study advances the notion that novel flow regimes are widespread, and simplify the functional structure of riverine communities by filtering out taxa with nonadaptive traits and by spatially synchronizing their dynamics. This is relevant in the light of ongoing and future hydrologic alteration due to climate non-stationarity and the new wave of dams planned globally.
新的水流模式是由大坝运行和淡水资源的过度分配造成的，这是全球变化带来的一种新的后果。然而，要预测淡水生物多样性对汹涌的水流模式变化的反应，需要克服环境水流科学中的两个挑战：从局部水平到河流景观水平理解生物多样性动态，以及从静态到时间变化的水流模式特征。在这里，我们使用时间序列方法（小波和多元自回归模型）来量化水流模式的变化，并将时变水流模式与多个可能通过扩散（即集合群落）连接的局部群落的动态联系起来。我们研究了美国佐治亚州布福德大坝下游的查塔胡奇河，并询问大型水电站大坝造成的水流模式变化如何控制下游无脊椎动物集合群落的长期功能轨迹。我们发现，水力发电造成的水锤峰值季节性变化使受水流影响的地点之间的特征丰度的时间波动同步。描述适应快速水流的三种生物特征状态受益于水力发电的水流管理，但不能弥补 16 种“输家”特征的下降。因此，集合群落的功能多样性对水锤峰值强度呈负响应，随机模拟表明，如果水锤峰值得到改善，在未来 4 年内功能多样性崩溃的风险将降低 17%，如果每隔一个季节应用水锤峰值，风险将降低 9%。最后，对美国东南部 97 个参考点和 23 个受大坝影响的河流点的分析表明，在受水电站影响的河流中，在与人类相关的尺度（12 小时、24 小时、1 周）上的水流变化相对常见。这项研究提出了一个观点，即新的水流模式是普遍存在的，通过过滤掉非适应性特征的分类单元，并通过空间同步它们的动态，简化了河流群落的功能结构。鉴于气候非稳定性和全球计划建造的新一波大坝带来的持续和未来的水文变化，这一点很重要。
