School of Life Sciences, Arizona State University, Tempe, Arizona 85287, USA.
Ann N Y Acad Sci. 2012 Feb;1249:227-46. doi: 10.1111/j.1749-6632.2011.06411.x. Epub 2012 Feb 13.
This paper was motivated by the 25th anniversary of the publication of Marc Reisner's book, Cadillac Desert: The American West and its Disappearing Water. Dams are ubiquitous on rivers in the United States, and large dams and storage reservoirs are the hallmark of western U.S. riverscapes. The effects of dams on downstream river ecosystems have attracted much attention and are encapsulated in the serial discontinuity concept (SDC). In the SDC, dams create abrupt shifts in continua of downstream changes in physical and biotic properties. In this paper, we develop a framework for understanding how channel geometry and network structure influence how the physical components of habitat and the biota rebound from discontinuities set up by large dams. We apply this framework to data describing the flow regime, temperature, sediment flux, and fish community composition below Garrison Dam on the Missouri River, Glen Canyon Dam on the Colorado River, and Flaming Gorge Dam on the Green River. Sediment flux in dam tailwaters is under strong control by channel geometry. By contrast, dam-related changes in temperature and flow variation are not significantly modulated by channel geometry or tributary inputs if flow volumes are small (Missouri and Colorado River tributaries). Instead, small tributaries provide near-native conditions (flow and temperature variation) and, as such, provide key refuges for biota from novel habitats in mainstem rivers below large dams. Unregulated tributaries that are large relative to their respective mainstem (e.g., Yampa River) provide refuges as well as significant amelioration of flow and temperature effects from upstream dams. Finally, the proportion of native fish increases with distance from dam and exhibits sharp increases near tributary junctions. These results suggest that tributaries-even minor ones in terms of relative discharge-act as key refugia for native species in regulated river networks. Moreover, large, unregulated tributaries are key to restoring continuity in physical habitat and the biota in large regulated rivers.
本文的灵感来源于马克·赖斯纳（Marc Reisner）的著作《凯迪拉克沙漠：美国西部及其消失的水》出版 25 周年。在美国的河流上，大坝无处不在，而大型水坝和水库则是美国西部河流景观的标志。大坝对下游河流生态系统的影响引起了广泛关注，并被概括为连续不连续性概念（SDC）。在 SDC 中，大坝在物理和生物特性的连续变化中造成了突然的转变。在本文中，我们提出了一个框架，用于理解河道几何形状和网络结构如何影响栖息地的物理组成部分和生物区系从大型水坝造成的不连续中恢复。我们将该框架应用于描述密苏里河上的加里森大坝、科罗拉多河上的格伦峡谷大坝和绿河上的火烈鸟峡大坝下游的水流状态、温度、泥沙通量和鱼类群落组成的数据。大坝尾部的泥沙通量受河道几何形状的强烈控制。相比之下，如果流量较小（密苏里河和科罗拉多河的支流），则与大坝相关的温度和流量变化不会受到河道几何形状或支流输入的显著调节。相反，小支流提供了接近自然的条件（水流和温度变化），因此为大型水坝下游干流中的生物提供了重要的避难所。相对于其各自的干流而言较大的未调节支流（例如扬帕河）提供了避难所，并显著减轻了上游大坝对水流和温度的影响。最后，原生鱼类的比例随着与大坝的距离而增加，并在支流交汇处附近急剧增加。这些结果表明，支流——即使从相对流量来看是较小的支流——在受调节的河流网络中也是本地物种的关键避难所。此外，大的、未调节的支流是恢复大型受调节河流中物理栖息地和生物连续性的关键。
