Surface-water hydrodynamics and regimes of a small mountain stream-take ecosystem

The hydrology of streams and takes has been well. studied as separate ecosystems; however, the behavior and implications of hydrologic linkages between these ecosystems have been little considered. We analyzed the surface-water hydrodynamics of a stream-take ecosystem for 3 years in the Sawtooth Mountains, Idaho, USA to understand how this coupled aquatic ecosystem behaved hydrologically. This analysis included quantifying streamflow regimes above and below the take, the expansion and contraction of the Lake, stream, and floodplain, and downstream responses to snowmelt and rainstorm events. Our results showed that flow regime metrics from both hydrology and ecology were similar between above and betow-lake reaches, but analysis that considered channel capacity and overbank flooding showed 2x more frequent and > 5x longer duration floods below the take compared to upstream reaches. The take surface area expanded by as much as 19% during snowmelt runoff because of a 0.5 m rise in the take level, and the Littoral zone expanded by an even greater proportion. The take had little influence on peakflows during spring snowmelt, though the inlet stream in the delta had a reduced flood magnitude compared to upstream stations. However, during large summer rainstorms when potential storage capacity was maximized, the take strongly attenuated peakflows downstream from the take. Water level changes at seven other stream-take ecosystems in the region showed a similar range of variation. Our results provide a case study of how coupled aquatic ecosystems behave hydrodynamically and underscore the need to consider the hydrologic connections and interactions that drive aquatic ecosystems. (c) 2006 Elsevier B.V. All rights reserved.