Designing flow regimes to support entire river ecosystems

Overcoming the physical limits of dam operations under nonstationarity will require creative approaches to flow management and modeling approaches that forecast the effects of management actions on multiple ecosystem components simultaneously. Using a novel multispecies modeling approach, we investigated the cross-ecosystem effects of environmental flow regimes designed for specific ecosystem outcomes. We reveal tradeoffs associated with flow regimes targeting riparian vegetation, fishes, and invertebrates. The different frequencies associated with each flow regime in some cases caused non-target ecosystem components to become locally extirpated within 50 years. By incorporating multiple flow frequencies, the natural flow regime enabled a balanced but sub-optimal response of the three ecosystem components (mean 72% of designer flow). Although returning to a natural flow regime may not be possible in highly managed rivers, novel flow regimes must incorporate diverse frequencies inherent to such a regime and accomodate the sometimes conflicting requirements of different taxa at different times.