Water Resources Research Act Program

Details for Project ID 2019MT151B

Assessing the costs and benefits of beaver dam analogs to create resilience to climate change for aquatic ecosystems

Institute: Montana
Year Established: 2019 Start Date: 2019-06-01 End Date: 2020-05-31
Total Federal Funds: $15,000 Total Non-Federal Funds: $29,999

Principal Investigators: Lisa Eby

Abstract: The removal of beaver from the North American landscape has been a contributor to increased stream channel incision and loss of connection between stream channels and their floodplains. These geomorphic changes lead to a landscape with lower water storage, lower base flows, and warmer water temperatures. In response to a warming climate, managers in the western US are increasingly using Beaver Dam Analogs (BDAs) as a technique for restoring streams. The changes that result from these human made dams created from natural materials are apparent, as they reconnect streams to their floodplains and increase water storage. Less well established are the other changes in ecosystems that result from BDAs, including: changes in discharge and stream temperature; nutrient and carbon stocks and fluxes; fish habitat quality, fish assemblages, and fish movement. Depending on the nature and balance of these ecosystem level changes, BDAs could provide additional benefits to watersheds or negative impacts. For example, by increasing organic matter retention it increases resources available at the base of the food web. To the extent that such structures retain nutrients, it could argue for the expansion of the use of BDAs for mitigating potential nutrient impairments on working landscapes. However, there are also concerns about whether these structures may also do more harm than good for native trout in western Montana where these structures and subsequent beaver establishment are occurring in a novel landscape with lower base flows, in a climate with warmer temperatures, and with ubiquitous nonnative species. In many western Montana systems, the resulting slower, more complex habitat may facilitate exotic brook trout over native cutthroat trout or provide slower water and vegetation for exotic northern pike—a voracious predator on eastern Montana native minnow communities. A better understanding of both the effects of BDAs on ecosystem processes and their interactions with fish and their habitat will help resolve concerns and identify where to focus efforts to meet watershed and native trout conservation goals for more efficient and effective management. To examine the ecosystem effects of BDAs, we will use a BACI (before, after, control, impact) design on at least four paired Montanan streams. Such a design allows the paired streams to be studied before and after one stream in each pair receives an impact (BDA installation) allowing us to discern the effects of the BDA as distinguished from temporal variability. Installation will be done in collaboration with the US Forest Service - Lolo National Forest, the Clark Fork Coalition, and National Wildlife Federation. In each stream, we will evaluate discharge, stream temperature, nutrient and carbon pools and fluxes, fish habitat quality, as well as fish assemblage composition and movement. This will allow us to test whether BDAs will: increase late summer flows; buffer extremes in seasonal temperatures and reduce maximum temperatures downstream of the installation; increase nutrient and carbon retention and processing; change stream habitat characteristics such as habitat types (pool, riffle, etc.), substrate composition, large woody debris, bank erosion, and incisement; result in an increase in fish abundances and growth rates, shift in species composition to be dominated by exotic fish; allow fish to pass at higher flows but provide resistance to movement at lower flows. This will be a broad experimental framework for expanding our understanding of BDAs for this region, and we expect it to lead to additional interdisciplinary synergies to evaluate a wide array of potential changes to the system.