Water Resources Research Act Program

Details for Project ID 2016MT301B

Impacts of river flow and temperature on salmonfly productivity and terrestrial subsidy

Institute: Montana
Year Established: 2016 Start Date: 2016-03-01 End Date: 2018-02-28
Total Federal Funds: $30,000 Total Non-Federal Funds: $83,098

Principal Investigators: Lindsey Albertson

Abstract: Water flow and temperature regimes in Montana’s rivers are shifting due to climate change, damming, and diversion for agriculture. Although a considerable amount of research has studied the impacts of these changes on fish, the impacts on aquatic insects are relatively unknown. This knowledge gap is critical for sustaining ecosystem function and productivity in Montana’s rivers because aquatic insects indicate river health, support the food web, and directly benefit the economy by serving as a draw for anglers who visit Montana to fish using aquatic insects as bait. We will use is the iconic salmonfly, Pteronarcys californica, to ask how shifting water resources related to hydrology and temperature will drive shifts in aquatic insect ecology and productivity. Pteronarcys is a large aquatic macroinvertebrate that spends the larval portion of its lifecycle within gravels on the riverbed. Pteronarcys then emerges from the water in spectacular, synchronized hatches in early summer to live the adult portion of its lifecycle in the terrestrial, riparian habitat. As it emerges from the water, Pteronarcys provides a significant food pulse to fish, birds, and other animals, making it a particularly important indicator organism for the impacts of shifting water resources on biomass production across the land-water interface. Water discharge levels and temperature are important cues that initiate Pteronarcys emergence. In snowmelt-fed rivers, reduced snowpack levels and warmer spring temperatures are shifting peak discharge to occur earlier in spring, leading to periods of low- and warm-flows in the late summer. These changes have strong implications for both the aquatic larval and terrestrial adult life stages of insects that inhabit rivers, with important implications for the food web, fishing, and productivity of terrestrial-aquatic linkages. We hypothesize that changes to snowmelt are shifting when adult Pteronarcys are hatching. Additionally, larvae that over-summer are likely experiencing low- and warm-flows, but no research has addressed how altered late summer flows might affect growth, feeding strategies, and mortality of Pteronarcys larvae. We will document Pteronarcys densities, emergence timing, and productivity in two Montana rivers and link ecological factors to shifting water resources using a combination of field surveys and laboratory experiments to explore how water temperature and low-flow regimes influence Pteronarcys populations. In 2016-2017, present-day densities and emergence timing dates on the Madison and Gallatin Rivers will be compared to those from the past five decades using historical datasets and time-series analysis. We will couple these analyses of natural Pteronarcys populations with detailed experiments at Bozeman’s U.S. Fish and Wildlife Service Fish Technology Center (FTC) to investigate how water temperature and low-flow mechanistically affect Pteronarcys growth, feeding habits, and mortality using temperature controlled experimental mesocosms. These approaches will allow us to evaluate the status of Pteronarcys populations in two Montana rivers and demonstrate whether temperature and water flow are likely to drive shifts in Pteronarcys ecology. These aquatic insects are particularly sensitive to changes in the availability of snowmelt runoff, and a complete understanding of water resources allocated to and managed for freshwater biota will benefit substantially from including aquatic insects.