Watershed Symposium 2019

Watershed-Scale Nutrient Budgets and eDNA Following a Utah Megafire

Summary:
In late 2018 a wildfire burned over 600 square kilometers in Utah County. We are collecting water samples and have high-frequency chemistry stations to study the sediment and nutrient budgets of burned and unburned watersheds. We use this information to assess rate of ecosystem recovery following wildfire and potential implications for Utah Lake.

Full Abstract:
Wildfire in western forests can substantially restructure water flow through soil, groundwater, and river networks. These changes, along with disturbance of terrestrial and aquatic habitat can affect carbon and nutrient budgets with consequences for downstream reservoirs and lakes. The overall amount of runoff following a fire as well as its water quality are of great interest for the Wasatch Front and other rapidly growing urban areas in semi-arid ecosystems. Here, we report the initial results of a replicated observational study of watersheds in and around the 2018 Pole Creek Fire Complex. This “megafire” covered broad gradients of elevation, vegetation type, and human management, offering a unique opportunity to identify ecological factors and best management practices to protect wildlife habitat and watershed resources. With support from the Utah Department of Natural Resources, we instrumented 24 watersheds with flow and water chemistry sensors. These stations collected high-frequency pH, temperature, conductivity, oxygen, turbidity, and redox potential measurements, allowing quantification of snowmelt and periodic extreme precipitation event pulses, when most of the lateral flux occurs. We also collected weekly to monthly water samples from ~80 watersheds, which we analyzed for a broad suite of chemical and optical parameters. We analyzed these data to assess the role of wildfire extent and severity in determining a watershed’s ecohydrological signature and to explore ecological covariates including elevation, aspect, vegetation type, and watershed size. There were extreme and persistent differences in sediment transport and nutrient dynamics, which differed based on catchment characteristics. The burned catchments experienced repeated debris flows in the year following the fire, which disrupted aquatic life but also created new habitat, particularly in previously degraded reaches. We discuss the challenges and opportunities of high-frequency monitoring networks and more broadly the implications of increased megafires for water availability and aquatic habitat in Utah.