Beaver-Mediated Ponds Provide Cold Water Refugia in a Degraded Desert Stream

Authors: Melody Feden, Howard Whiteman

Year: 2018

Abstract

Temperature is one of the most important habitat parameters for freshwater organisms. Water temperature can limit growth, reproduction, and the distribution of aquatic species. In some areas, climate change is increasing air temperature and reducing snowpack, resulting in an increased need for cold water refugia in stream ecosystems. In the last few decades the North American beaver (Castor canadensis), once almost completely extirpated from the United States, has seen population increases due to decreased trapping and a changing narrative about their importance to stream ecosystems. Yet, there is still a lack of understanding of how beaver dam building activities affect stream temperature dynamics. In this study, I tested the hypothesis that beaver ponds decrease stream temperatures more than riffle habitat. In addition, I investigated whether beaver ponds stratify and create cold water refugia. Research was conducted in Kimball Creek, a third order stream in the Colorado River basin. At 1800m in elevation, it is considered a high desert ecosystem that gets approximately 10 inches of precipitation per year and is degraded because of current and historic cattle grazing and agricultural activities. Kimball Creek has a dense beaver population with approximately 20 dams per stream kilometer. To investigate the effects of beaver pond habitats on stream temperature, I choose 10 beaver ponds with 10 corresponding riffle habitats of similar length, and installed temperature loggers at the inflow and the outflow of each habitat. In seven of the beaver ponds, I installed temperature loggers at the deepest point of the pond, with 2-3 loggers spaced equally from the bottom to the top of the water column. Preliminary results indicate that beaver ponds do not increase stream temperature more than riffle habitats and that they do create cold water refugia that differs from the surface temperature by up to 5?. These beaver-mediated cold water refugia could allow for greater survivability and species distribution for cold water species in desert aquatic ecosystems.