David Walters, PhD

David has been a research ecologist with the USGS since 2008. Prior to that, he was an ecologist for the U.S. EPA, National Exposure Research Laboratory for 6 years. He is a freshwater ecologist with broad training in stream ecology, human impacts on aquatic ecosystems, and ecotoxicology. His current research topics include food webs and contaminant flux, aquatic-riparian linkages, stream fish ecology, land use and climate change, and invasive species. 

Current Projects/Areas of Interest

• Riparian indicators of contaminant exposure at Great Lakes Areas of Concern (AOCs) 
  We are investigating contaminant flux from aquatic to nearby terrestrial (riparian) shoreline habitats. In particular we use riparian spiders (many of which feed almost exclusively on adult aquatic insects) to characterize contamination at these sites and to evaluate the effectiveness of their remediation. 
• Leaky rivers: Nutrient retention and productivity in Rocky Mountain streams under alternative stable states
  This project investigates how the volume of wood and log jams have declined in Rocky Mountain streams since European settlement, how the loss of wood affects stream geomorphology, communities, nutrient cycling, and productivity, and what management actions can be taken to restore lost ecosystem functions.
• Mechanisms for metal uptake and trophic transfer in stream and riparian food webs in mineralized landscapes
  We are investigating how metals in streams (derived from natural geologic sources as well as mines) are transferred from streams to riparian zones and how this contamination alters ecological linkages between these systems.  This work combines large-scale field studies with mesocosm experiments to better understand processes driving the patterns we observe in nature. 
• “Metal webs” for the Grand Canyon 
  We are developing quantitative food webs to measure metal flux (mercury, selenium, and other trace metals) in the Colorado and Little Colorado rivers in Grand Canyon.  These studies will identify key pathways of metal exposure to important fish species, such as the endangered humpback chub. 
• Consequences of climate change for alpine lake-stream networks and native fishes in the southern Rocky Mountains 
  This project investigates the importance of alpine lakes in the ecology of native cutthroat trout and how lakes could mitigate the negative effects of rising temperatures on these threatened populations.