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David Walters

Research Ecologist

Contact Info

Short Biography

Ph.D. Ecology, University of Georgia (UGA), 2002.

M.S. Conservation Ecology, UGA, 1997.

B.A. Anthropology, UGA, 1991.

I have been a research ecologist with USGS since 2008.  Prior to that, I was an ecologist for the US EPA, National Exposure Research Laboratory for 6 years.  I am a freshwater ecologist with broad training in stream ecology, human impacts on aquatic ecosystems, and ecotoxicology.  Current research topics include food webs and contaminant flux, aquatic-riparian linkages, stream fish ecology, land use and climate change, and invasive species.  I currently lead the Aquatic Ecology and Contaminants Team at the Fort Collins Science Center.  Our team investigates various human impacts to aquatic and riparian systems using field studies, manipulative experiments, and modeling.

Examples of Current Projects

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.

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Journal Articles and Book Chapters

Kraus, J.M., J. Pomeranz, A. Todd, D.M. Walters, R.B. Wanty, and T.S. Schmidt. In Press. Aquatic pollution increases use of terrestrial prey subsidies by stream fish. Journal of Applied Ecology.  DOI: 10.1111/1365-2664.12543.

Walters, D.M. E.J. Rosi-Marshall, T. A. Kennedy, W.F. Cross, and C.V. Baxter.  2015. Mercury and selenium accumulation in the Colorado River food web, Grand Canyon, USA. Environmental Toxicology and Chemistry. 34:2385-2394.

Wanty, R.B., L.S. Balistrieri, J.S. Wesner, D.M. Walters, F. Podda, G.De Giudici, C. Stricker, T.S. Schmidt, J.M. Kraus, P. Lattanzi, R.E. Wolf, and R. Cidu. 2015. What zinc isotopes might tell us about biological uptake in systems contaminated with heavy metals.  Procedia Earth and Planetary Sciences 13:60-63.

Walters, D.M., D.F. Raikow, C.R. Hammerschmidt, M.G. Mehling, A. Kovach, and J.T. Oris. 2015. Methylmercury bioaccumulation in stream food webs declines with increasing primary production. Environmental Science and Technology. 49:7762-7769.

Glotzbecker, G.J., J.L. Ward, D.M. Walters and M. J. Blum. 2015. Turbidity alters female choice and increases male courtship effort between native and invasive riverine fishes.  Freshwater Biology. 60:1784-1793.

Wohl, E., B.P. Bledsoe, R.B. Jacobson, N.L. Poff, S.L. Rathburn, D.M. Walters, and A.C. Wilcox.  2015. The natural sediment regime in rivers: broadening the foundation for ecosystem management.  BioScience 65:358-371.

Wesner, J.S., J.M. Kraus, T.S. Schmidt, D.M. Walters, and W.H. Clements. 2014.  Metamorphosis enhances the effects of metal exposure on the mayfly, Centroptilum triangulifer. Environmental Science and Technology 48:10415-10422.

Kraus J.M., D.M. Walters, J.S. Wesner, C.A. Stricker, T.S. Schmidt, and R.E. Zuellig. 2014.  Metamorphosis in insects alters risk of contaminant exposure in food webs. Environmental Science and Technology 48:10957-10965.

Kraus, J.M., T.S., Schmidt, D.M. Walters, R.B. Wanty, R.E.  Zuellig, and R.E. Wolf.  2014. Cross-ecosystem impacts of pollution: stream metals reduce contaminant and resource flux to terrestrial food webs. Ecological Applications 24:235-243.

Walters, D.M., R.E. Zuellig, H.J. Crockett, J.F. Bruce, P.M. Lukacs, and R.M. Fitzpatrick. 2014. Barriers impede upstream spawning migration of flathead chub. Transactions of the American Fisheries Society 143:17-25.

Nietch, C.T., E.L. Quinlan, J.M. Lazorchak, C.A. Impelliteri, D.F. Raikow, and D.M. Walters. 2013. Effects of a chronic lower range of triclosan exposure to a stream mesocosm community. Environmental Toxicology and Chemistry 32:2874-2287.

Schmidt, T.S., J.M. Kraus, D.M. Walters, R.B. Wanty, and W.H. Clements. 2013. Emergence flux declines disproportionately to larval density along a stream metals gradient. Environmental Science and Technology 47:8784-8792.

Dang, V.D., D.M. Walters, and C.M. Lee.  2013. Assessing ongoing sources of dissolved phase polychlorinated biphenyls (PCBs) in a contaminated stream. Environmental Toxicology and Chemistry 32:535-540.

Ward, J.L. M. J. Blum, D.M. Walters, N.M. Burkhead, B.J. Freeman, and B.A. Porter. 2012. Discordant introgression in a rapidly expanding hybrid swarm.  Evolutionary Applications 5:380-392.

Dang, V.D., D.M. Walters, and C. M Lee. 2012. Historical changes in polychlorinated biphenyls (PCBs) contaminated sediments in Twelvemile Creek, South Carolina (USA). American Journal of Environmental Science 8:11-15.

Blum, M., Bagley, M., Walters, D. M., Jackson, S., Chaloud, D. and Cade, B.S. 2012. Genetic diversity and species diversity of stream fishes covary with habitat and land use across a glaciation boundary. Oecologia 168:93-95.

Angradi, T.R., D.W. Bolgrien, T.M. Jicha, M.F. Moffett, M.S. Pearson, D.L. Taylor, J.M. Lazorchak, D.M. Walters,  B.H. Hill, K.A. Blocksom, C.M. Elonen, L.E. Anderson, and T.P. Hollenhorst. 2011. An assessment of stressor extent and biological condition in the North American Mid-continent great rivers (USA). River Systems 19/2:143-163.

Walters, D.M. M.A. Mills, B.S. Cade, and L.P. Burkhard.  2011. Trophic magnification of PCBs and its relationship to the octanol-water partition coefficient.  Environmental Science and Technology 45:3917-3924.

Raikow, D.F., Walters, D.M., K.M. Fritz, and M.A. Mills. 2011. The distance that contaminated aquatic subsidies extend into lake riparian zones. Ecological Applications 21:983-990.

Walters, D.M., K.A. Blocksom, J.M. Lazorchak, T.M. Jicha, T.R. Angradi, and D.W. Bolgrien. 2010. Mercury contamination in fish in mid-continent great rivers of the United States: Importance of species traits and environmental factors.  Environmental Science and Technology 44:2947-2953.

Blum, M., D.M. Walters, N.M. Burkhead, B.J. Freeman, and B.A. Porter. 2010. Reproductive isolation and the expansion of an invasive hybrid swarm. Biological Invasions 12:2825-2836.

Dang, V.D., D.M. Walters, and C. M Lee. 2010Transformation of chiral polychlorinated biphenyls (PCBs) in a stream food web. Environmental Science and Technology 44:2836-2841.

Walters, D.M., M.A. Mills, K.M. Fritz, and D.F. Raikow.  2010.  Spider-mediated flux of PCBs from contaminated sediments to terrestrial ecosystems and potential risks to arachnivorous birds. Environmental Science and Technology 44:2849-2856.

Blocksom, K.A., D.M. Walters, T.M. Jicha, J.M. Lazorchak, T.R. Angradi, and D.W. Bolgrien.  2010.  Persistent organic pollutants in fish tissue in the mid-continental great rivers of the United States.  Science of the Total Environment 408:1180-1189.

Walters, D.M., A.H. Roy, and D.S. Leigh. 2009.  Environmental indicators of macroinvertebrate and fish assemblage integrity in urbanizing watersheds. Ecological Indicators 9:1222-1233.

Rashleigh, B., M.C. Barber, and D.M. Walters. 2009. Foodweb modeling for polychlorinated biphenyls (PCBs) in the Twelvemile Creek Arm of Lake Hartwell, South Carolina, USA. Ecological Modelling 220:254-264.

Johnson, B.R., K.M. Fritz, K.A. Blocksom, and D.M. Walters. 2009. Larval salamanders and channel geomorphology are indicators of hydrologic permanence in forested headwater streams.  Ecological Indicators 9:150-159.

Walters, D.M., K.M. Fritz, and R. Otter.  2008. The dark side of subsidies: Adult stream insects export organic contaminants to riparian predators. Ecological Applications 18:1835-1841.

Fritz, K.M., B.R. Johnson, and D.M. Walters. 2008. Environmental indicators of hydrologic permanence in forested headwater streams. Journal of the North American Benthological Society 27:690-704.

Walters, D.M., M. Blum, B. Rashleigh, B.J. Freeman, B.A. Porter, N.M. Burkhead. 2008. Red shiner invasion and hybridization with blacktail shiner in the upper Coosa River, USA. Biological Invasions 10:1229-1242.

Rybczynski, S.M., D.M. Walters, K.M. Fritz, and B.R. Johnson. 2008. Comparing the trophic position of stream fishes using stable isotope and gut contents analyses. Ecology of Freshwater Fish 17:199-206.

Walters, D.M. K.M. Fritz, B.R. Johnson, J.M. Lazorchak, and F.H. McCormick. 2008. Influence of trophic position and spatial location on polychlorinated biphenyl (PCB) bioaccumulation in a stream food web. Environmental Science and Technology 42:2316-2322.

Walters D.M., et al. 2007. Reach-scale geomorphology affects organic matter and consumer δ13C in a forested Piedmont stream. Freshwater Biology. 52:1105-1119.

Walters, D.M., D.S. Leigh, M.C. Freeman, B.J. Freeman, and C.M. Pringle. 2005. Effect of urbanization on fish assemblages and habitat quality in a Piedmont river basin. Pages 69-86 in Brown, L. R., R. M. Hughes, R. Gray, and M. R. Meador (eds), Effects of Urbanization on Stream Ecosystems. AFS, Symposium 47, Bethesda, Maryland.

Walters, D.M., D.S. Leigh, and A.B. Bearden. 2003. Urbanization, sedimentation, and the homogenization of fishes in the Etowah River Basin, Georgia Piedmont, USA. Hydrobiologia 494:5-10.

Walters, D.M., D.S. Leigh, M.C. Freeman, B.J. Freeman, and C.M. Pringle. 2003. Geomorphology and fish assemblages in a Piedmont river basin, USA. Freshwater Biology 48:1950-1970.

Walters, D.M. and B.J. Freeman. 2000. Distribution of Gambusia (Poeciliidae) in a southeastern river system and the use of fin ray counts for species identification. Copeia 2000(2):555-559.



My Science Topics

Science Topic
Ecology and Environmentaquatic ecosystems
Ecology and Environmentbenthic ecosystems
Ecology and Environmentbiodiversity
Ecology and Environmentecosystems
Ecology and Environmentenvironmental assessment
Ecology and Environmentfreshwater ecosystems
Ecology and Environmenthabitat alteration

My USGS Science Strategy Areas

Understanding Ecosystems & Predicting Ecosystems Change

The Role of Environment and Wildlife in Human Health

Climate Variability & Change

Aquatic Ecosystems and Contaminants

Image of Current Focus for Aquatic Ecosystems and Contaminants

My research focuses on three broadly related themes, human impacts on aquatic ecosystems, food webs, and aquatic-riparian linkages. A common goal of this research is to separate natural and anthropogenic sources of variation influencing the characteristics of aquatic habitats and their assemblages. In doing so, I focus on identifying the relationships among landscapes, habitat, water quality, and biological communities and how these relationships are altered by various stressors such as land use change, invasive species, dams, and contaminants.  In recent years my research has expanded to investigate interactions between native and invasive fishes, the flux of contaminants through aquatic and riparian food webs, and contaminant effects on aquatic-riparian linkages. Virtually every aspect of my research benefits through collaboration with other specialists including geomorphologists, engineers, hydrologists, toxicologists, biogeochemists, geneticists, and modelers.

Contact Information

David Walters
2150 Centre Avenue Bldg C
Fort Collins, CO 80526
970-226-9230 - Fax
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