David Walters, PhD
Dr. David Walters is a Supervisory Research Ecologist at the Columbia Environmental Research Center.
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.
Education and Certifications
Ph.D. Ecology, University of Georgia (UGA), 2002
M.S. Conservation Ecology, UGA, 1997
B.A. Anthropology, UGA, 1991
Science and Products
Food web controls on mercury fluxes and fate in the Colorado River, Grand Canyon
Contaminant subsidies to riparian food webs in Appalachian streams impacted by mountaintop removal coal mining
Thermal variability drives synchronicity of an aquatic insect resource pulse
Lotic freshwater: Rivers
The natural wood regime in rivers
Pulsed salmonfly emergence and its potential contribution to terrestrial detrital pools
A diverse suite of pharmaceuticals contaminates stream and riparian food webs
Riparian spiders indicate the magnitude and sources of polychlorinated biphenyl (PCB) contamination at a large contaminated sediment site
Shifting stream planform state decreases stream productivity yet increases riparian animal production
Importance of growth rate on mercury and polychlorinated biphenyl bioaccumulation in fish
Chronic wasting disease—Status, science, and management support by the U.S. Geological Survey
Holy flux: Spatial and temporal variation in massive pulses of emerging insect biomass from western U.S. rivers
Non-USGS Publications**
**Disclaimer: The views expressed in Non-USGS publications are those of the author and do not represent the views of the USGS, Department of the Interior, or the U.S. Government.
Science and Products
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Food web controls on mercury fluxes and fate in the Colorado River, Grand Canyon
Mercury (Hg) biomagnification in aquatic food webs is a global concern; yet, the ways species traits and interactions mediate these fluxes remain poorly understood. Few pathways dominated Hg flux in the Colorado River despite large spatial differences in food web complexity, and fluxes were mediated by one functional trait, predation resistance. New Zealand mudsnails are predator resistant and a tAuthorsDavid Walters, Wyatt F. Cross, Theodore Kennedy, Colden V. Baxter, R. O. Hall, Emma J. RosiContaminant subsidies to riparian food webs in Appalachian streams impacted by mountaintop removal coal mining
Selenium is highly elevated in Appalachian streams and stream organisms that receive alkaline mine drainage from mountaintop removal coal mining compared to unimpacted streams in the region. Adult aquatic insects can be important vectors of waterborne contaminants to riparian food webs, yet pathways of Se transport and exposure of riparian organisms are poorly characterized. We investigated Se conAuthorsLaura C. Naslund, Jacqueline R. Gerson, Alexander C. Brooks, David Walters, Emily S. BernhardtThermal variability drives synchronicity of an aquatic insect resource pulse
Spatial heterogeneity in environmental conditions can prolong food availability by desynchronizing the timing of ephemeral, high‐magnitude resource pulses. Spatial patterns of water temperature are highly variable among rivers as determined by both natural and anthropogenic features, but the influence of this variability on freshwater resource pulse phenology is poorly documented. We quantified waAuthorsHeidi E. Anderson, Lindsey K. Alberson, David WaltersLotic freshwater: Rivers
Ecosystems associated with rivers are intricately connected to their entire watershed. The river ecosystem includes the channel of active water flow, floodplain, and riparian and hyporheic zones. This ecosystem is shaped by interactions among the natural flow of water, sediments within the river and entering the river, and large wood regimes within the riparian zone. River integrity describes theAuthorsEllen Wohl, R. O. Hall, David WaltersThe natural wood regime in rivers
The natural wood regime forms the third leg of a tripod of physical processes that supports river science and management, along with the natural flow and sediment regimes. The wood regime consists of wood recruitment, transport, and storage in river corridors. Each of these components can be characterized in terms of magnitude, frequency, rate, timing, duration, and mode. We distinguish the naturaAuthorsEllen Wohl, Natalie Kramer, Virgina Ruiz-Villanueva, Daniel Scott, F. Comiti, Angela M Gurnell, Hervé Piégay, Katherine B. Lininger, Kristin Jaeger, David Walters, Kurt D. FauschPulsed salmonfly emergence and its potential contribution to terrestrial detrital pools
Adult aquatic insects are a globally important subsidy in terrestrial food webs. However, our understanding of their importance is largely limited to studies that measure predation of live insects by terrestrial predators. Yet the flux of adult aquatic insects to terrestrial detrital pools may also be an important subsidy pathway, particularly in cases where insect production exceeds the consumptiAuthorsJeff Wesner, David Walters, Robert E. ZuelligA diverse suite of pharmaceuticals contaminates stream and riparian food webs
A multitude of biologically active pharmaceuticals contaminate surface waters globally, yet their presence in aquatic food webs remain largely unknown. Here, we show that over 60 pharmaceutical compounds can be detected in aquatic invertebrates and riparian spiders in six streams near Melbourne, Australia. Similar concentrations in aquatic invertebrate larvae and riparian predators suggest directAuthorsErinn K. Richmond, Emma J. Rosi, David M. Walters, Jerker Fikk, Stephen K. Hamilton, Tomas Brodin, Anna Sundelin, Michael R. GraceRiparian spiders indicate the magnitude and sources of polychlorinated biphenyl (PCB) contamination at a large contaminated sediment site
We investigated PCB contamination at the Ashtabula River Area of Concern (AOC) following remedial dredging using araneid and tetragnathid spiders. PCB concentrations remain elevated in the AOC compared to reference conditions. Patterns of contamination were strikingly similar between taxa, but were higher in tetragnathids at the most contaminated sites. Spider PCB homolog distributions identifiedAuthorsDavid M. Walters, Ryan R. Otter, Johanna M. Kraus, Marc A. MillsShifting stream planform state decreases stream productivity yet increases riparian animal production
In the Colorado Front Range (USA), disturbance history dictates stream planform. Undisturbed, old-growth streams have multiple channels and large amounts of wood and depositional habitat. Disturbed streams (wildfires and logging < 200 years ago) are single-channeled with mostly erosional habitat. We tested how these opposing stream states influenced organic matter, benthic macroinvertebrate secondAuthorsMichael P. Venarsky, David M. Walters, Robert O. Hall, Bridget Livers, Ellen WohlImportance of growth rate on mercury and polychlorinated biphenyl bioaccumulation in fish
To evaluate the effect of fish growth on mercury (Hg) and polychlorinated biphenyl (PCB) bioaccumulation, a non–steady‐state toxicokinetic model, combined with a Wisconsin bioenergetics model, was developed to simulate Hg and PCB bioaccumulation in bluegill (Lepomis macrochirus). The model was validated by comparing observed with predicted Hg and PCB 180 concentrations across 5 age classes from 5AuthorsJiajia Li, G. Douglas Haffner, Gordon Patterson, David M. Walters, Michael D. Burtnyk, Ken G. DrouillardChronic wasting disease—Status, science, and management support by the U.S. Geological Survey
The U.S. Geological Survey (USGS) investigates chronic wasting disease (CWD) at multiple science centers and cooperative research units across the Nation and supports the management of CWD through science-based strategies. CWD research conducted by USGS scientists has three strategies: (1) to understand the biology, ecology, and causes and distribution of CWD; (2) to assess and predict the spreadAuthorsChristina M. Carlson, M. Camille Hopkins, Natalie T. Nguyen, Bryan J. Richards, Daniel P. Walsh, W. David WalterHoly flux: Spatial and temporal variation in massive pulses of emerging insect biomass from western U.S. rivers
The river stonefly, Pteronarcys californica (aka salmonfly), is an iconic insect in rivers of western North America due to its large size and its support of economically important species like wild trout (Nehring et al. 2011). Their emergence generates a large economic subsidy to local communities, as anglers from around the world travel to western rivers to fish the salmonfly “hatch” (e.g., WilloAuthorsDavid Walters, Jeff S. Wesner, Robert E. Zuellig, Dan A. Kowalski, Matt C. KondratieffNon-USGS Publications**
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.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). Amer. J. Env. Sci. 8:11-15.Walters, D.M., et al. 2010. Mercury contamination in fish in mid-continent great rivers of the United States: Importance of species traits and environmental factors. Env. Sci. Tech. 44:2947-2953.Walters, D.M., A.H. Roy, and D.S. Leigh. 2009. Environmental indicators of macroinvertebrate and fish assemblage integrity in urbanizing watersheds. Ecol. Ind. 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. Ecol. Mod. 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. Ecol. Ind. 9:150-159.Walters, D.M., et al. 2008. Red shiner invasion and hybridization with blacktail shiner in the upper Coosa River, USA. Bio. Inv. 10:1229-1242.Walters, D.M., et al. 2008. The dark side of subsidies: Adult stream insects export organic contaminants to riparian predators. Ecol. App. 18:1835-1841.Walters, D.M. et al. 2008. Influence of trophic position and spatial location on polychlorinated biphenyl (PCB) bioaccumulation in a stream food web. Env. Sci. Tech. 42:2316-2322.Fritz, K.M., B.R. Johnson, and D.M. Walters. 2008. Physical indicators of hydrologic permanence in forested headwater streams. Jour. Nor. Amer. Benth. Soc. 27:690-704.Rybczynski, S.M., D.M. Walters, et al. 2008. Comparing the trophic position of stream fishes using stable isotope and gut contents analyses. Eco. Freshw. Fish 17:199-206.Walters D.M., et al. 2007. Reach-scale geomorphology affects organic matter and consumer δ13C in a forested Piedmont stream. Freshw. Bio. 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., et al. 2003a. Geomorphology and fish assemblages in a Piedmont river basin, USA. Freshw. Bio. 48:1950-1970.Walters, D.M., et al. 2003b. Urbanization, sedimentation, and the homogenization of fishes in the Etowah River Basin, Georgia Piedmont, USA. Hydrobiologia 494:5-10.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 2000:555-559.Kraus, J. M., Schmidt, T. S., Walters, D. M., Wanty, R. B., Zuellig, R. E. and Wolf, R. E. (2014), Cross-ecosystem impacts of stream pollution reduce resource and contaminant flux to riparian food webs. Ecological Applications, 24: 235–243. doi: 10.1890/13-0252.1**Disclaimer: The views expressed in Non-USGS publications are those of the author and do not represent the views of the USGS, Department of the Interior, or the U.S. Government.
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