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.
David Walters, Ph.D.
Biography
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.
Education
- Ph.D. Ecology, University of Georgia (UGA), 2002
- M.S. Conservation Ecology, UGA, 1997
- B.A. Anthropology, UGA, 1991
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.
Science and Products
Date published: April 7, 2021
Status: Completed Flood Redistributes Mercury in Grand Canyon Aquatic Food Webs
Scientists coupled the concepts of energy flow through food webs with measurements of mercury in organic matter and animals to estimate mercury fluxes and fate during an experimental flood in the Colorado River. The flood redistributed mercury in simple, upstream food webs but not in more complex, downstream food webs.
Contacts: David Walters, Ph.D.
Date published: October 28, 2019
Status: Active Areas of Concern: Technical Guidance for Assessing Remedy Effectiveness, Restoration, and Revitalization at Great Lakes AOCs and Great Lake Legacy Act (GLLA) Sites
Technical Guidance for Assessing Remedy Effectiveness, Restoration, and Revitalization at Great Lakes AOCs and Great Lake Legacy Act (GLLA) Sites
Contacts: David Walters, Ph.D.
Attribution: Great Lakes Restoration Initiative Cost Center
Date published: February 2, 2017
Status: Active Aquatic Experimental Laboratory (AXL)
Aquatic invertebrates are a key component of freshwater ecosystems, and an understanding of aquatic invertebrate taxonomy is central to freshwater science. The U.S. Geological Survey Aquatic Experimental Lab (AXL) at the Fort Collins Science Center has developed the North American Aquatic Macroinvertebrate Digital Reference Collection (NAAMDRC) to provide users with a graphic tool to aid in...
Contacts: David Walters, Ph.D., Robert E Zuellig, Ph.D., Boris Kondratieff
Date published: August 30, 2016
Status: Archived Aquatic Ecology and Contaminants
The Aquatic Ecology and Contaminants Team investigates critical ecological processes operating in aquatic and riparian ecosystems and how these processes are affected by human activities. We address questions through a combination of field studies, laboratory experiments, and modeling, while working at multiple levels of biological organization from cells through ecosystems. Topics include...
Attribution: Fort Collins Science Center
Date published: July 5, 2016
Status: Active Climate Change and Trout
Cold-water fishes like trout, salmon, and charr are especially vulnerable to shifting conditions related to climate change; for example, warmer temperatures and more variable hydroclimate. Native cutthroat trout of the southern Rocky Mountains now only occupy a tiny fraction of their historic habitats because of stressors such as non-native fishes, habitat fragmentation, and detrimental land...
Date published: July 5, 2016
Status: Active Effects of Contaminants on Linked Aquatic and Terrestrial Food Webs
Most aquatic insects live in fresh water as larvae and move to land as flying adults to complete their life cycle. Although often ignored, the emergence of adults can transfer the effects of contamination from aquatic to terrestrial ecosystems as the adults are eaten by predators such as spiders, birds, and bats.
Date published: January 22, 2021
Trace metals in water and biota in and near headwater streams in the Colorado Mineral Belt
This data release includes sampling location data, field-collected water chemistry data, cation and anion concentration data for water and tissues of submerged aquatic vegetation, aquatic insect larvae, adult aquatic insects and riparian spiders from 35 first- and second-order sub-alpine streams that ranged over several orders of magnitude in metal concentrations but were similar in elevation...
Attribution: Contaminant Biology, Columbia Environmental Research Center
Date published: January 1, 2020
Consumption rates and total mercury concentration of food items and consumers collected at six sites on the Colorado River in the Grand Canyon, USA, 2007-2009
Mercury flux and fate (whether mercury was retained in the aquatic ecosystem or exported to the riparian ecosystem via blackfly emergence) was calculated based on animal consumption rates and total mercury concentration of diet items. Consumers and their gut contents were collected at six sites on the Colorado River in the Grand Canyon. Sites ranged from 0-367 river kilometers downstream of L...
Date published: February 8, 2017
Zinc concentrations and isotopic signatures of an aquatic insect (mayfly, Baetis tricaudatus)
To create this dataset the authors exposed larval mayflies (Baetis tricaudatus) to an aqueous zinc gradient (3-340 µg Zn/l) and measured the change in zinc tissue concentrations at different stages of metamorphosis and changes in stable isotopes (δ15N and δ13C) in unexposed B. tricaudatus. Zinc concentrations in larvae and adults were positively related to aqueous concentrations.
Attribution: Fort Collins Science Center
Date published: February 2, 2017
North American Aquatic Macroinvertebrate Digital Reference Collection (NAAMDRC)
Aquatic invertebrates are a key component of freshwater ecosystems, and an understanding of aquatic invertebrate taxonomy is central to freshwater science. The North American Aquatic Macroinvertebrate Digital Reference Collection (NAAMDRC) was created by the USGS Aquatic Experimental Lab (AXL) to provide users with high-quality digital microscopy photographs.
Year Published: 2021
Insect-mediated contaminant flux at the land–water interface: Are ecological subsidies driving exposure or is exposure driving subsidies?
Chemical contamination of freshwaters is a global problem. In the United States alone, millions of kilometers of rivers and hectares of lakes and wetlands are impaired from contamination by chemicals including mercury, pesticides, polychlorinated biphenyls (PCBs), and trace metals (US Environmental Protection Agency, 2017). Efforts to...
Kraus, Johanna M.; Wesner, Jeff S.; Walters, David
Year Published: 2021
Examining historical mercury sources in the Saint Louis River estuary: How legacy contamination influences biological mercury levels in Great Lakes coastal regions
Industrial chemical contamination within coastal regions of the Great Lakes can pose serious risks to wetland habitat and offshore fisheries, often resulting in fish consumption advisories that directly affect human and wildlife health. Mercury (Hg) is a contaminant of concern in many of these highly urbanized and industrialized coastal...
Janssen, Sarah E.; Hoffman, Joel C.; Lepak, Ryan F.; Krabbenhoft, David P.; Walters, David; Eagles-Smith, Collin; Peterson, Greg; Ogorek, Jacob M.; DeWild, John F.; Cotter, Anne M; Pearson, Mark; Tate, Michael T.; Yeardley, Roger B.; Mills, Marc A.
Year Published: 2021
Variation in metal concentrations across a large contamination gradient is reflected in stream but not linked riparian food webs
Aquatic insects link food web dynamics across freshwater-terrestrial boundaries and subsidize terrestrial consumer populations. Contaminants that accumulate in larval aquatic insects and are retained across metamorphosis can increase dietary exposure for riparian insectivores. To better understand potential exposure of terrestrial insectivores to...
Kraus, Johanna M.; Wanty, Richard; Schmidt, Travis S.; Walters, David; Wolf, Ruth E.
Year Published: 2020
Introduction: Ecological subsidies as a framework for understanding contaminant fate, exposure, and effects at the land-water interface
Ecologists have long recognized that ecological subsidies (the flow of organic matter, nutrients, and organisms between ecosystems) can strongly affect ecosystem processes and community structure in the recipient ecosystem. Animal movements, organic matter flows, and food web dynamics between linked aquatic and terrestrial systems can also...
Walters, David; Kraus, Johanna M.; Mills, Marc A.
Year Published: 2020
Practical considerations for the incorporation of insect-mediated contaminant flux into ecological risk assessments
Insect-mediated contaminant flux is truly an interdisciplinary concept that merges ideas from many technical areas of science (e.g., environmental chemistry, landscape ecology, and entomology). This chapter introduces risk assessors to this emerging and ecologically relevant concept by distilling the main mechanisms that drive insect-mediated...
Otter, Ryan R.; Beaubien, Gale B.; Olson, Connor I.; Walters, David; Mills, Marc A.View Citation
Otter, R.R., Beaubien, G.B., Olson, C.I., Walters, D.M., and Mills, M.A., 2020, Practical considerations for the incorporation of insect-mediated contaminant flux into ecological risk assessments, in Kraus, J.M., Walters, D.M., and Mills, M.A., eds., Contaminants and Ecological Subsidies: The Land-Water Interface: Cham, Springer International Publishing, p. 179-195. https://doi.org/10.1007/978-3-030-49480-3_9
Year Published: 2020
Synthesis: A framework for predicting the dark side of ecological subsidies
In this chapter, we synthesize the state of the science regarding ecological subsidies and contaminants at the land-water interface and suggest research and management approaches for linked freshwater-terrestrial ecosystems. Specifically, we focus on movements of animals with complex life histories and the detrital inputs associated with animal...
Kraus, Johanna M.; Wessner, Jeff; Walters, DavidAttribution: Columbia Environmental Research Center, Fort Collins Science Center, Ecosystems, Region 4: Mississippi Basin
View Citation
Kraus, J.M., Wesner, J., and Walters, D.M., 2020, Synthesis: A framework for predicting the dark side of ecological subsidies, in Kraus, J.M., Walters, D.M., and Mills, M.A., eds., Contaminants and Ecological Subsidies: The Land-Water Interface: Cham, Springer International Publishing, p. 343-372. https://doi.org/10.1007/978-3-030-49480-3_14
Year Published: 2020
Uranium bioaccumulation dynamics in the mayfly Neocloeon triangulifer and application to site-specific prediction
Little is known about the underlying mechanisms governing the bioaccumulation of uranium (U) in aquatic insects. We experimentally parameterized conditional rate constants for aqueous U uptake, dietary U uptake, and U elimination for the aquatic baetid mayfly Neocloeon triangulifer. Results showed that this species accumulates U from both the...
Henry, Brianna L.; Croteau, Marie-Noële; Walters, David; Miller, Janet L.; Cain, Daniel J.; Fuller, Christopher C.
Year Published: 2020
Do two wrongs make a right? Persistent uncertainties regarding environmental selenium-mercury interactions
Mercury (Hg) is a pervasive environmental pollutant and contaminant of concern for both people and wildlife that has been a focus of environmental remediation efforts for decades. A growing body of literature has motivated calls for revising Hg consumption advisories to co-consider selenium (Se) levels in seafood and implies that remediating...
Gerson, Jacqueline R.; Walters, David; Eagles-Smith, Collin; Bernhardt, Emily S.; Brandt, Jessica E
Year Published: 2020
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....
Walters, David; Cross, Wyatt F.; Kennedy, Theodore; Baxter, Colden V.; Hall, R. O.; Rosi, Emma J.
Year Published: 2020
Contaminant 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...
Naslund, Laura C.; Gerson, Jacqueline R.; Brooks, Alexander C.; Walters, David; Bernhardt, Emily S.
Year Published: 2019
Thermal 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...
Anderson, Heidi E.; Alberson, Lindsey K.; Walters, David
Year Published: 2019
Thermal 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...
Anderson, Heidi E.; Albertson, Lindsey K.; Walters, DavidPre-USGS Publications
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
Date published: April 26, 2021
Flood Redistributes Mercury in Grand Canyon Aquatic Food Webs
Scientists coupled the concepts of energy flow through food webs with measurements of mercury in organic matter and animals to estimate mercury fluxes and fate during an experimental flood in the Colorado River. The flood redistributed mercury in simple,...
Date published: September 25, 2020
Literature Review: Environmental Selenium-Mercury Interactions
Mercury is a pervasive environmental pollutant and contaminant of concern for both people and wildlife.