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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

link
A rainbow trout seen on the Colorado River in Glen Canyon National Recreation Area

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.
By
Contaminant Biology, Environmental Health Program, Toxic Substances Hydrology
link

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.
Learn More
link
Long-jawed spider on tree branch

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
link

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
Learn More
link
An image of an Ephemeroptera Heptageniidae Epeorus longimanuis.

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 the...
By
Ecosystems, Colorado Water Science Center, Fort Collins Science Center
link

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 the...
Learn More
link
Scientists work on insect traps in the Prairie Pothole region of North Dakota.

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 land...
By
Fort Collins Science Center
link

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 land...
Learn More
link
A cutthroat trout up close. James Roberts photo. USGS.

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...
By
Ecosystems, Fisheries Program, Fort Collins Science Center
link

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...
Learn More
link
The aquatic lab at the Fort Collins Science Center. David Walters photo, USGS.

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.
By
Ecosystems, Fort Collins Science Center
link

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.
Learn More

Adult aquatic insect emergence, insect pesticide concentrations and water chemistry of wetlands in the Prairie Pothole Region, North Dakota, USA, 2015-16

This data release includes sampling location data, field-collected wetland attribute data, field-collected water chemistry data, laboratory-processed water chemistry data (anions, cations, alkalinity, nutrients, chlorophyll a concentrations, dissolved organic carbon, and specific ultraviolet absorbance, pesticide concentrations), dry mass of adult aquatic insects emerging from the surface of the w
By
Columbia Environmental Research Center

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, geo
By
Contaminant Biology, Columbia Environmental Research Center

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

Consumption rates and total mercury concentration of food items and consumers collected at six sites on the Colorado River in the Grand Canyon. Sites ranged from 0-367 river kilometers downstream of Lees Ferry (AZ, USA). Samples were analyzed for total Hg using cold vapor atomic fluorescence (CVAF, Tekran Model 2600 CVAF spectrometer) following EPA Method 7474. Consumption rate samples were collec
By
Ecosystems, Contaminant Biology, Columbia Environmental Research Center

Polychlorinated biphenyl concentrations and lipid content in riparian spiders at the Ashtabula River Area of Concern, USA

We measured polychlorinated biphenyl (PCB) concentrations in two taxa of riparian spiders from nine sites in 2011 at the Ashtabula River Area of Concern. We analyzed the extracts for 122 congeners following EPA method SW846 Method 8270D using gas chromatography mass spectrometry in the selective ion monitoring (SIM) mode. All target compounds were quantified using the method of internal standards,
By
Fort Collins Science Center

Zinc concentrations and isotopic signatures of an aquatic insect (mayfly, Baetis tricaudatus)

Insect metamorphosis often results in substantial chemical changes that can fractionate isotopes and alter contaminant concentrations. We exposed larval mayflies (Baetis tricaudatus) to an aqueous zinc gradient (3-340 g Zn/l) and measured the change in zinc tissue concentrations at different stages of metamorphosis. We also measured changes in stable isotopes (δ15N and δ13C) in unexposed
By
Fort Collins Science Center
Filter Total Items: 53

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 mitigate the risks of contamination have largely focused on aqu
By
Ecosystems, Columbia Environmental Research Center, Fort Collins Science Center

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 regions, one of which is the Saint Louis River estuary (SLRE)
By
Ecosystems, Water Resources, Forest and Rangeland Ecosystem Science Center, Fort Collins Science Center, Upper Midwest Environmental Sciences Center, Upper Midwest Water Science Center

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 aquatically-derived trace metals, metal concentrati
By
Ecosystems, Columbia Environmental Research Center, Geology, Geophysics, and Geochemistry Science Center

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 influence contaminant fate, exposure, and effects at the l
By
Ecosystems, Columbia Environmental Research Center

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 contaminant flux and integrating them together so that
By
Ecosystems, Columbia Environmental Research Center

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 and plant matter delivered to freshwaters. We present
By
Ecosystems, Columbia Environmental Research Center, Fort Collins Science Center

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 surrounding water and diet, with waterborne uptake prev
By
Ecosystems, Water Resources, Fort Collins Science Center

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 aquatic ecosystems with ecosystem-scale Se additions cou
By
Ecosystems, Forest and Rangeland Ecosystem Science Center, Fort Collins Science Center

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 t
By
Ecosystems, Columbia Environmental Research Center

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 organisms are poorly characterized. We investigated Se con
By
Ecosystems, Columbia Environmental Research Center

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 pulse phenology is poorly documented. We quantified wa
By
Ecosystems, Columbia Environmental Research Center

Lotic 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 the
By
Ecosystems, Fisheries Program, Columbia Environmental Research Center

Pre-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

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.

By
Ecosystems, Water Resources, Colorado Water Science Center, Fort Collins Science Center
link

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...

Read Article
link

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...

Read Article
link

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...

Read Article
link

Literature Review: Environmental Selenium-Mercury Interactions

Mercury is a pervasive environmental pollutant and contaminant of concern for both people and wildlife. 

Read Article

Science and Products

  • Science
    link
    A rainbow trout seen on the Colorado River in Glen Canyon National Recreation Area

    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.
    By
    Contaminant Biology, Environmental Health Program, Toxic Substances Hydrology
    link

    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.
    Learn More
    link
    Long-jawed spider on tree branch

    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
    link

    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
    Learn More
    link
    An image of an Ephemeroptera Heptageniidae Epeorus longimanuis.

    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 the...
    By
    Ecosystems, Colorado Water Science Center, Fort Collins Science Center
    link

    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 the...
    Learn More
    link
    Scientists work on insect traps in the Prairie Pothole region of North Dakota.

    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 land...
    By
    Fort Collins Science Center
    link

    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 land...
    Learn More
    link
    A cutthroat trout up close. James Roberts photo. USGS.

    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...
    By
    Ecosystems, Fisheries Program, Fort Collins Science Center
    link

    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...
    Learn More
    link
    The aquatic lab at the Fort Collins Science Center. David Walters photo, USGS.

    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.
    By
    Ecosystems, Fort Collins Science Center
    link

    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.
    Learn More
  • Data

    Adult aquatic insect emergence, insect pesticide concentrations and water chemistry of wetlands in the Prairie Pothole Region, North Dakota, USA, 2015-16

    This data release includes sampling location data, field-collected wetland attribute data, field-collected water chemistry data, laboratory-processed water chemistry data (anions, cations, alkalinity, nutrients, chlorophyll a concentrations, dissolved organic carbon, and specific ultraviolet absorbance, pesticide concentrations), dry mass of adult aquatic insects emerging from the surface of the w
    By
    Columbia Environmental Research Center

    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, geo
    By
    Contaminant Biology, Columbia Environmental Research Center

    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

    Consumption rates and total mercury concentration of food items and consumers collected at six sites on the Colorado River in the Grand Canyon. Sites ranged from 0-367 river kilometers downstream of Lees Ferry (AZ, USA). Samples were analyzed for total Hg using cold vapor atomic fluorescence (CVAF, Tekran Model 2600 CVAF spectrometer) following EPA Method 7474. Consumption rate samples were collec
    By
    Ecosystems, Contaminant Biology, Columbia Environmental Research Center

    Polychlorinated biphenyl concentrations and lipid content in riparian spiders at the Ashtabula River Area of Concern, USA

    We measured polychlorinated biphenyl (PCB) concentrations in two taxa of riparian spiders from nine sites in 2011 at the Ashtabula River Area of Concern. We analyzed the extracts for 122 congeners following EPA method SW846 Method 8270D using gas chromatography mass spectrometry in the selective ion monitoring (SIM) mode. All target compounds were quantified using the method of internal standards,
    By
    Fort Collins Science Center

    Zinc concentrations and isotopic signatures of an aquatic insect (mayfly, Baetis tricaudatus)

    Insect metamorphosis often results in substantial chemical changes that can fractionate isotopes and alter contaminant concentrations. We exposed larval mayflies (Baetis tricaudatus) to an aqueous zinc gradient (3-340 g Zn/l) and measured the change in zinc tissue concentrations at different stages of metamorphosis. We also measured changes in stable isotopes (δ15N and δ13C) in unexposed
    By
    Fort Collins Science Center
  • Publications
    Filter Total Items: 53

    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 mitigate the risks of contamination have largely focused on aqu
    By
    Ecosystems, Columbia Environmental Research Center, Fort Collins Science Center

    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 regions, one of which is the Saint Louis River estuary (SLRE)
    By
    Ecosystems, Water Resources, Forest and Rangeland Ecosystem Science Center, Fort Collins Science Center, Upper Midwest Environmental Sciences Center, Upper Midwest Water Science Center

    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 aquatically-derived trace metals, metal concentrati
    By
    Ecosystems, Columbia Environmental Research Center, Geology, Geophysics, and Geochemistry Science Center

    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 influence contaminant fate, exposure, and effects at the l
    By
    Ecosystems, Columbia Environmental Research Center

    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 contaminant flux and integrating them together so that
    By
    Ecosystems, Columbia Environmental Research Center

    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 and plant matter delivered to freshwaters. We present
    By
    Ecosystems, Columbia Environmental Research Center, Fort Collins Science Center

    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 surrounding water and diet, with waterborne uptake prev
    By
    Ecosystems, Water Resources, Fort Collins Science Center

    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 aquatic ecosystems with ecosystem-scale Se additions cou
    By
    Ecosystems, Forest and Rangeland Ecosystem Science Center, Fort Collins Science Center

    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 t
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    Ecosystems, Columbia Environmental Research Center

    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 organisms are poorly characterized. We investigated Se con
    By
    Ecosystems, Columbia Environmental Research Center

    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 pulse phenology is poorly documented. We quantified wa
    By
    Ecosystems, Columbia Environmental Research Center

    Lotic 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 the
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    Ecosystems, Fisheries Program, Columbia Environmental Research Center

    Pre-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
  • Web Tools

    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.

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    Ecosystems, Water Resources, Colorado Water Science Center, Fort Collins Science Center
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    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...

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    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...

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    link

    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...

    Read Article
    link

    Literature Review: Environmental Selenium-Mercury Interactions

    Mercury is a pervasive environmental pollutant and contaminant of concern for both people and wildlife. 

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