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
Per- and Polyfluoroalkyl Substance Exposure and Effects Research at Columbia Environmental Research Center (CERC)
Flood Redistributes Mercury in Grand Canyon Aquatic Food Webs
Areas of Concern: Technical Guidance for Assessing Remedy Effectiveness, Restoration, and Revitalization at Great Lakes AOCs and Great Lake Legacy Act (GLLA) Sites
Aquatic Ecology and Contaminants
Climate Change and Trout
Effects of Contaminants on Linked Aquatic and Terrestrial Food Webs
Total PCB concentrations in sediment, water, macroinvertebrates and spiders and the lower Ottawa River (Toledo, OH) between 2009-2015
Plant and insect pollinator diversity data from Conservation Reserve Program fields across an agricultural gradient in eastern Iowa
Modeled Pacific salmon escapement biomass and nutrient and contaminant concentrations across western North America, 1976-2015
Assessment of Mercury and Mercury Stable Isotopes in Sediments and Biota from Reservoirs and Remedial Zones within the Saint Louis River, Minnesota
Images and Identifications of Wild Bees Collected in Eastern Iowa, 2019
Acute and chronic toxicity of two perfluoroalkyl substances to Neocloeon triangulifer
Total mercury, methylmercury, and isotopic composition in various life stages of boreal chorus frogs (Pseudacris maculata) at two subalpine ponds in the Rocky Mountains, CO, USA, 2015
Pesticide residues in passive samplers and bee tissue from Conservation Reserve Program fields across an agricultural gradient in eastern Iowa, USA, 2019 (ver 2.0, October 2023)
Survival, growth, behavior and mercury concentrations of mayflies exposed to elevated dietary methylmercury and aqueous selenium
Mercury concentrations, isotopic composition, biomass, and taxonomy of stream and riparian organisms in the vicinity of Yellow Pine, Idaho, 2015-2016.
Salt Marsh Turbidity at Mockhorn Island, VA; Plum Island, MA; York River, VA; and Altamaha River, GA
Adult aquatic insect emergence, insect pesticide concentrations and water chemistry of wetlands in the Prairie Pothole Region, North Dakota, USA, 2015-16
PCB concentrations in riparian spiders (Tetragnathidae) consistently reflect concentrations in water and aquatic macroinvertebrates, but not sediment: Analysis of a seven-year field study
Evolutionary and ecological correlates of thiaminase in fishes
A novel approach to assessing natural resource injury with Bayesian networks
Mercury isotope values in shoreline spiders reveal transfer of aquatic mercury sources to terrestrial food webs
Identifying invertebrate indicators for streamflow duration assessments in forested headwater streams
Perfluorooctanesulfonate adversely affects a mayfly (Neocloeon triangulifer) at environmentally realistic concentrations
Complex life histories alter patterns of mercury exposure and accumulation in a pond-breeding amphibian
Evaluation of Ziram as an oral toxic bait chemical for control of grass carp Ctenopharyngodon idella
Ecotoxicological studies indicate that sublethal and lethal processes limit insect-mediated contaminant flux
Riparian spiders: Sentinels of polychlorinated dibenzo-p-dioxin and dibenzofuran-contaminated sediment
GPS data from 2019 and 2020 campaigns in the Chesapeake Bay region towards quantifying vertical land motions
PCB exposure is associated with reduction of endosymbionts in riparian spider microbiomes
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.
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.
Science and Products
- Science
Per- and Polyfluoroalkyl Substance Exposure and Effects Research at Columbia Environmental Research Center (CERC)
The Columbia Environmental Research Center’s Per- and Polyfluoroalkyl Substance (PFAS) team conducts research focusing on the occurrence, fate, and toxicity of PFAS compounds in aquatic and terrestrial systems. Laboratory capabilities include dedicated analytical instrumentation and experimental facilities to allow USGS scientists to analyze a wide range of sample types including water, sediment...Flood Redistributes Mercury in Grand Canyon Aquatic Food Webs
S cientists 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.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) SitesAquatic 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...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...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. - Data
Filter Total Items: 18
Total PCB concentrations in sediment, water, macroinvertebrates and spiders and the lower Ottawa River (Toledo, OH) between 2009-2015
Polychlorinated biphenyl (PCB) concentrations were measured in the lower Ottawa River in 2009 before dredging and after dredging in 2011, 2012, 2013, and 2015. Media collected for analysis included sediment, water, macroinvertebrates, and tetragnathid spiders at 18 stations. At each station 16 surface sediment core samples (top 15 cm) were collected and composited together with a mechanical mixerPlant and insect pollinator diversity data from Conservation Reserve Program fields across an agricultural gradient in eastern Iowa
This data release includes sampling location identification and timing data as well as plant and insect pollinator taxonomic information in Conservation Reserve Program fields. Sampling took place during July and August of 2019. Fields were located on private land managed for the U.S. Department of Agriculture Conservation Reserve Program in eastern central Iowa, U.S.A.Modeled Pacific salmon escapement biomass and nutrient and contaminant concentrations across western North America, 1976-2015
The data contain yearly modeled estimates of Pacific salmon escapement (in annual metric tons of wet mass) from 1976 to 2015 across four regions of western North America. A second data file contains modeled estimates of contaminant or nutrient concentrations in Pacific Salmon. The modeled estimates were derived from Bayesian generalized linear models (contaminant or nutrient concentrations) or froAssessment of Mercury and Mercury Stable Isotopes in Sediments and Biota from Reservoirs and Remedial Zones within the Saint Louis River, Minnesota
This data release includes mercury concentrations and mercury stable isotope measurements measured in sediments and biological tissues collected from the Saint Louis River located in Minnesota. Sediments and biota were collected by the U.S. Geological Survey, U.S. Environmental Protection Agency, U.S. Army Corps of Engineers, and federal contractors (Battelle) from 2017-2021. Collection regions inImages and Identifications of Wild Bees Collected in Eastern Iowa, 2019
Bees were collected in 24 fields across eastern Iowa in summer 2019. This data collection was part of a pesticide study funded by the USGS Ecosystems Mission Area- Environmental Health Program. Bees were collected using the sweep net method and then were immediately placed on dry ice in the field. Bees were kept frozen to prevent degradation. In the lab, each wild bee was photographed from one orAcute and chronic toxicity of two perfluoroalkyl substances to Neocloeon triangulifer
Dataset consists of 4-day, 14-day, and full life responses of laboratory cultured mayflies (Neocloeon triangulifer) to perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA). Responses were measured as survival at 4 days, 14 days, pre-emergent nymph (PEN) stage, and emergence; 14-day length; number of days to PEN stage, and imago live weight. Water quality and analytical chemistry reTotal mercury, methylmercury, and isotopic composition in various life stages of boreal chorus frogs (Pseudacris maculata) at two subalpine ponds in the Rocky Mountains, CO, USA, 2015
Mercury is an atmospherically transported contaminant found even in relatively pristine habitats. Once accumulated at the base of the food web, mercury can move between animals that are linked trophically. Pond-breeding amphibians may be particularly important vectors of mercury flux from remote freshwater to terrestrial systems because they feed on algae and detritus as tadpoles and metamorphosePesticide residues in passive samplers and bee tissue from Conservation Reserve Program fields across an agricultural gradient in eastern Iowa, USA, 2019 (ver 2.0, October 2023)
This data release includes sampling location, pesticide concentrations in passive samplers (silicone bands) and bees foraging in Conservation Reserve Program fields. Sampling took place during July and August of 2019. Fields were located on private land managed for the U.S. Department of Agriculture Conservation Reserve Program in eastern central Iowa, U.S.A.Survival, growth, behavior and mercury concentrations of mayflies exposed to elevated dietary methylmercury and aqueous selenium
Survival and size of mayflies at each life stage, as well as MeHg concentrations in diatoms and mayflies exposed to low and high MeHg concentrations and a range of selenomethione (SeMet) concentrations.Mercury concentrations, isotopic composition, biomass, and taxonomy of stream and riparian organisms in the vicinity of Yellow Pine, Idaho, 2015-2016.
This data release includes sampling location data; field-collected stream attribute data; laboratory-analyzed chemistry concentrations (total mercury, methyl mercury) and isotopic composition (total mercury, carbon, and nitrogen) for stream biota (seston, periphyton, benthic insects, emerging adult insects, riparian spiders, and fish); density, body length, and taxonomic information for benthic inSalt Marsh Turbidity at Mockhorn Island, VA; Plum Island, MA; York River, VA; and Altamaha River, GA
We measured turbidity along transects from channel to marsh interior for 4 sites along the east coast of the United States at: Mockhorn Island, on the Eastern Shore of VA, USA; Plum Island in MA, USA; Goodwin Islands on the York River, VA USA; and the Altamaha River estuary, in GA, USA.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 - Multimedia
- Publications
Filter Total Items: 69
PCB concentrations in riparian spiders (Tetragnathidae) consistently reflect concentrations in water and aquatic macroinvertebrates, but not sediment: Analysis of a seven-year field study
Tetragnathid spiders have been used as sentinels to study the biotransport of contaminants between aquatic and terrestrial environments because a significant proportion of their diet consists of adult aquatic insects. A key knowledge gap in assessing tetragnathid spiders as sentinels is understanding the consistency of the year-to-year relationship between contaminant concentrations in spiders andAuthorsRyan R. Otter, Marc A. Mills, Ken M. Fritz, James M. Lazorchak, Dalon P. White, Gale B. Beaubien, David WaltersEvolutionary and ecological correlates of thiaminase in fishes
Thiamine (vitamin B1) is required by all living organisms in multiple metabolic pathways. It is scarce in natural systems, and deficiency can lead to reproductive failure, neurological issues, and death. One major cause of thiamine deficiency is an overreliance on diet items containing the enzyme thiaminase. Thiaminase activity has been noted in many prey fishes and linked to cohort failure in salAuthorsFreya Elizabeth Rowland, Catherine A. Richter, Donald E Tillitt, David WaltersA novel approach to assessing natural resource injury with Bayesian networks
Quantifying the effects of environmental stressors on natural resources is problematic because of complex interactions among environmental factors that influence endpoints of interest. This complexity, coupled with data limitations, propagates uncertainty that can make it difficult to causally associate specific environmental stressors with injury endpoints. The Natural Resource Damage AssessmentAuthorsFreya Elizabeth Rowland, Christopher James Kotalik, Bruce G. Marcot, Jo Ellen Hinck, David WaltersMercury isotope values in shoreline spiders reveal transfer of aquatic mercury sources to terrestrial food webs
The transfer of aquatic contaminants, including mercury (Hg), to terrestrial food webs is an often-overlooked exposure pathway to terrestrial animals. While research has implemented the use of shoreline spiders to assess aquatic to terrestrial Hg transfer, it is unclear whether Hg sources, estimated from isotope ratios, can be successfully resolved to inform site assessments and remedy effectiveneAuthorsSarah E. Janssen, Christopher James Kotalik, Collin Eagles-Smith, Gale B. Beaubien, Joel C. Hoffman, Greg Peterson, Marc A. Mills, David WaltersIdentifying invertebrate indicators for streamflow duration assessments in forested headwater streams
Streamflow-duration assessment methods (SDAMs) are rapid, indicator-based tools for classifying streamflow duration (e.g., intermittent vs perennial flow) at the reach scale. Indicators are easily assessed stream properties used as surrogates of flow duration, which is too resource intensive to measure directly for many reaches. Invertebrates are commonly used as SDAM indicators because many are nAuthorsKen M. Fritz, Roxolana O. Kashuba, Gregory J. Pond, Jay R. Christensen, Laurie C. Alexander, Benjamin J. Washington, Brent R. Johnson, David Walters, William T. Thoeny, Paul C. WeaverPerfluorooctanesulfonate adversely affects a mayfly (Neocloeon triangulifer) at environmentally realistic concentrations
Of the emerging contaminant types thought to threaten freshwater biota, per- and polyfluoroalkyl substances appear to be particularly widespread, and limited studies conducted with these compounds thus far indicate insects may be particularly sensitive to them. This study investigated the short- and long-term effects of two commonly detected compounds on the laboratory-reared mayfly Neocloeon triaAuthorsDavid J. Soucek, Rebecca A. Consbrock, Erin L. Pulster, Brittany G. Perrotta, David Walters, Jeffery SteevensComplex life histories alter patterns of mercury exposure and accumulation in a pond-breeding amphibian
Quantifying how contaminants change across life cycles of species that undergo metamorphosis is critical to assessing organismal risk, particularly for consumers. Pond-breeding amphibians can dominate aquatic animal biomass as larvae and are terrestrial prey as juveniles and adults. Thus, amphibians can be vectors of mercury exposure in both aquatic and terrestrial food webs. However, it is stillAuthorsFreya Elizabeth Rowland, Erin L. Muths, Collin Eagles-Smith, Craig A. Stricker, Johanna M. Kraus, Rachel A. Harrington, David WaltersEvaluation of Ziram as an oral toxic bait chemical for control of grass carp Ctenopharyngodon idella
The grass carp, Ctenopharyngodon idella, is an invasive species in North America that has been recorded in 45 states with breeding populations in several major river basins. Established populations of grass carp have had cascading, negative effects on aquatic ecosystem structure and function. Oral piscicide baits have been examined as a potential method to manage invasive grass carp. Our goal wasAuthorsNile E. Kemble, Keith Grabner, David W. Whites, David Walters, Michael J. Hooper, Jeffery SteevensEcotoxicological studies indicate that sublethal and lethal processes limit insect-mediated contaminant flux
Merolimnic insects can accumulate and transport considerable amounts of aquatic contaminants to terrestrial systems. The rate of contaminant biotransport, termed insect-mediated contaminant flux (IMCF), depends on emergent insect biomass and contaminant accumulation, both functions of environmental concentration. Here we develop a mathematical model of IMCF and apply it to three ecotoxicological sAuthorsC.I Olson, G.B Beaubien, R.R Otter, David Walters, Mills. M.ARiparian spiders: Sentinels of polychlorinated dibenzo-p-dioxin and dibenzofuran-contaminated sediment
Polychlorinated dibenzo-p-dioxin and polychlorinated dibenzofuran (PCDD/F) are persistent, toxic, and bioaccumulative. Currently, PCDD/F monitoring programs primarily use fish and birds with potentially large home ranges to monitor temporal trends over broad spatial scales; sentinel organisms that provide targeted sediment contaminant information across small geographic areas have yet to be develoAuthorsGale B. Beaubien, Dalon P. White, David Walters, Ryan R. Otter, Ken M. Fritz, Brian Crone, Marc A. MillsGPS data from 2019 and 2020 campaigns in the Chesapeake Bay region towards quantifying vertical land motions
The Chesapeake Bay is a region along the eastern coast of the United States where sea-level rise is confounded with poorly resolved rates of land subsidence, thus new constraints on vertical land motions (VLM) in the region are warranted. In this paper, we provide a description of two campaign-style Global Positioning System (GPS) datasets, explain the methods used in data collection and validatioAuthorsGabrielle Troia, Sarah Stamps, R. Russell Lotspeich, James M. Duda, Kurt J. McCoy, William Moore, Philippe Hensel, Ryan Hippenstiel, Thomas McKenna, David C. Andreasen, Charles Geoghegan, Thomas P Ulizo, Madeline Kronebusch, Joel A. Carr, David Walters, Neil WinnPCB exposure is associated with reduction of endosymbionts in riparian spider microbiomes
Microbial communities, including endosymbionts, play diverse and critical roles in host biology and reproduction, but contaminant exposure may cause an imbalance in the microbiome composition with subsequent impacts on host health. Here, we examined whether there was a significant alteration of the microbiome community within two taxa of riparian spiders (Tetragnathidae and Araneidae) from a siteAuthorsBrittany G Perrotta, Karen A. Kidd, David WaltersNon-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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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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