Aquatic Ecology and Contaminants

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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 use and climate change effects on stream ecosystems and organisms, interactions between native and invasive fi shes, the flux of contaminants through aquatic and riparian food webs, and contaminant effects on aquatic-riparian linkages.

A dragonfly in the wetlands in Southeast North Dakota.

A dragonfly in the wetlands in Southeast/Central ND - Stutsman and Kidder counties, ND in grassland and on farms. Public domain.

Effects of Contaminants on Linked Aquatic and Terrestrial Food Webs - Principal Investigator - Johanna Kraus

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. Our scientists are investigating how contaminants move from streams, rivers, and lakes into riparian zones and how contamination alters the ecological linkages between these systems. We use large-scale field studies in various aquatic ecosystems, ranging from mountain headwater streams to the Great Lakes, and conduct complementary experiments at the new aquatic experimental laboratory at the Fort Collins Science Center. The mesocosm facility in our state-of-the-art laboratory is designed to replicate the coupled aquatic-riparian ecosystems. Results from these studies are helping managers to better evaluate water-quality criteria, to design and implement restoration plans for contaminated aquatic systems, and to assess the effectiveness of remedial actions.



Scientists tend to insect traps in the wetlands of the Prairie Pothole region on North Dakota.

Scientists tend to insect traps in the wetlands of the Prairie Pothole region in Stutsman and Kidder counties, North Dakota in grassland and on farms. Public domain.


Pesticides in the Prairie Pothole Region - Principal Investigator - Johanna Kraus

Wetlands of the northern Great Plains are crucial feeding grounds for migrating birds and waterfowl embedded in an agricultural landscape. Land use and hydrology can affect adult aquatic insects – crucial prey for critically declining populations of insectivorous birds. Current studies focus on effects of current-use pesticides on adult aquatic insects to inform decision making about contaminants of emerging environmental concern.






Potential Toxicity of Multiple Metals Associated with PGE Deposits - Principal Investigator - Travis Schmidt

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

The aquatic lab at the Fort Collins Science Center. Public domain.

In this study we will conduct a series of mesocosm studies to examine the toxicity of cobalt, copper, nickle, and zinc to natural communities of invertebrates. A mesocosm study is labor intensive, requires comprehensive chemical and biological analyses, and involves:

  • deployment of well-washed rocks in a pristine stream for 40 days to allow colonization of macro invertebrates;
  • retrieval of those rocks that are then placed in 36 flow-thru “streams” at the Aquatic Experimental Lab (USGS-Fort Collins);
  • manipulation of metal concentrations in the “streams;"
  • daily collection of emergent adults during the 30-day experiment;
  • multiple measurements of water quality (temperature, pH, dissolved major and minor ions, and DOC) during the experiment; and, at its conclusion,
  • identification and counting of larval invertebrates in each stream. Each experiment simultaneously considers impacts of individual metals and binary metal mixtures on the health of the invertebrate communities.


A Giant salmonfly, an iconic insect of western U.S. trout streams.

Giant salmonfly, an iconic insect of western U.S. trout streams. Photo by Robert Zuellig, USGS. 

Monitoring Salmonfly Populations in Western Rivers: Implications for Riparian Food Webs - Principal Investigator - David Walters

Salmonflies are iconic insects in Western streams and are often associated with Gold Medal trout fisheries. Many famous “hatches” are thought to be declining, but quantitative population data are lacking. We are working with our partners at Colorado Parks and Wildlife (CPW) to develop simple, repeatable methods for quantifying the annual salmonfly emergence. These methods will be transferred to other resource managers and citizen scientists, allowing for the first West-wide assessment of trends in salmonfly populations. In addition, we are using these population data to quantify carbon flux to riparian ecosystems related to salmonfly hatches to determine their importance to riparian predators and food webs.


Leaky rivers: Nutrient retention and productivity in Rocky Mountain streams under alternative stable states - Principal Investigator - David Walters

Logjams are common on mountain streams draining old-growth forest in the Front Range of Colorado.

Logjams are common on mountain streams draining old-growth forest in the Front Range of Colorado. Photo by M. Venarsky, USGS.

Streams of the southern Rocky Mountains (and elsewhere) suffer legacy effects of beaver trapping, wood removal, timber harvest, log floating, and other activities that have greatly reduced the size and along-stream frequency of logjams. Such streams are “dam-impoverished” ecosystems with greatly reduced capacity for organic matter storage and processing, and thus exhibit effects opposite to rivers where dam construction has greatly altered stream structure and function. Subsequently, the jam loss has reduced the productive capacity of headwater stream networks, reducing their ability to store nutrients and to grow animal biomass (secondary production).  We are working in headwater streams in Rocky Mountain National Park and surrounding National Forests to better understand the legacy of human land use and lost animal production on stream and riparian ecosystems.


Image: A Rainbow Trout Rests Among Cobble Substrate in Panther Creek

A rainbow trout rests among cobble substrate in Panther Creek downstream of Big Deer Creek, central Idaho. Public domain.

Climate Change and Trout - Principal Investigator - James Roberts

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 management practices. Using a combination of field and modeling approaches, we address how climate may influence native cutthroat trout and how conservation strategies can be tailored in a climate-smart approach to maximize conservation benefits under recent and projected climate conditions. Our research includes modeling surface temperatures for mountain lakes, and examining how altered thermal and hydrologic regimes affect critical life history events, such as spawning migrations. Ultimately, we will integrate these ecological patterns into state-of-the-art decision support models and use these models as tools to aid in the conservation of native cutthroat trout populations.


Collecting sediment in a backwater of the Manistique River

Collecting sediment in a backwater of the Manistique River and Harbor Area of Concern (AOC) on Michigan’s Upper Peninsula. Aquatic insects accumulate contaminants like PCBs in their tissues as larvae, then transfer them to predators such as spiders when the emerge from the water.

Riparian indicators of contaminant exposure at Great Lakes Areas of Concern (AOCs) Principal Investigator - David Walters

Many rivers, harbors, and nearshore environments in the Great Lakes are contaminated by legacy contaminants, many of which may have been introduced into these ecosystems many decades ago. We are investigating contaminant flux from aquatic sediments to aquatic insects and then to terrestrial (riparian) predators. Specifically, 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.




A juvenile humpback chub being released into the Colorado River

A juvenile humpback chub being released in the Little Colorado River, Grand Canyon. Photo: R. Wanty, USGS.




“Metal webs” for the Grand Canyon - Principal Investigator - David Walters

We are developing quantitative food webs to measure metal flux (mercury, selenium, uranium and other trace metals) in the Colorado River and Little Colorado River in the Grand Canyon. These studies aim to identify key pathways of metal exposure to important fish species, such as the federally endangered Humpback Chub, and to track the flux of metals from the rivers to their adjacent riparian zones. Selenium and mercury concentrations in fish and invertebrates in the Grand Canyon has become a hot topic for regulators, scientists, and the public in the U.S. due to their toxicological implications for wildlife and humans.






A typical rapid on the Colorado River in the Grand Canyon.

A typical rapid on the Colorado River in the Grand Canyon. These habitats are hot spots of aquatic insect production and emergence, and they may be important habitats for linking the aquatic and riparian food webs in the Grand Canyon. Photo: Freshwaters Illustrated/USGS.

Ecological Responses to Fish Reclamation Treatments - Principal Investigator - Travis Schmidt 

Piscicides have been used in Rocky Mountain stream and lakes to restore native fish populations. In the last two decades concerns over piscicide effects to non-target organisms, primarily aquatic invertebrates, has increased. Although piscicides have been used for more than 70 years the impact to invertebrate assemblages has not been well studied and is largely unknown. Given the importance a restoring native fish assemblages to State and Federal management agencies it is imperative to definitively evaluate impacts of these actions of all aquatic biota. Designing and implementing a robust scientific study to explore the effects of piscicides on aquatic invertebrates will provide a framework to evaluate alternative actions. We propose a multi-phased research approach to describe the anticipated and actual effects of piscicides to invertebrate communities in Rocky Mountain lakes and streams. To accomplish these goals a combination of field, laboratory and modeling approaches will be used. 


Lauren Hargis, USGS, deploys a rack of rock trays into the Poudre River, Colorado. Photo by: Chris Mebane, USGS.

Lauren Hargis, USGS, deploys a rack of rock trays into the Poudre River, Colorado. Photo by: Chris Mebane, USGS. Public domain.



NAWQA Surface Water Assessments: FORT Mesocosm Studies - Principal Investigator - Travis Schmidt 

Although there are ways of developing causal relationships between stressors and aquatic community responses without experimentation; some argue that experimental manipulation under controlled conditions is both critical and necessary to establish causation. Single species toxicity tests are the gold standard for developing toxicant biological response relationships however these tests are criticized for their lack of environmental realism and relevance to ecosystems.






Aquatic microinvertebrate image from the Aquatic Experimental Laboratory. USGS image, public domain.

Aquatic Experimental Laboratory (AXL)- Principal Investigators - David Walters and Robert E Zuellig, Ph.D.

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 identification and verification of aquatic macroinvertebrates.

AXL has developed a method for cataloging and digitizing reference specimens in such a way that a series of digital images provides enough information on key structures so a physical specimen is no longer necessary for verification. By using the most advanced and widely used taxonomic keys available, we have annotated important defining characteristics of each specimen so that non-expert technicians can more easily identify invertebrates found in aquatic samples.

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