An official website of the United States government.

This is not the current EPA website. To navigate to the current EPA website, please go to This website is historical material reflecting the EPA website as it existed on January 19, 2021. This website is no longer updated and links to external websites and some internal pages may not work. More information »

CADDIS Volume 3

Case Studies

These fourteen (14) case studies illustrate how assessors have developed and interpreted evidence to determine causes of biological impairments. They provide examples of how to organize an assessment report, analyze data, and present results. Most of the cases assess rivers and streams, but a few assess terrestrial ecosystems.

The process for identifying causes of biological impairments continues to improve. As a result you will note differences among the case studies. In some examples, comments have been inserted by the U.S. EPA editor or the authors. These comments are not meant to indicate errors in the analyses. Rather, they suggest alternative approaches that users may apply in future assessments.

The full list of case studies are listed in the box to the right. The dots displayed in the map below show the approximate locations of where these case studies occurred.

Map showing the states that are included in the case studies list.CADDIS Case Studies as Indicated on the US Map

Many of the following links exit the EPA web site Exit

Arkansas River, CO

This case study used several evidence lines to show that metal exposure impaired benthic macroinvertebrates.

Effect: Altered benthic invertebrate assemblage
Sources: Mining wastes
Probable causes: Mixed metals
Report: Arkansas River Case Study: Using Strength of Evidence Analysis. p. 4-11 in U.S. EPA (2000) Stressor Identification Guidance Document. U.S. Environmental Protection Agency, Washington DC. EPA/822/B-00/025.
Guidance, presentations, other:
Clements WH (1994) Benthic invertebrate community responses to heavy metals in the Upper Arkansas River Basin, Colorado. Journal of the North American Benthological Society 13:30-44.
Clements WH, Kiffney PM (1994) Integrated laboratory and field approach for assessing impacts of heavy metals at the Arkansas River, Colorado. Environmental Toxicology and Chemistry 13:397-404.
Clements WH, Carlisle DM, Lazorchak JM, Johnson PC (2000) Heavy metals structure benthic communities in Colorado mountain streams. Ecological Applications 10:626-638.
Kiffney PM, Clements WH (1994) Structural responses of benthic macroinvertebrate communities from different stream orders to zinc. Environmental Toxicology and Chemistry 13:389-395.
Kiffney PM, Clements WH (1994) Effects of heavy metals on a macroinvertebrate assemblage from a Rocky Mountain stream in experimental microcosms. Journal of the North American Benthological Society 13:511-523.
Nelson SM, Roline RA (1996) Recovery of a stream macroinvertebrate community from mine drainage disturbance. Hydrobiologia 339:73-84.

Top of Page

Willimantic River, CT

A screening assessment from a one-day workshop led to additional sampling. This sampling discovered an illicit toxic source, remediation of which led to improved aquatic life. This experience led the State to develop a causal assessment program. In turn, this program led the State to address impervious surface effects on stream condition.

Effect: Altered benthic invertebrate assemblage
Sources: Impervious surfaces, upstream impoundments, concrete channels, waste water treatment facility, industrial outfalls
Probable causes: Primarily a toxic effluent; secondarily sediment, altered food resources, increased temperature
Report: Bellucci C, Hoffman G, Cormier S (2009) An Iterative Approach for Identifying the Causes of Reduced Benthic Macroinvertebrate Diversity in the Willimantic River, Connecticut. U.S. Environmental Protection Agency, Cincinnati, OH. EPA/600/R-08/144.
TMDL: CTDEP (2001) Total Maximum Daily Load Analysis for the Upper Willimantic River (PDF)(16 pp, 382 K, About PDF). Connecticut Department of Environmental Protection, Stafford CT.

Top of Page

Little Floyd River, IA

This case study illustrates the difficulties of assigning specific cause to biological impairment. Challenges included data collected in different ways, small discrimination between acceptable and impaired streams, and the presence of multiple stressors. This case study demonstrates several strategic techniques to address these challenges.

Effect: Altered fish and benthic invertebrate assemblages and a fish kill
Sources: Row crop agriculture, hog production, wastewater treatment facility
Probable causes: Primarily substrate alteration; secondarily nutrient enrichment and episodic toxic ammonia concentrations
Manuscript: Haake DM, Wilton T, Krier K, Stewart AJ, Cormier SM (2010) Causal assessment of biological impairment in the Little Floyd River, Iowa, USA. Human and Ecological Risk Assessment 16(1):116-148.
Report: Haake D, Wilton T, Krier K, Isenhart T, Paul J, Stewart A, Cormier S (2008) Stressor Identification in an Agricultural Watershed: Little Floyd River, Iowa.  U.S. Environmental Protection Agency, Cincinnati, OH. EPA/600/R 08/131.
TMDL: IA DNR (2005) Total Maximum Daily Load For Sediment and Dissolved Oxygen, Little Floyd River, Sioux and O’Brien Counties, Iowa (PDF) (32 pp, 378 K, About PDF). Iowa Department of Natural Resources, TMDL & Water Quality Assessment Section.

Top of Page

Long Creek, ME

This detailed assessment illustrates the complexity of urban systems affected by many causes.

Effect: Altered benthic invertebrate assemblage, extirpated brook trout fishery
Sources: Commercial and industrial area, airport, dairy
Probable causes: Decreased dissolved oxygen, altered flow regime, decreased large woody debris, increased temperature and increased toxicity due to ionic strength
Report: U.S. EPA (2007) Causal Analysis of Biological Impairment in Long Creek, a Sandy-Bottomed Stream in Coastal Southern Maine (Final Report). U.S. Environmental Protection Agency, Washington DC. EPA/600/R-06/065F.

Top of Page

Presumpscot River, ME

This is one of first two Stressor Identification case studies. The study was performed prior to development of the SI Guidance, and it informed guidance development. The weight of evidence was heavily influenced by the lack of co-occurrence of the effect with other candidate causes and by manipulations at a pulp mill on the Androscoggin River. Reductions in total suspended solids at the pulp mill led to recovery.

Effect: Altered benthic invertebrate assemblage
Sources: Impoundment, paper and pulp mill
Probable cause: Total suspended solids with floc
Report: Presumpscot River, Maine. Ch. 6 in U.S. EPA (2000) Stressor Identification Guidance Document. U.S. Environmental Protection Agency, Washington DC. EPA/822/B-00/025.
TMDL: U.S. EPA (1998) New England’s Review of the Presumpscott River TMDL Memo (PDF) (12 pp, 14.1.Mb, About PDF). [Last accessed 02/03/10]
Guidance, presentations, other: Presumpscot River Plan Steering Committee (2002) Cumulative Impacts to Environmental Conditions on the Presumpscot River and its Shorelands (PDF) (DRAFT – As distributed at the June 2002 Public Meetings) (102 pp, 1.3 Mb, About PDF) . [Last accessed 02/02/10] Exit

Top of Page

Groundhouse River, MN

This screening assessment was done during a two-and-a-half day workshop. Findings were used to mount a more extensive watershed-scale assessment with additional data collection. Results of the screening assessment were confirmed and additional causes were characterized. The State adopted the Stressor Identification process and developed their own guidance and training materials.

Effect: Altered benthic invertebrate assemblage
Sources: Waste water treatment facility, agriculture
Probable causes: Sediment, nutrients
Report: Lane C, Cormier S (2004) Screening Level Causal Analysis and Assessment of an Impaired Reach of the Groundhouse River, Minnesota. U.S. Environmental Protection Agency, Cincinnati OH.
TMDL: Minnesota Pollution Control Agency (2009) Groundhouse River Total Maximum Daily Loads for Fecal Coliform and Biota (Sediment) Impairments (PDF) (377 pp, 9.3 Mb, About PDF).  [Last accessed 01/31/10] 
Guidance, presentations, other: Jasperson J (2008) Biota TMDL Protocols and Submittal Requirements (PDF) (124 pp, 1.9Mb, About PDF). Minnesota Pollution Control Agency. [Last accessed 01/31/10]
Minnesota Pollution Control Agency (2009) Setting the Course for Improved Water Quality – Tackling a Biological Impairment: The Groundhouse River TMDL Study Case Example (PDF) (47 pp, 987 K, About PDF). [Last accessed 01/31/10]

Top of Page

Bogue Homo, MS

This assessment was one of the first cases undertaken by the State. It resulted in the State's streamlined stressor identification process. The State performed more than 700 court-ordered causal assessments for total maximum daily load (TMDL) development. A standard candidate cause list and screening levels developed at the program's beginning increased assessment speeds.

Effect: Altered benthic invertebrate assemblage
Sources: Forestry, agriculture, reservoir
Probable causes: Primarily dissolved oxygen and altered food resources
Report: Hicks M, Whittington K, Thomas J, Kurtz J, Stewart A, Suter GW II, Cormier S (2010) Causal Assessment of Biological Impairment in the Bogue Homo River, Mississippi Using the U.S. EPA's Stressor Identification Methodology. U.S. Environmental Protection Agency, Cincinnati OH. EPA/600/R-08/143.
TMDL: MDEQ (2005) Phase 1: Total Maximum Daily Load Biological Impairment Due to Organic Enrichment/Low Dissolved Oxygen and Nutrients: The Bogue Homo River, Pascagoula Basin, Jones County, Mississippi (PDF) (44 pp, 681 K, About PDF). Mississippi Department of Environmental Quality, Office of Pollution Control, Jackson MS.
Guidance, presentations, other: MDEQ (2004) Draft Stressor Identification for the Bogue Homo River, Forrest and Perry Counties, Mississippi. Mississippi Department of Environmental Quality, Office of Pollution Control, Jackson MS.

Top of Page

Little Scioto River, OH

This is one of the first two Stressor Identification case studies. In addition to the original case, alternate formats for organizing data are presented in CADDIS.

Effects: Altered fish and benthic invertebrate assemblages
Sources: Channelized stream, creosote plant and treatment facility, industrial waste site, waste water treatment facilities
Probable causes: Altered habitat, PAHs, metal and ammonia toxicity in different segments
Manuscripts: Norton SB, Cormier SM, Suter GW II, Subramanian B, Lin ELC, Altfater D, Counts B (2002) Determining probable causes of ecological impairment in the Little Scioto River, Ohio, USA. Part 1: Listing candidate causes and analyzing evidence. Environmental Toxicology and Chemistry 21(6):1112-1124.
Cormier SM, Norton SB, Suter GW II, Altfater D, Counts B (2002) Determining the causes of impairments in the Little Scioto River, Ohio. Part 2: Characterization of causes. Environmental Toxicology and Chemistry 21(6):1125-1137.
Report: Little Scioto River, Ohio. Ch. 7 in U.S. EPA (2000) Stressor Identification Guidance Document. U.S. Environmental Protection Agency, Washington DC. EPA/822/B-00/025.
Guidance, presentations, other: Ohio EPA (2008) Biological and Water Quality Study of the Little Scioto River (PDF) (59 pp, 1.04Mb, About PDF). Ohio Environmental Protection Agency, Columbus OH. [Last accessed 02/02/10]

Top of Page

Touchet River, WA

This screening causal assessment was a novel application of the Stressor Identification process for several reasons. It involved a long river stretch, in an arid watershed of the northwestern U.S. It also marked the first use of endangered salmonids as a Stressor Identification endpoint. Specific alteration of the invertebrate assemblage aided analysis.

Effect: Altered benthic invertebrate assemblages and extirpation of salmonids
Sources: Wheat and irrigated agriculture, impoundments, logging, cattle raising
Probable causes: Primarily water temperature and sedimentation; secondarily toxics, low dissolved oxygen, alkaline pH, reduced detritus, reduced flow and reduced habitat complexity
Manuscript: Wiseman CD, LeMoine M, Cormier S (2010) Assessment of probable causes of reduced aquatic life in the Touchet River, Washington, USA. Human and Ecological Risk Assessment 16(1):87-115.
Report: Wiseman CD, LeMoine M, Plotnikoff R, Diamond J, Stewart A, Cormier S (2009) Identification of Most Probable Stressors to Aquatic Life in the Touchet River, Washington. U.S. Environmental Protection Agency, Cincinnati OH. EPA/600/R 08/145.
TMDL: Washington Department of Ecology. Walla Walla River Basin TMDL Water Quality Improvement Report (2007) and the Walla Walla Watershed TMDL Water Quality Implementation Plan (2008) with links to stressor-specific TMDLs. [Last accessed 05/27/18] 
Guidance, presentations, other: Adams K (2010) Guidance for Stressor Identification of Biologically Impaired Aquatic Resources in Washington State . Washington State Department of Ecology, Olympia WA. Publication No. 10-03-036.

Top of Page

Lake Washington, WA

This is a brief synopsis of a historically important causal assessment of a eutrophic system. Evidence of world-wide consistency of association established general causality. Modeling was important in establishing specific causality.

Effect: Cyanobacteria blooms
Sources: Waste water inputs
Probable causes: Phosphorus
Report: Lake Washington Case Study. p. 4-13 in U.S. EPA (2000) Stressor Identification Guidance Document.  U.S. Environmental Protection Agency, Washington DC. EPA/822/B-00/025.
Guidance, presentations, other: Summarized from Lehman JT (1986) Control of eutrophication in Lake Washington: Case Study. pp. 301-316 in Ecological Knowledge and Environmental Problem-Solving: Concepts and Case Studies. National Academy Press, Washington DC.

Top of Page

Clear Fork Watershed, WV

This case addresses a moderately sized drainage with several tributaries. Stressor-response relationships derived from field data prior to the assessment provided the primary evidence.

Effect: Altered benthic invertebrate assemblage
Sources: Mining, logging, agriculture, and residential development.
Probable causes: Sulfate/conductivity, organic and nutrient enrichment, acid mine drainage, residual metals (particularly aluminum) at moderately acidic pH, excess sediment, and multiple stressors
Report: Gerritsen J, Zheng L, Burton J, Boschen C, Wilkes S, Ludwig J, Cormier S (2010) Inferring Causes of Biological Impairment in the Clear Fork Watershed, West Virginia. U.S. Environmental Protection Agency, Office of Research and Development, National Center for Environmental Assessment, Cincinnati OH. EPA/600/R-08/146.
TMDL: WVDEP (2006) Appendix 1. Clear Fork (PDF) (14 pp, 372 K, About PDF) in Total Maximum Daily Loads for Selected Streams in the Coal River Watershed, West Virginia. Prepared by Water Resources and TMDL Center, Tetra Tech, Inc., Charleston WV.
Guidance, presentations, other: WVDEP (1997) An Ecological Assessment of the Coal River Watershed. West Virginia Department of Environmental Protection, Division of Water Resources, Watershed Assessment Program. Report number - 5050009 – 1997, pp. 93.

Top of Page

Elk Hills, CA (terrestrial)

This case study deals with a contaminated terrestrial site and an endangered wildlife population. This study illustrates the importance of spatial and temporal scales of causes and effects. Based on mathematical modeling to link causes with population changes, it reverses a prior assessment’s findings.

Effect: Decline in abundance of the endangered San Joaquin Kit Fox
Sources: Petroleum drilling, wastes, vehicles and drought
Probable causes: Predation and accidents
Report: U.S. EPA (2008) Analysis of the Causes of a Decline in the San Joaquin Kit Fox Population on the Elk Hills, Naval Petroleum Reserve #1, California. U.S. Environmental Protection Agency, Cincinnati OH. EPA/600/R-08/130.

Top of Page

Upper Arkansas River, CO (terrestrial)

This case study applied Stressor Identification to a highly mineralized area of the Colorado Rocky Mountains. Evaluated impairments were reduced vegetation, plant growth and species richness in meadows irrigated with Upper Arkansas River water. This study demonstrates aspects of the assessment process that may differ between aquatic and terrestrial systems.

Effect: Reduced plant growth and plant species richness
Sources: Mining, smelting, agriculture
Probable causes: Extrinsic metal with decreased pH (floodplain); extrinsic metal (irrigated meadows)
Report: Kravitz M (2011) Stressor Identification (SI) at Contaminated Sites: Upper Arkansas River, Colorado. U.S. Environmental Protection Agency, Cincinnati OH. EPA/600/R-08/029.

Top of Page

Birds of prey (terrestrial)

This synopsis explains that the link between DDT and peregrine falcon decline was not initially recognized. The connection was made by re-examining the impairment description. Eventually it was recognized that the specific effect was reproductive failure due to eggshell thinning.

Effect: Decline of birds of prey
Probable causes: DDT/DDE
Report: Revisiting the Impairment in the Case of DDT. p. 5-2 in U.S. EPA (2000) Stressor Identification Guidance Document. U.S. Environmental Protection Agency, Washington DC. EPA/822/B-00/025.
Guidance, presentations, other: Blus LJ, Henny CF (1997) Field studies on pesticides and birds: unexpected and unique relations. Ecological Applications 7:1125-1132. 
Grier JW (1982) Ban of DDT and subsequent recovery of reproduction in bald eagles. Science 218:1232-1234.

Top of Page