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AN ECOLOGICAL ASSESSMENT OF WESTERN STREAMS AND RIVERS
Citation:
STODDARD, J. L. AN ECOLOGICAL ASSESSMENT OF WESTERN STREAMS AND RIVERS. U.S. Environmental Protection Agency, Washington, DC, EPA/620/R-05/005 (NTIS PB-2010-106543), 2005.
Impact/Purpose:
The purpose of the assessment is fourfold: Report on the ecological condition of all perennial flowing streams and rivers with the exception of those considered 'Great Rivers,' (the lower Columbia, Snake, Missouri and Colorado Rivers). Describe the ecological condition of western streams and rivers with direct measures of plants, fish, and other aquatic life. Assessments of stream quality have historically relied solely on chemical analysis or sometimes on the status of game fish. Identify and rank the relative importance of chemical, physical and biological disturbances affecting stream and river condition. Encourage states to include these design and measurement tools as a portion of their State monitoring programs, so that future condition assessments will be ecologically and statistically comparable both regionally and nationally
Description:
In the 30 years since the passage of the Clean Water Act, Congress, the American Public and other interest parties have been asking the U.S. Environmental Protection Agency to describe the condition of the waters in the U.S. They want to know if there is a problem, how big the problem is if there is one, and whether the problem is widespread or occurs in hotspots. Additionally, they have been asking to understand the types of human activities that are affecting streams and rivers, and which are likely to be the most important. These are seemingly simple questions, and yet they have not been answered in a reliable way for past 30 years. This report presents the results of a unique collaboration between the U.S. Environmental Protection Agency and twelve western States, designed to answer these questions for the rivers and streams of the West.
Covering 42% of the land area, and 28% of the stream and river length in the lower 48 states, EMAP West is the largest monitoring and assessment effort designed to answer the questions being asked of EPA that has been conducted to date. The States and EPA collected biological, chemical and physical data at over 1340 perennial stream and river locations to assess the ecological condition of western waters and the most important factors affecting those conditions. Results provide clear pictures of the biological quality of flowing waters across the West, within each of three climatic zones, and in ten ecological regions. In partnership with the States and EPA Regions 8, 9, and 10, the EMAP program sent four-person teams to collect samples at sampling sites chosen by an innovative statistical design that insures representative results.
This information fills an important gap in meeting requirements of the Clean Water Act. The purpose of the assessment is fourfold:
Report on the ecological condition of all perennial flowing streams and rivers with the exception of those considered 'Great Rivers,' (the lower Columbia, Snake, Missouri and Colorado Rivers).
Describe the ecological condition of western streams and rivers with direct measures of plants, fish, and other aquatic life. Assessments of stream quality have historically relied solely on chemical analysis or sometimes on the status of game fish.
Identify and rank the relative importance of chemical, physical and biological disturbances affecting stream and river condition.
Encourage states to include these design and measurement tools as a portion of their State monitoring programs, so that future condition assessments will be ecologically and statistically comparable both regionally and nationally.
The results of these surveys show that only 51% of the stream and river length in the West could be considered in least-disturbed condition. Of the three climatic areas of the West, the mountains appear to be in the best shape with 56% of the length of flowing waters in least-disturbed condition. The plains and xeric regions present the most concerns with close to 50% of the length of streams and rivers in the most-disturbed conditions (42% and 46%, respectively).
The results also reveal what is most likely responsible for diminishing biological quality in flowing waters across the West. Disturbance of shoreline (or riparian) habitat was the most widespread stressor observed across the West, and in each of the three major regions. Mercury in fish was widespread across the xeric and plains areas but not the mountains. Non-native vertebrates, primarily fish, were very common across the entire West. Evaluation of the stressors most likely responsible for poor condition in the West is best understood by looking at both the extent of each stressor (i.e., how widespread it is) and the relative risk posed to aquatic biota when a specific stressor is present. High nitrogen concentrations are found in just over one-quarter of western streams, and fish communities are almost four times as likely to be in poor condition when nitrogen exceeds a critical threshold as when nitrogen is below these critical values. Excess salinity also poses a high relative risk to fish when it occurs, but is present in only 5% of the stream resource. From a management point of view, the highest priority stressors to address are those that are both common, and that pose high risk to biota.
We trust that this report will be useful for land managers, decision makers and citizens throughout the region. Readers who wish to know more about the technical background are directed to the scientific journals where the methodologies and supporting information already have been published and to the appendices of this report.