Relationships Among Exceedences of Chemical Criteria or Guidelines, the Results of Ambient Toxicity Tests and Community Metrics in Aquatic Ecosystems (Final)
This document is intended to be a technical resource for program offices, regions, states, and tribes interested in the application of these methods for evaluating the attainment of aquatic life use in streams and estuaries and for assessing the causes of impairment in affected systems.
In order to use bioassessments to help to diagnose or identify the specific environmental stressors affecting aquatic or marine ecosystems, a better understanding is needed of the relationships among community metrics, ambient chemical criteria or guidelines and ambient bioassays. However, these relationships are not necessarily simple, because metrics generally assess measurement endpoints are the community level of biological organization, while ambient criteria or guidelines and ambient bioassays assess measurement endpoints at the organism level. The relationship may be further complicated by the influence of other chemical and physical variables that affect the bioavailability and toxicity of chemical contaminants in the environment.
Since 1990, the U.S. Environmental Protection Agency (EPA) has conducted Environmental Monitoring and Assessment Program (EMAP) surveys of both wadeable stream and estuarine sites. These surveys have collected data on biotic assemblages, physical and chemical habitat characteristics and, in some cases, water and sediment chemistry and toxicity. Among these studies is a survey of wadeable streams in the Southern Rockies ecoregion of Colorado in 1994 and 1995 and as survey of estuaries in the Virginian Province of the eastern United States from 1990 to 1993. Streams in the Southern Rockies ecoregion are affected by contamination from hardrock metal mining, while the estuarine sites may be affected by sediment contamination by polyaromatic hydrocarbons (PAHs) and metals.
We characterized streams as metals-affected based on exceedence of hardness-adjusted metals criteria for Cd, Cu, Pb and Zn in surface water; on water column toxicity tests (48-hour Pimephales promelas and Ceriodaphnia dubia survival); on exceedence of sediment threshold effect levels (TELs); or on sediment toxicity tests (7-day Hyalella azteca survival and growth). Estuarine sites were characterized as affected by sediment contamination based on exceedence of sediment guidelines or on sediments toxicity tests (i.e., 10-day Ampelisca abdita survival). Then, assemblage metrics were compared among affected and unaffected sites to identify metrics, particularly richness metrics, were less in groups of sites identified as affected by metals with the criteria or bioassays, while other metrics were not. Fish metrics were less sensitive to the metal contamination, but this lack of sensitivity is likely because of the low diversity of fish assemblages in these Rocky Mountain streams.
Similarly at the estuarine sites, a number of benthic metrics differed between the groups of sites segregated using the organism-level measure, while other metrics did not. This variation among metrics depends on the sensitivity of the individual metrics to the stressor gradients of interest as many metrics may not measure the community response characteristic of a specific stressor. The differences between groups for the more sensitive metrics imply that a relationship exists between the organism-level effects assessed by ambient chemistry or ambient bioassays and the community-level effects assessed by community metrics. Moreover, the organism-level effects are predictive to some extent of the community-level effects.
|May 2005||Report internal review draft completed.|
|Sep 2005||Internal review completed and comments addressed.|
|Jan 2006||External review draft released for comments.|
|May 2006||External review completed and comments addressed.|
|Sep 2006||Final report cleared.|
|Feb 2007||EPA announces the Final document has been posted to the NCEA Web site.|
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