Relationships Among Exceedences of Sediment Guidelines, the Results of Ambient Sediment Toxicity Tests, and Community Metrics in Estuarine Systems

Abstract

To use bioassessments to help diagnose or identify the specific environmental stressors affecting estuaries, we need a better understanding of the relationships among sediment chemistry guidelines, ambient toxicity tests, and community metrics. However, this relationship is not simple because metrics generally assess the responses at the community level of biological organization whereas sediment guidelines and ambient toxicity tests generally assess or are based on the responses 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. Between 1990 and 1993, the U.S. Environmental Protection Agency (USEPA) conducted an Environmental Monitoring and Assessment Program (EMAP) survey of estuarine sites in the Virginian Province of the eastern United States. The surveys collected data on benthic assemblages, physical and chemical habitat characteristics, and sediment chemistry and toxicity. We characterized these estuarine sites as affected by sediment contamination based on the exceedence of sediment guidelines or on ambient sediment toxicity tests (i.e., 10-day Ampelisca abdita survival). Then, benthic invertebrate metrics were compared among affected and unaffected sites to identify metrics sensitive to the contamination. A number of benthic invertebrate metrics differed between groups of sites segregated using the organism-level measures whereas other metrics did not. The difference among metrics appears to depend on the sensitivity of the individual metrics to the stressor gradient represented by metals or persistent organic toxics in sediments because the insensitive metrics do not effectively quantify the changes in the benthic invertebrate assemblage associated with these stressors. The significant relationships suggest that a relationship exists between the organism-level effects assessed by chemistry or ambient toxicity tests and the community-level effects assessed by community metrics and that the organism-level effects are predictive, to some extent, of community-level effects.