title: Assessing causation of the extirpation of stream macroinvertebrates by a mixture of ions.
abstract: Increased ionic concentrations are associated with the impairment of benthic invertebrate assemblages. However, the causal nature of that relationship must be demonstrated so that it can be used to derive a benchmark for conductivity. The available evidence is organized in terms of six characteristics of causation: co-occurrence, preceding causation, interaction, alteration, sufficiency, and time order. The inferential approach is to weight the lines of evidence using a consistent scoring system, weigh the evidence for each causal characteristic, and then assess the body of evidence. Through this assessment, the authors found that a mixture containing the ions Ca(+), Mg(+), HCO 3(-), and SO 4(-), as measured by conductivity, is a common cause of extirpation of aquatic macroinvertebrates in Appalachia where surface coal mining is prevalent. The mixture of ions is implicated as the cause rather than any individual constituent of the mixture. The authors also expect that ionic concentrations sufficient to cause extirpations would occur with a similar salt mixture containing predominately HCO 3(-), SO 4(2-), Ca(2+), and Mg(2+) in other regions with naturally low conductivity. This case demonstrates the utility of the method for determining whether relationships identified in the field are causal.
authors.affiliation: National Center for Environmental Assessment, U.S. Environmental Protection Agency, Cincinnati, Ohio, USA.
authors.forename: Susan M
authors.initials: SM
authors.lastname: Cormier
authors.forename: Glenn W
authors.initials: GW
authors.lastname: Suter
authors.forename: Lei
authors.initials: L
authors.lastname: Zheng
authors.forename: Gregory J
authors.initials: GJ
authors.lastname: Pond
mesh_terms: D000818:Animals; D001061:Appalachian Region; D015984:Causality; D003032:Coal Mining; D004784:Environmental Monitoring / Q000379:methods*; D006801:Humans; D007448:Invertebrates / Q000145:classification / Q000254:growth & development / Q000502:physiology*; D007477:Ions / Q000032:analysis; D045483:Rivers / Q000737:chemistry*; D014874:Water Pollutants, Chemical / Q000032:analysis*; D014877:Water Pollution, Chemical / Q000706:statistics & numerical data
chemical_list: D007477:Ions; D014874:Water Pollutants, Chemical