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Abstract-Because increased ionic strength has caused deleterious ecological changes in freshwater streams, thresholds for effects are needed to inform resource-management decisions. In particular, effluents from surface coal mining raise the ionic strength of receiving streams. The authors developed an aquatic life benchmark for specific conductance as a measure of ionic strength that is expected to prevent the local extirpation of 95% of species from neutral to alkaline waters containing a mixture of dissolved ions in which the mass of SO. Extirpation concentrations of specific conductance were estimated from the presence and absence of benthic invertebrate genera from 2,210 stream samples in West Virginia. The extirpation concentration is the 95th percentile of the distribution of the probability of occurrence of a genus with respect to specific conductance. In a region with a background of 116 mS/cm, the 5th percentile of the species sensitivity distribution of extirpation concentrations for 163 genera is 300 mS/cm. Because the benchmark is not protective of all genera and protects against extirpation rather than reduction in abundance, this level may not fully protect sensitive species or higher-quality, exceptional waters. Environ. Toxicol. Chem. 2013;32:263-271. # 2012 SETAC

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 þ , Mg þ , HCO À 3 , and SO À 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 À 3 , SO 2À 4 , Ca 2þ , and Mg 2þ 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. Environ. Toxicol.

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Abstract-The authors describe a methodology that characterizes effects to individual genera observed in the field and estimate the concentration at which 5% of genera are adversely affected. Ionic strength, measured as specific conductance, is used to illustrate the methodology. Assuming some resilience in the population, 95% of the genera are afforded protection. The authors selected an unambiguous effect, the presence or absence of a genus from sampling locations. The absence of a genus, extirpation, is operationally defined as the point above which only 5% of the observations of a genus occurs. The concentrations that cause extirpation of each genus are rank-ordered from least to greatest, and the benchmark is estimated at the 5th percentile of the distribution using two-point interpolation. When a full range of exposures and many taxa are included in the model of taxonomic sensitivity, the model broadly characterizes how species in general respond to a concentration gradient of the causal agent. This recognized U.S. Environmental Protection Agency methodology has many advantages. Observations from field studies include the full range of conditions, effects, species, and interactions that occur in the environment and can be used to model some causal relationships that laboratory studies cannot. Environ. Toxicol. Chem. 2013;32:255-262. # 2012 SETAC

Biological surveys have become a common technique for determining whether aquatic communities have been injured. However, their results are not useful for identifying management options until the causes of apparent injuries have been identified. Techniques for determining causation have been largely informal and ad hoc. This paper presents a logical system for causal inference. It begins by analyzing the available information to generate causal evidence; available information may include spatial or temporal associations of potential cause and effect, field or laboratory experimental results, and diagnostic evidence from the affected organisms. It then uses a series of three alternative methods to infer the cause: Elimination of causes, diagnostic protocols, and analysis of the strength of evidence. If the cause cannot be identified with sufficient confidence, the reality of the effects is examined, and if the effects are determined to be real, more information is obtained to reiterate the process.

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ACKNOWLEDGMENTSThis report was prepared under 3 work assignments of EPA contract #68-C7-0014 to Tetra Tech, Inc. Authors of this report are Jeroen Gerritsen, June Burton, and Michael T. Barbour. We thank Maggie Passmore and Jim Green of EPA Region 3 for helpful guidance, discussions and review. The biological index was made possible by the intensive data collection efforts and discussion of West Virginia DEP; in particular, Janice Smithson, Jeffrey Bailey, Pat Campbell, and John Wirts. This report was prepared with the assistance of Jeffrey White, Erik Leppo, and Brenda Fowler. A Stream Condition Index for West Virginia Wadeable StreamsTetra Tech, Inc. iv March 28, 2000 (Revised July 21, 2000 THIS PAGE LEFT INTENTIONALLY BLANK A Stream Condition Index for West Virginia Wadeable StreamsTetra Tech, Inc. v March 28, 2000 (Revised July 21, 2000 Tetra Tech, Inc. vi March 28, 2000 (Revised July 21, 2000 THIS PAGE INTENTIONALLY LEFT BLANK A Stream Condition Index for West Virginia Wadeable StreamsTetra Tech, Inc. vii March 28, 2000 (Revised July 21, 2000 LIST OF FIGURES Tech, Inc. viii March 28, 2000 (Revised July 21, 2000 LIST OF TABLES EXECUTIVE SUMMARYOver the past century, land use activities such as mining, agriculture, urbanization, and industrialization have seriously threatened the quality of surface waters by contributing to nonpoint-source pollution. In West Virginia, the investigation of these nonpoint sources of water pollution has become a priority. indicator of ecosystem health and can identify impairment with respect to the reference (or natural) condition. The index includes six biological attributes, called metrics, that represent elements of the structure and function of the bottom-dwelling macroinvertebrate assemblage. Metrics are specific measures of diversity, composition, and tolerance to pollution, that include ecological information.The SCI is to be used as the basis for bioassessment in West Virginia and has been calibrated for a long-term biological index period extending from April through October. A data analysis application has been developed to ensure consistency in data management and analysis throughout the state as DEP biologists conduct biological monitoring.Benefits expected from the implementation of the WV SCI will apply to a broad spectrum of management programs, including:characterizing the existence and severity of point and nonpoint source impairment;targeting and prioritizing watersheds and ecosystem management areas for remedial or preventive programs; evaluating the effectiveness of nonpoint source best management programs; screening ecosystems for use attainability; and developing a basis for establishing biocriteria that relate to regional water quality goals, an EPA priority.The West Virginia SCI was tested with independent data collected in 1998 and was able to correctly identify the majority of the stream sites stressed in some way by human disturbance or pollution. Index scores were divided into 5 proposed rating categories for reporting on the condition...