Ionic Stress in Appalachian Headwater Streams Are Total Dissolved Solids Toxic? 10 th percentile=impairment threshold Kentucky Indicator Taxa Low Conductivity High Conductivity West Virginia Indicator Taxa Low Conductivity High Conductivity N=59 N=25N=21N=18 < >750 CONDUCTIVITY Conductivity Intolerant Richness N=59 N=25N=21N=18 < > 750 CONDUCTIVITY % Conductivity Tolerant Indicator Species Analysis (Headwater/Spring Season) Gregory J. Pond and Margaret E. Passmore, U.S. EPA Region 3, Wheeling, WV Teresa Norberg-King, U.S. EPA ORD, Duluth, MN Gregory J. Pond and Margaret E. Passmore, U.S. EPA Region 3, Wheeling, WV Teresa Norberg-King, U.S. EPA ORD, Duluth, MN CONCLUSIONS Response to Conductivity (KY & WV headwater streams) This analysis found many taxa significantly related to high or low conductivity. The KY and WV datasets yielded similar taxa lists, but some differences were noted. The tables below are sorted by highest Indicator Value (IV). Two metrics were created from these lists and boxpots showing their relation to conductivity are shown below EPT GENERA >1000 WV EPT vs. Conductivity Tracheal Gills – used in respiration and ion regulation Concentrated Hemolymph (insect blood) Urine and Frass -- active H 2 O and salt loss Eating and Drinking -- active H 2 O and salt intake passive H 2 0 intake passive salt loss Dilute Freshwater Courtesy WVDEP Tracheal Gills and Active Ion Uptake Gill surfaces are covered in chloride cells, the site of ion exchange ↘ 1.Certain species can regulate the number of active cells 2.Within a species, the number of active cells is inversely related to the salinity of the medium 3.Species with abundant chloride cells appear vulnerable due to overexposure to various ions Courtesy WVDEP Possible Physiological Mechanisms Vulnerable/SpecialistsTolerant/Generalist s High Chloride Cell Density Low Chloride Cell Density Courtesy WVDEP Not an Acute Effect? Most Sensitive Life Stage? Background Region 3 and our component states are currently struggling to develop Total Maximum Daily Loads (TMDLs) for total dissolved solids (TDS). The toxicity testing literature indicates that changes in the concentrations and types of major cations and anions can be both acutely and chronically toxic to aquatic life, in the absence of any other toxicant. These tests are typically conducted using synthetic salt solutions. Some of these tests mimic the makeup of various types of effluents, but lack other toxicants found in the effluents. Adverse endpoints include death, and effects on reproduction and growth. In the southern coal fields of Region 3, where alkaline coal mine drainage is common, TDS and/or elevated conductivity have been identified as a primary stressor to aquatic life in many biologically- impaired streams. These streams are naturally very dilute with conductivities measured at < 40 uS/cm. However, alkaline coal mine drainage routinely increases conductivity to uS/cm due to increased mineralization of the mine overburden on the mined areas and in associated valley fills. The elevated conductivity and ionic changes are thought to interfere with normal osmoregulation in invertebrates. Field studies of macroinvertebrate communities from Kentucky, Virginia, and West Virginia coal fields have shown that conductivity explains the most variance in commonly used benthic assessment metrics. Because macroinvertebrates have evolved in and are adapted to very dilute streams in the region, ionic imbalance is a probable physiological mechanism of impairment. Empirical data from the West Virginia and Kentucky coalfields suggest that % of macroinvertebrate IBI’s score below established impairment thresholds (based on the reference condition) when conductivity is greater than 500 u S/cm. Mayflies (Ephemeroptera) appear to be highly sensitive to TDS in the region. Acute and chronic endpoints of particular ions have been established for commonly used test organisms such as Ceriodaphnia; however, few toxicological studies have been carried out using sensitive Appalachian macroinvertebrates. Furthermore, the toxicity testing literature indicates No Observed Effects Concentrations (NOECs) that are typically 2—3 times higher than the TDS thresholds suggested by the empirical data. Our research interests include testing organisms that are more representative of the native Appalachian fauna, taking into account various life stages, temperatures, and other variables that may define the critical exposures. Region 3 has been awarded a grant to work with ORD-Duluth and USGS to conduct laboratory experiments to determine toxicity of various ions or total dissolved solids to indigenous aquatic life. Research Objectives/Outcomes: 1. A literature review of the bioassay research on TDS or conductivity. 2. An analysis and summary of available empirical datasets in Region 3 and surrounding states to develop empirical relationships between TDS/conductivity and the condition of aquatic life. 3. Bioassay results using synthetic salts that mimic typical southern Appalachian coal field ambient samples (but lack other potential stressors like Selenium) and several commonly cultured species to establish both acute and chronic endpoints (eg. LC50s, LOECs and NOECs). Longterm research objectives may include more relevant species of Appalachian mayflies, stoneflies and caddisflies, various life stages (e.g. nymphs and eggs), and various temperatures. 4.Recommendations for defensible TDS/conductivity thresholds that would be protective of the typical Appalachian macroinvertebrate community. 5.We have been also testing for metals associated with periphyton/ aufwuchs scrapings on rocks below valley fills to explore routes of exposure other than the water column. Many of the conductivity intolerant taxa are “scrapers” and eat the periphyton/aufwuchs RARE Project It is obvious, from the empirical data, that elevated conductivity has strong effects on sensitive Appalachian benthic communities. Although TDS may serve as a surrogate to actual toxicants, it is logical to conclude that conductivity can affect osmoregulation or cause dehydration in freshwater taxa. However, preliminary toxicity and growth (molting) tests showed that sensitive Epeorus and Peltoperla were not affected by mine effluent after a 6d exposure period. Because these and other taxa are absent from waters with high TDS, we think there are chronic effects or toxicity to other life stages (eggs, early instar nymphs). Moreover, there is evidence that higher temperatures (e.g., 20˚ C) causes lower toxicity thresholds in Isonychia mayflies (Kennedy 2000). Thus, the effect of temperature will be addressed in the future rounds of bioassay tests. 10 th percentile=impairment threshold TaxonCond TypeIVMeanSDp-value Ephemerella< Leuctra< Amphinemura< Epeorus< Baetis< Paraleptophlebia< Stenonema< Drunella< Isoperla< Cinygmula< Rhyacophila< Dolophilodes< Haplopera< Leptophlebiidae< Stempellinella< Oulimnius< Heptageniidae< Acroneuria< Ameletus< Pteronarcys< Neophylax< Yugus< Heleniella<