Evaluation of the Effects of Mining Related Contaminants on Freshwater Mussels (Bivalvia: Unionidae) in the Powell River of Virginia and Tennessee

Abstract

The Powell River is located in southwestern Virginia and northeastern Tennessee, USA and supports a diverse freshwater mussel assemblage of 29 extant species. Throughout the river major ion and trace element concentrations have increased over the last several decades due to extensive surface coal-mining in the headwaters in Virginia. As watershed area affected by mining has increased, mussel populations have declined, especially in Virginia where populations have been severely reduced or extirpated. The upper watershed now has been extensively mined for coal, causing widespread effects on water and sediment quality. To investigate how mining may be affecting mussel populations, I first conducted a laboratory bio-assay to assess the effects of elevated major ions and the trace element nickel (Ni) on growth and survival of juvenile mussels, including one common species (Villosa iris) and one endangered species (Epioblasma capsaeformis). No significant differences in overall survival between treatments and control were observed for either species over a 70 day test period. Total growth was not significantly different between treatments and control for either species. However, overall growth varied significantly (p=0.009) between species, with V. iris (2.49 mm) exhibiting greater growth compared to E. capsaeformis (1.97 mm). Results suggest that major ion chronic toxicity alone or in combination with Ni at or below my test concentration is not a likely source of toxicity to juvenile mussels in the Powell River. Secondly, I conducted a field study in the Powell River using two cohorts of juveniles of Villosa iris to assess the effects of trace elements and PAH contamination related to mining on mussel survival and growth. Specific conductance was elevated throughout the Powell River, where site means ranged from 450 to 900 µS/cm. While mortality was high at all eight sites it was not significantly different among these sites (p>0.28); however, growth of juvenile mussels was significantly higher (p<0.001) in the lower river in Tennessee. Regression analysis showed significant relationships (p<0.001) of river kilometer with temperature, specific conductance, and aqueous major ion concentrations. A principal component analysis (PC) was conducted on all trace element data. Growth of Cohort 1 on Day 106 was best explained by the PC dominated by aqueous major ion concentrations (p<0.0001, R2= 0.65) and growth of Cohort 2 on Day 106 was best explained by specific conductance (p<0.0001, R2= 0.68). Growth of Cohort 2 at Day 423 was best explained by tissue trace element concentration PC1 and PC2 (p<0.0001, R2= 0.73). This study suggests major ions and select trace elements (Ba, Ni, Fe, Se, and Sr) in the Powell River are negatively affecting the growth of freshwater mussels and that the source of these contaminants is primarily from mining in the headwaters.