Relative Toxicity of Nickel, Potassium, and Chloride to Endemic Freshwater Gastropods in the Cahaba River Basin

Abstract

Alabama is host to unprecedented freshwater gastropod endemism and increasing habitat change through urbanization and rural farmland development. Many freshwater gastropods are restricted to single catchments and are thus vulnerable to the environmental pollution associated with human activities. Previous studies have demonstrated the toxic capacity of nickel, potassium, and chloride (i.e., common urban and agricultural toxicants) to species present in Alabama. The goal of this thesis research is to further characterize the relative toxicity among three chemicals and three species/groups endemic to the Cahaba River in the Mobile River basin. We collected juvenile and adult prosobranch gastropods (Somatogyrus georgianus, Elimia cahawbensis, and Elimia spp.) from the Cahaba River and its tributary, Sixmile Creek, and conducted 18 96-hour acute toxicity tests split evenly among the three toxicants. The snails collected were approximately 60-120 days old based on knowledge of spawning seasons, although we used size as a proxy for age during field collection. We found nickel to be the most toxic pollutant tested, followed by potassium, and chloride. Among juvenile snails, S. georgianus was the most sensitive species/group to nickel and potassium, whereas Elimia spp. was the most sensitive species/group to chloride. The relative trends across species/groups changed for adult snails, although the relative sensitivity among the toxicants remained the same. This thesis research confirms the toxic capacities for nickel, potassium, and chloride and suggests novel trends in the effects of age on the toxicity of heavy metals to Elimia snails. Additionally, through comparisons with published literature, this thesis reinforces the use of hardness-based Water Quality Criteria for conservation and management.