What Factors Influence Freshwater Molluscan Survival in the Conasauga River?

Abstract

Recent biological inventory data shows a consistent decline in molluscan abundance and biodiversity in the Conasauga River Basin in Northwest GA. This study was initiated to monitor sediment and water quality by stable nitrogen isotope ratio analyses (IRMS) of snails and sediments, permeable membrane devices (PMD), polar organic chemical integrative samplers (POCISTM), and conventional water quality analyses for the Conasauga River Basin. Atrazine, metalochlor, prometon, and simazine were the most frequently detected herbicides throughout the basin. Most of the ambient concentrations of detected organic contaminants are at or near the method detection limit and all are well below any aquatic life criteria. Recent evaluation of water quality criteria for ammonia and nitrate suggest that these criteria levels are not protective for mussels. Data suggests that a shift to livestock and row crop land-use results in greater water nutrient levels and increased &#948;15N signatures for aquatic snails. Mean &#948;15N values for snails collected at national forest sites are significantly different from &#948;15N in snails collected in agricultural areas of the Conasauga River Basin (Student t-test, p<0.05). &#948;15N signatures of cow manure (6.71&#8240; wet, 8.40&#8240; dry) and poultry manure treated soil (9.47?) were similar to those of the snails collected in the agricultural areas of the Conasauga. Dissolved nitrate had elevated &#948;15N signatures that reflected the upper range of &#948;15N signatures for the aquatic snails. Elevated nitrogen isotope signatures indicate the fact that a shift in land use within in the basin is impacting the dominant nitrogen source to the aquatic environment. Continued evaluation of water quality criteria levels are needed to determine if aquatic habitats are viable for mussel reproduction, growth, and survival.