Land-use and water-quality threats to current and historical Cryptobranchus alleganiensis streams across multiple ecoregions

Freshwater systems have experienced greater biodiversity loss than any other systems on Earth. The Hellbender Cryptobranchus alleganiensis (Daudin, 1803), a fully aquatic salamander species endemic to streams and rivers across the Midwestern and Eastern United States, has experienced drastic declines due to habitat degradation, accelerated sedimentation, aquatic contaminants, and infectious diseases. Although declining water quality is often suggested as a major contributing factor to Hellbender population declines, few studies have evaluated the effects of land use on water quality and Hellbender population status across multiple watersheds and ecoregions. In this study, we sought to understand the relationships between Hellbender population declines with both anthropogenic land use and water quality. We sampled 30 stream sites across a gradient of land use and Hellbender population status in Tennessee and North Carolina, USA, to evaluate relationships between Hellbender populations, water quality, and concentrations of heavy metals and the herbicides glyphosate and atrazine, the latter which we measured via a novel passive sampling technique. We found ecoregion-level differences in atrazine, Cd, pH, and conductivity, with the Interior Plateau ecoregion having the greatest variance in water-quality measurements. Although % watershed development was not different among ecoregions given the sites evaluated, Blue Ridge watersheds were overall less developed than watersheds in the Interior Plateau. We also found relationships between declining Hellbender population status and both increased watershed development and declining estimates of water quality, suggesting that increased anthropogenic watershed disturbance can lead to water-quality declines that can negatively affect the species. Because this research focused on assessing the prevalence of commonly encountered aquatic contaminants, our results and study design are applicable to lotic habitats within the evaluated ecoregions and similar habitats throughout the geographic range of the Hellbender. Our study highlights parameters that should be considered when investigating the effect of anthropogenic disturbance and declining water quality on Hellbender population status and emphasizes the importance of effective land management strategies that reduce anthropogenic effects to freshwater systems.