The development and use of a spatially explicit model for river otters to evaluate environmental hazards: a case study on the Department of Energy's Savannah River Site

The Department of Energy's (DOE) Savannah River Site (SRS) faces a legacy of radionuclide and metal contamination from industrial processes that occurred throughout the site. Northern river otters (Lontra canadensis) are appropriate receptors for studying the effects of long-term, low-level contamination because they are long-lived, higher trophic level organisms susceptible to accumulating high levels of pollutants. The purpose of this study was to use latrine surveys to examine patterns of wetland latrine usage; explicitly model northern river otter resource selection on the landscape level; and utilize the model results within an ecological risk assessment (ERA) framework to assess potential effects of metals and radiocesium (Cs-137) on the population for the SRS as a case study. River drainages and associated wetlands were surveyed for latrine sites and scats were collected and analyzed for Cs-137 activity to validate model results. The spatially explicit resource model predicted otter drainage reach use and was used in an ERA to develop exposure models for nine heavy metals as well as Cs-137 on the SRS population of river otters. The evaluation predicted that the only contaminant occurring at high enough levels to cause population effects was mercury and that the observed concentrations were probably not high enough to cause significant impairment. However, multiple metals were above action level thresholds. The field validation process showed an unexpected preference for one man-made treatment wetland that was heavily contaminated, showing that the ERA process is complex and must be approached using multiple scales.