This poster describes a draft conceptual risk assessment approach for analyzing the impacts of atmospheric sulfur deposition on mercury sensitive freshwater streams on a broad geographic scale. We will investigate the impact of changing sulfur deposition on concentrations of methylmercury in the streams. We will identify areas where atmospheric deposition of sulfur is the primary contributing source to the total sulfur concentration in the streams. This will allow us to more easily investigate the relationship between atmospheric and aquatic sulfur concentrations, and potentially make some general assumptions about how a change in atmospheric concentrations will affect aquatic methylmercury conditions.