NATURAL AND HUMAN IMPACTS ON STREAM DIATOM COMMUNITIES

Algae, especially diatoms, are crucial components of stream ecosystems, yet they are often neglected in biological assessments of stream impairment. They provide many important functional services and respond to a variety of chemical and physical variables, which makes them especially useful in stream assessments. For this study, 60 sites were sampled throughout southeastern Ohio, 24 within the Shade River basin, and 18 sites within the neighboring Leading Creek watershed. On the large regional scale, communities were significantly associated with phosphate, a gradient of ionic composition (calcium, magnesium, sodium, and chloride), and forest connectedness, an indicator of human activity. Partial redundancy analysis, after forward selection of significant variables, revealed that the majority of species variation was explained by chemistry (25%) and to a lesser extent by spatial variables (12.3%), with only 6.3% explained by chemistry-spatial interactions. In the Leading Creek watershed, 6 sites were along an acid mine drainage impact gradient, 6 sites were impacted by mine discharge containing extremely high concentrations of dissolved solids, and 6 sites had no mine drainage, but some agricultural impairment. Correspondence analysis of species data formed three groups representing the aforementioned conditions, and discriminant analysis using chemical data (pH and conductivity) successfully classified 100% of the sites in the three categories. Percent similarity of communities in study sites to reference sites was negatively correlated (p <0.05) to measures of AMD, specifically sulfate, aluminum, iron, and manganese, i.e. diatom assemblages were less similar to reference sites as AMD impairment became more severe. Measures of species richness were also negatively correlated (p < 0.05) with increasing AMD impairment. Diatoms are extremely useful for investigating how humans have impaired streams, but a certain amount of variation is due to species distributions. In this study, diatoms were sensitive to stressors and variables operating on a range of spatial scales, from a small stream reach to large regional patterns and processes.