Using diatoms and biofilms to assess agricultural and coal mining impacts on streams, spatio-temporal variability, and successional processes

Aquatic organisms are excellent indicators of human impacts on stream ecosystems because they provide valuable services and integrate the effects of multiple stressors over time and space, which would be difficult to assess if only considering water chemistry. Agriculture and acid mine drainage (AMD) from historic coal mining contribute to the concentrations of nutrients, conductivity, and pH of streams; all of which are important to the presence and abundance of diatom species. Based on diatom responses to environmental conditions, this research (1) developed indices and examined relationships of metrics with chemistry and land use variables throughout the Western Allegheny Plateau of Ohio and two watersheds, (2) identified how habitat heterogeneity and sampling methods affect diatom diversity patterns and biomonitoring, (3) examined how spatial factors influence diatom assemblage structure and bioassessments, (4) characterized how temporal variability in seven reference and seven non-reference streams affects bioassessments, and (5) documented how AMD impacts biofilm succession, structure, and function as measured by extracellular enzymes. In anthropogenically impacted streams, diatom assemblages showed significant decreased similarity to reference sites, increased % high nutrient diatoms, increased % motile diatoms, and decreased % low nutrient diatoms associated with increased agriculture, and increased % acidophilic diatoms was associated with reduced alkalinity caused by AMD impacts. Intermediate percentages of epilithic habitat promoted diatom diversity, and multiple habitat samples had stronger relationships with watershed impacts than epilithic habitat samples. Spatial factors contributed to diatom assemblage structure likely because of species dispersal within watersheds and the region, but metrics were influenced less by spatial factors. Diatom metrics responded to two-week lags in PO 4-P concentrations, and samples collected toward the end of summer were good indicators of mean nutrient concentrations of the entire summer. All streams experienced similar seasonal changes in nutrients and diatom assemblage structure. Reference sites were consistently classified as minimally-impacted streams within a sampling season and among years, which supports their reliability as benchmarks for ecological integrity. AMD reduced diatom diversity, altered carbon dynamics, caused severe P limitation as indicated by a significant increase in phosphatase activity, and reduced algal biomass where aluminum precipitates coated substrata.