Bioassessment of agricultural effects on streams using biochemical compounds in benthic algae

Benthic algae form the base of stream food webs and have long been used as indicator organisms for biological monitoring in streams. Algal essential fatty acid (EFA) analysis is becoming common in studies of stream ecosystems. However, there has been little examination of appropriate EFA metrics, how algal assemblages vary in response to disturbance, vary through time, or compare to taxonomic composition. Additionally, algal stable isotope signals are affected by many environmental variables. The overall goal of this study was to assess how remediation of streams affected by agriculture, through the use of stream-associated best management practices (BMPs) can be measured through algal EFA and stable isotopes. This dissertation took place in the Upper Delaware River watershed in New York State, in which BMPs had been installed over multiple years (BMP age). Only EFAs expressed as mg/m2 consistently demonstrated significant differences between stream categories. BMPs reduced some effects of agriculture, particularly several forms of dissolved nitrogen, which corresponded with a significant decrease in benthic algal total EFA concentration. However, algal EFA concentrations did not detect a significant difference in the effectiveness of BMPs by age. Seasonally, agricultural effects and consequent BMP effects were greatest in the summer. Diatom communities in agricultural streams were composed mainly of biraphid taxa (Gomphonema and Navicula spp.), while mitigated and Reference streams were mainly monoraphid taxa such as Achnanthidium and Cocconeis spp. Diatom assemblage proportions decreased, while chlorophyte proportions increased in agricultural streams. Agricultural streams had higher concentrations of EFAs in assemblages with more chlorophytes and fewer diatoms. There were significant differences in aqueous δ13C and δ15N between reference streams and all agricultural stream categories. Algal δ 13C and δ15N values also differed significantly between Reference and Agricultural streams, but not among different applications of BMPs and streams lacking BMPs. BMPs did reduce agricultural effects, based on nutrient levels, benthic algal EFA content and taxonomic group proportions. However, stable isotopes in water and algae could still detect significant effects of agriculture, even following BMP mitigation. While the outcomes between EFA and stable isotope analysis produced variable results, both techniques show promise for future bioassessment purposes