Document Type

Master's Research

Degree Name

Master of Science




Robert B. Gillespie

Date of Award



The objective of this study was to determine if water quality or instream habitat had a greater impact on aquatic macroinvertebrate communities. In order to investigate the complex interactions of water chemistry and stream habitat, macroinvertebrates were collected from local streams with a history of herbicide use as part of a larger ecological assessment study. Macroinvertebrate data were compared to a variety of stream parameters. Laboratory bioassays were also conducted with a Daphnia species (Daphnia magna) and an amphipod species (Hyallela azteca) using water from the same local streams. Macroinvertebrate community response variables were correlated, through linear regression, to both instream habitat and water quality variables. While several instream habitat quality variables were significantly correlated with one or more macroinvertebrate metrics, this was true for only two water quality variables. This would indicate that variation in stream habitat, more than water quality, determines the macroinvertebrate community compositions within the study area. Sites with relatively greater nitrate concentrations were correlated with more impaired macroinvertebrate communities. Water quality effects were observed in both Daphnia and amphipod bioassays. Decreased survival was observed in amphipods exposed to water from sites with higher atrazine, total pesticide, and nitrate concentrations, when compared to both the less contaminated site and the reference treatments. However, increased reproduction was observed in Daphnia in all spring (high-exposure) creek treatments, when compared to fall (low-exposure) and reference treatments. Results from ecological assessments and bioassays indicate that future conservation practices should focus on improving stream habitat quality and reducing nitrate, while maintaining current water quality improvement practices.