Effects of Switchgrass Related Land-Use Changes on Aquatic Macroinvertebrates

This research examines if switchgrass-based land-management practices have the potential to influence aquatic macroinvertebrates through changes in stream flow and water quality. The number of taxa in Ephemeroptera, Plecoptera, and Trichoptera orders (EPT taxa richness/EPT-TR) is analyzed as an aquatic macroinvertebrate bioindicator in the context of regional environmental effects, and changes in stream flow and water quality. This dissertation is structured as three manuscripts that link together to address the overall research question.

The first manuscript focuses on identifying regional environmental variables that influence EPT-TR across ecoregions in Tennessee. The influences of temperature, precipitation, geology, soil, stream flow and velocity on EPT-TR differ among ecoregions and also set the context for local-scale factors.

The second manuscript uses multilevel regression models to evaluate the effects of stream flow and water quality on EPT-TR in the midst of regional environmental factors in Tennessee. Stream flow is found to be statistically significant in influencing EPT-TR across ecoregions, and total nitrogen, phosphorus and sediment are statistically significant within specific ecoregions. However, the magnitude of these effects is very small in the midst of the effects from regional factors. By testing the significance of EPT-TR in explaining water quality, EPT-TR is not found to be a strong indicator of water-quality changes in Tennessee under the conditions of this study.

The third manuscript uses the Soil and Water Assessment Tool (SWAT) to compare stream flow and water quality from a baseline scenario and switchgrass management scenario at the Nolichucky watershed in Tennessee. Stream flow increased and nitrogen and phosphorus concentrations decreased under the switchgrass scenario. Regression models relating EPT-TR and monthly stream flow and water quality from SWAT showed increase in EPT-TR in the switchgrass scenario, but these increases are within the margin of error of monthly estimates. The influence of switchgrass management on EPT-TR cannot be detected under current model assumptions.

Overall, results of the whole study show that EPT taxa are affected by factors that operate at different spatial and temporal scales, and impacts due to switchgrass-management related stream flow and water quality changes cannot be detected in the current spatial context.