Exploring how Clean Water Act enforcement influences stream macroinvertebrate communities

Enforcement is a key feature of the Clean Water Act. The Clean Water Act’s National Pollutant Discharge Elimination System (NPDES) permit program regulates effluent into streams that may impact aquatic life. Yet, authorities do not always enforce permits when violations occur. My research examines macroinvetebrate survey data near NPDES permitted facilities in Kentucky and Tennessee to determine the influence of enforcement actions on aquatic biodiversity. Pre-existing data from the Environmental Protection Agency and state agencies was used to make quantitative and spatial comparisons.

My first study used multiple regression to explore whether enforcement and freshwater community indicators changed together. North Carolina Biotic Index (NCBI) and Percent Clingers both significantly covaried with enforcement in fourth and fifth order streams (p=0.048** and p=0.056* respectively). Enforcement and Ephemeroptera-Plecoptera- Trichoptera (EPT) taxon richness also had a significant relationship in an ecoregion subset encompassing the Mississippi Valley Loess Plains, Interior River Valleys & Hills, and Southeastern Plains (p=0.079*). Taxon Richness covaried with enforcement in eastern ecoregions of my study area (p = 0.095*).

My second study used linear regression and a differencing design to see whether time and/or distance influenced the observed covariance relationship seen in my first study. EPT composition downstream of NPDES sources improved in time since enforcement (p= 0.056*) and distance from where the discharges occurred (p= 0.051*). NCBI in communities downstream of an NPDES facility also improved as distance from the facility increased (p= 0.098*).

My research suggests that National Pollutant Discharge Elimination System enforcement has a positive influence on aquatic macroinvertebrate communities. Yet, some authorities suggest NPDES permit enforcement is decreasing nationwide. Understanding the relationship between biodiversity and enforcement in aquatic habitats may encourage authorities to reassess enforcement trends regionally and nationally.