Small scale wastewater treatment plant effluent influences on aquatic macroinvertebrate assemblage, functional feeding groups, and productivity

Abstract

The purpose of this stream-scale study is to evaluate the impacts of minor wastewater treatment plant effluents (<1 MGD) on low order headwater systems in the Southern Appalachian Mountains. Benthic macroinvertebrates, common cations and elements, and stream physicochemical parameters were measured in 5 reference and 3 effluent-impacted streams in western North Carolina. Aquatic invertebrates were collected using a modified North Carolina Department of Environmental Quality macroinvertebrate sampling protocol and keyed to the lowest possible taxonomic level and used to compute community biological index scores, diversity indices, and the percentage of trophic feeding guilds. Unlike those of reference sites, benthic communities in impacted streams did not strictly follow the River Continuum Concept predicted feeding group distributions or trends. Overall trends among impacted sites were variable and correlated to increased ion concentrations as well as increased nutrients and levels of primary production. Increased abundance and richness of collector-gatherers, decreased abundance of Ephemeroptera and Plecoptera, an increase in Trichoptera and Diptera taxa, and lower water quality as indicated by higher stream biological index scores downstream from effluent outfalls were found when compared to upstream control sites. Regression analyses found that temperature, discharge, conductivity, pH, and elevation variables best predicted shifts in several macroinvertebrate taxa metrics in reference verses impacted streams. Non-metric dimensional scaling plots showed that temperature, conductivity, and multiple dissolved ions significantly differentiate these sites. The results of this study are significant as they provide insight into how small-scale wastewater treatment plant effluents impact aquatic assemblages, ecosystem function, and health at the stream-scale. These findings promote why thorough consideration should be given to wastewater treatment plant design, location in the watershed headwaters, and legal regulation as anthropomorphic impact to the environment continues to expand.