Interactive effects of wastewater effluent on stream food webs

Wastewater effluent and trace aquatic contaminants are an emerging concern in aquatic ecology. With my research, I specifically focused on three main aspects: environmentally relevant chemical mixtures, the correlates of variation in connected aquatic and streamside food webs across a gradient of wastewater effluent, and the effects of caffeine on stream food webs and implications for linked riparian food webs. First, I compared two methods for defining mixtures commonly co-occurring chemicals in freshwater systems (Pearson Correlation and Principal Components Analysis) using a USGS dataset spanning 140 sample locations across the U.S. The analysis of correlation coefficients better characterized mixtures than Principal Components Analysis. These methods allowed me to identify several key groups of chemicals: wastewater related chemicals, polycyclic aromatic hydrocarbons, and reproductive hormones. Second, I conducted a large-scale observational study of potential predictors of stream microbial (using 16s and 18s genetic sequencing and nutrient content) and invertebrate assemblages and streamside insects across 12 wastewater facilities in Northwest Ohio. I found nutrients that were associated with wastewater were correlated with changes in microbial community composition and nutrient content of biofilms, which was directly and indirectly related to benthic macroinvertebrate communities and streamside aerial arthropods. This study provided insight on potential pathways of the effects of wastewater effluent but more work was needed to determine specific mechanisms. To tease apart the multiple possible effects of a common chemical components of wastewater effluent on linked stream and streamside food webs, I designed a manipulative study introducing caffeine to local streams via chemical diffusing substrata. Caffeine addition decreased the photosynthetic pigment chlorophyll a and caffeine increased N:P in exposed biofilm. Further, Structural Equation Modeling indicated that the caffeine treatment also had a direct negative impact on benthic macroinvertebrate biomass and this strongly reduced emergent insects. Thus, caffeine negatively affected both stream macroinvertebrates and emergent insects. My research helps identify the best methods for determining commonly co-occurring chemical mixtures and encourages environmentally relevant toxicity testing. I’ve also provided evidence of both wastewater effluent and caffeine altering assemblages of receiving streams and potentially those of nearby riparian zones