Impacts of Wastewater Effluent on Temperate Stream Fish Assemblage Structure
Anthropogenic disturbances are relatively common in freshwater systems; however, documenting and understanding disturbance-specific impacts on aquatic communities remains an area of needed focus. We examined the effects of wastewater treatment plant (WWTP) effluent on fish assemblage structure using 26 riffle sites positioned along two tributaries of the Niangua River, Missouri, USA (West Fork—WWTP effluent present, and East Fork—WWTP effluent absent). Comparisons of rarified species richness (i.e., using interpolation and extrapolation) indicated that α diversity was similar between forks, despite the West Fork having greater raw species richness. Multivariate analyses of fish assemblage structure (β diversity) revealed a significant difference between East and West Fork sites characterized by presence of Etheostoma flabellare (Fantail Darter) and greater abundances of Cottus bairdii (Mottled Sculpin), a heat-intolerant species, in East Fork sites. Analyses of abiotic site characteristics demonstrated that the West Fork generally contained smaller substrates and had warmer water temperatures during winter months, the latter of which may relate to WWTP effluent release in the upper West Fork. These results highlight significant structural differences between riffle fish assemblages in the presence and absence of WWTP effluent, suggesting effluent release may have localized and downstream impacts on stream community structure.
Map depicting the 26 sites sampled in the East (n = 10, gray circles) and West (n = 16, black circles) Forks of the Niangua River during the study. The three circles with X’s represent the sites where temperature loggers were deployed, and the WWTP outfall is located immediately south of W1 (right). Map inset (upper left) depicts the location of Missouri in the U.S., and inset (lower left) shows the location of the upper Niangua River drainage in Missouri.
Rarefied species richness within both the East and West Forks. Solid lines represent interpolation of species accumulation and dashed lines represent extrapolation of species richness if additional individuals were to be captured (gray = East Fork; black = West Fork). The black triangle represents observed species richness in the West Fork, and the gray circle represents observed richness in the East Fork. 95% confidence intervals are depicted for both accumulation curves.
nMDS based on Bray-Curtis similarity, depicting fish assemblage relationships among all study sites (West Fork: black triangles represent individual sites and the dark shaded hull encompasses sites; East Fork: gray circles represent individual sites and the light shaded hull encompasses sites). Upper panel depicts relationships among all 26 summer samples; lower panel depicts relationships among all summer samples and the four sites revisited during the following winter. Sites revisited are labeled ending with “w.”
Relationships between abundance of C. bairdii (per site) and upstream site distances (km) from the lower confluence (with the Niangua River proper). West Fork sites are depicted with black triangles, and East Fork sites are depicted as gray circles. Linear trend lines show relationships in each fork and further illustrate findings from ANCOVA.
Principal component analyses illustrating abiotic relationships among sites in both the East and West Forks. Upper panel depicts the abbreviated dataset (i.e., only includes the 13 sites where all abiotic variables were collected). Measures of depth and % gravel best explained variation represented by PC1 (i.e., values increase towards the positive), and discharge and % pebble explained variation represented by PC2. Lower panel depicts substrate relationships among all 26 sites. PC1 explains variation in % gravel and % cobble among sites, whereas PC2 explains variation in % pebble and further % gravel variation among sites. For both panels, West Fork sites are represented by black triangles and are encompassed by the dark shaded hulls and East Fork sites are represented by gray circles and are encompassed by the lighter shaded hulls.
Stream temperatures from one East Fork site and two West Fork sites measured 15 January 2020 through 15 February 2020. East Fork site temperature is represented by a solid gray line, and temperatures from West Fork sites are represented by a black dotted line for the WWTP “outfall” and a black dashed line for the further downstream site.
Contributor Notes
Associate Editor: W. L. Smith.