Research sponsored by the USGS/NIWR Water Resources Act Program 104b Grant (Fiscal Year 2023-2024)
Report Title
Evaluating longitudinal declines in water quality in the Conasauga River using aquatic macroinvertebrates
Principal Investigator(s)/Authors and Affiliation
Dr. Seth Wenger
University of Georgia
Abstract
The Conasauga River in Northwest Georgia is nationally recognized for its aquatic biodiversity, much of which is imperiled. The river supports five federally listed fish and seven federally listed mussel species and has been identified as a top priority watershed for conservation in the southeastern USA (Elkins et al. 2019). As many as 30% of the native mussel species in the Conasauga may be extirpated (Evans 2001, Walters et al. 2003), and numerous fish species have declined precipitously in abundance since 2000 (Nagy et al. 2024), including the federally endangered Amber Darter (Percina antesella) and the federally threatened Frecklebelly Madtom (Noturus munitus; Freeman et al. 2017, Stowe et al. 2020). The mechanisms contributing to declining aquatic species have yet to be identified.
The headwaters of the Conasauga River lie in the Chattahoochee National Forest in the Blue Ridge Mountains, but the river quickly enters a highly productive agricultural valley after exiting the national forest (Fig. 1; Bumpers et al. 2019). Shortly downstream of the National Forest boundary agricultural land use increases to ~ 19% of the entire watershed (Figure 1; Bumpers et al. 2019). Nitrogen (N) and phosphorus (P) concentrations in the Conasauga River are consistently high compared to EPA reference conditions, and episodically spike to very high levels (Sharpe and Nichols 2007, Lasier et al. 2016, Bumpers and Freeman 2017). Nutrients, contaminants, and sediment from agricultural activities may negatively affect water quality and impair the habitat of aquatic species in the river.
The density and biomass of aquatic insects can be measured to assess water quality impairment. Changes in community composition versus changes in total community biomass can provide insights into potential effects on higher trophic levels. For instance, fish communities may not be affected by water quality impairment if the quantity of prey does not change, even if the taxonomic composition does. However, if water quality results in overall declines in prey biomass, fish could become resource-limited and thus have their carrying capacity reduced as a result of indirect effects of water quality. We estimated invertebrate abundance, biomass, and species composition in the Conasauga River along a longitudinal gradient in landuse to assess if the Conasauga River has depressed invertebrate biomass. We evaluated if 1) invertebrate populations and communities differed along this longitudinal gradient and 2) if invertebrate biomass in the Conasauga is lower than expected compared to similar rivers. Here we summarize findings from year 1 of a two-year project.