MICROPLASTIC DISTRIBUTIONS IN RURAL RESERVOIR SYSTEMS

Microplastics are contaminants of emerging concern due to their known and unknown harm to ecological and human health. Prior research demonstrates that the main pathway of microplastics to the global ocean is through fluvial systems. However, rivers are often dammed to create reservoirs that provide drinking water, flood control, and recreation to nearby communities. The role of these impoundments in microplastic transport and storage is nevertheless understudied, with both reservoir morphology and particle characteristics potentially impacting microplastic distributions. As an example, microplastic densities influence their propensity to remain suspended in the water column or deposit into bed sediment, thereby presenting differing ecological risks to littoral, limnetic, and benthic habitats. Because microplastics can enter the circulatory system, contain endocrine-disrupting compounds that may inhibit hormone production and cause immune suppression, or travel through the food chain, evaluating their distributions in reservoir systems is critical in determining their environmental risks. We thus assessed microplastic distributions across the Kaskaskia River watershed in central Illinois, United States, including at both upstream (Lake Shelbyville) and downstream (Carlyle Lake) impoundments of the river. To do so, we acquired in situ water quality data (e.g., turbidity, specific conductivity, pH), surface water samples (by hand into glass bottles), and bed sediment samples (with a ponar sampler into high density polyethylene containers) at sites across Lake Shelbyville (n = 26), Carlyle Lake (n = 24), and the Kaskaskia River (n = 5) on 6-7 June 2024. Triplicate environmental samples (n = 3) and duplicate water blanks (n = 1) were also obtained. Our preliminary data showed that water column turbidity was highest in the river and near the inlets of both reservoirs. While future work involves quantifying and characterizing microplastics in our samples, we expect their concentrations to be highest in both water and sediment near the reservoir inlets because of elevated debris loads from the river and subsequent settling processes as water slowly transits the impoundments. Our findings could inform microplastic mitigation and management strategies for rural communities that are already impacted by water quality issues due to industrialized agriculture.