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Microplastics in a Small Stream: Storm Response in a Tributary to the Tennessee River
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Researchers used hydrograph separation techniques to investigate whether residential septic systems are a significant source of microplastics to a headwater stream on the Cumberland Plateau. By comparing microplastic concentrations at different points in the storm hydrograph against chemical indicators of septic effluent, they assessed the relative contributions of groundwater, interflow, and surface runoff in transporting plastic particles.
Streams have emerged as a major source of microplastic pollution to shallow marine ecosystems. The ecological impacts are still coming into view, but most view microplastics as a significant threat to aquatic ecosystem health. The origins of microplastics in high-order streams are believed to include degradation of macroplastics, wastewater, and industrial waste. In this study, we use a hydrograph separation technique to investigate whether residential septic systems in shallow soils are a major source of microplastic particles and fibers to smaller headwater streams draining from the Cumberland Plateau. The study site, Mountain Creek, is a 1st order stream in a low-density developed residential area that has septic waste management and is equipped with a USGS stream gage. The concentration of microplastics was determined using the Nile Red dye method and classified by shape. Stream chemistry was plotted on piper diagrams to help chemically distinguish streamflow components. We plot the concentration of microplastics at different points in the stream hydrograph (rising limb, peak, falling limb) against the relative contributions of groundwater, interflow, and runoff to help determine which type of flow is transporting more microplastics. These are compared to chemical indicators of septic effluent (chloride, nitrate, fluoride) to determine whether septic systems can be considered a major source of microplastics and their dominant pathway to the stream channel.
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Microplastics in the Tennessee River: Are Small Streams a Major Source?
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A three-month study of headwater streams in Eastern Tennessee found that residential septic systems and recreational swimming areas contribute substantial microplastic loads to tributaries feeding the Tennessee River. These overlooked rural and recreational sources suggest that microplastic contamination of freshwater systems is more widespread than wastewater treatment plant emissions alone would indicate.
Microplastics in the Tennessee River and Three Tributary Urban Creeks
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Researchers sampled microplastic concentrations in the Tennessee River and three urbanized tributary creeks, finding high and highly variable abundances ranging from fewer than 5 to over 75 particles per liter. Linear fibers dominated all samples, and microplastic levels were most strongly linked to local factors such as proximity to runoff discharge pipes and low-flow accumulation zones.
Microplastic Accumulation Along an Urbanized and Elevational Gradient in Thetennessee River Watershed
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Researchers examined how microplastic concentrations vary along an urbanization gradient and across elevations in the Tennessee River watershed, tracing how land use and topography shape plastic transport through river systems. The findings demonstrate that even remote or elevated areas are not insulated from microplastic deposition, challenging the assumption that distance from urban centers provides protection.
Microplastic Concentration and Type in a Central Illinois Urban Stream
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Researchers measured microplastic concentrations in a small urban stream in central Illinois and found levels orders of magnitude higher than those in major rivers like the Chicago or Danube, with downstream concentrations reaching 2,000 particles per cubic meter. The findings suggest small urban waterways may be underestimated but significant pathways for funneling microplastics into larger water systems.
Elevated Microplastic Concentration in a Small Tributary Stream Under High-flow Conditions: Implications for the Mohawk River, New York
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Microplastic concentrations in a small New York tributary stream surged to 125 particles per cubic meter during high-flow conditions—roughly ten times the low-flow baseline—correlating with storm drain inflow and sewage leakage. This demonstrates that rainfall events dramatically amplify microplastic transport from urban infrastructure into waterways, with implications for downstream river and drinking water contamination.
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