Environmental effects of road runoff on Little Black Creek

We are studying the extent of environmental impairment caused by road-induced stormwater runoff in an urban stream. In addition to characterizing water quality and testing for toxicity, we are also evaluating the movement of contaminated sediments during runoff events. Preliminary data suggest that road runoff is contributing nutrients, suspended sediment, and oil and grease to Little Black Creek (Muskegon County, MI). Mean total phosphorus in road runoff was 0.25 mg/L, compared to in-stream concentrations of 0.01 mg/L at baseflow and 0.03 mg/L during storm conditions. Similarly, average ammonia concentrations in road runoff were 0.17 mg/L, compared to 0.04 mg/L (baseflow) - 0.06 mg/L (stormflow) in-stream. Oil and grease averaged 3.5 mg/L, which was more than 2 X the concentration measured in Little Black Creek during baseflow or storm conditions. Road runoff also stimulated sediment movement, with average bedload transport rates of 2 kg/min downstream of runoff inflows, compared to 0.4 kg/min upstream. At this point, we have not detected any runoff impacts on biota during toxicity tests on the zooplankter Ceriodaphnia dubia or the alga Selenastrum capricornutum. Future analyses include additional biotic assays, metals quantification, and an engineering assessment examining possible retrofits to minimize the impacts of road runoff to Little Black Creek.