EFFECTS OF LAND USE AND SEASON ON MICROORGANISM CONCENTRATIONS IN URBAN STORMWATER RUNOFF

This study investigated differences in pathogen and indicator organism concentrations in stormwater runoff between different urban land uses and seasons. Stormwater samples collected from storm sewers draining small municipal separate storm sewer systems shown to be free of cross connections within an urban watershed dominated by a single land use were analyzed for pathogens (Pseudomonas aeruginosa and Staphylococcus aureus) and indicator organisms (total coliform, fecal coliform, fecal streptococcus, enterococcus, and E. coli). The samples were collected from three land-use designations (high-density residential, low-density residential, and unlandscaped commercial) in all four seasons. Flow-weighted samples were collected using automatic samplers connected to flow meters. Rain gauges in the drainage basin recorded the event while the flow meter recorded flow velocity, water level, pH, dissolved oxygen, conductivity, and temperature of the runoff. Organism concentrations from high-density residential areas were higher than those associated with low-density residential and landscaped commercial areas. Concentrations of organisms were significantly affected by the season during which the samples were collected. The lowest concentrations were observed during winter.The results will help watershed managers target BMPs or treatments to land uses having higher runoff loads having greater impact on lowering the total load to a receiving water.