NUTRIENT AND FECAL MICROBE CONTAMINATION IN THE OTTER CREEK WATERSHED, MADISON COUNTY, KENTUCKY

Contamination by nutrients and fecal microbes is a widespread, chronic problem for surface streams as forms of non-industrial pollution. The Otter Creek watershed covers over 168 square kilometers of north-central Madison County, Kentucky, and is affected by some urban runoff from the town of Richmond, but mostly by agriculture, mainly cattle farming, and by rural and suburban areas that utilize septic systems. Samples were collected from representative sites and measured for dissolved nutrients (ammonium, NH₄⁺; nitrate, NO₃^-; and phosphate, PO₄^3-) and fecal microbes (total coliform bacteria and Escherichia coli) using colorimetric and IDEXX methods, respectively.

Nutrient concentrations are generally higher than those of pristine streams. Dissolved ammonium concentrations generally lie below ~0.2 mg/L N-NH₄ with most samples approaching zero. Nitrate concentration generally lies below 5 mg/L N-NO₃ but spike upward at the sewage treatment plant discharge and continue to be high downstream. Orthophosphate displays concentrations below 0.2 mg/L in the entire watershed excepting the sewage treatment plant discharge and stations downstream that show 0.9 to 1.4 mg/L. E. coli concentrations commonly occur between 500 and 1,500 cfu/100mL within the watershed.

Comparison to a national database allows for assessment of contaminant levels. Based on comparisons of land-use from both our sites and the database, our data most closely matches mixed land-use areas. When comparing our data to these areas, median nitrate levels are greater than the national median, whereas ammonium and phosphate levels were lower. The principal source for nitrate and phosphate is a sewage treatment plant that handles waste from Richmond and vicinity, with secondary sources including runoff from the town of Richmond and cattle pasture. Cattle feces seem to be a major source for ammonium and fecal microbe contamination. E. coli assays showed that only 19 percent of the water samples are suitable for bathing according to EPA standards, 40 percent are suitable for recreation, and 60 percent recommend no extended human contact.