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

The Otter Creek watershed receives a variety of point- and non-point-source contaminants that threaten its water quality. The watershed drains the town of Richmond, Kentucky in its northern portion but primarily is situated in rural areas with cattle pasture and scattered residences. To assess water quality and to identify sources of contaminants, we collected water samples at 42 sites chosen to represent a variety of land uses and potential sources of pollution.

Water samples were taken on four days throughout the summer of 2023. We measured nutrient concentration (nitrogen as nitrate and ammonium, and phosphorus as phosphate) using established colorimetric methods, and generated fecal microbe counts (Total Coliform and Escherichia coli) using IDEXX materials and procedures.

Nutrient concentration varies widely. Ammonium levels are generally near zero with a highest recorded concentration of 5.4 mg/L N-NH₄. The mean and highest nitrate values are 0.5 mg/L and 7.7 mg/L N-NO₃, respectively. Median phosphate concentration is 0.02 mg/L P-PO₄ with a maximum value of 0.5 mg/L. E. coli counts have median value of 1,212 cfu/100 mL with many samples showing the technique limit of 2419.6 cfu/100 mL. The most consistent high nitrate and phosphate concentrations were found within the discharge of a sewage treatment plant and decreased progressively at downstream stations. Highest ammonium concentrations and highest E. coli counts were found at sites with active cattle pasture.

Both point- and non-point-source contamination occurs in the Otter Creek watershed. Compared to national data, nitrate and phosphate concentrations only occasionally spike higher than median national values for agricultural areas, mostly due to contributions from the sewage treatment plant. Ammonium levels are also below national median concentration. Fecal microbe counts commonly exceed the EPA standard of No human contact recommended (>575 cfu/100 mL) amounting to 49% of all samples. Sampling during five field seasons (2013-2015; 2022 and 2023) shows consistent contaminant sources and similar levels of nutrient and fecal microbe contamination. Addressing these identified contamination sources can lead to improved water quality of the Otter Creek watershed.