Concentration and Sources of Fecal and Organic Pollution in an Agricultural Watershed1

Fecal contamination and organic pollution of an agricultural drainage in northeast Indiana was high. Bacterial counts (total coliform, TC; fecal coliform, FC; and fecal streptococcus, FS) and biochemical oxygen demand (BOD) were used to assess waste concentrations. Coliform counts indicated that sections of the drainage receiving septic effluent had waste concentrations far in excess of public health standards (mean FC = 550,000/100 ml). Areas of drainage remote from septic tank pollution were found to occasionally meet federal public health standards for whole body contact recreation but generally these areas had twice the allowable limit of 200 FC/lOO ml. Bacterial contamination was highest during runoff events when the median values for TC, FC, and FS were 5,3, and 17 times greater, respectively, than the median values during low stream discharge. Surface flows carried contaminants from unconfined livestock operations and fecally contiminated sediment was transported by high waters. During one runoff event a BOD loading of 36.7 kg/km2 was recorded and the peak BOD concentration observed was 16 mg/l. A discharge of liquid manure from a confined livestock operation caused a major fish kill. Pollution from septic tanks and unconfined livestock is greatest at high stream discharge when dilution reduces the impact on aquatic life. (KEY TERMS: bacterial pollution; BOD; agricultural runoff; coliform bacteria; fish kill; water pollution sources.)