title: Escherichia coli loading at or near base flow in a mixed-use watershed.
abstract: This study analyzed the occurrence of Escherichia coli in a mixed land-use watershed with human, cattle, and wildlife fecal inputs located in a karstic geologic region using synoptic monitoring (samples taken throughout the watershed system) during base-flow conditions. The objective of the study was to evaluate the occurrence of E. coli during base-flow conditions for several months at seven different main channel and nine different tributary sampling sites in the Stock Creek watershed, a 49.3-km(2) basin located in Knoxville, TN. Escherichia coli densities were measured using the Colilert (Defined Substrate Technology) method. The instantaneous loads for E. coli were determined from measured flow rates and E. coli densities, with the highest loading rates observed in the late fall. The study indicated a strong correlation between E. coli load rate (colony-forming units [CFU]/d), 7-d antecedent precipitation, and turbidity. Water quality data, however, also exhibited a spatial dependency; for example, the E. coli load rate was better correlated with turbidity in the slower draining basin tailwater sampling sites than in the faster draining upstream headwater sampling sites. In the headwater sites, the E. coli load rate was better correlated with 7-d antecedent precipitation than turbidity.
authors.affiliation: Center for Environmental Biotechnology, The University of Tennessee, Knoxville, TN 37996, USA. rgentry@utk.edu
authors.forename: Randall W
authors.initials: RW
authors.lastname: Gentry
authors.forename: John
authors.initials: J
authors.lastname: McCarthy
authors.forename: Alice
authors.initials: A
authors.lastname: Layton
authors.forename: Larry D
authors.initials: LD
authors.lastname: McKay
authors.forename: Dan
authors.initials: D
authors.lastname: Williams
authors.forename: Shesh R
authors.initials: SR
authors.lastname: Koirala
authors.forename: Gary S
authors.initials: GS
authors.lastname: Sayler
mesh_terms: D000818:Animals; D000829:Animals, Domestic / Q000382:microbiology; D000835:Animals, Wild / Q000382:microbiology; D002417:Cattle; D011232:Chemical Precipitation; D002947:Cities; D015169:Colony Count, Microbial; D004926:Escherichia coli / Q000302:isolation & purification*; D005243:Feces / Q000382:microbiology*; D005618:Fresh Water / Q000382:microbiology*; D006801:Humans; D009391:Nephelometry and Turbidimetry; D011786:Quality Control; D011891:Rain; D013714:Tennessee; D013997:Time Factors; D014871:Water Microbiology; D014872:Water Movements; D014881:Water Supply / Q000032:analysis*