Identifying fecal pollution sources using 3M™ Petrifilm™ count plates and antibiotic resistance analysis in the Horse Creek Watershed in Aiken County, SC (USA)

Abstract

Sources of fecal coliform pollution in a small South Carolina (USA) watershed were identified using inexpensive methods and commonly available equipment. Samples from the upper reaches of the watershed were analyzed with 3M(™) Petrifilm(™) count plates. We were able to narrow down the study's focus to one particular tributary, Sand River, that was the major contributor of the coliform pollution (both fecal and total) to a downstream reservoir that is heavily used for recreation purposes. Concentrations of total coliforms ranged from 2,400 to 120,333 cfu/100 mL, with sharp increases in coliform counts observed in samples taken after rain events. Positive correlations between turbidity and fecal coliform counts suggested a relationship between fecal pollution and stormwater runoff. Antibiotic resistance analysis (ARA) compared antibiotic resistance profiles of fecal coliform isolates from the stream to those of a watershed-specific fecal source library (equine, waterfowl, canines, and untreated sewage). Known fecal source isolates and unknown isolates from the stream were exposed to six antibiotics at three concentrations each. Discriminant analysis grouped known isolates with an overall average rate of correct classification (ARCC) of 84.3 %. A total of 401 isolates from the first stream location were classified as equine (45.9 %), sewage (39.4 %), waterfowl (6.2 %), and feline (8.5 %). A similar pattern was observed at the second sampling location, with 42.6 % equine, 45.2 % sewage, 2.8 % waterfowl, 0.6 % canine, and 8.8 % feline. While there were slight weather-dependent differences, the vast majority of the coliform pollution in this stream appeared to be from two sources, equine and sewage. This information will contribute to better land use decisions and further justify implementation of low-impact development practices within this urban watershed.

Cohesive Channel Response to Watershed Urbanization: Insights from the Sand River, Aiken SC

“…This type of anthropogenic forcing has been shown to reduce biotic richness and enhance the dispersal of invasive plants and seeds [14][15][16][17]. Water quality issues also arise because urbanization leads to increased concentrations and loads of chemical pollutants [14,[18][19][20], alters water nutrient content [20][21][22][23], and exacerbates issues arising from non-point source pollutants [14,24,25]. The consistently observed ecological impacts and associated stream system degradation is termed "urban stream syndrome" [5,26], which has seen a global marked increase over the past century due to a rapid increase in human population and associated rise in human interactions with natural systems [5,15,[26][27][28][29].…”