RISING CONCENTRATIONS OF E. COLI IN CHOCCOLOCCO CREEK

Choccolocco Creek is a tributary of the Coosa River, a major waterway in eastern Alabama. In recent years, the concentration of E. coli within Choccolocco Creek has steadily increased. Data from a local volunteer organization shows that in 2015, the E. coli concentrations exceeded the EPA limit of 235 coliforms per 100mL in 27% of their samples ¹. Five years later in 2020, 50% of samples exceeded the limit. The high concentrations of E. coli in the creek put the health and safety of the community at risk. Here, we describe a preliminary report that investigates the temporal changes in stream hydrology of Choccolocco Creek and how they might relate to E. coli contamination.

USGS stream gauge data have been collected from a site in Choccolocco Creek near Oxford, AL since 2008. The hydrograph shows that the creek’s discharge is seasonally dependent, with highest annual discharge in the spring at about 3,000 cfu and the lowest annual discharge in the fall around 10 cfu ². It can be inferred that pollution would be worse in the summer when discharge is low and there are not precipitation events to dilute E. coli concentration. Additionally, if faulty residential septic tank systems are polluting groundwater with E. coli, then we should see higher concentrations during baseflow exclusive, low discharge periods.

The current USGS discharge data do not appear to correlate to the E. coli concentration data. There are two E. coli sampling sites about 6 and 13 miles downstream from the USGS gauging station. Using a Spearman correlation, we assessed the relationship between the E. coli concentrations and the corresponding discharge from the summer months of 2015-2019. We found no statistical significance between the two data sets. These results suggest that there is a need for more consistent high-dimensional data to be gathered so that we can understand the source, fate, and transport of E. coli pollution.

(1) Swim Guide https://www.coosariver.org/swimguide/.

(2) USGS National Water Interface System https://waterdata.usgs.gov/nwis/nwismap/?site_no=02403310&agency_cd=USGS.