Project: E. coli in freshwaters - spatial and temporal distribution and relationship with nutrients in Carter Creek sub-catchments

Investigators: Cara Harclerode, Jacqui Aitkenhead-Peterson and Terry Gentry

Fifteen small sub-catchments of the Carter Creek watershed encompassing the twin cities of Bryan and College Station in SE Texas are being sampled to quantify E.coli geographical distribution and the effect of freshwater nutrients on their numbers. Sampling these sites commenced in late June 2007. Samples are collected using a sterile whirlpak bag every two weeks. Samples are analyzed for E. coli with 4 hours of collection. Aliquots are quantified for pH and conductivity and the remainder of the sample is syringe filtered through ashed (400° C for 5 hours) Whatman GF/F filters (0.7 µm nominal pore size) for nutrient analysis. Samples are frozen until analysis. Dissolved organic carbon (DOC) and total dissolved nitrogen (TDN) are quantified using a Shimadzu TOC-V analyzer, anions using ion chromatography and in-organic nitrogen, ammonium and nitrate using a Westco Scientific discrete analyzer.

Impairment by E. coli has put Carter Creek on the EPA 303d listing for impaired waters since 1999 and high nutrients since 2006. Our study suggests that the geographical source of E. coli in Carter Creek lies within the Burton Creek sub-watersheds upstream of the waste water treatment plant (Figure 1). Counts of E. coli forming units are extremely high and can reach up to 64,000 colony forming units (CFU) per 100 mL of creek water during a rain event.

To date we have found no correlation between E. coli counts and nutrient concentrations.