Water Quality in Urban and Rural Sub-Catchments.

Carter Creek in Brazos County, Texas, has been on the EPA 303(d) List for bacterial impairment since 1999 and for nutrient impairment since 2006.  Considering this chronic impairment, a study was developed to investigate the geographical source of E. coli and various nutrients over the course of one year.  Fifteen nested subcatchments were monitored twice monthly for E. coli, dissolved organic carbon (DOC), total dissolved nitrogen (TDN), chloride, fluoride, nitrate, sulfate, phosphate, sodium, potassium, magnesium, calcium and ammonium.   An urban subcatchment contributes the largest E. coli load to Carter Creek, averaging 7294 CFU/100 mL, and a rural headwaters site contributes the least, averaging 1355 CFU/100 mL.  Mean dissolved organic carbon (DOC) among study sites ranged from 26-60 mg/L and total dissolved nitrogen (TDN) ranged from 0.9-11.27 mg/L.