Using bacterial and mitochondrial DNA markers to assess fecal pollution sources in stream water and sediments of a mixed land-use watershed.

Abstract

Aims: Although stream bed sediment can be an important reservoir of fecal bacteria and pathogens, it is rarely analyzed when assessing microbial water quality. This study aims to identify fecal contamination sources in stream water and sediment and evaluate the impact of rainfall events on microbial water quality in a mixed land-use watershed.

Methods and results: Quantitative polymerase chain reaction (qPCR) was employed to quantify human-, cattle-, and chicken-associated genetic markers during dry and wet periods in the Middle Tallapoosa watershed in Alabama, USA. Human- and cattle-associated markers were consistently detected in water samples, irrespective of precipitation, whereas chicken-associated markers were predominantly found following significant rainfall events. In the sediment, all markers were detected at higher concentrations but with lower frequency than in the water. E. coli concentrations in water samples correlated significantly with 2-day antecedent rainfall and streamflow and were substantially lower than in the sediment.

Conclusions: Humans and cattle were the primary contamination sources in the study area, and runoff from storms and sediment contributed to fecal contamination in the streams.