Hurricane Harvey has caused unprecedented devastation to huge parts of southeastern Texas, particularly damaging the wastewater infrastructure resulting in release of sewage contamination into environmental waters. The purpose of this study was to conduct a preliminary assessment of fecal indicator bacteria (E. coli and enterococci) and human-associated fecal genetic markers (Human-associated Bacteroidales), measured using qPCR assays, across a Texas river impacted by Hurricane Harvey. Water samples were collected along the Guadalupe River during September – December 2017. The most heavily flooded sites showed highest abundance of fecal indicator bacteria and human-associated Bacteroidales markers indicating that a large number of sewage overflows and stormwater runoff occurred during Harvey flooding. These findings suggest that high levels of human fecal contamination were introduced into waterways draining into the Gulf of Mexico and impaired surface water quality. The human-associated Bacteroidales markers exhibited low to slightly strong correlation with conventional fecal indicators suggesting the variable occurrence of different markers and uncertainty of enterococci and E. coli for detection of human fecal pollution. In general, results of this initial microbiological contaminant assessment will serve as baseline information for follow-on studies to monitor existing and emerging public health risks to residents of Texas and potential long-term environmental impacts upon the water resources in the impacted regions.

The microbial source tracking study undertaken in the Guadalupe River after Hurricane Harvey substantiates that the large number of sewage overflows and stormwater runoff occurred during Harvey flooding introduced high levels of fecal bacteria in environmental waters. On the other hand, based on the qPCR data the low correlation between human-associated Bacteroidales and the conventional fecal indicator assays such as Entero1 highlights the ambiguity of enterococci as robust human fecal pollution surrogates. In addition, relatively high levels of enterococci and E. coli were found in the samples with low to moderate levels of human-associated Bacteroidales markers, with Entero1 signals being consistently higher than the other markers. This may be due to variable persistence of different markers after release from their hosts. Because E. coli and enterococcus concentrations are not specific for human feces, it may be noted that counts of these indicator organisms may overstate the public health risks associated with stormwater runoff. This has been suggested in previous studies; altogether, these data supports the use of Bacteroidales markers as effective indicators of human fecal contamination. These findings also illustrate the extent in which E. coli and enterococci levels may be uncoupled to evidence of human sewage contamination in the environment.

Confronting water quality deterioration from fecal contamination remains a significant challenge for many countries in the world, especially during and after natural disasters, and can cause serious human health risks as well as severe environmental and as economic repercussions. For instance, surveys in the aftermath of Hurricane Katrina identified several cases of Vibrio infections and gastrointestinal illness. Example of an economic impact is when fecal indicator bacteria concentrations in coastal waters exceed standards, beaches are closed or posted with water quality advisories. High levels of fecal pollution are the primary cause of river and stream impairment in the United States according to the National Water Quality Inventory, with numerous often uncharacterized contamination sources. Hence, accurate and reliable fecal source identification methods are essential for mitigating bacterial contributions to waterways and maintaining water quality. In the current study, we have evaluated the presence and abundance of fecal indicator bacteria and human-associated markers in water samples collected along an impacted Texas waterway in the weeks following Hurricane Harvey. These data will provide the required information to produce a dynamic fecal source model for surface waters impacted by sewage overflows caused due to extreme flooding. The findings of this initial microbiological contaminant assessment will serve as the baseline information for follow-on studies to monitor existing and emerging public health risks to residents of Texas and potential long-term environmental impacts upon the water resources in the impacted regions.

Last Modified: 01/25/2019
Modified by: Vikram Kapoor