UH researchers conclude Hurricanes Katrina, Rita effects on environmental water quality were short-lived

University of Hawaiʻi at Mānoa
Grieg Steward, (808) 956-6775
Department of Oceanography
Posted: May 11, 2007

HONOLULU — University of Hawaiʻi researchers recently published the results of a National Science Foundation (NSF)-funded collaborative investigation of microbial contamination in the water and sediments around New Orleans in the aftermath of Hurricane Katrina and Rita, which struck the Gulf Coast in fall of 2005. The work, appearing this week in the advance online edition of Proceedings of the National Academy of Sciences of the U.S.A., suggests that the influence of contaminated floodwaters on water quality of Lake Pontchartrain was relatively short-lived and limited to coastal areas. The report also suggests that there are chronic sources of sewage contamination in soils and drainage water in the city that appear to be unrelated to the flooding caused by Hurricane Katrina.

The UH team contributed to the project by investigating how the concentrations of pathogenic bacteria and alternative microbiological indicators of sewage contamination varied in the canals and coastal waters of Lake Pontchartrain in the months following the hurricanes. The pathogens they studied included Vibrio cholerae, the causative agent of cholera, Vibrio parahaemolyticus, which causes gastroenteritis, and Vibrio vulnificus, which can cause gastroenteritis and severe wound infections.

The results from UH suggest that the warm, brackish waters of Lake Pontchartrain that flooded the city in August and September would have been ideal breeding ground for Vibrio species, such as Vibrio vulnificus, and may have contributed to the increased incidence of infections and deaths due to vibrio infections reported by the Center for Disease Control and Prevention. The abundance of vibrio species in the lake declined in the subsequent months as water temperature in the lake dropped below 10 C.

The seasonal lowering of water temperature in temperate climates has been reported to reduce the concentrations of pathogenic Vibrio species in coastal waters. This is in contrast to the subtropical coastal waters of Hawaiʻi, where the temperatures are warm enough to allow the growth of these pathogens year-round.

"Some pathogenic Vibrios not only grow better at warmer temperatures, but also prefer brackish water to full strength seawater," noted Grieg Steward, assistant professor in the Department of Oceanography. "As a consequence, seasonal changes in rainfall, which affect the salinity of confined coastal areas, probably have a greater influence than temperature on the distribution of pathogens like Vibrio vulnificus in Hawaiʻi," he said.

The team‘s measurements of fecal indicators suggested that sewage-tainted waters pumped from the streets of New Orleans back into Lake Pontchartrain temporarily degraded water quality along the shoreline, but had little effect further out into the lake. Sewage contamination was no longer detectable in nearshore waters after several months, but the 17th Street canal, through which drainage water from the city is routinely pumped, continued to show evidence of contamination a year later.

The members of the UH team are affiliated with the Pacific Research Center for Marine Biomedicine (PRCMB) at UH Mānoa, one of four Centers for Oceans and Human Health in the country currently funded by NSF and the National Institute of Environmental Health Sciences (NIEHS). Team members included: Principal Investigator Grieg Steward and graduate student Olivia Nigro of the Department of Oceanography, Principal Investigator Roger Fujioka and graduate student Gayatri Vithanage of the Water Resources Research Center, post-doctoral researcher Walter Betancourt, and PRCMB Director Ed Laws. The work was conducted in collaboration with researchers from two other Centers for Oceans and Human Health located at the University of Miami and Woods Hole Oceanographic Institution, along with researchers from Georgia College and State University, Florida International University and Louisiana State University.

To view the published work, visit http://www.pnas.org/cgi/content/abstract/0610552104v1.

For more information, visit: http://www.pnas.org/cgi/content/abstract/0610552104v1