hilo bay
Hilo bay. (Photo credit: Hollyn Johnson)

A team of scientists from the University of Hawaiʻi at Hilo has published a paper in the Journal of Environmental Quality on how rainfall-driven runoff increases concentrations of harmful bacteria in Hilo Bay.

The scientists used culture-based methods to quantify the presence of Staphylococcus aureus (known informally as “staph”), methicillin-resistant Staphylococcus aureus (MRSA) and fecal indicator bacteria (FIB) in Hilo Bay and in soils, sands, rivers, wastewater and storm water within the Hilo watershed. These pathogen concentrations were then compared with rainfall and river discharge levels and water quality data. The results showed that staph and FIB concentrations increased with rainfall and river discharge. In terms of water quality, high turbidity (water cloudiness) was associated with higher bacteria concentrations, and high salinity with lower bacteria concentrations.

The paper is titled, “Rainfall and Streamflow Effects on Estuarine Staphylococcus aureus and Fecal Indicator Bacteria Concentrations.” The authors are Louise Economy, an alumna of UH Hilo’s tropical conservation and environment science graduate program who is currently employed by the Hawaiʻi Department of Health; Tracy Wiegner, UH Hilo professor of marine science; Ayron Strauch, a hydrologist with the Department of Land and Natural Resources; Jonathan Awaya, UH Hilo professor of biology; and Tyler Gerken, a UH Hilo alumnus who is currently a graduate research assistant at the University of Washington.

Wiegner noted that Hawaiʻi has the highest level of community acquired staph infections in the country. “It’s two times the rate of the rest of the U.S.,” she said. “That may be because it’s warmer here or because people are in the water more.”

“Staph is an opportunistic pathogenic bacterium, meaning that given the right conditions it can cause disease,” said Economy. “It can invade wounds and cause boils, rashes and even flesh-eating disease. These infections are becoming more and more common in the community and affecting people who were previously healthy.”

The project is based on Economy’s undergraduate and graduate work at UH Hilo, supervised by Wiegner, as well as work done by Gerken, also supervised by Wiegner, while he was at UH Hilo earning his baccalaureate degree in environmental science.

Swimmers beware

The scientists hope their work can be used to predict water quality conditions based on rainfall patterns and to help assess the health risks faced by swimmers, surfers and other recreational water users in Hilo Bay.

“We are trying to develop real-time models using the water quality buoys, river discharge gauges and rainfall data to be able to make real time predictions,” said Wiegner. “The idea is that you could look at your phone and see what your risk is before going in the water.”

Until then, she advises swimmers and surfers to stay home after a heavy rainfall, since rainfall and turbidity are associated with higher pathogen concentrations. “A good rule of thumb for recreational water users is if the water is brown, turn around,” she said. “You don’t want to go in with open cuts, and if you do go in, you should always rinse off.”

The project was funded through the Hauʻoli Mau Loa Foundation and the U.S. Geological Survey Pacific Islands Climate Adaptation Science Center. Undergraduate student research was supported by the National Science Foundation through UH Hilo’s Pacific Internship Programs for Exploring Science and UH Mānoa’s Center for Microbial Oceanography: Research and Education and by the National Institutes of Health through the Students of Hawaiʻi Advanced Research Program.

Read the full story at UH Hilo Stories.

—By Leah Sherwood, a UH Hilo tropical conservation biology and environmental science graduate student