Marine scientists at the University Hawaii in Hilo conducted a sensational experiment along the coast of Kahaluʻu Bay, south of Kailua-Kona. The team introduced a small amount of fluorescein dye, which glows bright green in sunlight, into the sewer system of a local home. The test was designed to determine if the dye would reach shore and, if so, how quickly.
“In fact, the dye appeared at a spring on the shore, which told us that the sewage from at least one house, possibly several, was in Kahaluʻu Bay,” said Steve Colbert, a UH Professor of marine sciences in Hilo who is leading the study.
Kahaluʻu Bay is home to a unique coral reef ecosystem and is also one of the state’s most popular snorkeling spots. According to the County of HawaiiMore than 400,000 people visit the shallow, near-shore reef every year to observe the diverse marine fauna, colorful fish and coral colonies.
Faster flow rate
UH The Hilo researchers said what surprised them most during the tests was how quickly the groundwater transported the wastewater to the shore.
“We measured groundwater flow rates of 275 m/day,” said Colbert. “For houses with septic tanks nearby Ali’i Drive, sewage can reach the shore in less than six hours. In other words, a toilet flush at high tide can be on the shore at the next low tide.”
Colbert noted that this was faster than any flow rate the researchers had measured at Keaukaha, Hilo, and twice as fast as the fastest current at Puakō.
Rising sea levels
The research team included UH Hilo student Ihilani Kamau is studying how rising sea levels due to global warming are affecting wastewater infrastructure and water quality in Kailua-Kona.
“Another goal is to document and identify wastewater pollution hotspots along the Kailua-Kona coast and determine which local wastewater disposal systems and wastewater treatment infrastructure will be affected by sea level rise,” said Kamau, who studies tropical conservation biology and environmental science.
Research at Kahaluʻu Beach Park is part of a larger project funded by the Pacific Islands Climate Adaptation Science Center, a collaboration between UH Hilo, UH Mānoa and the US Geological Survey.
For more information, see UH Hilo Stories.
—By Susan Enright
