Shorelines, streams see higher bacteria after heavy rains
Task force: Results at Maliko Bay and Wailuku Stream expected as areas subject to runoff
Maliko Bay and Wailuku Stream had the highest levels of fecal bacteria out of 18 sites tested between Peahi and Waihee Beach Park this month, which came as no surprise to the citizens group that monitors water quality around Maui.
Ocean coastlines and bays that are susceptible to stormwater runoff tend to have larger amounts of enterococcus, a fecal bacteria that can be carried down from farms and agricultural lands during the heavy rains.
“Based on the recent weather during our testing in January, nothing seemed to stand out too much,” said Greg Masessa, coordinator for the Surfrider Foundation Maui’s Blue Water Task Force. “The high levels of bacteria are present where there is typically heavier (rainfall) and more common mauka of our testing sites, which make sense due to the large amount of runoff, as well as the amount of agricultural land above.”
The Blue Water Task Force is a citizen science water testing program that administered the tests. To complement state beach water quality monitoring programs under the Hawaii Department of Health, the task force provides additional water quality information from local beaches and surf breaks, as well as a few freshwater sources of pollution like stormwater outlets, rivers and creeks that discharge into the ocean.
Surfrider chapters are located on Oahu, Kauai, Maui and Hawaii island.
In conjunction with DOH, they hope to “protect public health at the beach.”
“Surfrider chapters use this volunteer water testing program to raise awareness of local pollution problems and to bring together communities to implement solutions,” Masessa said.
Samples from 18 testing sites are taken to Donna Brown, an instructor in the Marine Biology Department at the University of Hawaii Maui College, for testing of enterococcus fecal indicator bacteria.
Results are published online as soon as the lab tests are processed.
“Enterococcus is fecal bacteria that comes from warm-blooded animals like humans or cows. It indicates the likelihood of the presence of disease-causing pathogens,” Masessa said.
Enterococci can enter shorelines through sewage and wastewater systems, stormwater runoff, boats, runoff from ag land and polluted groundwater, soil and sand.
In normal amounts, the bacteria is not all dangerous. However, in high levels it can “cause bacterial infections that can be a health hazard and even life-threatening, especially for those who are most susceptible to infection,” he explained.
Based on water quality standards set by DOH, enterococcus levels should be between 0 and 35 MPN per 100 milliliters of water to be considered “low bacteria.” MPN refers to the estimated number of viable cells in a given volume of the sample size.
Medium bacteria levels are between 36 and 130 MPN per 100 mL, and high bacteria levels are generally 130 or more.
According to the Blue Water Task Force, Wailuku Stream’s enterococcus levels were at 144 on Jan. 14; 85 on Dec. 2; 30 on Oct. 28; and 571 on Sept. 24. About 81 percent of samples collected at this site meet water quality standards set by DOH.
Only 49 percent of samples collected at Maliko Bay meet state water quality standards. Enterococcus levels at this site were at 223 on Jan. 14; 153 on Dec. 2; 41 on Oct. 28; and 41 on Sept. 24.
Hawaii’s typical rainy season falls around November through March, which is reflected in the data.
“The enterococcus levels are much higher after periods of heavy rainfall. This rain leads to more runoff which carries the enterococcus bacteria,” Masessa said. “This runoff picks up bacteria from pigs, goats or even dogs that wash into the ocean, often from streams. Many people don’t know this and assume it is from human waste.”
Areas with portions of large agricultural land mauka of the testing sites tend to have much higher bacteria levels than other spots.
“Maliko, Waiehu, Wailuku, Waihee are all at the outflow, or close to the outflow, of a stream and all seem to have higher enterococcus counts month over month due to concentrating the runoff from the surrounding land,” he said.
K Bay, or Kuiaha Bay, Sugar Cove and Kanaha Beach Park tested within the medium bacteria standards.
K Bay was tested in March, September and October and had low levels of bacteria, staying below 20 MPN per 100 mL. The most recent water sample from Jan. 14 shows a large increase of enterococci (114 MPN per 100 mL) following consistent rainy days in Haiku. This is still within medium DOH standards but in the trajectory of entering high levels of bacteria.
The remaining sites that were tested and had low levels of enterococci as of January included the Kahului Treatment Plant, Kahului Harbor, Kanaha-Kalialinui Stream, Paia Bay, Kuau Bay, Mama’s Fish House beach, the east and west shorelines of Hookipa Beach Park, Waiehu Stream and Waihee Beach Park.
Areas like Baby Beach and the Kahului Treatment Plant may be lower because of “strong currents and less rainfall in those areas,” he said.
Continuing to collect data will help water quality teams to suggest the best mitigation options to reduce stormwater runoff, higher bacteria levels and damage to coastlines.
For more information, visit maui.surfrider.org.
* Dakota Grossman can be reached at email@example.com.