West and South Maui beaches are seeing a rising trend in poor water quality as coastal erosion worsens and harsh storm surges pollute the shorelines, according to a recently released report.
The Coastal Water Quality Report 2016-2021 was put together by Hui O Ka Wai Ola, a group of scientists and community volunteers that helps to keep track of trends of pollutant levels.
“Coral reefs are culturally, economically and ecologically vital to the livelihood to the people of Maui and to all the islands in Hawaii,” said Liz Yannell, the hui’s senior team lead, during a virtual Know Your Ocean Speaker Seminar Series hosted by the Maui Nui Marine Resource Council on Wednesday night. “They’re just so fragile and susceptible to even the slightest changes in ocean parameters.”
Hui O Ka Wai Ola monitors water quality along 40 miles of Maui’s coastline from Honolua Bay to Papalaua and from Maalaea to the ‘Ahihi- Kina’u Natural Area Reserve.
The hui’s work is done in part by the marine council, The Nature Conservancy and West Maui Ridge to Reef Initiative and supplemented by state Department of Health monitoring.
Since 2016, Hui O Ka Wai Ola has collected and analyzed over 3,200 water quality samples from 48 sites, confirming that high levels of turbidity (measure of water clarity) and nitrates are prevalent at all these sites.
The program currently monitors 29 sites every three weeks from West to South Maui.
TURBIDITY A CONCERN IN WEST MAUI
According to the hui’s recent report, the primary issue in West Maui is turbidity, as all 19 tested sites from Honolua to Papalaua exceed DOH standards of 0.2 NTU (Nephelometric Turbidity Unit).
Levels of 6 NTU or higher are found at five West Maui sites, such as Kaopala Bay and Kahana Village. Pohaku Beach, also known as “S-Turns,” has the highest level of turbidity and is “greatly impacted” by coastal erosion, Yannell said.
“Over time, we’re seeing an increase in turbidity in West Maui driven by coastal erosion and it’s really just worsening because of sea level rise,” she said. “All of these big spikes are a big concern and that’s why we continue to sample.”
After the Dec. 18 storm that caused a brown water event at Honolua Bay, samples taken two days later showed that water quality was at 40.5 NTU. Three weeks later, Honolua still had 13.27 NTU, which is an example of how sediment can take a long time to flush out.
Turbidity has increased at Ukumehame, but is declining at Olowalu, according to the report. Oneloa Bay, which has large sand dunes and minimal coastal erosion, is consistently the cleanest sample site.
Turbidity in South Maui is less of an issue “due to the lack of rainfall,” Yannell said, and is generally caused by coastal erosion as well as storms, such as the heavy rain and flooding that swept through the island last week.
“But because it’s so dry, as we all just saw over the weekend, when it rains heavily Upcountry, all that dry and loose soil allows rainwater to wash lots of sediment down into our shores,” she added.
Turbidity is moderately high from Maalaea Harbor to about Cove Park (peaking 20 NTU, averaging 3.5 NTU) in South Kihei and then becomes much lower from the Wailea to Makena beaches, but still exceeds DOH standards, she said.
Waipuilani Beach Park has the highest levels of turbidity, where levels are two times higher than other South Maui sites.
NUTRIENTS AN ISSUE IN SOUTH MAUI
The six-year trend shows that the biggest issue for South Maui is that the water has high nutrient levels, like nitrates and nitrogen and ammonia, often fueled by agricultural practices and wastewater.
Nitrates, mainly fertilizers and wastewater that seep into groundwater systems, are very prevalent from Maalaea Harbor to South Kihei, Yannell said. They can also be carried to coastal waters in streams and runoff.
All tested sites exceed DOH standards of 1.5 micrograms of nutrients per liter.
“When nutrients are in excess, they encourage an overgrowth of algae in the ocean and can disrupt the chemical balance and overall health of the ecosystem,” she said. “Corals really thrive in low nutrient inputs and low turbidity. They really like clean water with some good movement.”
After the same Dec. 18 storm that caused flooding and runoff by Kihei Canoe Club in North Kihei, Yannell said she was shocked at the amount of axis deer feces that collected along the shoreline.
While the overpopulation of deer is not a new problem for Maui County, it was “eye opening to me how much they impacted our waters in ways I hadn’t realized before,” she said.
“All of that poop is just flowing into the ocean, (along with) bacteria,” she said. “They are part of the problem of why the dirt Upcountry is so loose.”
Over the past six years, Cove Park “really stands out” because levels are more than two times higher than any other South Maui site, she explained. Even on days when the water is not brown, it’s still high in nutrients and phosphorus.
Cove Park has reached peaks of nitrate levels between 500 and 1,200 mg/L, which is “crazy high,” she said.
But, on a positive note, water quality data at Kealia Pond (a 691-acre National Wildlife Refuge) show consistently low levels of nutrients as these wetlands filter nitrates and sediment.
Wetlands serve as a natural buffer to coastal waters, and can mitigate storm surges and runoff, she said.
In West Maui, nitrates “far exceed” DOH standards at Kapalua, Kaopala, Napili, Pohaku, and Hanakao’o (Canoe Beach).
Pohaku Beach has had peaks of up to 500 mg/L since 2016 and studies by the hui indicate that “wastewater might be a contributing factor” as there are still cesspools located mauka of the beach and sewage lift stations that have not been updated in awhile that “may be leaking,” she said.
This area also used to be a “legacy hotspot” for sugarcane and pineapple, so “we’re still seeing the effects of fertilizers and pesticides from the past coming into this area,” she added.
However, levels at Kapalua – a beach that had peaks over 300 mg/L – have dropped significantly in the last two years. In 2019, improvements were made to the utilities and sewer lines.
“We quickly afterwards started to see drops in nitrate levels and it feels like a big success story,” Yannell said. “It reminds us that the changes we make and the work we do together can truly make a difference.”
Some of the solutions suggested by the hui in response to water quality concerns include upgrading utility technology to reduce nitrate inputs from sewage infrastructure, stabilizing beach erosion hotspots, reducing impacts of recreational activities and maintaining sediment capture systems, among other mitigating strategies.
Another option is to improve upland management, including fire control and ungulate populations, especially axis deer, to prevent additional sediment runoff during storms, according to the report.
The hui also has launched a Brown Water Watch program that seeks visual data, or photos, including the use of drones, from the community.
Photos would be used to advocate, support and document water quality work by “showing change over time,” The Nature Conservancy’s Kim Falinski said Wednesday night. And with permission, photos will be shared on social media networks and with the DOH.
“Everybody’s eyes and these photos become the way we can really see where the water is going, how dirty it is, and what we can do,” Falinski said.
Photos can be sent to [email protected] or people can use the hashtag #BrownWaterWatch on Instagram.
To view the full report, visit www.huiokawaiola.com/findings.html.
* Dakota Grossman can be reached at [email protected].