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Researchers: Cove Park tops nutrient levels tied to wastewater

Hui O Ka Wai Ola measures water quality at 29 South and West Maui beaches over five years

The water at Cove Park is murky Thursday afternoon. Water quality testing by Hui O Ka Wai Ola at 29 West and South Maui beaches continues to show Cove Park has the top levels of nutrients tied to wastewater. Excess nutrients can encourage algal overgrowth and disrupt the ecosystem. — The Maui News / MATTHEW THAYER photo

Cove Park is known as a popular surfing spot in Kihei — but for local water quality researchers, the site is recognized for the highest nitrate levels tied to wastewater on the leeward coast.

“Cove has very, very high levels — more than any other leeward Maui site by far,” Tiara Stark, Hui O Ka Wai Ola program senior team lead, said during an online presentation Wednesday. “Past studies show wastewater influence from the Kihei treatment plant is present in nearshore areas by Cove Park, and this is a likely driver of elevated nutrients here.”

Stark discussed the work of Hui O Ka Wai Ola ocean water quality monitoring program that tests 29 Maui beaches on the south and west sides. The volunteer-based citizen scientist group has been gathering data for five years to supplement state Department of Health coastal water quality monitoring.

Wednesday’s talk, presented by Maui Nui Marine Resource Council, detailed Hui O Ka Wai Ola’s findings on coastal water quality trends and how the information helps drive watershed management.

Cove Park’s nutrient values are up to 25 times higher than the standard and are staying relatively stable, according to Stark.

Reagan Riley of Seattle catches a wave Friday while taking a surf lesson at Kalama Park near Cove Park in Kihei. — The Maui News / MATTHEW THAYER photo

“However documents do show increases in the influent at Kihei Wastewater Reclamation Facility from new industrial sources are present, so we are curious, and it would be useful to investigate if we see any changes in the data and if those correlate with differences of what’s going on with the wastewater reclamation plant,” she added.

Another “hot spot” in South Maui for nutrients is Ulua Beach. While its levels are much lower than Cove Park, the site is distinct because nutrients there are primarily derived from wastewater.

Stark said Ulua Beach is close to Wailea Onsite Disposal Systems and injection wells, which could be possible sources of wastewater.

While corals at Ulua Beach have a high resilience ranking, The Nature Conservancy data on coral bleaching has observed degradation of corals there.

“This could be a possible place for restoration efforts to prevent further degradation,” Stark said.

Maui Waveriders surf instructor Ina “Wave Daddy” Tagaloa (right) waits for the next wave while teaching a family from Seattle to surf at Kalama Park near Cove Park Friday morning. While long popular with surfers, Cove Park continues to have some of the highest nitrate levels tied to wastewater among more than two dozen sites monitored for water quality in West and South Maui. — The Maui News / MATTHEW THAYER photo

A highlight of the hui’s data is Kapalua Bay, where the group observed a “statistically significant drop” in nitrogen that coincided with the sewage infrastructure upgrades by the County of Maui in spring 2019.

“While we can’t prove that it was the upgraded sewage infrastructure that improved water quality, it certainly seems likely, and we do plan to follow up and verify if there is a correlation,” Stark said. “This is a pretty cool observation — it really, really highlights the importance of long-term data sets, and how we can really check and determine whether management actions are working.”

For West Maui sites, the main issues are high turbidity — or low water clarity — and high nutrient levels.

Suspended particles negatively impact adults corals because access to light is restricted. Turbidity exceeds state standards at all 19 sites, according to the hui.

In South Maui, the issue is switched. Sites there have high nutrient levels followed by high turbidity. All 13 sites exceed at least one state standard for nutrients.

High nitrogen levels from human activities enter nearshore waters through submarine groundwater discharge, streams or runoff. Excess nutrients encourage algal overgrowth and disrupt the ecosystem. Agricultural practices and wastewater are the main sources of these nutrients in Maui’s waters.

The hui has conducted 100 samples in West Maui and 75 samples in South Maui for assessment against 12 water quality parameters.

Physical parameters include pH, dissolved oxygen, temperature, salinity and turbidity. Chemical parameters cover nitrate, ammonia, total nitrogen, phosphate and silicate, among others.

For the full discussion, presented by Maui Nui Marine Resource Council as part of its “Know Your Ocean Speaker Series,” visit facebook.com/MNMRC. For information on Hui O Ka Wai Ola and publicly available data, visit www.huiokawaiola.com.

* Kehaulani Cerizo can be reached at kcerizo@mauinews.com.

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