Preliminary data shows impacts of wildfire on Lahaina coastal waters

Preliminary data on coastal water quality monitoring in West Maui was presented Wednesday at a public speaker series featuring Andrea Kealoha, Ph.D., an assistant professor of Oceanography at the University of Hawaiʻi at Mānoa.

“When trying to understand the impact of the Lahaina wildfire to coral reefs and water quality, we don’t really have a perfect analogy because as far as we know, there’s never been an urban wildfire adjacent to a coral reef,” Kealoha said. “So we know that rural fires can lead to sedimentation, hypoxia and algal blooms. But what happens when you also release contaminants associated with urban infrastructure?”

Challenged by the unprecedented nature of an urban wildfire adjacent to a coral reef, Kealoha and a research team at the University of Hawaiʻi at Mānoa began to study coral and reef health in October 2023.

The team collected water samples from 11 sites in West Maui, including five sites within the burn zone and two control sites, to study carbonate chemistry, nutrients, metals, organic contaminants and microbial communities. They also took samples offshore and after rain events and collected additional data from over 20 sensors.

Kealoha presented the preliminary data at a Know Your Ocean Speaker Series hosted by Maui Nui Marine Resource Council on March 6.

Nutrient data

The tests included concentration of nitrates and phosphates—nutrients often associated with fertilizers, wastewater and runoff—over the four month period ending Feb. 1, 2024.

Kealoha noted elevated nitrate concentrations across most of coastal West Maui sites both inside and outside of the burn zone. Nitrate concentration spiked across the majority of the sites following a substantial rain event in January.

During all four months, a majority of the sites exceeded the water quality criteria of the Department of Health (DOH) for aquatic life. Kealoha said this is likely not related to ash and debris from the wildfires and more likely due to high levels of nitrates in West Maui streams.

“Our waters on Maui are eutrophic […] so I’m not super surprised by this,” Kealoha said. “The numbers are a little bit higher than I expected, but we don’t see any strong evidence for higher nitrate concentrations within the burn zone.”

Levels of phosphates were also elevated after the big rain event in January. Although there is no DOH limit for phosphate, Kealoha said that the concentrations recorded were nothing out of the ordinary.

Metal data

While there was no strong evidence that nutrients in waters were exacerbated near burn zones, three metal contaminants, associated with urban infrastructure, were notably apparent in water samples near burn zones.

Copper

Copper concentrations peaked within the burn zone, especially in the initial months following the fire, according to the data. Concentrations of copper, which are associated with antifouling paint used for boats, had reached EPA-determined acute and chronic toxicity for aquatic organisms at Lahaina Harbor from October to December 2023.

Kealoha emphasized that the high concentrations of copper were localized and did not show signs of impact to Olowalu or Kahekili.

Copper concentration in coastal reefs near the Lahaina burn-zone have since retreated and met EPA criterion for marine aquatic life this January. “Moving forward, it’s probably important to continue to monitor copper concentrations, particularly within the harbor,” said Kealoha.

Lead

Lead concentrations also spiked within the burn zone post-fire. Kealoha said lead is present in household items like paints, pipes, rubbers and plastics.

None of the concentration levels of lead measured were considered harmful to aquatic life, per EPA standards. “The lowest concentrations [of lead] were measured during our January event, so there’s no dilution effect that we’re seeing here,” said Kealoha.

Zinc

Zinc concentration tests also showed a larger concentration in the burn-zone areas. But unlike copper and lead concentrations, zinc peaked in the majority of all of the samples following the big rain event in January.

“This is different from copper and zinc where we saw higher concentrations of copper that were really close to the harbor and within the ferry pier,” said Kealoha. “Now we’re seeing zinc that’s more kind of widespread and following these runoff events.”

Even though the concentrations of zinc in the samples were not considered harmful to aquatic life, Kealoha expressed concern for coral life. Zinc concentration exceeded 10ppb in four of the samples taken in January.

“Studies have shown impacts at 10 parts per billion particularly for coral fertilization, so there could be some environmental ecosystem concerns with Zinc,” said Kealoha. “Not great numbers, and something to definitely keep an eye on moving forward.”

Hypoxia

The team also used sensor data to collect oxygen concentration at three sites in Lahaina (Waikuli, Māla and Puamana) and two control sites (Kahekili and Olowalu).

The oscillations represent the day/night cycle of photosynthesis and respiration, colloquially known as the “heartbeat of the reef.” Low oxygen concentrations, also called hypoxia, occurs when a reef respires more than it photosynthesizes, and this poses a threat to marine ecosystems.

The results showed nighttime mild to moderate hypoxia for short periods, which Kealoha said “isn’t totally abnormal” in the present day. “At this point, we don’t think any of these trends are related to the Lahaina wildfire,” she said.

Kealoha noted that there was a significant reduction in photosynthesis during the period of time associated with the big rain, runoff event in January. “This is likely due to enhanced turbidity, which blocks sunlight on the reef. So potentially the addition of organic matter through runoff helps drive that.”

Kealoha said it’s possible these types of hypoxia events could become worse if there were an event that caused several consecutive days of runoff.

Impact on human health

While testing for contaminants is still in progress, Kealoha said the findings have not indicated a cause for concern for humans. Tests to determine the safety of consuming coastal fish from the area were not conducted or presented.

“It’s definitely at the forefront of everybody’s minds when you think about problems, especially for human health resulting from this, and so it’s something that is a priority for us,” said Ocean and Coastal Health Specialist Faculty Ilene Nalley.

The full recording of the Know Your Ocean Speaker Series featuring Andrea Kealoha will be available for viewing on YouTube.