WAILUKU - A University of Hawaii researcher believes that tracking an isotope of nitrogen in seawater can demonstrate that nutrients from injection wells are getting into the water.
The researcher, Meghan Dailer, told the County Council Water Resources Committee on Monday that laboratory experiments show that both native and alien algae species are nitrogen-deficient around Maui, so that nitrogen-enriched effluent could contribute to algae blooms.
The blooms of "turf algae," in turn, are blamed for smothering coral and coralline algae, contributing to the deterioration of reefs.
Dailer updated a presentation that Russell Sparks of the Department of Land and Natural Resources gave the council in July 2007, which pointed to injection wells at county sewage treatment plants as the cause of algae overgrowth.
Dailer, who is in the Hawaii Coral Reef Initiative at the UH Department of Botany, presented a novel way of detecting injection well effluent in seawater.
"Nitrogen is difficult to detect, because the ocean is a dynamic environment," she said.
However, the ratio between ordinary nitrogen with an atomic number of 14 and slightly heavier nitrogen-15 can signal the origin of the nitrogen. It does not, however, say anything about the total amount of nitrogen in the water.
Dailer said a survey was made all around the island in 2007, every mile in built-up areas and every five miles in remote areas, to compare the ratio of N14 to N15.
A high ratio of N15 is thought to indicate a source from a well, a low ratio a source from runoff, perhaps from excess fertilizer.
When the treated sewage, which still contains some biological material, is injected into a well, she said, bacteria act on it while it's there. Their action selectively favors N15.
Thus the presence of N15 suggests the presence of upwelling from sources that receive injection well water. The Department of Environmental Management injects about 11.7 million gallons a day of treated wastewater at Lahaina, Kihei and Kahului. Other, smaller operations inject or used to inject both sewage wastewater and other kinds of polluted water.
Attempts by Environmental Protection Agency researcher Wendy Wiltsie to detect injection well water in West Maui in the 1990s failed. Various methods, such as tagging the well water with a fluorescent chemical, failed to find the well water in the ocean.
That did not end efforts to link injection wells with algae blooms in the ocean.
Dailer said the N15 test is new, with samples going back only to 2003. However, she said, tests in Australia confirmed that the N14:N15 ratio is associated with injection wells.
She showed maps based on the 2007 samples that give higher N15 ratios close to the three county sewage treatment plants. One ratio, over 43, is the highest found in the research literature, she said. In remote areas, levels are as low as 0 to 3.
One area of heavy algal blooms is Tavares Bay in Paia. Dailer did extensive testing there. The location was not chosen for scientific reasons, she said, but because the Tavares family has owned the land since 1910, is concerned about the limu and offered access and security. It was a place where her experiments would not be vandalized, she said, although the algae situation is similar all along the Paia shoreline.
Council Member Mike Victorino wondered why there would be a bloom there, since there are no injection wells nearby.
Dailer said the N15 number at Tavares Bay is low, suggesting a nitrogen source from agricultural runoff.
Later, she was asked why there were no algae problems in the old days, when such runoff was less well-managed than today and when 30,000 people lived above Tavares Bay, none with sewers and many without even cesspools. Until Dream City was built and the people moved, untreated sewage flowed in open ditches into the ocean.
Dailer responded that there were no scientific reports from that period.
She said the Tavareses reported that algae blooms began to be a problem around 1985, when two things changed.
First, a foreign limu, Hypnea, was imported and it found the north shore to its liking. Second, sewer lines were dug along the shore. Dailer speculated that around Tavares Bay some subsoil barrier had been holding back the movement of groundwater. The digging may have breached that barrier, letting nutrient-laden water reach the bay.
Her lab experiments show that Hypnea grows well with extra nitrogen and shows a darker, purplish color. The color of Hypnea may give a rough measure of nitrogen availability, she said.
The role of micronutrients remains uncertain.
Other species, native and foreign, also respond to nitrogen, although not all in the same way. All four species tested responded more to nitrogen than to phosphorus, and they responded more when more nitrogen was added, she said.
She concluded that around Maui, the highest N15 ratios are close to sewage injection wells and that blooms of Hypnea and Ulva (a native) are driven by an excess of nutrients coming from human sources of one kind or another.
* Harry Eagar can be reached at heagar@mauinews.com.
