Study Analyzes Native Algae, Invasive Species and Groundwater Seeps in Hawai’i

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Groundwater-dependent coastal ecosystems benefit from reduced salinity and discharge of nutrient-rich groundwater.

According to a review published by a team of researchers from the University of Hawaii at Mānoa, native marine macroalgae (algae) thrive in environments created by natural groundwater seeps.

The review found that groundwater-dependent coastal ecosystems benefit from reduced salinity and discharge of nutrient-rich submarine groundwater (SGD).

And in areas where infiltrating groundwater is contaminated with excess nitrogen typical of sewage, the study found that an invasive species typically thrives in Hawaiʻi. The team determined that native macroalgae have adapted to SGD’s nutrient and salinity gradients, but that invasive algae outcompete natives near SGD with nutrient pollution.

The research team used thermal infrared imagery of the shoreline and natural chemical tracers to assess groundwater infiltration. Next, they documented the abundance of native and invasive algae species. Subsequently, the team measured the growth response of various algal species to conditions that simulated various undersea groundwater compositions, reported University of Hawaii News.

The native macroalgae studied showed faster growth and photosynthetic rates in natural groundwater seepage systems along coasts.

Modifying sustainable groundwater yields and improving wastewater treatment infrastructure to keep SGD reductions to a minimum and nitrogen inputs is difficult, according to the study, because rising groundwater levels globally and reduced groundwater recharge have a significant impact on coastal groundwater systems and their dependent ecosystems (GDE).

“There are several ways to improve the situation and prevent further deterioration of underwater groundwater discharge,” said Henrietta Dulai, lead author of the study and professor of Earth Sciences at UH. Mānoa School of Ocean and Earth Science and Technology, the University of Hawaii reported. ‘I News. “Recharge can be enhanced through land use choices by having more permeable urban surfaces and restoring native forests. Lower groundwater abstraction rates can be achieved through better water resource management and water reuse. Additionally, upgrading our wastewater treatment infrastructure in light of impending sea level rise should be a primary focus. »

According to the study, in order to preserve native GDEs, it is essential to preserve the flux of SGDs and control the associated nutrient loads.

“The bottom line is that if we’re going to maintain native macroalgae, we need to preserve the underwater groundwater discharge rate and control the associated nutrient loads,” said study co-author Celia Smith, Professor in botany at the UH Mānoa School of Life Sciences, and co-director of the marine biology graduate program, University of Hawaii News reported. “Keeping discharged groundwater as close to pure as possible should be a goal. Otherwise, we risk setting the stage for persistent, multi-year invasive algal dominance.

The team plans to continue their studies to determine the responses of native and invasive algae to the full range of groundwater discharges to inform biological control efforts that supplant native algae. The impacts of sea level rise on these plants will also be studied.

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