Date: 6/21/2016




Amato DW, Schuler C, Gibson V, Baker L, Bishop JM, Alegado RA, Glenn CR, Dulai H, Smith CM

(Abstract ID:29691)

Submarine groundwater discharge (SGD) is a source of land-based contaminants to coastal ecosystems, yet the impact of this process on marine biota remains understudied. To determine if plants assimilated SGD-derived nitrogen (N) on otherwise oligotrophic reefs, we compared the N parameters (δ15N values and N concentration) of naturally occurring macroalgae with those of surface water, coastal groundwater, and terrestrial groundwater in Hawaii and American Samoa. In addition, tissues of Ulva spp. were deployed for 5-6 days to determine the extent of nutrient pollution at 8 coastal sites in Hawaii. Reduced salinity, elevated 222Rn, and high nutrient levels in beach porewater and surface water relative to ambient marine water provided evidence that SGD was a substantial vector for nutrient delivery to all study sites. The highest δ15N values in algal and water samples were found adjacent to wastewater treatment facilities that dispose treated effluent into groundwater via injection wells in Hawaii. The lowest δ15N values and highest N concentrations in water and algal tissues were found at locations adjacent to sugarcane fields. On Tutuila, high δ15N values in nearshore algal and water samples, relative to a control site, suggest that wastewater was a source of N to reefs adjacent to three villages. In general, regions with little human impact had relatively low N concentrations and δ15N values. Within developed regions of Hawaii and American Samoa, SGD delivered N derived from wastewater and fertilizer to marine macroalgae across large spatial scales.

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5-2-16    Saving Our Reefs: Pollution Solutions

The Hawaii Humpback Whale National Marine Sanctuary, Kihei Maui

Talk Title: Is Submarine Groundwater Discharge a Chronic Threat to Maui’s Nearshore Reefs?


Wastewater input from sewage treatment plants and onsite disposal sewage disposal systems (OSDS) is a major source of nutrients to coastal reefs in Hawaii. While much is known about the impacts of nutrient loading due to streams and rivers, submarine groundwater discharge (SGD) is an often-unseen and understudied, yet nearly ubiquitous transport pathway for nutrients to nearshore reefs. Recent studies show that SGD enriched in wastewater, that originated from injection wells and OSDS, is present at many sites on Maui and Oahu. By comparing water quality with various biological parameters, we have identified clear relationships between land use, groundwater, nearshore waters, and reef health at multiple sites on Maui.



2-4-16  2016 Pacific Water Conference

Hawaii Water Environment Association,

Honolulu, Hawaiʻi

Talk title:

The Impact of Coastal Groundwater Quality on Hawaiian Reefs and Nearshore Waters

Daniel W. Amato, James M. Bishop, Robert Whittier, Celia M. Smith, Craig R. Glenn, and Henrietta Dulai.


Anthropogenic nitrogen derived from wastewater and agricultural activities poses a serious threat to coastal marine ecosystems worldwide. Although the nutrient transport to marine ecosystems via rivers and streams is fairly well known in Hawaiʻi, contaminant delivery via submarine groundwater discharge (SGD) and the ecological impact of this process remain poorly understood. The purpose of this study was to discriminate land-based sources of N present in the nearshore coastal waters on O‘ahu and Maui using algal bioassays, benthic community analyses, and geochemical methods. Common marine algae were collected and/or deployed at several sites on O‘ahu, and Maui. Site selection was informed by adjacent land use, known locations of wastewater injection wells, and previous estimates of environmental risk due to on-site sewage disposal systems (OSDS). Algal tissue nitrogen (N) parameters (δ15N, N %) were compared with the N parameters (δ15N and N concentration) of coastal groundwater and marine surface water. For O‘ahu, algal N parameters were compared with estimates of coastal groundwater N concentration derived from three dimensional groundwater models.

Wastewater was detectable and a major source of N at sites adjacent to high-volume wastewater injection wells and regions with a high density of OSDS. Compared to unimpacted locations, reefs adjacent to sugarcane land use or wastewater injection wells had the greatest abundance of macroalgae, low community diversity, and the highest concentrations of N in algal tissues, coastal groundwater, and marine surface waters. A significant positive relationship was identified between estimated wastewater-derived N concentration of coastal groundwater and the δ15N value of adjacent algal tissues. Eighty-two percent of the variation in algal δ15N values was explained by estimated N produced from OSDS and wastewater injection wells on O‘ahu. Correlations between N parameters of algal tissues with adjacent surface and coastal groundwater values indicate these bioassays provided a good measure of nutrient source and loading. This work advances the use and interpretation of algal bioassays by highlighting the importance of onshore-offshore trends in addition to deviations from initial N parameter values for the detection of N source and relative N availability. A conceptual model that uses Ulva tissue δ15N and N % to identify potential N source(s) and relative N loading is proposed for Hawaiʻi. These results support recent studies that indicate SGD is a significant transport pathway for anthropogenic pollutants with important biogeochemical implications. Minimizing contaminant loads to coastal aquifers will reduce pollutant delivery to coastal water and reefs in areas with SGD flux.



12-2-15 2nd Conference on Water Resource Sustainability Issues on Tropical Islands

Honolulu, Hawaiʻi

Poster Title: Detecting hot spots for algal blooms in shallow waters of American Samoa.

Daniel Amato, Christopher Shuler, Veronica Gibson, Lydia Baker, Celia M. Smith, and Rosie Alegado.




52nd Annual Meeting of the Association for Tropical Biology and Conservation.
Honolulu, Hawaiʻi

Talk Title: Tracking land-based N to Hawaiian coral reefs: Is submarine groundwater discharge a chronic threat to water quality and reef health?

Daniel Amato, James Bishop, Craig Glenn, Henrieta Dulaiova, Celia Smith