Effects of Submarine Groundwater Discharge as a Vector for Sewage Effluent on Hawaiian Coral Reefs

EPA Grant Number: FP917273
Title: Effects of Submarine Groundwater Discharge as a Vector for Sewage Effluent on Hawaiian Coral Reefs
Investigators: Amato, Daniel W
Institution: University of Hawaii at Hilo
EPA Project Officer: Lee, Sonja
Project Period: August 1, 2011 through July 31, 2014
Project Amount: $126,000
RFA: STAR Graduate Fellowships (2011) RFA Text |  Recipients Lists
Research Category: Academic Fellowships , Fellowship - Water Quality: Coastal and Estuarine Processes


The primary purpose of this investigation is to determine the extent and impact of sewage pollution on Hawaii’s coral reefs. Two hypotheses will be tested: (1) Sewage effluent isotope tracer levels (515N) will be greater in areas proximal to wastewater treatment plants (WWTPs) utilizing injection wells compared to areas of low anthropogenic impact; (2) Sewage effluent isotope tracer levels (515N) will have a positive relationship with measures of submarine groundwater discharge and algal photosynthetic performance.


This study will focus on coastal areas adjacent to state operated WWTPs utilizing injection wells to determine if submarine groundwater discharge (SGD) is a vector for sewage effluent discharge to the coastline. An interdisciplinary, multi-tracer approach employing bioassays, biological surveys and chemical water analysis will be used to test these hypotheses. The productivity and chemical composition of marine algae will be analyzed to determine the impact of sewage-derived pollution on coastal reefs. Water samples collected from coastal aquifers and the near-shore water column will be analyzed for stable isotopes (C, N, O), radio isotopes (Rn, Ra) and elemental content to calculate hydrogeochemical processes such as SGD flux, coastal mixing rates and nutrient loading at specific sites in Hawaii. With the help of the Polynesian Voyaging Society, local educators, students and community groups, a statewide survey will be performed in Hawai’i to identify areas of sewage discharge to the near-shore environment. Crew members of the voyaging canoe, Hōkūlea, will assist volunteers with the collection of water quality and reef health data using GPS, waterproof cameras and benthic quadrats, digital water quality meters and algal collection protocols during a statewide sail.

Expected Results:

The results of this study will identify locations in the Hawaiian Islands where sewage effluent is discharged on coastal reefs. It is expected that low δ15N values will be found in macroalgal tissues in areas of low development and anthropogenic impact, and high 515N values will be found in areas of high development and anthropogenic impact. The highest 515N values are likely to be measured in areas proximal to WWTPs utilizing injection wells or developments using cesspools. Algal tissue 515N levels, growth rates and photosynthetic performance are expected to be elevated at impacted sites due to sewage-derived nutrient loading. It is expected that algal growth rates and photosynthetic performance will have a positive relationship with estimates of SGD flux and a negative relationship with salinity. SGD flux estimates and water analysis will be used to calculate nutrient loading at specific sites. One important conclusion that may arise from this investigation is a direct connection between terrestrial injection of sewage and biological processes in the coastal ocean. By utilizing an interdisciplinary approach including hydrological and algal physiological methodology, this study will be able to conclude that SGD is a vector or underlying process, facilitating this transmission of sewage pollution from injection wells to the marine environment.

Potential to Further Environmental / Human Health Protection

This study has great potential to highlight the extent and impact of sewage pollution on Hawaiian coral reefs while elucidating the interconnection between coastal aquifers and marine ecosystems. These results have important implications for the permitting, management and treatment of wastewater and sewage disposal in coastal areas. Most importantly, this study has the potential to educate and actively involve thousands of underrepresented community members in scientific research and ocean conservation in Hawaii.

Supplemental Keywords:

sewage, pollution, injection, effluent, marine, algae, groundwater, SGD, invasive, water, wastewater, aquifer, Hōkūlea, discharge

Progress and Final Reports:

  • 2012
  • 2013
  • Final