Impact of Submarine Groundwater Discharge on Marine Water Quality and Reef Biota of Maui

PLoS One. 2016 Nov 3;11(11):e0165825. doi: 10.1371/journal.pone.0165825. eCollection 2016.

Abstract

Generally unseen and infrequently measured, submarine groundwater discharge (SGD) can transport potentially large loads of nutrients and other land-based contaminants to coastal ecosystems. To examine this linkage we employed algal bioassays, benthic community analysis, and geochemical methods to examine water quality and community parameters of nearshore reefs adjacent to a variety of potential, land-based nutrient sources on Maui. Three common reef algae, Acanthophora spicifera, Hypnea musciformis, and Ulva spp. were collected and/or deployed at six locations with SGD. Algal tissue nitrogen (N) parameters (δ15N, N %, and C:N) were compared with nutrient and δ15N-nitrate values of coastal groundwater and nearshore surface water at all locations. Benthic community composition was estimated for ten 10-m transects per location. Reefs adjacent to sugarcane farms had the greatest abundance of macroalgae, low species diversity, and the highest concentrations of N in algal tissues, coastal groundwater, and marine surface waters compared to locations with low anthropogenic impact. Based on δ15N values of algal tissues, we estimate ca. 0.31 km2 of Kahului Bay is impacted by effluent injected underground at the Kahului Wastewater Reclamation Facility (WRF); this region is barren of corals and almost entirely dominated by colonial zoanthids. Significant correlations among parameters of algal tissue N with adjacent surface and coastal groundwater N indicate that these bioassays provided a useful measure of nutrient source and loading. A conceptual model that uses Ulva spp. tissue δ15N and N % to identify potential N source(s) and relative N loading is proposed for Hawai'i. These results indicate that SGD can be a significant transport pathway for land-based nutrients with important biogeochemical and ecological implications in tropical, oceanic islands.

MeSH terms

  • Biota / drug effects*
  • Coral Reefs*
  • Environmental Monitoring*
  • Groundwater / chemistry*
  • Hawaii
  • Nitrogen / metabolism
  • Rhodophyta / drug effects
  • Rhodophyta / metabolism
  • Ships*
  • Ulva / drug effects
  • Ulva / metabolism
  • Water Pollutants, Chemical / toxicity*
  • Water Quality*

Substances

  • Water Pollutants, Chemical
  • Nitrogen

Grant support

This paper is funded in part by a grant/cooperative agreement from the National Oceanic and Atmospheric Administration, Project R/HE-17, R/SB-12, R/WR-2, which is sponsored by the University of Hawaii Sea Grant College Program, SOEST, under Institutional Grant No. NA09OAR4170060, NA14OAR4170071 from NOAA Office of Sea Grant, Department of Commerce. The views expressed herein are those of the author(s) and do not necessarily reflect the views of NOAA or any of its subagencies; UNIHI-SEAGRANT-JC-14-42; http://seagrant.soest.hawaii.edu/research-0. Daniel W. Amato was supported by a STAR Fellowship Assistance Agreement no. FP-91727301-2, awarded by the U.S. Environmental Protection Agency. The EPA has not formally reviewed the work and does not endorse any products or commercial services mentioned in this publication; https://cfpub.epa.gov/ncer_abstracts/index.cfm/fuseaction/display.abstractDetail/abstract/9899/report/0. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.