Western Coastal & Marine Geology
From upper left hand moving clockwise: (1) Shallow, wave-scoured intertidal platform of north Kaloko-Honokōhau National Historical Park with sparse stoutly branching coral Pocillopora meandrina; (2) algae-covered intertidal platform of central Kaloko-Honokōhau National Historical Park, common where submarine groundwater discharge is persistent; (3) dense cover of soft coral Sarcothelia sp. (Anthelia) common of submarine groundwater seeps, central Kaloko-Honokōhau National Historical Park; (4) complex basalt topography with thin veneer of dense coral in north Kaloko-Honokōhau National Historical Park. (USGS photos by Eric Grossman.)
The aquatic resources of Kaloko-Honokōhau National Historical Park, including rocky shoreline, fishponds, and anchialine pools, provide habitat to numerous plant and animal species and offer recreational opportunities to local residents and tourists. A considerable amount of submarine groundwater discharge was known to occur in the park, and this discharge was suspected to influence the park’s water quality. Thus, the goal of this study was to characterize spatial and temporal variations in the quality and quantity of groundwater discharge in the park. Samples were collected in December 2003, November 2005, and April 2006 from the coastal ocean, beach pits, three park observation wells, anchialine pools, fishponds, and Honokōhau Harbor. The activities of two Ra isotopes commonly used as natural ground-water tracers (223Ra and 224Ra), salinity, and nutrient concentrations were measured. Fresh ground water composed a significant proportion (8–47 volume percent) of coastal-ocean water. This percentage varied widely between study sites, indicating significant spatial variation in submarine groundwater discharge at small (meter to kilometer) scales. Nitrate + nitrite, phosphate, and silica concentrations were significantly higher in nearshore coastal-ocean samples relative to samples collected 1 km or more offshore, and linear regression showed that most of this difference was due to fresh ground-water discharge. High-Ra-isotope-activity, higher-salinity springs were a secondary source of nutrients, particularly phosphate, at Honokōhau Harbor and Aiopio Fishtrap. Salinity, Ra-isotope activity, and nutrient concentrations appeared to vary in response to the daily tidal cycle, although little seasonal variation was observed, indicating that submarine ground-water discharge may buffer the park’s water quality against the severe seasonal changes that would occur in a system where freshwater inputs were dominated by rivers and runoff. Ra-isotope-activity ratios indicated that the residence time of water in the coastal ocean at the study sites was less than 1.6 days. We calculated water and nutrient fluxes into the coastal ocean at each study site. This study provides a baseline description of submarine ground-water discharge in Kaloko-Honokōhau National Historical Park and its effect on the park’s aquatic resources. We hope that it will allow park managers to better assess potential future changes in ground-water quality and quantity and conserve the park’s valuable resources.
Download this report as a 38-page PDF file (sir2008-5128_text.pdf; 6.4 MB).
View the Appendix files. Appendix 1 is a full listing of all samples collected for this study. It is presented here in both .doc and PDF formats (appendix folder; 2 files, 2.7 MB total).
View the Metadata files. The metadata are presented here in faq.html, .html, .txt, and .xml formats (metadata folder; 4 files, 136 kB total).
USGS Open-File Report 2007-1310, Submarine Ground Water Discharge and Fate Along the Coast of Kaloko-Honokōhau National Historical Park, Hawai‘i; Part I, Time-Series Measurements of Currents, Waves, Salinity, and Temperature: November 2005–July 2007, by M. Katherine Presto, Curt D. Storlazzi, Joshua B. Logan, and Eric E. Grossman (2007)
USGS Scientific Investigations Report 2010-5081, Submarine Ground Water Discharge and Fate Along the Coast of Kaloko-Honokōhau National Historical Park, Hawai‘i; Part 3, Spatial and Temporal Patterns in Nearshore Waters and Coastal Groundwater Plumes, December 2003-April 2006, by Eric E. Grossman, Joshua B. Logan, M. Katherine Presto, and Curt D. Storlazzi (2010)
For questions about the content of this report, contact Karen Knee or Eric Grossman.
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