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Stable Isotope and Geochemical Source-Tracking of Groundwater and Surface Water Pollution to Kāne‘ohe Bay, Hawai‘i.

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Title:Stable Isotope and Geochemical Source-Tracking of Groundwater and Surface Water Pollution to Kāne‘ohe Bay, Hawai‘i.
Authors:Dores, Daniel E.
Contributors:Geology & Geophysics (department)
onsite sewage disposal systems
local meteoric water line
stable isotopes
show 3 moresubmarine groundwater discharge
dissolved inorganic carbon
show less
Date Issued:Aug 2018
Publisher:University of Hawaiʻi at Mānoa
Abstract:Improved understanding of water resources and their contamination is an emerging priority for Pacific Islands to protect limited freshwater supplies, prevent environmental degradation in coastal environments, and improve public health. This study addresses these concerns through understanding island-wide groundwater recharge and pollution pathways to groundwater and the coastal ocean on the island of Oʻahu, particularly in the Kahaluʻu region of Kāneʻohe Bay of east Oʻahu. We investigate delivery and differentiation of contaminated groundwater to streams and nearshore coastal waters in the Kahaluʻu region as a system representative of pollution dynamics in Pacific Islands. In this region, nutrient pollution is primarily sourced from onsite sewage disposal system (OSDS) release of untreated wastewater to the environment. OSDS usage is a widespread wastewater management practice in the U.S. and Pacific Islands, and OSDS coverage (unites per area) in the Kahaluʻu region is one of the densest in the State of Hawaiʻi, creating a marquee study for dynamics of raw sewage inputs to groundwater in aquifers of volcanic rock and valley fill sediments.
A multi-tracer investigation of water contamination in the Kahaluʻu region, including nutrient concentrations, stable nitrogen and oxygen isotopic compositions of nitrate, boron concentrations and isotopic composition, and common ion concentrations, identified locations of nutrient pollution to groundwater, streams, and nearshore environments. OSDS leachate is the primary source of nutrient pollution in the region, followed by agriculture. Shallow groundwater flow transports wastewater-derived nutrients to streams and submarine groundwater discharge (SGD), which in turn transports these nutrients to coastal environments and Kāne‘ohe Bay. In coastal settings, our isotopic measurements of nitrogen in Rhizophora mangle (red mangrove) foliage suggest further investigations are merited in R. mangle as a potentially promising new method of coastal pollution monitoring. In sum, the Kahaluʻu–Kāneʻohe Bay study presents a "type example" of transportation schematic of Pacific Island OSDS-sourced nutrient delivery through groundwater aquifers to fresh and saline surface waters as a function of OSDS density, unit distance to the water body, geochemical mixing and transformation dynamics, and local and regional subsurface variations that can exist between deep and shallow groundwater.
Congruent and ancillary to the above, an island-wide study of the stable hydrogen and oxygen isotopic compositions of precipitation was completed in order to better understand
relationships between groundwater, seasonality of precipitation, and locations of recharge. Results from a network of 16 precipitation collectors deployed for 1 year reveal that Oʻahu’s groundwater recharge is dominated by wet season precipitation and high altitudes, as opposed to dry season rainfall and the island’s coastal plains. In addition, we catalogue the first geospatial distribution of hydrogen and oxygen isotopic compositions of rainfall for O‘ahu and create the first local meteoric water line for O‘ahu. Combined with δ2H and δ18O values of groundwater, we derive localized groundwater recharge to regional aquifer storage. Results align with flow regimes interpreted in previous studies of O‘ahu’s hydrogeology.
Description:M.S. Thesis. University of Hawaiʻi at Mānoa 2018.
Rights:All UHM dissertations and theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission from the copyright owner.
Appears in Collections: M.S. - Geology and Geophysics

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