An exploration of the origins, evolution, and fate of inorganic chemical constituents in meteoric waters on the island of O'ahu, Hawai'i, USA
An exploration of the origins, evolution, and fate of inorganic chemical constituents in meteoric waters on the island of O'ahu, Hawai'i, USA
Date
2023
Authors
Brennis, Theodore Martin
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Lautze, Nicole
Department
Earth and Planetary Sciences
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Abstract
This study examines the inorganic composition of rainfall on Oʻahu, Hawaiʻi, as part of a broader effort to apply natural conservative geochemical tracers to water resource management problems in the State. Pacific Islands grapple with unique water resource challenges due to environmental vulnerability, climate dynamics, and heavy groundwater reliance. Urbanization, population growth, and decreasing rainfall trends also stress Oʻahu's freshwater resources. To address these water resource challenges, understanding the links between meteoric, ground-, and surface waters is crucial. This research consists of three components that use the inorganic chemistry of precipitation to better understand such links. First, we analyzed major ion sources in Oʻahu's rainfall, which revealed that ocean sea spray is the primary dissolved ion source, with perturbations from Asian continental dust, local sediment, and agriculture as dictated by broader weather patterns. Second, we analyzed rainfall stable isotopes (18O and 2H), which indicated that there are distinct geographical, seasonal, and precipitation source-related influences. High-elevation spring sampling also indicated that there are significant fog contributions to groundwater recharge. Finally, we investigated how rainfall chemistry evolves as it infiltrates the soil and present a method to assess changes in the stable isotope composition of precipitation during infiltration. These studies illuminate several key meteorological and physiographic dynamics that affect precipitation chemistry on Oʻahu and provide a baseline from which to assess future fluctuations. They underscore the impact of microclimates and moisture source on the stable isotope composition of precipitation, and highlight the need for topographically diverse, event-based precipitation sampling. Results from the third study highlight the importance of understanding chemical changes to precipitation during the process of infiltration. Cumulatively, these findings lay groundwork for utilizing natural geochemical tracers to understand groundwater flow paths and recharge processes on Oʻahu.
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Geochemistry,
Hydrologic sciences,
dissolved ions,
groundwater,
O'ahu,
precipitation,
soil moisture,
stable isotopes of water
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209 pages
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