Evaluation of microcontaminants as tracers for groundwater nutrient sources within mixed-use watersheds along the South Kohala coast of the Island of Hawaii

dc.contributor.advisor Dulai, Henrietta
dc.contributor.author McKenzie, Casey D.
dc.contributor.department Earth and Planetary Sciences
dc.date.accessioned 2023-02-23T23:57:35Z
dc.date.available 2023-02-23T23:57:35Z
dc.date.issued 2022
dc.description.degree M.S.
dc.identifier.uri https://hdl.handle.net/10125/104682
dc.subject Environmental management
dc.subject Environmental geology
dc.subject Land use planning
dc.subject groundwater tracer
dc.subject mixed-use watershed
dc.subject nitrate contamination
dc.subject submarine groundwater discharge
dc.title Evaluation of microcontaminants as tracers for groundwater nutrient sources within mixed-use watersheds along the South Kohala coast of the Island of Hawaii
dc.type Thesis
dcterms.abstract Anthropogenic nutrient loading of coastal environments is a known contributor to marine ecosystem health decline in Hawai‘i, and submarine groundwater discharge (SGD) has been shown to serve as a pathway to fuel nutrient delivery to coastal zones. Anthropogenic sources that may supply nitrogen (N) to groundwater include agricultural practices, resorts and golf courses that utilize fertilizers in landscaping applications, an abundance of homes outfitted with cesspools, and input from wastewater infrastructure. SGD provides a means of conveying land-derived nutrients to the coastal ocean and hence facilitates N-transport to coastal zones. Analysis of SGD enabled the exploration of the spatial distribution of groundwater composition and its relation to land-use. Previous research identified the presence of SGD in the study area, and we targeted and sampled 45 coastal springs and 20 upland wells along a 14 km long coastline in South Kohala, Hawai‘i. A wide range in nutrient concentrations was observed in SGD and well samples, with N loads well above 100 μM (1000-fold above marine levels). Some, but not all, δ15N-NO3- signatures suggest that N observed in SGD is of wastewater origin. We utilized known microcontaminants as novel tracers for identifying which land-use categories arehydrologically and chemically connected to SGD and, therefore, may be nutrient sources to the coastline. Microcontaminants of interest included pharmaceuticals commonly present in cesspool waste, restricted use pesticides and herbicides utilized in landscaping practices, and common detergents used in commercial industry that utilize public sewage infrastructure. To determine groundwater flow paths, δ18O-H2O allowed calculation of estimated recharge elevations to estimate upstream end members of flow lines. Spatial analysis of land uses and practices (LUP) along flow lines was utilized to quantify LUP overlying groundwater flow. δ18O-H2O of groundwater also contributed evidence of where groundwater flow paths from Kohala, Mauna Kea and Mauna Loa volcanoes may potentially converge along the South Kohala coastline. When comparing flow path analysis to developed scoring methods, upstream contribution of microcontaminants to groundwater pathways confirmed that microcontaminants could serve as land-use tracers throughout the length of the flow path. Microcontaminant scoring geochemically connected up-stream land uses to coastal SGD seeps along hydrological flow paths. Spatial analysis of microcontaminant distribution in SGD and LUP scoring revealed that caffeine, carbamazepine, sulfamethoxazole has strong correlation with presence of OSDS, confirming their suitability as wastewater specific tracers.
dcterms.extent 104 pages
dcterms.language en
dcterms.publisher University of Hawai'i at Manoa
dcterms.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.
dcterms.type Text
local.identifier.alturi http://dissertations.umi.com/hawii:11627
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