The highly porous karst limestone of the Yucatan Peninsula promotes infiltration of rainwater into the subsurface, where it becomes part of the Yucatan Aquifer. The combination of high subsurface porosity, high evapotranspiration, and seasonal droughts results in relative scarcity of lakes or drinkable water at the surface. The majority of past and present people living on the Yucatan Peninsula have depended on groundwater resources for domestic purposes. Whereas coastal karst aquifers such as the one in the Yucatan Peninsula are important water resources, they are highly vulnerable to climate-related changes such as sea level (SL) rise, increased hurricane intensity and extended droughts. With ongoing development along the eastern coast of the Yucatan Peninsula (Quintana Roo), predicted increases in storm intensity, and rising population and potential pollutant output, it has become imperative to study the seasonal and long-term effects of climate and human activity on the Yucatan Aquifer.
Like many coastal karst aquifers, the Yucatan Aquifer is stratified according to density, with the Meteoric Water Mass (MeWM) flowing towards the coast on top, and the Marine Water Mass (MaWM) flowing inland on the bottom. The current basis of our knowledge about how the two water masses interact has been from short-term instrumental monitoring and numerical modelling, which is useful for understanding straightforward relationships between salinity, precipitation and temperature across the two water masses and have paved the way for more complex analyses to be completed using the simple principles to guide geochemical studies of sediment within the systems. Generally, sediment cores have been analysed discretely using various methods including grain size analysis, micropaleontology, WD-XRF, and others, however the recent rise of µXRF Core Scanning provides a quicker, more cost effective and higher-resolution method for studying climate-related patterns in sediment cores.
This thesis outlines and provides robust evidence for three new methods of using µXRF-CS to determine past and present climatological changes and their relationship to sediment elemental counts. We provide the first outline of the seasonal and spatial controls of geochemical changes in sedimentation in a coastal cave system (Yax Chen), using four years of in situ sediment collection. We then provide the first calibrated record of past salinity based on Cl counts within sediment cores taken from shallow lakes. Although instrumental monitoring has provided evidence that the aquifer is impacted by modern wet and dry periods, the effect of past climate on the aquifer has not been investigated. We provide the first record of water-column mixing at three locations within coastal Quintana Roo. This demonstrates that there has been a long-term climate impacts to coastal Yucatan Peninsula groundwater, which may be scaled to other karst islands and provides evidence that increased hurricane frequency and/or magnitude could change the baseline salinity of the fresh MeWM. / Dissertation / Doctor of Philosophy (PhD) / The porous limestone (karst) geology of the Yucatan Peninsula results in percolation of rainwater down into the subsurface where it is held in the vast Yucatan Aquifer that past and present people have depended on for water resources. Such aquifers are highly vulnerable to human activity and also climate change via increased sea level rise, hurricane intensity and droughts. The Yucatan Aquifer is made up of two separate water masses that have different salinities, and can interact physically and chemically due to changes in climate and weather. Sediment cores can be used to look at subannual geochemical changes which reflect long term behaviour of the aquifer, but first the relationship between sediment change and climate must be established. This thesis uses an iTRAX X-Ray Fluorescence Core Scanner (XRF-CS) to investigate changes in surface water and groundwater over the past 6000 years, and provides the first record of rainfall-induced mixing in a coastal karst aquifer. We also provide evidence of rapid salinity change in shallow lakes associated with intense dry periods, and reveal relationships between cave sedimentation and surface vegetation coverage.
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/25951 |
| Date | January 2020 |
| Creators | McNeill-Jewer, Chelsi |
| Contributors | Reinhardt, Eduard, Earth and Environmental Sciences |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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