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.

No description available.

Groundwater is a very important resource since water volumes stored underground are much larger compared with those located at the surface, such as rivers and lakes. Aquifers supply a high percentage of freshwater for human consumption as well as supplying economic activities like industry, agriculture, and livestock production. Among them, karst aquifers stand out due to their special hydrologic characteristics and behaviour. In karst aquifers, infiltration occurs faster in comparison with unconsolidated aquifers, due to high permeability features at the surface like dolines, karren, epikarst, and swallow holes that allow precipitating water to recharge the aquifer at higher rates. Nevertheless, these characteristics also increase the aquifer’s susceptibility to being affected by pollution generated by anthropogenic practices. With a low natural pollutant degradation capacity, karst systems mostly experience problems related with water quality rather than water quantity. At present, this represents a significant challenge because a high percentage of the world population is settled on karst areas and is solely dependent upon karst aquifers to fulfil their necessary water supply. A good example to represent this case is the Yucatan Peninsula. The Peninsula is a transboundary limestone platform, covering parts of Mexico, Belize, and Guatemala, whose characteristics do not allow surface streams to generate. Therefore, the karstic aquifer provides water for nearly 4.5 million inhabitants within Mexican territory; this estimation excludes water volumes used for economic activities. The anthropogenic impacts over this karst aquifer have generated problems for water intended for human consumption, furthered by weak environmental regulations that allow the disposal of wastewater without adequate treatment. In the Mexican state of Yucatan, roughly 10% of the population has access to public sewer services where wastewater is treated. Additionally, the use of fertilizers and pesticides is not regulated in agricultural areas, while pig farming is an increasing activity, which fails to keep the necessary standards for the proper disposal of pig slurry. Similar situations can be found around the world, thus the development of plans and strategies to preserve karst groundwater quality that aim to find a balance between resource protection and regional development is increasingly necessary. One important tool emerged to support decisions regarding groundwater protection: the groundwater vulnerability concept. However, due to the hydrologic differences among detritus and karst aquifers, the vulnerability concept, which was first promoted for the former aquifer type, necessitated the development of a specialized vulnerability method to consider the natural characteristics of karst landscapes. Nevertheless, due to the high heterogeneity and anisotropy present in karst systems several methodologies to estimate karst groundwater vulnerability have arisen. Current methodologies are theoretical approximations to differentiate areas where an assumed pollutant particle, released at the surface, is more likely to reach the aquifer due to the natural characteristics of the area. These methods have shown themselves to be useful in defining protection areas and in highlighting regions in which further studies can be performed. However, the high subjectivity and exclusion of anthropogenic influences as part of the analysis is a drawback for these methods. In order to estimate karst groundwater vulnerability for current and future scenarios, an integrated approach is highly necessary. Since most of the methods focus solely on the travel time of a theoretical pollutant from the surface towards groundwater or to a spring, inclusion of pollutants residence time and concentration as parameters to estimate vulnerability is of the uttermost importance. To reach this goal, it is necessary to investigate current intrinsic-based methods in terms of their applicability and regional congruence in order to highlight advantages and probable misclassifications among them and to propose improvements. Pollutant residence time and concentration can be estimated from modelling, which can highlight areas where pollution can represent a problem due to anthropogenic practices, such as wastewater disposal and water extraction fields influencing groundwater flow. Other problems to be contemplated are the data availability and the variable processes by which areas are classified as vulnerable or not. Evaluation of multiple criteria to define degrees of vulnerability is complicated, since several factors, such as subjectivity, data quality, scale, and regional conditions, will always be present. This work presents the results from the application of eight karst groundwater vulnerability methods to the Yucatan karst and outcomes from solute transport. Important considerations are explained in order to improve the workflow for intrinsic groundwater vulnerability assessment. Possible parameters, to be included as part of vulnerability analysis, are evaluated by modelling, demonstrating the importance of anthropogenic impacts for current vulnerability scenarios. Results obtained in this research are displayed as the basis for an Integrated Karst Aquifer Vulnerability (IKAV) method proposed as an alternative for vulnerability studies.

Geological and geophysical investigations of the Chicxulub meteorite impact structure have been ongoing since its scientific recognition in 1991 Hildebrand et al. 1991). The structure is of important significance because it is currently the only known impact crater that is linked to a global catastrophe, the Cretaceous/Tertiary boundary that occurred 65 Ma years ago. Major climatic and biological changes occurred at this interval that include the disappearance of 70% of all living species, in particular the dinosaurs. A global iridium anomaly along with the occurrence of shocked quartz grains characterize a thin clay layer this interval that led to the search for a large meteorite impact crater on continental crust. A large “volcanic” igneous province identified by oil exploration boreholes on the NW region of the Yucatán Peninsula was eventually recognized as a vast impactite deposit associated with a 180 km wide crater. Until 2002, only small grab and chip samples had been described from Chicxulub. This lack of sampling and, thus, poor understanding of the cratering conditions at Chicxulub led the International Continental Drilling Program (ICDP) to fund and drill the Yaxcopoil-1 borehole. The Yaxcopoil-1 (Yax-1) borehole was drilled 60 km south-southwest from the center of the Chicxulub meteoritic impact. It intersected 794.63 m of post-impact cover rocks, 100.31 m of impactites, and 616.03 m of Cretaceous target rocks, terminating at a final depth of 1510.97 m. The impactite interval, as well as several selected samples from the Cretaceous target rocks, is the focus of this scientific investigation. In conjunction with this work, the Yax-1 core was studied by numerous international research groups and is, thus, currently one of the best studied continuous diamond drill core from an impact crater. This petrographic and geochemical investigation provides further understanding on the primary and secondary conditions that influenced the formation of the Yax-1 impactites and selected target rocks. Five units have been recognized in the impactite interval. These subdivisions are based on macro- and microscopic observations and are complemented by geochemical characteristics. Unit 1 (795-822 m) comprises subrounded melt rock particles that are poorly sorted, yet show a progressive gradation with height, are self supported, show perlitic devitrification texture, and are generally fine-grained. Unit 2 (823-846 m) and Unit 3 (846-861 m) are relatively similar, as they both consist of a groundmass-supported breccia with melt rock particles that are angular, fluidal, and vesiculated in texture. The groundmass in both units is pervaded by numerous carbonate-veinlets and decreases in volume towards Unit 3 because of compaction. Unit 2 and Unit 1 are both altered to a predominantly green colour by the pervasive conversion of silicate phases from clay minerals. Unit 3 is of a variegated character and is suggested to be the less altered unit bove Unit 4. Unit 4 (861-885 m) comprises a massive yet brecciated microcrystalline impact melt rock. It is primarily of a silicate composition and contains only minor secondary carbonate crystals. All lithic fragments are of silicate compositions. Unit 5 (885-895 m) shows the greatest variation in the proportion of melt rock particles and lithic fragments. The melt rock particles contain numerous microlites that crystallized below the glass-transition temperature. These are suspended in a carbonate groundmass that is either of a primary impact melt origin or of a secondary nature. Units 1 and 5 both contain foraminifera fossils and greater proportions of carbonate clasts than any other units. All unit show shock metamorphic characteristics, i.e., planar deformation features, ballenquartz, and checkerboard feldspar. Geochemical results have been obtained by various analytical techniques in order to constrain cratering and alteration processes at various sampling scales. Main results reveal that samples from units 1 and 2 have been leached of their alkali elements, show negative Ce anomalies on a microscopic scale, and show less major element variation on a bulk sample scale than lower units. The groundmass in units 1 to 3 comprises a microcrystalline calcite and altered alkali element-, Ca- and Si- rich cement. In units 2, 3, and 5 melt rock particles are of a heterogeneous composition. In Unit 1, melt rock particles are highly altered, therefore volatile rich, and are of a more homogeneous composition than those of other units. On a bulk sampling scale, the silicate component for the whole impactite sequence shows remarkable homogeneity. Major and trace element compositions show that this component and Unit 4 are typical of the upper continental crust. The carbonate component is more calcite rich than dolomitic and most likely represents strong secondary alteration. No significant sulfur content was measured compared to published known target rock values. The contents of the siderophile elements, including Ni, Co, Ir, and Cr, do not indicate the presence of a significant extraterrestrial component in the Yax-1 impactites. Cretaceous rocks were also sampled in order to provide compositional constraints with the impactites and observe any shock related metamorphic features. Petrographic observations indicate that the Cretaceous rocks in the Yaxcopoil-1 drill core likely register a multistage deformation history that spans the period from pre- to post-impact. Contrary to previous studies that claimed evidence for the presence of impact melt breccia injection veins, no evidence was found from samples located between 1347–1348 m depth for the presence of melt breccia. An emplacement mechanism for the impactite sequence is proposed with regards to cratering. Unit 5 is interpreted as an early ejecta deposit that was emplaced following the passage of the initial ejecta curtain during the excavation stage of cratering. Unit 4 is an allogenic siliceous melt rock body that originated primarily from the fusion of the silicate crystalline basement. The origin of Unit 4 is based on geochemical and petrographic arguments, i.e., no carbonate component to the melt could be detected and only igneous/metamorphic mineral/rock fragments were observed in it. It is suggested Unit 4 was emplaced as an outward flow of fused crystalline basement rocks from the collapsing central uplift or it may have also been deposited from the fallback of a large melt bomb. Brecciation occurred post-deposition as fragments fit together like pieces of a jigsaw puzzle. Units 2 and 3 represent unreworked fallback suevite deposits. Vesiculated melt rock particles are a testimony of the volatile rich nature of the collapsing impact plume. Volatiles are believed to have helped disperse the suevite and inhibited the melt rock particles from undergoing compositional homogenization. Unit 1 represents a reworked fallback deposit that formed from the resurge of seawater into the impact basin. Unit 2 is the altered equivalent of Unit 3 and along with Unit 1 underwent significant post-depositional phyllosilicate alteration from circulating fluids at the top of the suevite pile.

Thesis advisor: Amy Frappier / Tropical cyclones (TCs), known as hurricanes in the Atlantic and Typhoons in the Pacific, are among the most destructive and deadly natural disasters that occur on Earth. Attempts to understand how TCs relate to the global climate system, and future risk assessments are dependent upon having records of TC activity that pre-date the modern meteorological records, which are commonly not older than 130 years (Nott, 2003). Paleotempestology is a sub-discipline of paleoclimatology that attempts to extend the TC record beyond the meteorological record through the use of proxies. Presented here is the establishment of a paleotempestology proxy based on clastic mud being suspended in the water column by floods caused by TCs and deposited in stalagmite CH-1, collected in June of 2007 from Cenote Chaltun-Ha, a low-lying cave from the Yucatán Peninsula. CH-1 was dated by a combination of <super>210</super>Pb, U/Th, and layer counting techniques, creating an age model for its entire length. The years with mud layers were compared to the historical TC record from 1852-2006. Nineteen mud layers were identified for this time period. All of the mud layers deposited in years with at least one TC passing within 330 km of Cenote Chaltun-Ha. A total of 265 mud layers were identified in CH-1 dating from 198 BC to 2006 AD. Relatively high TC frequency, ~16 mud layers/century, was recorded in CH-1 from 198 BC to ~1233 AD. This period was followed by eight centuries of relatively low TC frequency, ~7 mud layers/century. The low frequency period hit a low point in the 1600s with 4 mud layers. Since the 1600s the TC frequency recorded in CH-1 has been on the rise, indicating possible periods of higher than present TC frequency in the future for the Yucatán region. This trend of high TC frequency followed by a sudden drop and subsequent increase is also reported in published sand overwash deposit research. &#948;;<super>18</super>O and &#948;;<super>13</super> values collected from CH-1 provide insight into the timing of regional droughts. A low &#948;;<super>18</super>O value from 1815 provides evidence that "The Year Without a Summer" caused by the 1815 eruption of the Tambora volcano in Indonesia had a climatic effect on the Yucatán. A land-use signal related to the agricultural production boom of Agave Fourcroydes, a succulent plant known as Henequen, in the early 20th century was also detected in &#948;;<super>13</super>C values. / Thesis (MS) — Boston College, 2010. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Geology and Geophysics.

Submerged caves, locally referred to as cenotes, can be found throughout the Yucatan Peninsula of Mexico. These nutrient poor, aphotic “underground estuaries” lack photosynthetic primary productivity, but are often found underlying high primary productivity areas such as mangroves and tropical forests. Adjacent ecosystems contribute organic carbon to the cave systems via percolation, where it is then utilized by the obligate, cave-dwelling fish and invertebrates. Another potential pathway through which organic carbon can enter the cave food web is through chemosynthesis. Chemoautotrophic sulfur-oxidizing or nitrifying bacteria have been found in the hydrogen sulfide layer or in the sediments of some anchialine caves. Our study utilizes 13C/12C and 15N/14N stable isotopes as well as 14C radiocarbon dating to determine and compare the sources of organic matter entering a coastal anchialine cave (Cenote Aak Kimin) versus an inland cave (Cenote Maya Blue) in the Yucatan Peninsula. Stable isotopes have long been employed in tropic investigations. This study, however, is the first to utilize radiocarbon isotopes in anchialine caves. The use of both stable and radiocarbon isotopes as source indicators provides greater discrimination in systems that contain numerous carbon sources or indistinct trophic levels, particularly to distinguish between chemoautotrophic versus photosynthetically derived carbon. Results indicate that chemosynthetically derived organic carbon contributes substantially to the diet of some crustaceans, such as the stygobitic shrimp Typhlatya, while other species remain dependent on detrital inputs. Depleted δ13C values and aged radiocarbon values (as low as -47.51‰ and 1840 yrs. for Typhlatya spp.) in comparison to particulate and sediment δ13C values (lowest -32.07‰ and -28.43‰, respectively). A comparison of isotopic values between Cenote Aak Kimin and Cenote Maya Blue suggests that the trophic web of the coastal cave incorporates more photosynthetic or detrital carbon, while the inland cave, with more depleted 13C and 14C values, relies more heavily on chemoautotrophic carbon. Within both systems, however, distinct photosynthetic and chemoautotrophic levels were identified. Water quality parameters, especially dissolved oxygen and pH, support the hypothesis of bacterial activity at the halocline. Anchialine systems in the Yucatan Peninsula are threatened due to increases in tourism, development, and pollution. Quantifying and qualifying the inputs of organic carbon is vital for the management and conservation of the area’s freshwater resources.

Most settlement pattern research and GIS analysis of the ancient Maya of the Northern Yucatan have focused on water availability in a dry landscape where cenotes are often the only water source. While water is of paramount importance, permanent settlement secondarily requires farmable soil, a resource often as precious as water in many parts of the Yucatan. The dynamics between these resources reveal areas of ideal settlement and more challenging landscapes for which the Maya developed strategies to overcome environmental conditions. A region of the southwest "Cenote Zone", however, appears to have presented the ancient Maya with insurmountably poor environmental conditions despite abundant water resources. The lack of dense population and stone architecture in this area emphasizes the lack of a simple correlation between cenotes and settlement. This thesis uses GIS analysis to identify and explore such problematic settlement areas to better understand the factors and complexities involved in the more successful settlements of neighboring regions.

No description available.

Evaluation de l'efficacité et de l'innocuité de la microcuriethérapie à base de microparticules d'holmium pour le traitement du gliobastome induit chez un modèle porcinAuteur: Seyed Mehrdad KHOSH NEVISMot clés: U87, miniporc, glioblastome, modèle animal, Yucatan, microcuriethérapie, Holmium-166, nanoparticulesRésumé: L’objectif de notre étude a été de tester une modalité thérapeutique moins invasive (microcuriethérapie), en phase préclinique sur un modèle animal porcin, pour le traitement du GB. 1) Nous avons développé un nouveau modèle de GB en implantant la lignée U87 dans le cerveau du miniporc (Yucatan). Les images scanner ont montré la présence de tumeurs chez tous les miniporcs. 2) Nous avons évalué l’injectabilité d’holmium non radioactif (ho-165) après injection stéréotaxique dans le cerveau de miniporcs sains. L’holmium était bien circonscrit aux zones d’injection et a été validée pour les essais ultérieurs d'injections intra-tumorales. 3) Nous avons réalisé des injections d’ho-165, directement dans la tumeur d’un modèle de GB U87. La faisabilité des injections d’ho-165 a été testée chez le miniporc en utilisant un système d’injection préclinique spécifique. Les résultats de cette étude ont montré que la suspension de nanoparticules d’ho-165 pouvait être injectée, avec précision, dans la tumeur. 4) L’étape finale a été d’évaluer l’efficacité du traitement à base de nanoparticules d’ho-166 en microcuriethérapie sur le modèle de GB du miniporc. Notre étude a démontré un très bon contrôle tumoral et l’absence d’effets toxiques / Evaluation of treatment efficacy and safety of microbrachytherapy with holmium microparticles in porcine induced glioblastoma model.Author: Seyed Mehrdad KHOSH NEVISKeywords: U87, minipig, gliobastoma, animal model, Yucatan, Microbrachytherapy, Holmium-166, nanoparticlesResumé: The aim of our study was to apply a less invasive therapeutic method (microbrachytherapy) for the treatment of GB in a preclinical phase on a suitable animal model.1) First, we developed a new model of GB in Yucatan minipig by implantation of U87 cell line in the brain. All implanted minipigs demonstrated macroscopic tumors on CT acquisitions. 2) In parallel, the injectability of the non-radioactive Holmium (Ho-165) in healthy brain was assessed. Holmium was circumscribed to the injection area and was found to be suitable for future intratumoral injections. 3) In the next step, the feasibility of injection of ho-165 was tested in minipigs GB model using specific injection system. Results showed that the ho-165 nanoparticles suspension can be injected precisely inside the cerebral tumor using our prototype injection system. 4) The final step was the evaluation of treatment efficacy using radioactive ho-166, as microbrachytherapy, in Yucatan GB model. Our trial demonstrated an excellent efficiency in tumor control and the absence of toxic effects

La présente recherche vise à réévaluer et définir le panorama sociolinguistique actuel de la variété dialectale mexicaine connue autrement comme l’espagnol yucatèque. Cette modalité linguistique arbore des traits qui la caractérisent indépendamment de la norme traditionnelle mexicaine. Ces traits ont déjà été étudiés amplement dans la littérature spécialisée, mais nous en présenterons quelques exemples tirés de notre recherche. Après la présentation de la théorie de base (chapitre 1) et la littérature générale (chapitre 2), nous allons présenter notre recherche et les exemples plus représentatifs de cette variété dans les niveaux phonétique et phonologique, morphosyntaxique et lexico-sémantique (chapitre 3). Finalement, nous allons approfondir la notion de deux phénomènes grammaticaux peu traités— le verbe espagnol quitarse (‘s’en aller, partir’) et l’aspect asegurativo (à) de l’espagnol de Yucatan (chapitre 4). Pour notre étude, nous avons visité dix communautés (six municipios et quatre comisarías) dans l’état de Yucatan, sur une période de six mois obtenant ainsi 63 « conversationnes » qui nous fournit les fondements indispensables à notre analyse. Nous avons pris en ligne de compte les 42 premières conversations, obtenant ainsi un total de 42 heures et 45 minutes du verbatim, qui furent transcrites et rédigées dans un corpus linguistique de 834 pages. Le groupe étudié est composé de 25 hommes (10 monolingues et 15 bilingues Espagnol-Maya) et 17 femmes (10 monolingues et 15 bilingues Espagnol-Maya). Les personnes avec qui nous avons discuté ont également été réparties en trois catégories, selon l’âge. L’échantillonnage général obtenu nous sert à exemplifier abondamment les traits typiques de la variété yucatèque courante. Nous prendrons également soin de décrire et caractériser d’autres phénomènes moins étudiés que l’on retrouve dans le parler naturel chez les yucatèque(e)s. / The present work was planned with the idea of studying and learning more about aspects of the variety of spoken Spanish nowadays in the State of Yucatan (español yucateco). We emphasize the linguistic and social aspects. The linguistic variation has been the object of many studies in the past, and was described as presenting specific traits. We presented some of these specific traits with the examples obtained from our research in the Yucatan State. After some considerations of theoretical nature (chapter 1); and the review of the specialized literature (chapter 2); our research highlights some of the most representative examples of this dialectal variety (chapter 3) at the structural levels of phonetics and phonology, morphology and syntax, and lexicology and semantics. Finally, two phenomena that have not been studied much are presented in the final chapter. These two phenomena are the verb quitarse (to leave), and the assertive aspect of Yucatan Spanish (chapter 4). In order to attain these objectives, it was necessary to create a corpus of our own. A field study was planned, developed and conducted over six months of intensive travel in six selected communities of the Yucatan State. We gathered a total of 63 conversations. For this project, we only analyze the first 42 conversations. This information represented 43 hours and 45 minutes of verbatim, and was transcribed into an 834-page document. Our study group was formed by 25 men (10 Spanish monolingual and 15 Spanish-Mayan bilingual) and 17 women (10 Spanish monolingual and 7 Spanish-maya bilingual). They are distributed into three main generational groups. Our sample was mainly used to provide examples of the study traits, found in the literature, in the Spanish spoken currently by the Yucatecan population as well as to identify other phenomena less studied.