Ring Of Cenotes Research Articles

Hydrogeophysical Evaluation of the Karst Aquifer near the Western Edge of the Ring of Cenotes, Yucatán Peninsula

In this work, electrical resistivity tomography was carried out together with physical hydrogeology techniques to evaluate the karst aquifer in the northwest region of the Yucatán Peninsula in a study area near the western edge of the Ring of Cenotes of the Chicxulub Crater. In addition, based on a systematic compilation of open-access data of water levels reported for the peninsular aquifer, maps of groundwater isolines and groundwater flows were generated using IDW interpolation, Empirical Bayesian Kriging, and the Flow Net method. From these results, a shallow aquifer is observed, with the presence of heterogeneities such as possible dissolution conduits and/or flooded caverns, approximately 20 m below ground level, formed by the dissolution processes of limestone rocks. On a regional scale, the geomorphological influence of the Ring of Cenotes on groundwater flows was observed. In general, the flow directions observed from these maps coincide with those conceptualized for this region of the peninsular aquifer. Nevertheless, some differences were observed depending on the interpolation method used. Our results contribute to hydrogeological studies carried out in the periphery of this ring, where the vulnerability of the aquifer to anthropogenic contamination has been highlighted due to the intrinsic features of the karst environment.

Groundwater Quality in the Yucatan Peninsula: Insights from Stable Isotope and Metals Analysis.

High surface water-groundwater connectivity characterizes watersheds underlain by karsts, increasing contaminant transport risks. However, karsts are highly complex, making research necessary to understand the transport of contaminants from the surface, through the aquifer, to discharge areas. In Yucatan, the lack of waste water treatment raises the risk of groundwater contamination. We monitored stable isotopes (δ18 O-NO3 and δ15 N-NO3 ), cadmium, and lead to document waste water contamination and transport during the rainy and dry seasons, using water samples collected along the Ring of Cenotes during each season. Specific conductance and pH showed no consistent seasonality, with conductance ranging from 0.5 to 55 mS/cm and pH ranging from 6.6 to 8.6 for most samples. Nitrate concentrations in the cenotes averaged 205 ± 260 μM and no seasonal pattern was observed. Cd and Pb concentrations were 0.1 to 37.9μg/L and 0.2 to 243.2μg/L, respectively. Nitrate stable isotope values were 2.6 to 27.2‰ for δ18 O and 1.2 to 20.7‰ for δ15 N. The statistical relationship between δ15 N and δ18 O, in dry season samples, indicated that denitrification was occurring. A scale measure for waste water recognition showed: (1) high variability among sites probably related with dry/rainy seasons and/or diverse anthropogenic activities; and (2) specific water quality variables that contribute to contamination at each site during each season. Importantly, our analyses indicate that in the area surrounding the Ring of Cenotes, waste water exhibits spatial and temporal patterns related to complex transport and dilution processes, as is the case in karsts in general.

Regional Hydrogeochemical Evolution of Groundwater in the Ring of Cenotes, Yucatán (Mexico): An Inverse Modelling Approach

The Ring of Cenotes (RC) extends along the edge of the Chicxulub crater, in the limestone platform of the Yucatan Peninsula (YP), where groundwater shows two preferential flow paths toward the coast near Celestun and Dzilam Bravo towns. The objectives of this study were to describe the regional hydrogeochemical evolution of the groundwater in the RC, and its association with the dissolution/precipitation of the minerals present along its pathway to the ocean. These objectives results were obtained by: (a) characterizing groundwater hydrogeochemistry; (b) calculating calcite, dolomite, and gypsum saturation indexes in the study area; and (c) developing a hydrogeochemical model using PHREEQC (U. S. Geological Survey) inverse modelling approach. The model predictions confirmed that there are two evolution pathways of the groundwater consistent with the preferential flow paths suggested in a previous regionalization of the RC. On the western path, where groundwater flows towards Celestun, marine intrusion influences the hydrogeochemical processes and represents a risk for the freshwater. On the eastern path, where groundwater flows toward Dzilam Bravo, rainfall has an important effect on the hydrogeochemical processes, evidenced by a higher concentration in sulfates during droughts than during rainy periods. Then, monitoring of marine intrusion and phases dissolution in the RC is highly recommended.

Karstic aquifer structure from geoelectrical modeling in the Ring of Sinkholes, Mexico

Groundwater models based on terrain resistivity can show the diverse properties and processes occurring between fractures, boreholes and conduits. Using electrical resistivity tomography, a conceptual model was created of the aquifer within the Ring of Cenotes, which surrounds the Chicxulub Crater on the Yucatan Peninsula, Mexico. Determining the hydrogeological parameters of an aquifer is vital since they determine flux and hydrodynamic patterns. In karstic environments, conventional techniques are not effective at recording heterogeneities such as fracture zones and conduits. Six transects were investigated among areas near cenotes (sinkholes) and aguadas (small surface-water bodies), as well as areas lacking these formations. The resulting profiles reached up to 30 m deep and showed an aquifer consisting of a fractured matrix saturated with freshwater. The matrix exhibiting resistivity values from 3 to 250 Ωm, lying under a vadose zone with values from 300 to 25,000 Ωm. Aguadas and cenotes are surface manifestations of the aquifer’s internal structure, which is a network of caves and conduits. In the Ring of Cenotes, the presence of these surface formations indicates increased hydraulic conductivity in their vicinity, with smaller conduits or fractures providing lesser conductivity in areas further away.

Connectivity in a Karst System Using Electrical Resistivity Tomography and Network Theory.

The Ring of Cenotes (RC) is an alignment of numerous cenotes (sinkholes) in a semicircular form (with a radius of 100 km) located in northwestern Yucatán, México. The formation roughly coincides with a concentric ring that corresponds to a buried structure, which has been identified as the product of a meteor impact, known as the Chicxulub crater. Secondary permeability generated by the fracturing and faulting of the sedimentary sequence in the Chicxulub crater has favored the karstification process and therefore the development of underground rivers that transport water from the mainland to the sea. This study implements the network theory to study the hydrological connectivity between a group of 11 cenotes within the RC. Eight electrical resistivity tomography transects were used as an empirical basis. Each transect was acquired directly in the field using the SuperSting R1/IP equipment with a dipole-dipole configuration. An adapted version of the reliability algorithm for communication networks was used as a theoretical model. We found evidence of the existence of water cavities in the study area. We made a network from the data and assigned connection probabilities among cenotes as a function of the separation length and the number of water cavities, as well as their size.

Risk Perception and Chronic Exposure to Organochlorine Pesticides in Maya Communities of Mexico

ABSTRACTIn order to analyze risk perception related to the use and handling of organochlorine pesticides (OCP) in agricultural and livestock activities among Maya communities of Yucatan, Mexico, and to study their impact on public health and the environment, we conducted an analytical study applying 274 semi-structured interviews in 11 municipalities in the zone called “Ring of Cenotes.” The harmful effects of agrochemicals on water supplies, soils, air, and human health were considered, including the indoor use of pesticides to preserve harvest products. Recent studies showed high levels of OCP in groundwater. A generalized low risk perception related to human health and the environment due to pesticide use was found. Likewise, social parameters were analyzed, including the educational level, as well as risk factors related to groundwater karst vulnerability. Pesticides that have been banned by international conventions are still in use. The occurrence of some diseases such as cervical cancer, with a very high prevalence at the national level, and the practice of obtaining drinking water from polluted wells and sinkholes, may be associated with this low risk perception and with poor social conditions. Establishing programs on health education, agro-ecological production alternatives, and water chemical quality monitoring is recommended.

Sources and distribution of organic matter along the Ring of Cenotes, Yucatan, Mexico: Sterol markers and statistical approaches

The Yucatan Peninsula is a large low lying platform of limestone, dolomite and evaporite deposits, forming an extensive and mature karst aquifer with many sinkholes locally called cenotes. In Yucatan, the only source of drinking water is groundwater and its quality could be impaired by: (i) infiltration of contaminants and (ii) saltwater intrusion. To investigate the sources of organic matter in this aquifer, sediment samples (46) were collected from cenotes and analysed using gas chromatography–mass spectrometry. Sterol analysis, coupled with principal component analysis (PCA), allowed us to distinguish three sources of natural organic matter (e.g. marine, autotrophic and terrigenous) and to detect an anthropogenic input (e.g. fecal contamination). Good consistency was observed between the source assignment and the land use context (forest, agricultural, rural or urban areas) and the season, except for some of the samples where a direct correlation could not be made. The latter cases are most likely a result of the karstic character of the system.

Fecal sterols, seasonal variability, and probable sources along the ring of cenotes, Yucatan, Mexico

Rapid development in Yucatan has had a dramatic impact on the environment, especially the water supply. Groundwater is the only source of water in Yucatan, since surface water is virtually absent due to the karstic nature of the soil. The ring of cenotes (RC) is a geological feature which functions as a source of water and as nodes in the underground river system that canalizes water towards the coast. Numerous productive and domestic activities take place around the RC in the absence of wastewater treatment or sewage systems. Consequently, a number of researchers have hypothesized that pollutants could migrate from the land surface to the underlying aquifer and, eventually, to the coast. Therefore, the present study investigates the relationship among sources of fecal sterols and their levels in cenotes, using the expected levels of fecal sterols obtained by a spatial analysis of the sources and a Pollution Source Index. Accordingly, expected levels are compared with the detected levels of fecal sterols in 5 areas around the RC. Regarding levels, observed during a sampling campaign carried out along the RC during September 2011 (rainy season) and May 2012 (dry season), varied from low to high concentrations of sterols (0.5–2396.42μgg−1) and fecal sterols (0.3–1690.18μgg−1). These concentrations showed no relationship between neighboring cenotes, where similar fecal sterol concentrations or gradients were expected. When comparing expected fecal sterols levels with the detected ones, only two of the five analyzed areas concur, suggesting that no clear relationship exists among sources and fecal sterols levels at the regional scale. Multivariate analysis showed that fecal sterols were associated with sterols and fine grain particulates during the rainy season, which suggests co-transport. During the dry season, fecal sterols associated with fine grain particulate and organic matter, which indicates a change to a deposition phenomenon. These findings indicate that defining a relationship among sources and fecal sterols levels is highly difficult and this could be the result of the absorption or migration through an intricate conduit, crack, or fracture karst system. Nevertheless, the “source-levels approach”, used in this study, was consistent for the northeast edge and the middle western part of the RC. New and more extensive research should be done to assess the environmental fate of fecal sterols, especially considering the intricate karstic system and its compound retention capacity.

Contamination by organochlorine pesticides in the aquifer of the Ring of Cenotes in Yucatán, México

AbstractBanned or restricted organochlorine pesticides in many countries worldwide are still in use in developing countries for agricultural and livestock activities, as well as for vector control in public health campaigns. The present study was conducted to map estimated concentrations of organochlorine pesticides in a karstic region in the Yucatan Peninsula, Mexico, known as ‘Ring of Cenotes’. Water samples from 20 sinkholes (‘cenotes’) were collected during the dry and rainy seasons in 2010–11, analysed by gas chromatography and maps of pesticide concentrations were produced using geographical information system. Results show the presence of banned pesticides, all of them exceeding the limits stated by the Mexican Official Norm. The number and concentration of pesticides during the dry season were qualitatively and quantitatively higher than in the rainy season. The spatial distribution of pesticide concentrations shows that causes of pesticide pollution in the aquifer of the Ring of Cenotes are multifactorial.

Conservation status of the inland aquatic crustaceans in the Yucatan Peninsula, Mexico: shortcomings of a protection strategy

The Yucatan Peninsula (YP), Mexico, is a large karstic Neotropical system hosting a highly diverse crustacean fauna related to epigean and subterranean aquatic habitats. There are more than 40 hypogean endemic species, thus qualifying as a subterranean biodiversity hotspot. In view of the relevance of both the YP karstic aquifer and its related crustacean fauna, the spatial distribution of 212 species from 1165 geo-referenced records of the inland aquatic crustaceans were analysed in relation to the geographic coverage of protected natural areas (PNAs) of the YP. The data analysed were obtained from sources including the authors' own observations, published literature, and institutional and government databases. The YP is an area with ​​a high biodiversity of continental crustaceans and is also an important area of endemism worldwide. However, most of the crustacean fauna is at risk. Only 18.5% of the crustacean species recorded in the YP and only 3.2% of the endemic forms are distributed within the limits of a protected area. In addition, only five of the 48 endemic species are listed in the Mexican Official Standard (NOM-059-2010) and none of them occurs in a protected area. The groups with the highest endemism are the Remipedia and Ostracoda, each with two known YP endemic species. Peracarids are also highly endemic in the YP (62%), followed by Copepoda (27%), Decapoda (18%), and Branchiopoda (1.5%). Currently, the areas of most concern, owing to high tourist pressures, are the ‘Corridor Tulum - Puerto Morelos’ and the ‘Ring of Cenotes’, both having significant numbers of endemic forms. A revision of the PNAs' management programmes to incorporate aquatic ecosystems and biota, the expansion of selected PNAs to provide protection to critical unprotected areas, and increased research activities focused on the aquatic fauna are recommended actions. Copyright © 2013 John Wiley & Sons, Ltd.

Regionalization based on water chemistry and physicochemical traits in the ring of cenotes, Yucatan, Mexico

Assessing water quality in aquifers has become increasingly important as water demand and pollution concerns rise. In the Yucatan Peninsula, sinkholes, locally known as cenotes, are karst formations that intercept the water table. Cenotes are distributed across the peninsula, but are particularly dense and aligned along a semi- circular formation called the Ring of Cenotes. This area exhibits particular hydrogeological properties because it concentrates, channels, and discharges fresh water toward the coasts. In this study, we identify spatial and temporal variations in chemical and physical variables at twenty-two cenotes to identify groups that share similar characteristics. Water samples from each cenotes were taken at three depths (0.5, 5.5, and 10.5 m) and during three seasons (dry, rainy, and cold-fronts season). Field measurements of pH, temperature, electrical conductivity, and dissolved oxygen were taken, and the concentrations of major ions (K + ,N a + ,M g 2+ ,C a 2+ ,H CO { ,S O 2{ 4 ,C l 2 and NO { ) were quantified. Identifying regions of the cenotes were done by applying multivariate statistical techniques (PCA, PERMANOVA, CAP). The chemical variables revealed spatial trends among the cenotes. We identified three main regions. Region 1 is associated with sea-water encroachment and high levels of sulfate that travel through preferential groundwater flowpaths from evaporites in the southern Yucatan Peninsula; Region 2 is a recharge zone, and Region 3 is characterized by sea water encroachment and by the high chemical and physical variability associated with groundwater flow from the east.

Caracterización hidrológica de la región costera noroccidental del estado de Yucatán, México

Se realizó una clasificación del territorio noroccidental del estado de Yucatán, basado en un enfoque físico-geográfico que considera la cuenca hidrogeológica de Chicxulub como unidad de planificación y desarrollo. La particularidad de esta cuenca radica en que posee condiciones de unidad geográfica natural muy específicas. En los 3 198 km2 que abarca el área en estudio y de acuerdo con el ambiente geológico, el régimen climático, las características hidrológicas, los suelos existentes, las formaciones vegetales y los factores antropogénicos, se lograron diferenciar dos Unidades Geográficas Funcionales de primer orden: a) Llanura kárstica, litoral, marino-acumulativa, muy baja (H < 2 msnm), de edad cuaternaria y b) Llanura kárstica, denudativa, baja (H < 9 msnm), de edad terciaria. Del mismo modo, se identificaron cinco unidades de segundo orden, ocho unidades de tercer orden y 26 unidades de cuarto orden. Se describieron las principales características del clima, como un factor determinante de las regulaciones hidrológicas de la región, y se analizó la dinámica hidrológica superficial y subterránea de las principales unidades del paisaje. Se encontró que la situación actual de la costa es de fuerte inestabilidad, donde dominan los procesos erosivos en las playas y donde se predice un incremento acelerado del nivel del mar por fenómenos como el calentamiento global, además del fuerte impacto ocasionado por la infraestructura habitacional y productiva, la deforestación y la construcción de espolones y escolleras en el litoral. Se sugiere realizar estudios sobre las descargas de agua dulce, a través de manantiales submarinos en el litoral yucateco, sobre los procesos de formación del acuitardo costero, los procesos de disolución del karst yucateco, y caracterizar la dinámica hidrológica del anillo de cenotes y su influencia en la zona litoral.

The Yucatan peninsula: biogeographical history 65 million years in the making

The fourth biennial meeting of the International Biogeography Society (IBS) in Merida, Yucatan in January 2009 represented a double opportunity for Mexican biologists. First, it fostered the integration of the large community of Mexican biogeographers with the activities of the IBS. Second, the meeting allowed us to welcome a large number of delegates from distant parts of the world who were able to visit what has been considered an obligate destination for nature lovers and cultural tourists alike: the Yucatan peninsula. As Edward O. Wilson pointed out, besides economic power every country has two additional and important types of wealth: cultural and natural. Cultural richness is a naturally embedded component of the Mexican way of life.

Geological and archaeological implications of strontium isotope analysis of exposed bedrock in the Chicxulub crater basin, northwestern Yucatan, Mexico

The surface geology of the site of the Chicxulub impact crater in northwestern Yucatan, Mexico, has not been studied extensively since the discovery of the crater almost two decades ago. Strontium isotope (87Sr/86Sr) measurements in carbonate rock outcrops reveal near-uniform strontium signatures of 0.70905 inside the ring of cenotes (water-filled sinkholes), which represents the rim of the crater basin. Measured strontium isotope ratios were used to infer rock ages, employing the marine Sr isotope curve. We estimate the age of the exposed limestone within the Chicxulub crater basin to be late Miocene to early Pliocene, representing the age of the youngest sediment fill. Discovery of a large terrain of near-uniform strontium isotope ratios in northwestern Yucatan offers new geoarchaeological opportunities to track ancient Maya migration and determine sources of manufactured goods. Our results have implications for applying the Sr isotope method to Maya archaeological sites, such as Mayapan, the last Maya capital, and Chichen Itza.

Water Resources of the Chunchucmil Maya

Chunchucmil, on the Yucatán Peninsula, was densely populated in the Maya Late Classic period (ca. a.d. 550–830), even though it depends principally on groundwater. In the 1990s, hydrologic investigations were conducted to determine whether groundwater could have met domestic and agricultural needs. The region's groundwater is near the surface and is influenced by sea‐level fluctuations; however, geochemical analysis revealed that groundwater quality is not affected by mixing with seawater. The potential exists for high and spatially extensive nitrate contamination in this karstic area, yet water‐quality analyses revealed only moderate levels of nitrate in the groundwater. Agricultural limitations are imposed by chloride, total dissolved solids, and salinity, as indicated by electrical conductivity; domestic water use is limited by the presence of nitrate, sulfate, and chloride. Throughflow in the ring of cenotes (sinkholes) around the Chicxulub impact crater may explain the movement and spatial distribution of water‐quality constituents in Chunchucmil's groundwater.

Delimitation of a hydrogeological reserve for a city within a karstic aquifer: the Merida, Yucatan example

Merida is the largest city in southeastern Mexico, where the urban supply is obtained mainly from three wellfields outside of the urban limits in a karst aquifer that is particularly vulnerable to contamination. Merida, Yucatan has a population greater than 600 000 inhabitants. The city obtains its freshwater from a thin (<50 m thick) sole-source aquifer. This aquifer also supplies water to satisfy the industrial and agricultural needs of the region. In order to help in maintaining an adequate water supply for the city, a detailed study has been conducted to determine the best area to establish a hydrogeological reserve zone (HRZ). A polygon of 900 km 2 was chosen southwest of the city. This area is upgradient from Merida, no industrial activity is present, and there are two natural boundaries that bound the proposed HRZ. These are no-flow boundaries that have developed as a result of the second boundary: a high permeability zone locally known as the ring of cenotes (ring of sinkholes). The major current obstacle to designate this area as a hydrogeological reserve is an industrial landfill that is present in within the proposed area. As part of the establishment of the HRZ, the landfill should be relocated, and a comprehensive ground water quality study should be conducted to determine the actual water quality of the aquifer.

Determination of flow characteristics in the aquifer of the Northwestern Peninsula of Yucatan, Mexico

Flow characteristics were studied in the Northwestern Peninsula of Yucatan, Mexico. The Yucatan aquifer is a mature karst system, influenced by the Ring of Cenotes (sinkholes). This zone of aligned sinkholes is a high-permeability zone with respect to its surroundings. The aquifer is unconfined within the study area. Water-level measurements at 48 locations were made in June and October 1994; they were measured up to four times in October. Water levels in a limited group of wells showed variations up to 60% during October 1994 whereas others had variations of the order of 5% in the same period. By studying the resulting equipotential regimes, a highly variable zone (HVZ) was identified. Drain characteristics are significantly different from the rest of the study area, which leads to the hypothesis that the HVZ represents an independent subsystem of interconnected fractures. To determine directions of high permeability within the study area, azimuthal resistivity surveys were conducted at 22 locations. Resistivity curves particularly in the HVZ show two or more peaks, each indicating a direction of high permeability. Directions of high permeability are interpreted to be preferential directions of aligned fractures. Comparison with the two different equipotential regimes in October 1994 shows that in the majority of the cases the direction of the hydraulic gradient coincides with the direction of one fracture system. The hydraulic gradient can be considered to be the major control in the dissolution process at least in the HVZ, resulting in the selective opening of the fractures. Peaks in the resistivity curves are of the same order of magnitude. This shows that both regimes of equipotential lines and the corresponding changes of the hydraulic gradients are sufficiently frequent to be able to create different fracture systems with a comparable fracture density. The variations of the equipotential regime in time may have severe consequences in terms of the risk of aquifer contamination in the highly variable zone. Contaminants, generated mainly in the city of Merida, are generally believed to flow towards the north coast of the Peninsula. However, reversals in the hydraulic gradient may allow contaminants to flow towards the southeast of the city, at least for limited periods in the year.

Hydrogeological Investigations in Northwestern Yucatan, Mexico, Using Resistivity Surveys

AbstractEight Schlumberger soundings and four Wenner anisotropy measurements were conducted in the northwestern section of the Yucatan Peninsula for hydrogeological investigations of a karst aquifer. This system is influenced by a circular high permeability zone (Ring of Cenotes) probably related to the Chicxulub Impact Crater. Schlumberger soundings and Wenner anisotropy measurements show that the karst aquifer can be modeled as an electrically anisotropic medium. Anisotropy is related to preferential permeability directions channeling ground‐water flow within the aquifer. Directions of maximum permeability were determined using Wenner anisotropy measurements. Electrical soundings were conducted at different sites near the Ring of Cenotes. Resistivity values decrease toward the Ring of Cenotes supporting the hypothesis that selected segments of the Ring have high permeability. Several soundings were conducted in order to study lateral permeability variations along the Ring. A high permeability section can be identified by low resistivity models and is related to a zone of high cenote density. A low permeability section of the Ring was found showing high resistivity models. This zone overlaps with an area of low cenote density. Electrical soundings were used to determine the depth of the fresh‐water lens; the interface was detected along two profiles perpendicular and parallel to the Ring of Cenotes resulting in a depth that ranged from 18 m near the coast up to 110 m in the southeastern part of the study area. The predicted depths of the interface using electrical methods showed a good correlation with Ghyben‐Herzberg and measured interface depths at some sites. Discrepancies between calculated and interpreted interface depths at two sites may be explained by horizontal‐to‐vertical permeability anisotropy.

Ring of Cenotes (sinkholes), northwest Yucatan, Mexico: Its hydrogeologic characteristics and possible association with the Chicxulub impact crater

A 180-km-diameter semicircular band of abundant karst sinkholes (Ring of Cenotes) in northwest Yucatan, Mexico, coincides approximately with a concentric ring of the buried Chicxulub structure, a circular feature manifested in Cretaceous and older rocks, that has been identified as the product of the impact of a bolide. The ring, expressed in Tertiary rocks, marks a zone of high permeability as shown by (1) the sinkholes themselves, (2) breaks in the coastal dune system and high density of springs where the ring intersects the coast, and (3) water-level transects characterized by a decline in water level toward the ring. Any direct relation that exists between the Ring of Cenotes and the Chicxulub structure bears on regional hydrogeology. If the layer or zone responsible for the ring is deeply buried, it may act as a barrier to the movement of ground water across the main flow direction. Shallower zones of horizontal permeability could result in less complete diversion of ground water. Through its influence on Yucatan aquifer characteristics, the ring may provide a link between modern environmental problems and astrogeology. Possible origins for the Ring of Cenotes are (1) faulting, perhaps reactivated by post-Eocene–mid-Miocene basin loading, (2) permeability in a buried reef complex developed in the shallow Paleocene sea around the crater rim, or (3) breccia collapse occasioned by consolidation or by solution of evaporite components. If the ring developed on ancient faults, it may outline hydrothermal systems and mineral deposits produced during Paleocene cooling of the Chicxulub melt sheet.