Sierra De Las Cruces Research Articles

Modelling the effects of climate and land-cover changes on the potential distribution and landscape connectivity of three earth snakes (Genus Conopsis, Günther 1858) in central Mexico.

Anthropogenic land use and climate change are the greatest threats to biodiversity, especially for many globally endangered reptile species. Earth snakes (Conopsis spp.) are a poorly studied group endemic to Mexico. They have limited dispersal abilities and specialized niches, making them particularly vulnerable to anthropogenic threats. Species distribution models (SDMs) were used to assess how future climate and land-cover change scenarios might influence the distribution and habitat connectivity of three earth snakes: Conopsis biserialis (Taylor and Smith), C. lineata (Kennicott), and C. nasus (Günther). Two climate models, CNRM-CM5 (CN) and MPI-ESM-LR (MP) (Representative Concentration Pathway 85), were explored with ENMeval Maxent modelling. Important SDM environmental variables and environmental niche overlap between species were also examined. We found that C. biserialis and C. lineata were restricted by maximum temperatures whereas C. nasus was restricted by minimum ones and was more tolerant to arid vegetation. C. biserialis and C. lineata were primarily distributed in the valleys and mountains of the highlands of the TMBV, while C. nasus was mainly distributed in the Altiplano Sur (Zacatecano-Potosino). C. lineatahad the smallest potential distribution and suffered the greatest contraction in the future whereas C. nasus was the least affected species in future scenarios. The Sierra de las Cruces and the Sierra Chichinautzin were identified as very important areas for connectivity. Our results suggest that C. lineata may be the most vulnerable of the three species to anthropogenic and climate changes whereas C. nasus seems to be less affected by global warming than the other species.

Field observations of Ambystoma altamirani at near-freezing conditions in the Sierra de las Cruces, Mexico

Field observations of Ambystoma altamirani at near-freezing conditions in the Sierra de las Cruces, Mexico

Understanding the processes in a historically relevant thermal and mineral spring water by using mixing and inverse geochemical models.

The thermal mineral water of Peñón de los Baños spa (Mexico City) has been used for over 500years starting in pre-Hispanic times and is famous for the treatment of various pathologies. It has a temperature of 45°C, which is rich in HCO3-, and its main trace elements are B, Li and Fe, which confers healing effects. Concerns about the sustainability of this important spa have motivated this study to understand the thermal system, possible hydraulic and hydrochemical changes over time and its implications. Stable water isotope data indicate that the thermal water sources originate from local precipitation at Sierra de las Cruces with a recharge elevation of approximately 2770m above sea level. The recharged water percolates through volcanic and carbonate rock formations and ascends via fault structure conduits, where it eventually is extracted 25km downstream in Peñon de los Baños. During the gravity-driven deep circulation of up to 4.9km, the groundwater is heated up to 136-160°C. A comparison of past and current water levels and water chemical analyses indicates a water table drop and few variations in the chemical composition, confirming the presence of anthropic impact on water quality. Due to the heavy groundwater extractions in Mexico City, the spring water flow has ceased, and water must be pumped now from a 203-m deep well. In addition, the concentration of bicarbonate, sodium and chloride has been reduced by half since the onset of groundwater development. The therapeutic effects of this thermal mineral water are at risk due to the alteration of the chemical signature. However, new and different therapeutical uses may prevent a future deterioration or closure of this historically important thermal spa. It is crucial to establish a monitoring program of the thermal mineral water and reducing or minimizing nearby urban extractions which tap the regional flow component to preserve the properties of the thermal water.

Impact of climate and land cover changes on the potential distribution of four endemic salamanders in Mexico

Anthropogenic changes, such as land use and climate change, are the greatest threats to biodiversity, especially for amphibians, which are the most endangered vertebrate class worldwide. Species distribution modelling was applied to assess how expected future climate and land cover change scenarios might influence the geographic distribution and habitat connectivity of four salamanders endemic to Mexico: Aquiloeurycea cephalica (Cope, 1865), Isthmura bellii (Gray, 1850), Pseudoeurycea robertsi (Taylor, 1939), and Pseudoeurycea leprosa (Cope, 1869). For this, the Community Climate System Model (CCSM4) with two Representative Concentration Pathways (RCP 45 and RCP 85) and two modelling methods (Maxent in ENMeval and an ensemble model in biomod2) were used. The most important environmental variables explaining the distribution of the target species, as well as the environmental niche overlap between them, were also determined. Abies forest cover was one of the most important variables explaining the current distribution of P. robertsi (contribution of 39%), P. leprosa (contribution of 18%), and A. cephalica (contribution of 22%) with a positive effect. The distribution of these three species was also limited by maximum temperatures, whereas the I. bellii distribution was more limited by minimum temperatures. The environmental niches of P. leprosa and A. cephalica were significantly similar (D = 0.637, I = 0.801, p-value = 0.02), as well as the environmental niches of P. robertsi and P. leprosa (D = 0.640, I = 0.797, p-value = 0.01). As expected, all salamander species were predicted to face a reduction in their potential distribution (reductions between 2.64 and 32.16%) and landscape connectivity (reductions between 4.93 and 73.92%) under future scenarios of climate and land cover change. Different models and scenarios were inconsistent in determining which species’ distribution would suffer the biggest reduction in the future. However, P. robertsi suffered the largest reduction in connectivity under both scenarios of climate change. Similarly, our results suggest that Sierra de las Cruces and Corredor Biológico Chichinautzin are very important areas in terms of connectivity. Unfortunately, great losses of Abies and Pinus forests were also predicted to occur in these areas between 2011 and 2014. According to these findings, the preservation of Abies forests of the Trans-Mexican Volcanic Belt is essential to preserve P. robertsi, P. leprosa, and A. cephalica salamanders, whereas the preservation of Corredor Biológico Chichinautzin and Sierra de las Cruces is essential to maintain landscape connectivity for P. leprosa, A. cephalica, and I. bellii. Thus, these areas should be prioritized in conservation programs.

Distribution and Population Structure of Ambystoma altamirani from the Llano de Lobos, State of México, Mexico

Ambystoma altamirani is an endangered salamander found in high mountain streams in the vicinity of México City, and its populations might be threatened by urban growth. Here we report our research on a previously unstudied population of A. altamirani at the Llano de Lobos in the Sierra de las Cruces. The study ran from September 2018 to September 2019. The number of observed individuals was relatively constant across months. The only months when we observed gilled adults were February and July, and the only months when we saw juveniles without gills were January, February, and August, suggesting that the transformation of juveniles to adults takes place twice a year, once in January–February and once in July–August. We observed egg masses in December and January, and larvae from March to May and also in July. The sex ratio was significantly female-biased (about 2:1). We observed A. altamirani at 3 of the 25 permanent sites during the study period. Our comparison of the characteristics of occupied sites with those of unoccupied sites suggests that availability of sunlight (i.e., less cover) and low levels of human impact are important for occupancy by A. altamirani. These findings are consistent with observations of other populations of A. altamirani, suggesting that these characteristics might be important in their management and conservation.

Geology and stratigraphy of the Mexico Basin (Mexico City), central Trans-Mexican Volcanic Belt

ABSTRACT We present a new geological map of the Mexico Basin (Mexico City) based on field descriptions, a compilation of data from previous publications, and new 40Ar/39Ar geochronology data. The oldest rocks described in the Mexico Basin are Cretaceous limestones, overlaid by Oligocene (26.0 Ma) and Miocene (22.8–5.0 Ma) volcanic successions, followed by Pliocene-Pleistocene (3.7–1.2 Ma) to Recent volcanic rocks around the basin. The Mexico basin is surrounded by volcanic ranges mainly andesitic and dacitic in composition: Sierra de Guadalupe (∼20 to ∼13 Ma), Sierra de las Cruces (3.7–0.03 Ma), Sierra Nevada (1.4 Ma to Recent), and Sierra de Chichinautzin (1.2 Ma to Recent). The basin has formed and evolved through complex tectonic and volcanic events: A NNW and NNE-Cañón de Lobos trending reverse fault affected the Cretaceous basement, the NW-SE Mixhuca normal fault displaced Oligocene-Miocene volcanics, the NE-SW Tenochtitlan fault system displaced Plio-Pleistocene rocks, and finally E-W normal faults affected the most recent volcanic rocks, paleosols, and lacustrine sediments.

Effects of nonnative Rainbow Trout on two species of endemic Mexican amphibians

Introduction of nonnative salmonids into fishless aquatic ecosystems often can have negative effects on these ecosystems. Amphibians appear to be particularly susceptible to the introduction of trout. Nonnative Rainbow Trout (Oncorhynchus mykiss) have been introduced to Mexico, including to streams in the mountains around Mexico City that are home to several endemic Mexican amphibians. We examined the effect of Rainbow Trout on the distributions of 2 endemic Mexican amphibians, Ambystoma altamirani and Hyla plicata, in the Sierra de Las Cruces. Ambystoma altamirani was never found at sites with Rainbow Trout, and H. plicata was observed only once at sites with Rainbow Trout. Stream site characteristics, for the most part, did not vary among streams occupied by different species, suggesting environmental variables were not primarily responsible for the species distributions. Our results provide strong circumstantial evidence that the introduction of Rainbow Trout in streams in the Sierra de Las Cruces has a negative effect on the distribution of native Mexican amphibians.

Hydrochemical assessment of Hydrological Environmental Services in the recharge area in the Southwest of Mexico City

The aquifer recharge area that supplies water to Mexico City is being protected with the implementation of land use restrictions and with the use of payment schemes for maintaining environmental services (PES). In order to assess the effects of PES in the conservation soil area, the chemical and isotopic compositions of water from springs were characterized and the water baseline chemistry was established to provide a useful standard to monitor the water resources and to support the decision-making under current water management policies. A total of 32 water samples taken in four field surveys, during the dry and rainy season, and background chemical data from different information sources, were studied. The water salinity increases from southwest to northeast towards the urbanized area. The chemical composition of water is due to the occurrence of natural chemical interactions between water and rocks in aquifers and to the presence of effluents generated by human activities. In the forest area, water chemistry has not changed significantly over the past three decades and there are no major discernible trends in the compiled water chemistry data, suggesting that PES has contributed in part to maintain the initial condition in the aquifer recharge area. The natural reference levels proposed have allowed the current chemical conditions in the system to be understood and can be implemented to monitor water resources in the area of conservation soil in the Sierra de Las Cruces with an acceptable degree of reliability.

Natural History, Phenology, and Stream Use ofHyla plicatafrom the Arroyo los Axolotes, State of Mexico, Mexico

Abstract: Understanding the status of hylid frogs in Mexico is often hindered by a lack of understanding of basic natural history. We report on the natural history and phenology of H. plicata from the Arroyo Los Axolotes, Sierra de las Cruces, state of Mexico, as well as its co-occurence with Ambystoma altamirani. Adult Hyla plicata arrive at the stream in March and April, and oviposition takes place in June. Metamorphosis takes place in September and October. Hyla plicata are found in sites along the Arroyo las Axolotes that are wider and deeper, with higher levels of dissolved oxygen and slower water speeds than sites where they are not found. Their distribution is not affected by water temperature. Hyla plicata used sites with white-yellow and tan-brown substrates more than sites with black substrates. Types of substrates and vegetation at sites with and without H. plicata did not differ. Our results suggest that H. plicata requires stream reaches that are wider, deeper, and with slower flowing water, ...

Diet of LarvalAmbystoma altamiranoifrom Llano de los Axolotes, Mexico

Abstract Ambystoma altamiranoi is an endangered endemic salamander found in the Transvolcanic Belt of Mexico. Unfortunately, relatively little is known about its ecology. Here we report on the diet of larval A. altamiranoi from a population in Llano de los Axolotes, Sierra de las Cruces, State of Mexico, Mexico. Empty stomachs were found in 13.3% of individuals. Ostracods and gastropods dominated the diet of A. altamiranoi, together accounting for 89.9% of prey items consumed. The remainder of the diet consisted primarily of insects. Our observations suggest that the diet of A. altamiranoi is relatively narrow and that resources may be limited (relatively high frequency of empty stomachs), suggesting that factors that could impact the availability of ostracods and gastropods might have serious consequences for these endangered salamanders.

Multivariate Analysis, Mass Balance Techniques, and Statistical Tests as Tools in Igneous Petrology: Application to the Sierra de las Cruces Volcanic Range (Mexican Volcanic Belt)

Magmatic processes have usually been identified and evaluated using qualitative or semiquantitative geochemical or isotopic tools based on a restricted number of variables. However, a more complete and quantitative view could be reached applying multivariate analysis, mass balance techniques, and statistical tests. As an example, in this work a statistical and quantitative scheme is applied to analyze the geochemical features for the Sierra de las Cruces (SC) volcanic range (Mexican Volcanic Belt). In this locality, the volcanic activity (3.7 to 0.5 Ma) was dominantly dacitic, but the presence of spheroidal andesitic enclaves and/or diverse disequilibrium features in majority of lavas confirms the operation of magma mixing/mingling. New discriminant-function-based multidimensional diagrams were used to discriminate tectonic setting. Statistical tests of discordancy and significance were applied to evaluate the influence of the subducting Cocos plate, which seems to be rather negligible for the SC magmas in relation to several major and trace elements. A cluster analysis following Ward's linkage rule was carried out to classify the SC volcanic rocks geochemical groups. Finally, two mass-balance schemes were applied for the quantitative evaluation of the proportion of the end-member components (dacitic and andesitic magmas) in the comingled lavas (binary mixtures).

New constraints on the subsurface geology of the Mexico City Basin: The San Lorenzo Tezonco deep well, on the basis of 40Ar/39Ar geochronology and whole-rock chemistry

The San Lorenzo Tezonco deep well, drilled in 2012 by “Sistema de Aguas de la Ciudad de México” (Water Supply System of Mexico City) in the Mexico Basin to a depth of 2008m, offers an excellent opportunity to explore the subsurface stratigraphy and general geology of the region. Unfortunately, only chipped samples from this well were recovered, which were examined and analyzed for whole-rock chemistry, 40Ar/39Ar, and U–Pb zircon geochronology, in order to reconstruct the lithology of the well. Contrary to previous deep wells of the Mexico Basin, no basement sedimentary rocks were found in this one. While the upper 70m are composed of lacustrine sediments associated with Lake Texcoco, volcanic rocks make up the majority of the well and range in age from more than 18Ma to 0.25Ma. Andesitic lavas are the most abundant products of the stratigraphic column, followed by acidic products represented by dacitic and rhyolitic lavas and ignimbrite deposits. Less abundant are basaltic andesite lavas appearing in the upper and lower parts of the column. The thickest sequence of the well is represented not only by Miocene volcanic rocks ranging from 5 to 17Ma, suggesting a period of intense volcanic activity in this area producing mainly andesitic lavas, but also by thick rhyolitic ignimbrite deposits dated at 5Ma. These deposits suggest the presence of a caldera structure, probably buried by subsequent volcanic products and lacustrine sediments. Trace element concentrations suggest that volcanism is likely produced in a subduction environment with typical negative anomalies of Nb, Ta, Ti, and P and positive anomalies in Pb and Cs. We correlated the well units with units outcropping in mountain ranges in the surrounding area, with the recognition of the following units or formations: Eocene Andesite, San Nicolás Basaltic Andesite, Tepoztlán Formation, Miocene Volcanism, Sierra de las Cruces, and Chichinautzin Volcanic Field products. By correlating the two closest deep wells (Mixhuca and Tulyehualco) we conclude that the San Lorenzo Tezonco well is located in a graben-like structure hosting the Santa Catarina volcanic range.

Geochemical evolution of groundwater beneath Mexico City

The geochemical evolution of groundwaters along a 24km flow beneath Central Mexico City path from the Sierra de las Cruces towards Lake Texcoco has been investigated using stable isotopes, radiocarbon and major and trace elements to determine the natural baseline conditions, the extent of any contamination and the effectiveness of the overlying aquitard seal. Modern groundwaters of low salinity (<200mgl−1) are found up to 11km from the outcrop area and groundwater ages of up to 6000yrbp occur in the middle part of the section. Groundwater stable isotope ratios δ18O and δ2H lie close to the global meteoric water line, indicating that the groundwater originates from local rainfall. The groundwater chemistry may be interpreted as the result of inputs from the source area with progressive water–rock interaction down the horizontal flow gradient. A redox boundary is found at 9km along the line of section, coincident with the start of the confined section. Relatively low nitrate concentrations (below 9mgl−1 NO3–N) are found in the aerobic waters; low concentrations of NO3 in the aerobic waters and low Cl reflect inputs prior to the modern development. Some elements (Cr, U, As, Se, Sb) increase their concentration with distance (time) as far as the redox boundary, but low concentrations occur in the reducing aquifer section. The chemistry of several major ions (Mg, Na/Cl, K) as well as trace elements such as Li, Rb, Ba reflect the weathering of the basaltic mineral assemblage (feldspars and mafic minerals) and their increases are generally proportional to residence time; phosphate, F and I concentrations indicate a probable source from apatite in the basaltic or rhyolitic rocks. A borehole in the east of the city (some 17km downgradient) intercepted thermal water (Si geothermometry indicates 163°C at depth). This water gives a distinctive composition indicating possible addition of metamorphic CO2 which has then reacted with the igneous rocks. Increases in B and Cl are derived from volatiles trapped in the glass or vesicular basalt. A thermal anomaly found in the middle section of the heavily pumped aquifer is interpreted as the up-coming of warmer water from medium to greater depth mainly from basalts, rhyolites and possibly limestones.The geochemistry indicates that groundwater beneath Mexico City is of good quality and there is no obvious evidence of leakage of inorganic compounds from surface sources of contamination through the aquitard. The younger groundwater drawn from the western outcrop area is generally of good inorganic quality. Increased drawdowns in the confined aquifer have induced flow of warmer water with higher Cl from depth. The resources in the aquifer represent an important reserve of good quality water which need to be properly managed as a high quality resource as part of integrated plans for the City's future supplies.

Palaeomagnetism of Late Miocene to Quaternary volcanics from the eastern segment of the Trans-Mexican Volcanic Belt

A systematic palaeomagnetic study in the eastern part of the Trans-Mexican Volcanic Belt includes 39 Miocene, Pliocene and Quaternary volcanic rocks in the southeastern Mexico Basin (Sierra Nevada and Sierra de Rı́o Frı́o), the Altiplano area, and the Palma Sola Massif. A total of 430 samples have been selectively demagnetized using mostly alternating field demagnetizing methods, supplemented by thermal analyses. Most characteristic remanences are carried by low-Ti titanomagnetites, with occasional titanohematites or slightly maghemitized low-Ti titanomagnetites, of similar direction. Seven sites were discarded because they presented intermediate directions, hydrothermal alteration or were remagnetized by lightning strikes. The mean directions of 32 sites, together with 24 sites from Sierra de las Cruces in the western Mexico basin, indicate rocks older than 2 Ma are rotated some 10° counterclockwise with respect to Quaternary rocks, whereas there is no rotational difference between Miocene and Pliocene rocks. Statistical analyses between different regrouped populations confirm that the rotational pattern is due to the age of the volcanics rocks but not to their spatial distribution. The Quaternary mean direction from the three Mexico Basin ranges is consistent with the geographical reference pole. In contrast, the Pliocene mean direction from volcanic rocks of the Altiplano area and the Sierra de Las Cruces is slightly rotated some 10° westwards with respect to the reference direction from North America. No significant rotations have been observed in the eastern TMVB (from the western Mexico Basin to the border of the Altiplano), between late Miocene and late Pliocene time. It suggests that a very small, counterclockwise vertical-axis rotation may have been taken place in this segment of the TMVB between late Pliocene and Quaternary times. Comparisons of these results with a summary of the available palaeomagnetic data in the area indicate that the previously reported Quaternary rotations are of questionable reliability, and that the large counterclockwise rotations, reported in Cretaceous to Miocene rocks, probably took place before the late Miocene. These new palaeomagnetic data support the idea that the eastern TMVB since the late Miocene, has been a zone of extension with a little, left-lateral shear component.