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High‐quality records of hydroclimate variability in central Mexico during the last 2000 years are necessary to better understand human–environment interactions in Mesoamerica. Of particular interest are the climatic conditions during the Epiclassic period (ad 600–900), as droughts have been associated with a cultural demise occurring around ad 900–1000. We reconstruct the hydroclimate history of the last 2000 years based on a sediment record from a drought‐sensitive lake located near one of the most important Epiclassic city‐states in Mesoamerica. Titanium concentrations, pollen and diatoms give a consistent environmental signal of five droughts occurring at about: (i) ad 50–250, (ii) ad 700–950, (iii) ad 1200–1300, (iv) ad 1450–1550 and (v) ad 1760–1820. Some droughts were associated with cooler climatic conditions, and all of them framed major historical events. Our results show that the great cultural development of the Epiclassic period (ad 600–900) was framed by a scenario of drought conditions followed by abandonment at ad 900–1000. A brief return to moister conditions is recorded before another drought during the time of the fall of the city‐state of Tula (1200). European contact (1521) and the War of Independence (1810–20) also occurred during times of drought. [ABSTRACT FROM AUTHOR]

Lake Chalco, in Central Mexico, has a long diatom record which provides an excellent opportunity to document the biotic and hydrological responses of this ecosystem to orbital‐ and millennial‐scale climatic variability during the last 150 ka. Detrended correspondence analysis was used to evaluate the ecological turnover and to identify diatom species associations throughout the sequence. Millennial‐scale climatic fluctuations were identified as peaks in freshwater (mostly small Fragilariaceae spp.) or as peaks in salt‐tolerant species. At orbital scales, species turnover involved changes between freshwater assemblages dominated by Stephanodiscus spp. – small Fragilariaceae spp. – Cocconeis placentula, present during low‐evaporation, cool intervals [late Marine Isotope Stage (MIS)6, MIS5d, MIS2] against salt‐tolerant taxa, dominated by Stephanocyclus and Cyclotella spp., in higher evaporation, higher salinity conditions (MIS5e, MIS5c–a, MIS4, MIS3, early MIS1). Comparatively, MIS6 and MIS5d seem to have been cooler (~ −6 to −7 °C) and wetter than MIS2 (~ − 4 to −5 °C). In contrast, MIS5e and early MIS1 (11.5–6 ka) had similar warmer, low lake level, saline conditions. In addition, MIS5 was a period of intense climatic change associated with wide‐amplitude orbital forcing that favored a Stephanocyclus–Cyclotella spp. ecological succession (S. meneghinianus, C. tlalocii, C. poyeka, S. quillensis). In contrast, smaller temperature changes were inferred during MIS4 and MIS3. [ABSTRACT FROM AUTHOR]

We present a palaeohydrological reconstruction of Lake Texcoco over the last 32.7 cal ka based on ostracod records consisting of two species, Candona patzcuaro and Limnocytherina axalapasco. Overall, the presence of these species suggests that Lake Texcoco was highly saline and experienced occasional desiccation periods. Moreover, this work helps improve our knowledge of L. axalapasco, an endemic species of central Mexico; their eggs could remain dormant‐resting to survive long dry periods. Four ostracod zones reflect the main environmental changes that occurred during the Late Pleistocene and Holocene. From 32.7 to 30 cal ka bp (Zone 4), Lake Texcoco's water levels were stable and alkaline with saline conditions. Zone 3, representing the period from 30 to 18 cal ka bp, includes a period of enhanced precipitation (greatest abundance of C. patzcuaro) from 30 to 26 cal ka bp. From 26 to 18 cal ka bp, an abundance of L. axalapasco reflects shallower and more saline conditions. The Last Glacial Maximum was characterised by cold and humid conditions with enhanced runoff, especially at 25.3, 21.9, and 20.7 cal ka bp. Zone 2 (18–7 cal ka bp) represents the driest period on record. Finally, shallow and saline lake conditions have prevailed over the last 7 cal ka (Zone 1). [ABSTRACT FROM AUTHOR]

A sediment record from Lake Chalco, Basin of Mexico, revealed the presence of two endemic ostracod species during the latter part of Marine Isotope Stages (MIS) 6 (146–130 ka) and MIS5 (130–72 ka), namely Candona alchichica and Limnocytherina axalapasco. Higher abundance of C. alchichica was found during MIS6, when prevailing conditions were cold, lake waters were fresh, and relatively deep bottom waters were anoxic. The species is typically associated with saline environments today, consistent with its presence in MIS5 sediments. The Chalco record, however, reveals that it coexisted with freshwater diatom species during MIS6. Thus, we suggest that C. alchichica had a wider salinity tolerance, ranging from freshwater to more saline environments. Examination of MIS5 substages provides further insights into ostracod species responses to changing lake conditions. During MIS5e, the lake water level declined and salinity and dissolved oxygen in the water column increased, thereby favouring L. axalapasco productivity, whereas C. alchichica productivity decreased. Enhanced runoff and lower than average evaporation during MIS5d coincided with the increasing abundance of C. alchichica, suggesting a period of relatively high lake level and more dilute waters. These environmental conditions, however, changed during MIS5c when lake stage dropped once again and L. axalapasco abundance increased. Shallow conditions during this substage were optimal for L. axalapasco. Subsequently, as the lake level continued to decline during MIS5b, both ostracod species disappeared from the sediment record. Finally, during MIS5a, runoff increased and both ostracod species reappeared in the record, with L. axalapasco dominating, suggesting another period of lake level recovery. Increased evaporation rates during the last part of this substage (75–72 cal ka BP) may have led to disappearance of ostracods from the sediment record. Overall, during MIS5, we detected higher L. axalapasco, which represent relatively shallow lake conditions. [ABSTRACT FROM AUTHOR]

Lake Chalco lies south of the Basin of Mexico and has been the subject of studies related to Late Quaternary climate variability. In 2016, the International Continental Scientific Drilling Program "MexiDrill Project" recovered a 520-m sediment record from Lake Chalco. Magnetic susceptibility measurements revealed substantial changes in sediment physical properties between 343 and 285 m depth, suggesting changes in composition associated with fluctuations in the depositional environment. We targeted sediments in the 343–285 m interval for high-resolution facies analysis, to develop a model of Lake Chalco formation. We identified three facies associations, using sediment composition, texture, mineralogy and micro-morphological characteristics: (1) detrital facies, consisting of laminated silt, massive sand, stratified silty sand, clast-supported gravel and matrix-supported gravel; (2) biogenic facies, which include diatom ooze and bivalve coquina; and (3) volcaniclastic facies, represented by clast-supported pumice deposits. We propose that formation of Lake Chalco occurred in four stages, which we identified by changes in sediment characteristics. The first stage was an alluvial delta environment, in which debris and hyper-concentrated flows were the main sediment transport agents. The second was characterized by turbulent flows in a fluvial deltaic environment, which alternated with laminar flows associated with floodplains. The third stage was a time of fluvio-lacustrine transition in the basin, with formation of the previously identified Paleo-Chalco-I Lake, in response to wet conditions. During the fourth stage, a deep eutrophic lake formed (Paleo-Chalco-II), with an origin that appears to have been related to regional volcanism. Our working age-depth model indicates establishment of the lake at ca. 400 ± 46 ka. This paper presents the only available record of the transition from alluvial to lacustrine sedimentation of Lake Chalco. Our results allow us to establish (1) how the lake was formed and what the phases of its development were, (2) how a major volcanic event altered and transformed the lacustrine sedimentation, and (3) which climatic conditions dominated during the lake formation. The age for the onset of the lacustrine sedimentation in Chalco is for the first time constrained to around 400 ka. This enables to expand our knowledge of the climate for a time for which there is no information from terrestrial records of tropical North America. [ABSTRACT FROM AUTHOR]

Aquatic pollen and non‐pollen palynomorphs (NPPs) from a 72‐m‐long sediment core from Lake Chalco in central Mexico document macrophyte vegetation and paleolimnological conditions during the last glacial (∼85–10.8 k cal a BP). We compared macrophyte vegetation and NPP records with data for authigenic carbonate deposition estimated from concentrations of total inorganic carbon. We estimated saline and variable trophic conditions during the last glacial. An association indicative of higher salinity conditions characterized by NPP and diatom assemblages characteristic of alkaline and saline environments is documented. Changes in hydrophyte taxa and microalgae assemblages were related to trophic level fluctuations. Higher salinity environments were contemporary with arid intervals reconstructed based on abundances of inorganic carbonate. Two main periods were evident in this record: (i) 85–29 k cal a BP [Marine Isotope Stage (MIS) 5b–MIS 3] characterized by saline conditions with high abundance of Type‐TXA, and variable high carbonate content, and (ii) 29–10.8 k cal a BP (MIS 2–MIS 1) when conditions changed to higher trophic levels and lower salinities, characterized by extremely low values of Type‐TXA and carbonate content. Spring and summer insolation and latitudinal position of the Intertropical Convergence Zone over the last glacial were considered as possible controllers of the recorded paleoenvironmental changes. [ABSTRACT FROM AUTHOR]

The primary scientific objective of MexiDrill, the Basin of Mexico Drilling Program, is development of a continuous, high-resolution ∼400 kyr lacustrine record of tropical North American environmental change. The field location, in the densely populated, water-stressed Mexico City region gives this record particular societal relevance. A detailed paleoclimate reconstruction from central Mexico will enhance our understanding of long-term natural climate variability in the North American tropics and its relationship with changes at higher latitudes. The site lies at the northern margin of the Intertropical Convergence Zone (ITCZ), where modern precipitation amounts are influenced by sea surface temperatures in the Pacific and Atlantic basins. During the Last Glacial Maximum (LGM), more winter precipitation at the site is hypothesized to have been a consequence of a southward displacement of the mid-latitude westerlies. It thus represents a key spatial node for understanding large-scale hydrological variability of tropical and subtropical North America and is at an altitude (2240 m a.s.l.), typical of much of western North America. In addition, its sediments contain a rich record of pre-Holocene volcanic history; knowledge of the magnitude and frequency relationships of the area's explosive volcanic eruptions will improve capacity for risk assessment of future activity. Explosive eruption deposits will also be used to provide the backbone of a robust chronology necessary for full exploitation of the paleoclimate record. Here we report initial results from, and outreach activities of, the 2016 coring campaign. [ABSTRACT FROM AUTHOR]

The ecology of aquatic protists such as testate amoebae is poorly known worldwide, but is almost completely unknown in lakes of the northern Neotropics. To address this knowledge gap, we analyzed testate amoebae (Amoebozoa: Arcellinidae) in lakes of the Lacandón Forest, one of the most biodiverse parts of southern México. We set out to evaluate the diversity of testate amoebae communities and assess whether testate amoebae taxa are reliable indicators of environmental variables dissolved oxygen and water depth. We collected 17 surface sediment samples from a range of water depths in six lakes across the Naha-Metzabok Biosphere Reserve, northeastern Chiapas state. We identified 15 testate amoebae taxa distributed across seven genera. Eleven were identified to species level and four to strain (infra-subspecific level), and taxa were distributed unevenly among samples. Distribution of taxa in samples was related to dissolved oxygen (DO) concentration in the water measured near the sediment surface. Arcella discoides and Centropyxis aculeata strain "aculeata" were the most tolerant of low oxygen concentrations, whereas the other taxa require higher DO levels. The influence of oxygen was also seen at the assemblage level. Sites with low DO concentrations had Shannon Diversity Index (SDI) values <1.5, an indication of stressful ambient conditions. We identified two species assemblage types, which are distinguished by their oxygen concentration requirements. Assemblage 1 was more diverse and possessed species that are intolerant of low oxygen concentrations, whereas Assemblage 2 possessed fewer, rarer, opportunistic species that tolerate stressful conditions. Low oxygen concentrations are related to water depth and the combination of these two variables is important in determining the composition of testate amoebae assemblages in Lacandón Forest lakes. Quantitative relationships between testate amoebae assemblages and water depth will enable use of sedimented amoebae remains for paleolimnological inference of past water level changes in lakes of the Lacandón Forest. [ABSTRACT FROM AUTHOR]

Three-dimensional urban cartography is needed for city changes' assessment. The variety of studies using 3D calculations of urban elements grows each year. Building and vegetation volumes are necessary to assess and understand spatio-temporal urban changeable environments. However, there are technical questions as to which method can improve 3D urban cartographic accuracy. The innovative part of this current study is the creation of a six-band hybrid obtained from LIDAR and WorldView2 synergy. Two different enhancement algorithms demonstrated the most important spectral features for the urban development and vegetation classes. Results indicated an improvement in accuracy by up to 21.3%, according to the Kappa coefficient. Both infra-red band and intensity band were the most significant, according to the principal components analysis. The synergy delimited classes and polygons, as well as the direct display of information regarding heights of elements and improving the extraction of roads, buildings and vegetation classes. [ABSTRACT FROM AUTHOR]

Question When did vegetation assemblages that occupy modern central Mexico appear within the context of the late Quaternary? Location Central Mexico. Methods We used modern and fossil pollen data sets from central Mexico to explore the evolution of regional vegetation through the late Quaternary. A total of 1397 samples (1357 fossil samples distributed in 17 records and 40 modern samples) were analysed through detrended correspondence analysis to evaluate the degree of analogy between modern and past vegetation assemblages, and regional vegetation compositional turnover through time. Results There was a high degree of analogy between modern and glacial vegetation, whereas the early and mid-Holocene were characterized by a high frequency of no-modern-analogue pollen assemblages. Vegetation turnover during the glacial time was characterized by both pulses of abrupt change and episodes of stability. In contrast, vegetation turnover was high through most of the Holocene. Both vegetation turnover and past vegetation analogy to modern were not synchronous in altitudinal zones, except for the past 2000 yrs, when pollen assemblages suggest a high vegetation analogy to modern-day throughout the region. Conclusions Human impacts on central Mexico regional vegetation were consistently evident during the last 2000 yrs, suggesting that biodiversity expressed in the modern vegetation assemblages incorporates a high anthropogenic imprint. High resemblance of glacial and modern landscapes suggests that the effect of human occupation on the landscape is similar to that exerted by glacial time environmental stress. However, loss of ecosystem connectivity under the modern pattern of landscape homogenization represents an unprecedented threat for regional biodiversity. [ABSTRACT FROM AUTHOR]

Seasonal dry tropical forest (STDF) is a widespread vegetation type in western Mexico. Generally, this type of forest develops in semihumid habitats where lacustrine basins are scarce, preventing documentation of the vegetation history and forest dynamics using a paleoecological approach. Here, we present a palynological record from the Santa Maria del Oro crater lake, located within the distribution area of the STDF and the adjacent dry oak forest which gives insight into the changes in diversity and human impact at this tropical site. Pollen data, in combination with geochemical analysis and microcharcoal data from a lacustrine sequence, are used to discuss vegetation change and diversity in the plant assemblages related to drought or anthropogenic activity over the last 5000 years. Our results show three distinct periods of drought in the basin, from 4200 to 3850, 3100 to 2300, 1570 to 1100 and 300 cal year BP, with changes in vegetation composition mainly related to a decrease in taxa diversity during these periods. Based on the presence of maize pollen, two periods of human activity (3790–2160 and 280 cal year BP to present) were detected with an increase in herbaceous pollen used as a surrogate for deforestation. These two disturbance periods, pre-Columbian and postcolonial, occurred during wet conditions in the basin. Our results highlight the correlation between El Niño events, drought and fire with changes in the composition and diversity of STDF. [ABSTRACT FROM AUTHOR]

High-altitude lakes are sensitive to modern and past climate changes. Given their low-water temperatures, alkalinity, and nutrient levels, small climatic differences can strongly affect their water chemistry, and/or biodiversity. In central Mexico, there are only two high-altitude lakes, and both are within the crater of the Nevado de Toluca volcano. Here, we present a paleolimnological record from one of these lakes: La Luna. Previous paleoenvironmental work showed that it was sensitive to the Little Ice Age (LIA) cooling. Our results show that sediment accumulation began ~6900 to 6100 cal. yr BP under periglacial conditions and that lake conditions were established ~6000 cal. yr BP. One tephra layer was dated to ~5600 cal. yr BP, with no evidence of more recent volcanic activity. The early stages of this lake (6000–4700 cal. yr BP) contained Cladocera and diatom assemblages with different species composition than modern assemblages. This early stage community structure was related to more mesic conditions and cooler winters inferred by the high abundance of planktonic Aulacoseira nivaloides and of Chydorus cf. sphaericus. The establishment of modern limnological conditions after 4700 cal. yr BP is inferred from Cladocera and diatom assemblages similar to recent samples. A reduction in A. nivaloides and low magnetic-susceptibility values suggest lower lakes levels, a trend consistent with lower available moisture in central Mexico after 4000 cal. yr BP. The rest of the sequence shows the impact of two cold periods, the first one around 3000 cal. yr BP, identified by a new increase in Chydorus cf. sphaericus. The second was the larger impact associated with the LIA (AD 1350–1910), and an increase in Cavinula pseudoscutiformis and Pinnularia microstauron suggesting an increase in lake water pH. Also, organic matter and photosynthetic pigments increased during this period showing an increase in nutrient levels and productivity. Finally, the coldest interval during the LIA (AD 1570–1890) is identified by an important reduction in arboreal pollen concentration which points to a wider environmental impact of this cold event. [ABSTRACT FROM AUTHOR]

Palaeoclimate research in subtropical arid Mexico is mainly focused to infer dynamics and geographic distributions of different precipitation regimes, but droughts have received less attention. We present a new sedimentary core record indicating orbital‐scale dynamics of droughts that occurred in central‐northern Mexico during the late Quaternary. This record is reconstructed from abundances of authigenic carbonate and windblown clastic sediments in a 1026‐cm‐long sediment core from the Santiaguillo ephemeral lake. The Marine Isotope Stage (MIS) 2 lacked drought, and at least two different droughts were centred at c. 13.5 ka and at c. 7 ka during the MIS 1. The drought of c. 13.5 ka in the Santiaguillo ephemeral lake was contemporary to an interval of droughts in the Basin of Mexico (central Mexico) and stronger aeolian activity in the Baja California peninsula (northwestern Mexico). This synchronous arid condition, observed in the subtropical as well as tropical Mexico, occurred during an interval of higher spring insolation, relatively warmer but fluctuating global temperature, and stronger El Niño‐Southern Oscillation. Unsuccessful radiocarbon dating for the lower part of the sediment core led to an assignment of uncertain chronology to droughts that occurred possibly between MIS 5 and MIS 3. Copyright © 2017 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

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The article discusses a workshop on scientific drilling project at Lake Basin in Mexico sponsored by the International Continental Scientific Drilling Program (ICDP) which funds geology projects and Universidad Nacional Autónoma de México from 4-8 March, 2012 in Mexico City, Mexico. The project main aim was evaluation of climate and ecological record preserved in the lake sediments. The workshop featured participants with specialization in borehole instrumentation technology.

Lakes are sensitive ecosystems to climatic change but in the tropics it is frequently difficult to evaluate as there are few long-term records. In this paper hydrochemistry and phytoplankton data during the 2009-2010 'El Niño' are contrasted with non-'El Niño' conditions (pre- and post- the 2009-2010 event) and with long-term (23 years) meteorological and paleolimnological data from a lake in eastern Mexico. Meteorological data provide evidence of a recent (since year 2000) warming trend, and paleolimnological data show that the diatom assemblage changed at this time to a more diverse association, including low abundances of a small Cyclotella species ( C. ocellata) and a small needle shaped species ( Fragilaria nanana) to the previously dominant assemblage ( Ulnaria delicatissima, Achnanthidium minutissimum). Phytoplankton associations during non-'El Niño' are consistent with the paleolimnological record ( U. delicatissima- A. minutissimum, + Staurastrum sp.) but they changed at the onset of 'El Niño' (May 2009), when N and P co-limitation favoured a Coelastrum reticulatum- C. ocellata assemblage. During 'El Niño' winter (February 2010) colder temperatures led to a longer mixing period and a whole water column deoxygenation event that favoured a particularly low diversity association ( Botryococcus sp.- Sphaerocystis sp.). The low diversity C. ocellata-bloom has no precedent for the last 23 years. The previous 1998-1999 'El Niño' had a similar low diversity assemblage but dominated by U. delicatissima. The different response of the phytoplankton to the two 'El Niño' events is related with the warmer conditions since the year 2000, that lead to more stable stratification periods and more frequent or intense nutrient limitation, particularly during the warmer than average 'El Niño' 2009-2010 summer. Under a global warming scenario, minor changes in ecosystem's base levels determine that even normal climatic variability events can cause unexpected changes in the ecosystem's diversity and species composition. [ABSTRACT FROM AUTHOR]

A new detailed pollen record of the penultimate glacial–interglacial–glacial cycle corresponding to the late marine isotopic stages (MISs) 6–3 (146–35 ka ago) has been obtained from Lake Chalco, in the Basin of Mexico. This record provides an insight into vegetation dynamics and climate variability at the northern limit of the American tropics. The pollen record displays a high temporal resolution with a mean sampling interval of ∼230 years. The changes in plant composition were reconstructed by pollen analysis and differences in plant composition between distinct periods were established. The wettest cold stage, indicated by a combination of diverse open vegetation and mesophytic taxa correlates with the penultimate late glacial MIS 6 (146–130 ka), when Lake Chalco was a deep freshwater lake. The penultimate interglacial MIS 5e (126.5–123.6 ka) shows a dominance of Pinus forests, with tropical taxa suggesting warmer than present conditions; environmental proxies indicate drier conditions and that the lake transitioned into a saline water body. Open communities and Pinus and Quercus forests with mesophytic taxa and, during the stadial periods, MIS 5 d, 5c, and 5 b (125–90 ka), with tropical taxa, characterize the record of interstadials. Pinus -dominated forests characterize the landscape during MIS 5a. MIS 5c to MIS 3 showed lower and variable evenness and palynological richness, along with an increase in fire activity. During MIS 4 and 3, a trend towards drier conditions was also recorded with enhanced carbonate precipitation and proxies indicating saline conditions. Tree-line changes in response to climate change and taxa migration were documented. A comparison with long records from the Greenland ice cores, the marine Cariaco Basin and insolation parameters revealed that the pollen data and the Pinus pollen accumulation rates evidence the response of the vegetation to glacial and interglacial changes and to millennial-scale variability. Wetter conditions were inferred to exist during the Greenland interstadials, while drier conditions persisted during Heinrich events. • Changes in plant composition and diversity in the Basin of Mexico encompassing late MIS 6 to MIS 3. • High taxonomic diversity and cold conditions characterize the late MIS 6 landscape. • Pinus forests with variable evenness and drier environments from the end of MIS 5 to MIS 3. • Pollen data highlight the influence of millennial-scale climate variability on plant communities. [ABSTRACT FROM AUTHOR]

We present a palaeohydrological reconstruction of Lake Chalco from 70 to 11.5 ka BP based on ostracod records consisting of three species: Limnocytherina axalapasco, Candona patzcuaro , and Cypridopsis vidua. Overall, the presence of these species helped investigate Lake Chalco water level fluctuations, and thus water salinity variations. Moreover, this work helped improve our knowledge of L. axalapasco and Candona alchichica , two endemic species of Central Mexico, the latter of which was replaced by C. patzcuaro after the cold and dry MIS4. Five ostracod zones reflect the main environmental changes that occurred during the Late Pleistocene. During 70–62 ka BP (Zone 5), shallow and very variable salinity conditions were inferred with a possible occupancy of submerged macrophytes. The Lake Chalco water level increased from 62 to 49 ka BP (Zone 4) and relatively less saline conditions were inferred. The warmer period from of 49–39 ka BP (Zone 3) was characterised by lower lake levels and a gradually increasing salinity. The evaporation rates continued to increase during 39–27 ka BP (Zone 2). However, a higher runoff input helped maintain a relatively high lake level. Later on, cold and dry conditions from 27 to 11.5 ka BP (Zone 1) inhibited the ostracod occupancy in Lake Chalco. • Paleoenvironmental reconstruction of Lake Chalco based on ostracod record from 70 to 11.5 ka BP. • Lake water salinity changes correlate with ostracod relative abundances changes. • Replacement of Candona alchichica by Candona patzcuaro after the cold and dry MIS4. [ABSTRACT FROM AUTHOR]

The ostracode fauna of the neartic-neotropical transitional zone has remained poorly known until this study. Ten ostracode species inhabit ten highland lakes (five maar lakes (phreatic/phreato-magmatic explosion origin), one volcanic-tectonic lake, three natural dams and one man-made dam) in East-central Mexico. Surface sediments from the deepest part and the littoral zone from all studied lakes were collected. Environmental variables (pH, temperature, dissolved oxygen, conductivity, TDS) were measured in situ and parallel water samples for chemical analysis were collected for habitat description. Widely distributed species in the study area (=5 lakes) include Cypridopsis vidua, Darwinula stevensoni and Eucandona cf. patzcuaro. Limnocytherina axalapasco is an endemic species and was collected in three maar lakes and in one man-made dam. Rare species included: Chlamydotheca arcuata?, Fabaeformiscandona acuminata?, Ilyocypris gibba?, Limnocythere friabilis?, Potamocypris smaragdina? and Potamocypris unicaudata?. Highest species richness (6 spp.) was found in the large and shallow Lake Metztitlán (2.6km2, 5.5m deep), with the lake water type HCO3 ->>SO4 ²->Cl- -- Ca2+>Na+>Mg2+. The rest of studied lakes (<63m, <27km²) had not more than three species. For instance, only two ostracode species were collected in Lake Alchichica, which is the largest, deepest and most saline studied maar lake. [ABSTRACT FROM AUTHOR]

The use of statistical models and machine-learning techniques along satellite-derived aerosol optical depth (AOD) is a promising method to estimate ground-level particulate matter with an aerodynamic diameter of ≤2.5 μm (PM2.5), mainly in urban areas with low air quality monitor density. Nevertheless, the relationship between AOD and ground-level PM2.5 varies spatiotemporally and differences related to spatial domains, temporal schemes, and seasonal variations must be assessed. Here, an ensemble multiple linear regression (EMLR) model and an ensemble neural network (ENN) model were developed to estimate PM2.5 levels in the Monterrey Metropolitan Area (MMA), the second largest urban center in Mexico. Four AOD-SDSs (Scientific Datasets) from MODIS Collection 6 were tested using three spatial domains and two temporal schemes. The best model performance was obtained using AOD at 0.55 µm from MODIS-Aqua at a spatial resolution of 3 km, along meteorological parameters and daily scheme. EMLR yielded a correlation coefficient (R) of ~0.57 and a root mean square error (RMSE) of ~7.00 μg m−3. ENN performed better than EMLR, with an R of ~0.78 and RMSE of ~5.43 μg m−3. Satellite-derived AOD in combination with meteorology data allowed for the estimation of PM2.5 distributions in an urban area with low air quality monitor density. [ABSTRACT FROM AUTHOR]

The Little Ice Age (LIA), AD 1350-1850, represents one of the most recent, persistent global climate oscillations. In Mexico, it has been associated with temperature decreases of 1.5-2 °C and mountain glacier advances, which are not accurately dated. We present new information about the nature of the LIA in central Mexico based on a decadal-resolution sediment sequence from high-altitude, tropical Lake La Luna, in the Nevado de Toluca volcano. We inferred past climatic and environmental changes using magnetic susceptibility, charcoal particles, palynomorphs, diatoms, cladoceran remains and multivariate statistics. The onset of the LIA corresponds with the beginning of a long-term trend to colder and drier climate ca. AD 1360-1910. The coolest and driest episode, ~AD 1660-1760, which corresponds with the Maunder Minimum in solar activity, was characterized by a cladoceran assemblage that showed the greatest dissimilarity to the modern one (no modern analogue), with the presence of cold-water species and Daphnia ephippia. The beginning of a warming trend ca. AD 1760, was identified by a diatom assemblage dominated by species with affinities for higher pH values (>6) and the greatest dissimilarity to the modern assemblage. This less cold, but still dry period, corresponds with historical reports of cattle and crop losses that predated the Mexican wars of Independence (AD 1810-1821) and Revolution (1910-1924). Modern conditions, established around AD 1910, resemble those during the Medieval Climate Anomaly (ca. AD 1200). No clear evidence of modern, human-induced environmental change was recorded, indicating that Lake La Luna is an ideal site in Mexico to monitor future impacts of global change. [ABSTRACT FROM AUTHOR]

Abstract: Central Mexico is a complex area with late Quaternary volcanic activity, climatic diversity and a long history of human occupation. Pollen, microcharcoal and magnetic susceptibility analyses of two sedimentary sequences from Lake Zirahuen in western central Mexico spanning the last 17,000years provide evidence of a highly dynamic environment. During the late glacial Pinus forest developed around the lake, indicating cold and dry conditions. During the last deglaciation climatic amelioration was recorded at 13.5ka, driving a strong and rapid change in vegetation composition and increase in lake levels. From the latest Pleistocene to early Holocene a hiatus, probably related to an erosive event, is recognized in the northern sequence. The central sequence spans the entire Holocene and reveals three periods of important ecological changes during the early Holocene. A first episode between 9.5 and 9.0ka with a decrease in pine forest seems to have been associated with summer insolation increases. A second peak of forest change at 8.2ka and was probably associated with the cold oscillation documented in the North Atlantic. A third abrupt change was evident from 7.5 to 7.1ka with an anomalous plant community related to wetter Holocene climates and possible to a volcanic event. An episode of dry conditions was recorded from 4.5 to 4.2ka, which was related to an increase in ENSO activity. Human influence over the landscape was evident from 3.5ka to the present. The Zirahuen records offer a complex history of a landscape characterized by short and long term vegetation changes associated with factors ranging from global climate to local disturbances. [Copyright &y& Elsevier]

Aerosol and meteorological remote sensing data could be used to assess the distribution of urban and regional fine particulate matter (PM2.5), especially in locations where there are few or no ground-based observations, such as Latin America. The objective of this study is to evaluate the ability of Modern-Era Retrospective Analysis for Research and Application, version 2 (MERRA-2) aerosol components to represent PM2.5 ground concentrations and to develop and validate an ensemble neural network (ENN) model that uses MERRA-2 aerosol and meteorology products to estimate the monthly average of PM2.5 ground concentrations in the Monterrey Metropolitan Area (MMA), which is the main urban area in Northeastern Mexico (NEM). The project involves the application of the ENN model to a regional domain that includes not only the MMA but also other municipalities in NEM in the period from January 2010 to December 2014. Aerosol optical depth (AOD), temperature, relative humidity, dust PM2.5, sea salt PM2.5, black carbon (BC), organic carbon (OC), and sulfate (SO42−) reanalysis data were identified as factors that significantly influenced PM2.5 concentrations. The ENN estimated a PM2.5 monthly mean of 25.62 μg m−3 during the entire period. The results of the comparison between the ENN and ground measurements were as follows: correlation coefficient R ~ 0.90; root mean square error = 1.81 μg m−3; mean absolute error = 1.31 μg m−3. Overall, the PM2.5 levels were higher in winter and spring. The highest PM2.5 levels were located in the MMA, which is the major source of air pollution throughout this area. The estimated data indicated that PM2.5 was not distributed uniformly throughout the region but varied both spatially and temporally. These results led to the conclusion that the magnitude of air pollution varies among seasons and regions, and it is correlated with meteorological factors. The methodology developed in this study could be used to identify new monitoring sites and address information gaps. [ABSTRACT FROM AUTHOR]

Abstract: Building up a scenario of Late Pleistocene–Holocene environmental change and human–landscape interactions in Central Mexico – one of the key areas for the natural and cultural history of America – requires development of local paleoenvironmental reconstructions. We studied the Tepexpan section at the edge of Texcoco a paleolake, near the mouth of Teotihuacan Valley as a multiproxy record of the environmental dynamics at the shore in the Basin of Mexico throughout the period of human occupation. The section is located in an ecotone affected by intensive and variable geomorphic processes and includes lacustrine, fluvial and volcanic sediments as well as paleosols. Our chronological scale is based on 6 AMS 14C dates from pollen concentrates and paleosol organic matter. The lower segment of the section dominated by the lacustrine sediments yielded pollen spectra; in the upper segment the record is based on the pedogenetic characteristics of paleosols. Different proxies agree in demonstrating the general trend (although some reversals are apparent) of decreasing effective moisture since MIS3: it is reflected first in the increase of herbaceous pollen after 27ka BP, the decrease of lake level, the cessation of lacustrine sedimentation and beginning of marsh soil development at 10ka BP and finally, the shift from hydromorphic to dryland semiarid pedogenesis in the Late Holocene. We assume that this trend was climatically controlled, whereas the deposition of sedimentary layers enriched with tephra are related to the pulses of volcanic activity; the pedosedimentary features associated with the upper soil are human-induced. Comparing the proposed scheme of environmental change with the archaeological record we propose that the initial settlers, Late Paleolithic hunters, could have utilized the wet swampy meadows which expanded on the Basin bottom as the lake level lowered and provided the niche for large herbivores during the Pleistocene–Holocene transition. Development of agriculture and the network of permanent settlements are believed to be linked to the formation of well drained soils. In the methodological perspective the study shows the potential of ecotones as highly dynamic and sensitive systems that may archive valuable paleoecological records. [Copyright &y& Elsevier]

Geochemical data obtained from X-ray fluorescence, physical properties, total organic and inorganic carbon content (TOC/TIC), and diatom analysis from a 6.61-m-long sedimentary sequence near the modern northern shore of Lake Zirahuen (101° 44′ W, 19° 26′ N, 2000 m asl) provide a reconstruction of lacustrine sedimentation during the last approximately 17 cal kyr BP. A time scale is based on ten AMS C dates and by tephra layers from Jorullo (AD 1759-1764) and Paricutin (AD 1943-1952) volcanoes. The multiproxy analyses presented in this study reveal abrupt changes in environmental and climatic conditions. The results are compared to the paleo-record from nearby Lake Patzcuaro. Dry conditions and low lake level are inferred in the late Pleistocene until ca. 15 cal kyr BP, followed by a slight but sustained increase in lake level, as well as a higher productivity, peaking at ca. 12.1 cal kyr BP. This interpretation is consistent with several regional climatic reconstructions in central Mexico, but it is in opposition to record from Lake Patzcuaro. A sediment hiatus bracketed between 12.1 and 7.2 cal kyr BP suggests a drop in lake level in response to a dry early Holocene. A deeper, more eutrophic and turbid lake is recorded after 7.2 cal kyr BP. Lake level at the coring site during the mid Holocene is considered the highest for the past 17 cal kyr BP. The emplacement of the La Magueyera lava flows (LMLF), dated by thermoluminiscence at 6560 ± 950 year, may have reduced basin volume and contributed to the relative deepening of the lake after 7.2 cal kyr BP. The late Holocene (after 3.9 cal kyr BP) climate is characterized by high instability. Extensive erosion, lower lake levels, dry conditions and pulses of high sediment influx due to high rainfall are inferred for this time. Further decrease in lake level and increased erosion are recorded after ca. AD 1050, at the peak of Purepechas occupation (AD 1300-1521), and until the eighteenth century. Few lacustrine records extend back to the late Pleistocene-early Holocene in central Mexico; this paper contributes to the understanding of late Pleistocene-Holocene paleoclimates in this region. [ABSTRACT FROM AUTHOR]

The article offers information on a study related to the incorporation of sustainable development at the Tecnológico de Monterrey in Mexico. It reports that the study aimed at providing information regarding the activities implemented by the institution in order to infuse sustainable development (SD) into the academic components. It discusses the experience of institution regarding SD implementation in the academic area. It informs that the inclusion of SD concepts into courses and curricula requires a support by several stakeholders within the institution.

Abstract: Pollen analysis on a 9.54-m sediment core from lake Chignahuapan in the upper Lerma basin, the highest intermontane basin in Central Mexico (2570 m asl), documents vegetation and limnological changes over the past ∼23,000 14C yr. The core was drilled near the archaeological site of Santa Cruz Atizapán, a site with a long history of human occupation, abandoned at the end of the Epiclassic period (ca. 900 AD). Six radiocarbon AMS dates and two well-dated volcanic events, the Upper Toluca Pumice with an age of 11,600 14C yr B.P. and the Tres Cruces Tephra of 8500 14C yr B.P., provide the chronological framework for the lacustrine sequence. From ca. 23,000 14C yr B.P. to ca. 11,600 14C yr B.P. the plant communities were woodlands and grasslands based on the pollen data. The glacial advances MII-1 and MII-2 correlate with abundant non-arboreal pollen, mainly grasses, from ca. 21,000 to 16,000 14C yr B.P., and at ca. 12,600 14C yr B.P. During the late Pleistocene, lake Chignahuapan was a shallow freshwater lake with a phase of lower level between 19,000 and 16,000 14C yr B.P. After 10,000 14C yr B.P., tree cover in the area increased, and a more variable lake level is documented. Late Holocene (ca. 3100 14C yr B.P.) deforestation was concurrent with human population expansion at the beginning of the Formative period (1500 B.C.). Agriculture and manipulation of the lacustrine environment by human lakeshore populations appear at 1200 14C yr B.P. (550 A.D.) with the appearance of Zea mays pollen and abundant charcoal particles. [Copyright &y& Elsevier]

Pollen data from 3860 m in the Agua El Marrano valley on the northwest side of Iztaccíhuatl volcano (southeastern part of the Basin of Mexico, 19°N), combined with data on the glacial chronology and tephrochronology, document Holocene climatic and vegetation changes near the present timberline. Glacial advances occurred between ∼ 12 000 and ∼ 10 500 cal. yr BP (Milpulco-1) and between 8300 and 7300 cal. yr BP (Milpulco-2). A 450-cm core was drilled in sediments accumulated in a Milpulco-1 moraine depression. The sequence covers the last 11 000 cal. yr BP, according to three 14C dates and the presence of a distinctive pumice deposit dated elsewhere at 5700 cal. yr BP. The pollen record of Agua El Marrano shows barren conditions after glacier retreat, followed by a gradual colonization by elements of the alpine grasslands around 10 900 cal. yr BP. This plant community remained until c. 7200 cal. yr BP. Between c. 7200 cal. yr BP and 6500 cal. yr BP coniferous forest grew close to or at the site, but alpine grasslands were re-established between 6500 cal. yr BP and c. 5000 cal. yr BP, apparently in connection with mid-Holocene dry conditions recorded in central Mexico. The upper timberline attained its modern altitude ( ∼ 4000 m) in the last 3000 years. During this period no significant changes are observed in the pollen spectra. Comparison with other palaeoecological records from central Mexico suggests that the timberline fluctuated in response to both temperature and precipitation changes during the Holocene. [ABSTRACT FROM AUTHOR]

Energy demand in Mexico is expected to increase in the foreseeable future; however, recently adopted national policies require that Mexico reduces its dependence on fossil fuel-based energy resources. In order to identify areas with a high potential for renewable energy production, based on agricultural by-products a geographic information system-based model was constructed. The model considered a set of enablers' layers (agriculture residue, roads, electrical network, population, land use) and a set of restrictors' layers (slope, natural protected areas, water bodies, natural vegetation, populated areas, airports, and historical sites). Eight crops were selected: maize, wheat, sugarcane, barley, sorghum, agave, paddy rice, and pecan nut. These were selected based on their residue production, as well as being the ones with sizable production volume in several regions across Mexico, as well as the characteristics of their residual biomass that can be used for generating energy or chemicals, without altering the primary intention for these crops, which is human and animal feed. Four models were developed using a weighted overlay algorithm to construct the enablers' layer while the restrictors' layer was created by selecting features with a given characteristic or by generating buffers from the layer's features. The results show that it is possible to generate up to 70,951 MWh of electricity or 18,373 Gg of Fischer–Tropsch liquids using only 60% of the residual biomass. The distribution of these energy sources in the country is highly variable depending on the type of crop selected with a concentration of the crop residues along the lowlands of the Gulf of Mexico and the Pacific Ocean and the central states of Guanajuato, Jalisco, and Queretaro. The study covers a very ample set of municipalities throughout the country, therein their relevance. Image 1 • 1st model of agricultural residue for energy and synthesis gases developed in Mexico. • Municipal crop residue allocated to agricultural areas improves the final models. • Distribution disparities of crop residues significantly affects the models results. • Electricity generation from crop residues estimated around 70,951 to 79,273 MWh/year. • Potential generation of Fischer-Tropsch liquids of 18,373 Gg/year. [ABSTRACT FROM AUTHOR]

Background: Drought periods are major evolutionary triggers of wood anatomical adaptive variation in Lower Tropical Montane Cloud Forests tree species. We tested the influence of historical drought events on the effects of ecological stress memory on latewood width and xylem vessel traits in two relict hickory species (Carya palmeri and Carya myristiciformis) from central-eastern Mexico. We hypothesized that latewood width would decrease during historical drought years, establishing correlations between growth and water stress conditions, and that moisture deficit during past tree growth between successive drought events, would impact on wood anatomical features. We analyzed latewood anatomical traits that developed during historical drought and pre- and post-drought years in both species. Results: We found that repeated periods of hydric stress left climatic signatures for annual latewood growth and xylem vessel traits that are essential for hydric adaptation in tropical montane hickory species. Conclusions: Our results demonstrate the existence of cause‒effect relationships in wood anatomical architecture and highlight the ecological stress memory linked with historical drought events. Thus, combined time-series analysis of latewood width and xylem vessel traits is a powerful tool for understanding the ecological behavior of hickory species. [ABSTRACT FROM AUTHOR]

Laminated sediments in a core from Alberca de Tacámbaro, western central Mexico, provide a high‐resolution record of palaeoclimatic variability for most of the Holocene. Using compositional and textural characteristics we identified 14 facies classified in biogenic, clastic and volcaniclastic groups, in which diatoms and other algal remains are the most common components. In addition to facies analysis, high‐resolution geochemical data from continuous core scanning XRF and the analysis of discrete samples for organic and inorganic carbon content, provide the basis for palaeoclimatic reconstruction. The age model indicates that the record spans from 9.4 cal ka bp toad 1760. Three main phases in the sequence are identified, controlled by millennial‐scale variability. During the period between 9.4 and 5.7 cal kabp, the lake is dominated by siliceous organisms. Drier conditions between 8.2 and 6.3 cal kabp are linked to decreases in summer insolation and solar irradiance. By 5.7 cal kabp, the change in sedimentation is related to the increase in El Niño Southern Oscillation frequency. Evidence of the occurrence of dry conditions during the archaeological Late Classic period (ad 600–900) and historical droughts are also documented in the Alberca de Tacámbaro record. Unprecedented changes in the landscape are recorded afterad 1520. [ABSTRACT FROM AUTHOR]

Copyright of TIP Revista Especializada en Ciencias Químico-Biológicas is the property of Universidad Nacional Autonoma de Mexico, Facultad de Estudios Superiores Zaragoza and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Tropical maar lakes are distinct ecosystems with unique ecological features. To comprehend, manage, and conserve these lakes, it is essential to understand their water sources, particularly groundwater, and the hydrogeochemical processes shaping their water chemistry. This research focuses on the maar lake Alchichica in central Mexico, known for harboring 18 new and endemic species and a ring of stromatolites. With groundwater discharge as the primary source, concerns arise over anthropic extraction impacts on water levels and stromatolite survival. Sampling six wells and one piezometer revealed major ion (Ca2+, Mg2+, K+, Na+, Cl−, HCO3−, SO42−) and trace element (Fe, Al3+, SiO2) concentrations. Geochemical evolution was explored through diagrams, geological sections, and inverse geochemical models using the PHREEQC code. Findings indicate groundwater evolving along controlled flow paths, and influencing chemical composition through water–rock interactions. The lake's unique conditions, resulting from the mixing of two flows, enable stromatolite formation. Water level reduction appears unrelated to evaporation at the sampled sites, suggesting a need for a broader study in a larger area. Analyzing the maar lake's hydrochemistry provides valuable insights into unique characteristics supporting high endemism in this ecosystem. This research enhances our understanding of groundwater's geochemical processes and hydrogeochemical evolution in maar lakes, with potential applications worldwide. [ABSTRACT FROM AUTHOR]

Copyright of Cuadernos.info is the property of Pontificia Universidad Catolica de Chile, Facultad de Comunicaciones and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

While hybridization and introgression can have a strong adaptive importance, it can impede divergence of species. Quercus magnoliifolia and Q. resinosa are two endemic oak species distributed across the Mexican highlands. These species diverged ecological and morphologically; however, no nuclear genetic differentiation is evident. In this study, we determined the mechanisms that shape patterns of genetic variation and establish the role of migration and hybridization in the evolutionary history of these two oak species. To do this, Bayesian approaches were used for inference on migration rates and directionality and timing of divergence between species using chloroplast microsatellites. We then integrated species distribution models to infer the geographic distribution of Q. magnoliifolia and Q. resinosa during Last Interglacial, Last Glacial Maximum, and Mid-Holocene time frames. We failed in distinguishing a unique genetic composition for each species. Chloroplast differentiation was more congruent with geography than the taxonomic status of each species. Our study revealed that after the divergence (c. 10 Mya) of these two oak species, high rates of introgression took place at the end of the Pleistocene. Furthermore, past distribution models predicted that Q. magnoliifolia and Q. resinosa have likely been in sympatry presumable since Last Glacial Maximum and Q. resinosa probably expanded geographically towards its current distribution around Mid-Holocene. This expansion was supported by testing migration models, suggesting recent establishment of Q. resinosa to the north of Trans-Mexican Volcanic Belt. We hypothesized that after Q. magnoliifolia and Q. resinosa diverged, colonization events followed by hybridization between oaks and long-distance seed dispersal occurred, explaining the present-day patterns of distribution of chloroplast diversity. We propose that divergence of species remains mainly on loci under natural selection, providing evidence on the "porous" nature of species boundaries among oaks. [ABSTRACT FROM AUTHOR]

Premise: Phylogeographical studies are fundamental for understanding factors that influence the spatial distribution of genetic lineages within species. Population expansions and contractions, distribution shifts, and climate changes are among the most important factors shaping the genetic compositions of populations. Methods: We investigated the phylogeography of an endemic oak, Quercus mexicana (Fagaceae), which has a restricted distribution in northeastern Mexico along the Sierra Madre Oriental and adjacent areas. Nuclear and chloroplast DNA microsatellite markers were used to describe the genetic diversity and structure of 39 populations of Q. mexicana along its entire distribution area. We tested whether population expansion or contraction events influenced the genetic diversity and structure of the species. We also modeled the historical distributional range of Q. mexicana (for the Mid Holocene, the Last Glacial Maximum, and the Last Interglacial) to estimate the extent to which climate fluctuations have impacted the distribution of this oak species. Results: Our results revealed high genetic diversity and low genetic structure in Q. mexicana populations. Ecological niche models suggested historical fluctuations in the distributional range of Q. mexicana. Historical range changes, gene flow, and physical barriers seem to have played an important role in shaping the phylogeographic structure of Q. mexicana. Conclusions: Our study indicates that the genetic structure of Q. mexicana may have been the result of responses of oak trees not only to heterogeneous environments present in the Sierra Madre Oriental and adjacent areas, but also to elevational and latitudinal shifts in response to climate changes in the past. [ABSTRACT FROM AUTHOR]

The development of hybrid plants can increase the production and quality of blue corn, and, thus, satisfy its high demand. For this development, it is essential to understand the heterotic relationships of the germplasm. The objectives of this study were to determine the effects of general (GCA) and specific (SCA) combining ability, as well as the reciprocal effects (REs) on the yields of 10 blue corn lines, and to select the outstanding lines. Diallel crosses were generated with 10 lines and evaluated at the Valle de México Experimental Station in Chapingo, Mexico, and Calpulalpan, Tlaxcala, Mexico. There were differences (p ≤ 0.01) in the hybrids, Loc, effects of GCA, SCA, and REs, and in the following interactions: hybrids × Loc, GCA × Loc, SCA × Loc, and RE × Loc. For GCA, lines Ll, L4, L6, and L9 stood out, with significant values of 3.4, 2.9, 2.9, and 3.1, respectively. For SCA, the hybrids featured were L4 × L10, L2 × L10, L1 × L10, L7 × L8, and L2 × L6, with values of 3.0, 2.5, 2.3, 2.3, and 2.2, and yields of 11.2, 10.2, 10.4, 10.4, and 10.5 t ha−l, respectively. There were no significant REs in these lines. Considerable effects of GCA and SCA were detected; therefore, we concluded that native populations had favorable dominance and additive genetic effects that could be used to support the development of high-yielding lines and hybrids. [ABSTRACT FROM AUTHOR]

This study presents a 100% renewable and diversified system taking advantage of the available energy potential of renewable energies in Mexico with a view to a planned energy transition in cooperation with the environment. The processes of change that are experienced worldwide in favor of the planet make us reflect and propose alternatives that break traditional schemes in the production of energy (for which reason Mexico cannot deviate from its current model). It is here that this research becomes a transcendental and important reference for decision-making and the transformation of the energy sector in Mexico. The current electrical system relies on fossil fuels that need to be replaced by renewable energy sources (and it is necessary to satisfy growing demands in the long term). The methodological process is carried out with the use of the 100% renewable energy market design tool EnergyPLAN, which puts the concept of intelligent energy into practice by 2050. Finally, after analyzing the results, it is concluded that a good energy mix for 2050 is 30% solar photovoltaic, 25% wind, 14.5% hydraulic, 13.8% CSP plants, and 16.7% other technologies. Surpluses may be sold to the United States and Central America through interconnection points. [ABSTRACT FROM AUTHOR]

Central Mexico exhibits a complex environment with wide topographic, climatic, and biological gradients. Lacustrine basins distributed along the region have been the source for numerous paleoenvironmental reconstructions, representing an exceptional opportunity for studying vegetation turnover dynamics across time and space. A total of 1397 fossil and modern pollen samples were ordinated through a Detrended Correspondence Analysis (DCA) to characterize the regional ecological space. Resulting DCA Axis 1 scores were related to a forest cover gradient. Aiming to generalize the interpretation of the analyzed records and given the clear altitudinal pattern shown by modern samples, paleoenvironmental interpretations were performed grouping fossil records according to their elevation. Euclidean distances among sites scores were used as estimators of ecological distance and summarized from two different approaches to observe turnover dynamics at different spatial scales: i) local turnover through time, and ii) ecological versus geographic distance. The regional late Quaternary vegetation dynamics were found mostly driven by global climatic events, whereas the Holocene was marked by more local factors such as precipitation regime and human occupation patterns. Strong local modulation in turnover dynamics was observed in the region. Additionally, we conclude that a palynological record produces results that are repeatable within 50 km, considering a maximum compositional turnover of 50%. [ABSTRACT FROM AUTHOR]

Genetic studies in the highlands of Mexico have revealed extensive intraspecific differentiation and highly structured genetic variation in rodents and other taxa. One of the most important and complex systems in these highlands is the Trans-Mexican Volcanic Belt (TMVB), a biogeographic region located in central Mexico. Recent studies suggest strong structure and undiscovered diversity within the TMVB highlands, which indicates more study of endemic species is warranted. One of these species is the endemic Volcano Harvest Mouse Reithrodontomys chrysopsis, which inhabits small and fragmented patches at high altitudes. This mouse is poorly known, under-represented in field collections, and has been the subject of few studies of phylogenetics, taxonomy, and evolutionary history. This study aimed to assess the phylogenetic and intraspecific relationships of R. chrysopsis throughout its known geographic distribution to better understand the evolutionary patterns of it and other TMVB mammals. Our phylogenetic analyses using Cytb and Fgb-I7 markers revealed that R. chrysopsis is sister to R. sumichrasti and R. megalotis, which contrasts with a previous hypothesis based on morphological data. Genetic differentiation, divergence time, and species delimitation analyses showed three main divergent lineages within R. chrysopsis, located at the western, central, and eastern TMVB. These lineages diverged during the Pliocene-Pleistocene interval. Our results support the hypothesis that volcanic activity and climatic oscillations during the Pleistocene in central Mexico promoted diversification processes within the TMVB. Further molecular and morphological studies will be needed to provide information for the taxonomic designation of the east divergent lineage detected herein. [ABSTRACT FROM AUTHOR]

Copyright of Hydrogeology Journal is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Green areas are important places for biodiversity conservation within cities, but their vegetation is affected by various anthropogenic factors. This study used an exploratory approach to examine the influence of urbanisation and air pollution-related factors on the indicators for the composition and structure of vegetation in an urban area in northeast Mexico. Based on the spatial analysis of the major air pollutants, four sampling categories were delimited (rural, low, moderate and high urbanisation). The differences between categories, based on vegetation structure, were determined using non-parametric Kruskal-Wallis tests. The Importance Value was calculated for the species. The floristic similarity was compared using NMDS and PERMANOVA unidirectional. The relationship between environmental variables and abundance of species was evaluated using CCA. One hundred and ten plant species were collected, including ten alien species. The highest abundance and species richness were registered in the rural site. The general tendency of vegetation structure is to plants decreasing with respect to the increase in the levels of urbanisation and air pollution present in the study area. The association between the environmental variables and plant communities along the urbanisation gradient was significant, being the relative humidity, the particles lower than 2.5 μm, the dew point and the heat index as the most important variables. The understanding of the nature and variability of vegetation within green areas contributes to increasing our knowledge about the distribution of the environmental services they provide and the composition of the faunal communities that depend on them. For this reason, this study relates the plants of a specific area of northeast Mexico with the environmental quality present in an urban area. [ABSTRACT FROM AUTHOR]

Simple Summary: Membracis mexicana is a treehopper widely distributed in the neotropical region where it is a minor pest of some crops. In Mexico, it is found in at least four biogeographic provinces (abiotic subdivision of biogeographic realms where assemblages of biota share an evolutionary history), and few species of insects have such wide distributions. Field observations indicate that there are different forms of this species, but so far, how the different forms appear and how they are distributed have not been recorded. To test whether the distribution of morphological and genetic variation was consistent with the regionalization of the biogeographic provinces, we analyzed the morphological and genetic variation of this species sampling a total of 303 insects and conducted a geometric morphometric analysis from the body shape and phylogeographical analysis using five sequenced genes. We found three different morphotypes of these species and two genetic groups; this means that one of the genetic groups shows two forms. These findings show that M. mexicana is a very variable species geographically structured by the conformation of biogeographic provinces. Membracis mexicana (Hemiptera: Membracidae) is distributed in four biogeographic provinces of Mexico. Field observations indicate that there are different forms of this species, but the distribution of the phenotype and the genetic variation of this species have not been clarified. The aim of this study was to quantify the phenotypic and genetic variation of M. mexicana and determine whether the configuration of biogeographic provinces impacts the distribution of this variation. To achieve this, we analyzed 307 photographs using 19 landmarks and geometric morphometrics to quantify the phenotypic variation in helmets. We sequenced five molecular markers for 205 individuals to describe the phylogeographic pattern. As a result, we identified three morphological configurations of the helmet of M. mexicana and two genetic lineages. The morphotypes are (1) a large and wide helmet with small dorsal spots, (2) a small and narrow helmet with large dorsal spots, and (3) a small and narrow helmet with small spots. Genetic lineages are distributed in southeast and western Mexico. The western lineage corresponds to two helmet morphotypes (1 and 2) and the southeast lineage to morphotype 3. We found that the larger helmets correspond to the western lineage and are distributed in Trans-Mexican Volcanic Belt and Pacific lowlands provinces, whereas the smallest helmets correspond to the southeast lineage and are present in the Veracruzan and Yucatan Peninsula provinces. [ABSTRACT FROM AUTHOR]

During the Pleistocene, the Yucatán Peninsula reached its greatest geographic extension, with 457,650 km2, but the rise of sea level after the Last Glacial Maximum (ca. 20,000–12,000 years ago) reduced its area to 225,182 km2 (50.8% reduction). These geographic extension changes likely modified the extension of different habitats throughout the peninsula, which may have also promoted morphological changes in the species that inhabit this region. Here, we tested if the reduction of the geographic size of the Yucatán Peninsula may have promoted changes in the body size of three fossil bird species and two modern bird species. We compared Late Pleistocene bird fossils specimens from Loltún, Yucatán, Mexico (ca. 28,000–11,700 ya), San Josecito Cave and Tlapacoya, and study skins of collected specimens. To assess the area‐scale ratio and to establish if body size changes occurred over time from a large to a small body size, we relied on the "island rule" as a framework; we also relied on Bergmann's rule, which postulates a decreasing in size from north to south in homeothermic species to recognize if these birds show a north to south cline. Based on body mass and measurements of the tarsometatarsi, a reliable proxy for the estimation of body size, we performed statistical analyses to test for differences between fossil and non‐fossil birds, as well as to test a gradient in body mass north to south. We found a statistically significant trend in body size changes through time, from small body sizes in fossil birds to larger body sizes in non‐fossil birds. These results suggest that relatively recent ecological factors related to the environmental carrying capacity may have promoted body size variations in birds from the Yucatán Peninsula. We also found that modern population of bird species follow Bergmann's rule. [ABSTRACT FROM AUTHOR]

Advances in technology have equipped paleobiologists with new analytical tools to assess the fossil record. The functional traits of vertebrates have been used to infer paleoenvironmental conditions. In Quaternary deposits, birds are the second-most-studied group after mammals. They are considered a poor paleoambiental proxy because their high vagility and phenotypic plasticity allow them to respond more effectively to climate change. Investigating multiple groups is important, but it is not often attempted. Biogeographical and climatic niche information concerning small mammals, reptiles, and birds have been used to infer the paleoclimatic conditions present during the Late Pleistocene at San Josecito Cave (~28,000 14C years BP), Mexico. Warmer and dryer conditions are inferred with respect to the present. The use of all of the groups of small vertebrates is recommended because they represent an assemblage of species that have gone through a series of environmental filters in the past. Individually, different vertebrate groups provide different paleoclimatic information. Birds are a good proxy for inferring paleoprecipitation but not paleotemperature. Together, reptiles and small mammals are a good proxy for inferring paleoprecipitation and paleotemperature, but reptiles alone are a bad proxy, and mammals alone are a good proxy for inferring paleotemperature and precipitation. The current paleoclimatic results coupled with those of a previous vegetation structure analysis indicate the presence of non-analog paleoenvironmental conditions during the Late Pleistocene in the San Josecito Cave area. This situation would explain the presence of a disharmonious fauna and the extinction of several taxa when these conditions later disappeared and do not reappear again. [ABSTRACT FROM AUTHOR]

The dissolved organic carbon (DOC) reservoir plays a critical role in the C cycle of marine and freshwater environments because of its size and implication in many biogeochemical reactions. Although it is poorly constrained, its importance in ancient Earth's C cycles is also commonly invoked. Yet DOC is rarely quantified and characterized in modern stratified analogues. In this study, we investigated the DOC reservoirs of four redox-stratified alkaline crater lakes in Mexico. We analyzed the concentrations and isotopic compositions of DOC throughout the four water columns and compared them with existing data on dissolved inorganic and particulate organic C reservoirs (DIC and POC). The four lakes have high DOC concentrations with great variability between and within the lakes (averaging 2 ± 4 mM; 1 SD, n=28 ; i.e., from ∼ 15 to 160 times the amount of POC). The δ13 C DOC signatures also span a broad range of values from -29.3 ‰ to -8.7 ‰ (with as much as 12.5 ‰ variation within a single lake). The prominent DOC peaks (up to 21 mM), together with their associated isotopic variability, are interpreted as reflecting oxygenic and/or anoxygenic primary productivity through the release of excess fixed carbon in three of the lakes (Alberca de los Espinos, La Preciosa, and Atexcac). By contrast, the variability of [DOC] and δ13 C DOC in the case of Lake Alchichica is mainly explained by the partial degradation of organic matter and the accumulation of DOC in anoxic waters. The DOC records detailed metabolic functions such as active DIC-uptake and DIC-concentrating mechanisms, which cannot be inferred from DIC and POC analyses alone but which are critical to the understanding of carbon fluxes from the environment to the biomass. Extrapolating our results to the geological record, we suggest that anaerobic oxidation of DOC may have caused the very negative C isotope excursions in the Neoproterozoic. It is, however, unlikely that a large oceanic DOC reservoir could overweigh the entire oceanic DIC reservoir. This study demonstrates how the analysis of DOC in modern systems deepens our understanding of the C cycle in stratified environments and helps to set boundary conditions for the Earth's past oceans. [ABSTRACT FROM AUTHOR]

High mountain lakes (HMLs) are considered unique and comparable ecosystems for monitoring global climate change. The food web structure can indicate the response of these ecosystems to ecological threats, such as fish introduction, by analyzing the trophic dynamics. Nonetheless, the food webs of tropical HMLs are less well-studied than temperate HMLs. The present study assessed the food webs of two neighboring (600 m apart) tropical HMLs, El Sol and La Luna, inside the crater of the Nevado de Toluca volcano, Mexico. It used stable isotopes (δ13C and δ15N) and Bayesian mixing models with different trophic discrimination factors and priors to assess the impacts of introduced rainbow trout, persisting only in the larger lake, El Sol. The food web in Lake El Sol was more complex than in Lake La Luna, mainly due to its larger size, extensive vegetated littoral zone, and being fueled by autochthonous primary production. In contrast, the smaller and fishless Lake La Luna has a reduced and bare littoral zone that harbored a simple food web substantially sustained by allochthonous carbon inputs. The persistence of introduced rainbow trout in Lake El Sol but not in Lake La Luna accentuated the differences between the lakes. The models suggested that rainbow trout fed on key consumers of littoral macroinvertebrates (70–80%) and pelagic zooplankton (20–30%), increasing the linkage between sub-networks. In both tropical HMLs, the species richness and herbivorous fraction were elevated compared with temperate HMLs, while the linkage density and omnivorous fraction were lower. Basal nodes dominated these tropical HMLs, and the vegetated littoral zone of Lake El Sol had more intermediate (omnivore) nodes. Our results showed the convenience of food web analysis to compare the effects of introduced fish in originally fishless lakes in different latitudes. [ABSTRACT FROM AUTHOR]

Fossil camelids (Artiodactyla, Camelidae) record for Mexican Late Pleistocene is constituted by Camelops hesternus, Hemiauchenia macrocephala, Hemiauchenia gracilis, and Palaeolama mirifica. It analysed dental microwear and carbon and oxygen stable isotopes in teeth enamel of C. hesternus, H. macrocephala and H. gracilis from two fossil sites (LC-PT, and LP-SA) in west-central Mexico, gaining knowledge about camelids palaeoecology (diet and habitat). Microwear and δ13C values indicate that C. hesternus from both sites had a browser diet with a preference for C3-C4 plants, while H. macrocephala from LC-PT was browser with a predilection for C3 plants, and H. gracilis from LC-PT had a mixed feeder diet with a preference for C3 plants. The δ18O and the aridity index show that camelids in central Mexico were evaporation-sensitive taxa. The results suggest that LC-PT had a heterogeneous environment composed of open areas and closed zones, temperatures between 13.95°C and 19.9°C and extreme seasonal changes. The environment in LP-SA was dominated by open areas, with small closed vegetation patches, a temperature of 16.29°C, and less seasonal variation. The aridity index indicates relatively drier conditions at LP-SA than at LC-PT. Camelid dietary ecology provides an initial reconstruction of a regional paleoenvironment, with diverse ecosystems present. [ABSTRACT FROM AUTHOR]

The timing and mechanisms of past hydroclimate change in northeast Mexico are poorly constrained, limiting our ability to evaluate climate model performance. To address this, we present a multiproxy speleothem record of past hydroclimate variability spanning 62.5 to 5.1 ka from Tamaulipas, Mexico. Here we show a strong influence of Atlantic and Pacific sea surface temperatures on orbital and millennial scale precipitation changes in the region. Multiple proxies show no clear response to insolation forcing, but strong evidence for dry conditions during Heinrich Stadials. While these trends are consistent with other records from across Mesoamerica and the Caribbean, the relative importance of thermodynamic and dynamic controls in driving this response is debated. An isotope-enabled climate model shows that cool Atlantic SSTs and stronger easterlies drive a strong inter-basin sea surface temperature gradient and a southward shift in moisture convergence, causing drying in this region. A stalagmite hydroclimate record (Tamaulipas, Mexico) from 62.5 to 5.1 ka showed (1) Atlantic and Pacific temperatures impacted precipitation changes and (2) there were dry conditions during Heinrich Stadials, possibly because moisture shifted south. [ABSTRACT FROM AUTHOR]