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The Tacaná volcano in southern Mexico, is one of the most important areas for conservation in the Mesoamerican biodiversity hotspot. Yet, traditional floristic inventories in the area have been limited by access to remote zones along its 4000 m elevation gradient. To achieve an accurate view of vegetation structure and spatial dynamics, we sampled moss pollsters from elevation locations along the entire Tacaná elevation gradient. We observed a strong correlation between pollen spectra and elevation variations, reflecting general vegetation patterns. Main vegetation types along the elevation gradient included tropical rain forest (from 500 to 1500 m), with relative high abundance of Moraceae, Ficus, Alchornea, Fabaceae and Bombacaceae. Montane rain forests were distributed from 2000 to 2500 m, and pollen spectra were dominated by Alnus, Clethra, Cyathea, Quercus, Alchornea, Ilex and Bombacaceae. Temperate forests were located at elevations ranging from 2800 to 3000 m, in association with Pinus-Alnus forests. Pinus forests were recorded at highest elevations from 3000 to 4000 m. In addition, relative humidity was the main factor determining elevation distribution and vegetation change in the area. We argue that up-climbing warm winds favor the distribution of tropical taxa towards higher elevations, thus allowing landscape plant connectivity. Biogeographic and local/regional factors –likely volcanism activity- might govern temperature fluctuations and immediate and long-term effects of the climatic distribution on the associated flora and on biodiversity as a whole. [ABSTRACT FROM AUTHOR]

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Part 1 of this study investigated evidence of biomass burning in global ice records, and here we continue to test the hypothesis that an impact event at the Younger Dryas boundary (YDB) caused an anomalously intense episode of biomass burning at ∼12.8 ka on a multicontinental scale (North and South America, Europe, and Asia). Quantitative analyses of charcoal and soot records from 152 lakes, marine cores, and terrestrial sequences reveal a major peak in biomass burning at the Younger Dryas (YD) onset that appears to be the highest during the latest Quaternary. For the Cretaceous-Tertiary boundary (K-Pg) impact event, concentrations of soot were previously utilized to estimate the global amount of biomass burned, and similar measurements suggest that wildfires at the YD onset rapidly consumed ∼10 million km2 of Earth’s surface, or ∼9% of Earth’s biomass, considerably more than for the K-Pg impact. Bayesian analyses and age regressions demonstrate that ages for YDB peaks in charcoal and soot across four continents are synchronous with the ages of an abundance peak in platinum in the Greenland Ice Sheet Project 2 (GISP2) ice core and of the YDB impact event (12,835–12,735 cal BP). Thus, existing evidence indicates that the YDB impact event caused an anomalously large episode of biomass burning, resulting in extensive atmospheric soot/dust loading that triggered an “impact winter.” This, in turn, triggered abrupt YD cooling and other climate changes, reinforced by climatic feedback mechanisms, including Arctic sea ice expansion, rerouting of North American continental runoff, and subsequent ocean circulation changes. [ABSTRACT FROM AUTHOR]

In developing countries, landfills of urban solid waste (USW) are a major source of contamination. One reason is the common practice of the illegal confinement of hazardous waste (HW). The contamination is mainly due to deficitary design location, operation and lack of liner, which enables the dispersion of pollutants. The aim of our work is to demonstrate the presence of heavy metals (HM) and arsenic (As) in USW of the closed dump of Morelia, which clandestinely confined HW for 20 years. Solid samples of USW were collected from eight opencast wells with different age of confinement. Composition, degradation status, physical-chemical characterization and analysis of HM and As were carried out. The results showed the presence of Pb, Cu, Ni, Zn, Cr, Fe and high concentrations of As. This study provides evidence about the usual and illegal practice of landfill HW together with USW; the hazard due to the presence of HM and As; the deficiency in the operation and closure; and, the lack of competent legislation on the subject. This information is essential to establish background information for improving laws and help decision makers in territorial planning to improve public and environment health. [ABSTRACT FROM AUTHOR]

Pleistocene fluvial sequences have been recognised in some regions of México as an important source of information on past environmental change using a wide range of proxies. However, this has not been attempted in Mexico's southernmost state of Chiapas until the current paper, where the main aim is to describe and date five new Late Pleistocene fossil rich sequences and to interpret their paleoenvironmental record and changes that they indicate. This interpretation is based on the sedimentology, pollen record and stable isotopes from vertebrate fossils together with the radiocarbon dating of the fluvial sediments. At Los Mangos and El Bajión fossil sites the fluvial sediment record reported here includes a conspicuous layer with aerodynamic Fe magnetic microspherules associated with the Younger Dryas (YD) meteorite impact which adds to the type of paleoenvironments in which such meteorite impacts have been recognised. The sediment dating indicates that the fossiliferous sites are Late Pleistocene in age, and they add new locations and information for México for this climatic phase. • We present a revisión, dating and interpretation of the Late Pleistocene megafauna from Chiapas State, southern Mexico. • Five fossiliferous fluvial sequences showed important changes in the river direction and energy during the Late Pleistocene. • Late Pleistocene paleoenvironment was mainly of savanna with sporadic trees. • First record of the Younger Dryas Meteorite layer preserved in fluvial sediments in Central America. • The megafauna assemblages are of Rancholabrean age. [ABSTRACT FROM AUTHOR]