Search

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.

The benefits provided by tropical rainforests are unevenly distributed throughout the landscape and are shaped by abiotic and biotic components that influence the spatial distribution and functional traits of the species involved. We tested whether environmental stratification of the rainforest in biophysical Landscape Units (LU), defined by topography and soil, is related to the spatial distribution of diversity, abundance and productivity (standing biomass) of tree assemblages that provide potential forest products (PFP). Considering that different PFP are associated with specific plant traits, we also tested whether a phylogenetic signal exists among the species that comprise specific use categories. Non-metric multidimensional scaling ordinations and permutational analysis of variance were based on the frequency, abundance and productivity of 129 species, the PFP of which were classified as fodder, food, fuelwood, medicinal, melliferous, ornamental, plywood and timber in 15 plots of 0.5 ha each. We constructed a phylogenetic tree of the studied species and analyzed the phylogenetic signal strength (D-statistic) among them. The spatial distribution of diversity and abundance of useful species changes among the LU. Specific PFP can be provided in contrasting habitat conditions, but generally not by the same species. The PFP categories that presented a phylogenetic signal were associated with wood characteristics (fuelwood and plywood) and the palatability of the leaves and reproductive structures (fodder). The Moraceae family was significantly related to fodder and plywood, whereas Meliaceae, Myrtaceae and Sapotaceae were mostly used for fuelwood. The medicinal species presented convergent traits distributed throughout the phylogeny. However, since our study included a broad variety of plant structures, it is possible that phylogenetic dispersion can change if we consider the specific uses within each category. Our findings show that the assemblages of PFP suppliers can be clustered through biophysical units based on soil and topography, and specific categories of PFP are often supplied by phylogenetically related species. This knowledge is fundamental in order to incorporate the high diversity of tree species and their potential uses into productive reforestation and agroforestry programs.

Maps of natural hazards are essential for the prevention or mitigation of disasters. The Nexpa River mountainous basin is in the Sierra-Costa region of the state of Michoacán, Mexico. The dispersed rural settlements in the basin, accessed through a network of mainly minor roads and tracks, are highly vulnerable in cases of catastrophic hydrometeorological events. Our study aimed to map flood zones and assess flood susceptibility in the basin on the basis of geopedology, topography, land cover and land use, to assess the vulnerability of local rural settlements and their network of roads and tracks. The land morphology was mapped and the weighted overlay technique was applied in a geographic information system to generate maps of susceptibility to flooding. Our results showed that 13% of settlements and 7% of the communication network are within flood zones. Maps based on environmental factors showed low to medium susceptibility to flooding. These methods are useful and effective for zones with little or no hydrometeorological information, and they can provide a robust source of information for decision makers regarding land planning to mitigate flood vulnerability.

This paper addresses the timing of accelerated soil erosion and landscape degradation in central Mexico. It shows data on erosion sequences in the Valley of Teotihuacan, an area where agricultural dates back to at least since 1100 BCE, and an ideal setting to test ideas on the effect of preconquest versus post-conquest anthropogenic impacts on the environment. The methods include stratigraphy, detailed description of soil profiles and soil micromorphology, along with analysis of pottery sherds and radiocarbon dating. A chronology of events for two catenas, focusing on periods of landscape stability and change, establish the sequence of erosion events from pre-Hispanic to modern times. Six erosion phases are recognized over the last 2000 years in Teotihuacan. Although results suggest that the most intense erosion occurred after Spanish conquest, in the 16th century, several erosion phases took place during pre-Hispanic times and also in the postcolonial period, including the 20th century. Probable causes for these impacts are related to settlement dynamics, population variability, and land use changes. Thus, it provides new information for the discussion on the timing and causes of erosion, sedimentation and landscape modification in the central Mexican Highlands during the late Holocene.

Anthropogenic changes during the past 2000 years in the Teotihuacan Valley imply that intensity of soil degradation varies depending on the land management practices and the intensity of soil use. As a part of a broader effort to reconstruct erosion dynamics in the Teotihuacan Valley through geoarchaeological approaches, our study applies a process-based watershed hydrology and upland erosion model, the Water Erosion Prediction Project (WEPP). The Geo-spatial interface for WEPP (GeoWEPP) was used to characterize locations of soil detachment and sediment deposition predicted in the watershed through time, based on current and reconstructed conditions in the valley. Climate, topography, soil and land use were used as inputs to WEPP to estimate surface runoff and soil loss rates for periods with different environmental and anthropogenic conditions: the Teotihuacan period (1–650 CE), the Aztec period (1325–1521 CE) and for modern times (after 1970 CE). Over a simulated and established timeframe for those periods, surface runoff and rate of soil loss were estimated to be higher during the Aztec period, when the area devoted to agriculture dominated the landscape. Land use change had a major impact on soil erosion. Comparison of the pre-Hispanic periods with current conditions shows that WEPP is useful in showing the roles of management and climate in environmental degradation. The results contribute to the scientific debate about the antiquity and causes of erosion in central Mexico. The research shows that land use is one of the foremost factors affecting soil erosion, both in ancient and modern periods, with particular impact during the Aztec period.

This article presents the results of a research on paleosols formation conditions in the Aguascalientes Valley, northern Mesoamerica, where paleoenvironmental reconstructions have been scarce. Records of environmental and climatic changes, as well as the alteration of the landscape are expressed in the memory of the soil. Soil micromorphology is the most efficient method to identify these changes. In paleosols, micromorphological features reflecting a certain soil forming process can be related to environments in which those processes took place. Paleoenvironmental reconstruction of the region consisted in identifying pedofeatures and other present soil attributes, grouping features into pedogenic facies under constant environmental conditions, examining the groundmass in order to detect features caused by erosion or sedimentation, and finally establishing a hierarchy between the different pedogenic facies, including erosional and sedimentary features if necessary. Specific statistical data analysis disclosed stratigraphical relationships. The results we obtained, such as illuvial clay coatings, redoximorphic nodules, and hypocoatings, revealed the most representative pedofeatures that developed under humid climate. Under a semiarid climate, representative pedofeatures that were revealed included micritic coatings and hypocoatings. A paleosol with ferruginous nodules and hypocoatings in groundmass, and at least one phase of dusty and high-birefringence yellow clay illuviation is proposed as stratigraphic marker for this area of the Aguascalientes Valley. Evidence indicates the sequence of events in the area was: (i) a large period of humid climate; (ii) a short period of climate change, from humid to semiarid, followed by subhumid; and (iii) a large period of semiarid climate, including the current one. The paleosols of the Aguascalientes Valley to a large extent preserve major trends in history and provide further evidence to define the 11 phases of stability (pedogenesis) in 8 cycles and to detect the interlayer phases of instability (sediment transport/deposition).

The paper provides new evidence on the pedogeomorphic history of the Valley of Teotihuacán, Mexico. The soil landscape here consists of Luvisol and "black soil", the micromorphology of which allowed us to (a) distinguish between in situ and inherited processes and (b) establish spatial relationships of erosion and sedimentation along a toposequence of three soil profiles. Soil profiles sites were selected by photointerpretation followed by verification on a toposequence from middle mountain slope to colluvial piedmont. Samples of these profiles were characterized by physical and chemical analyses, including micromorphological observation under a petrographic microscope. The results are summarized as geomorphic observations, description and analysis of soil profiles along a catena, and micromorphological features. The final data set permits recognition and interpretation of both present-day pedofeatures and inherited pedofeatures due to past hillslope processes. In the “black soil”, the key processes include development of vertic features, humification and CaCO3 accumulation; while micromorphology revealed fragments of illuvial clay along with disorthic ferruginous nodules. In the Luvisol, clay illuviation dominates and is associated with redoximorphic features. Strongly weathered pumice fragments and less weathered mineral and rock fragments were observed in the vertic horizons. Because the pedofeatures of the “black soil” strongly differ from those of the Luvisol, we can readily identify the cases where Luvisol materials were inherited by the “black soil”. Thus, the micromorphological observations allow us to propose that the “black soil” was likely to incorporate Luvisol materials that were earlier colluviated. The presumed erosional phase may correspond with climatic aridization.