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BackgroundMayas living in southeast Mexico have used soils for millennia and provide thus a good example for understanding soil-culture relationships and for exploring the ways indigenous people name and classify the soils of their territory. This paper shows an attempt to organize the Maya soil knowledge into a soil classification scheme and compares the latter with the World Reference Base for Soil Resources (WRB).MethodsSeveral participative soil surveys were carried out in the period 2000-2009 with the help of bilingual Maya-Spanish-speaking farmers. A multilingual soil database was built with 315 soil profile descriptions.ResultsOn the basis of the diagnostic soil properties and the soil nomenclature used by Maya farmers, a soil classification scheme with a hierarchic, dichotomous and open structure was constructed, organized in groups and qualifiers in a fashion similar to that of the WRB system. Maya soil properties were used at the same categorical levels as similar diagnostic properties are used in the WRB system.ConclusionsThe Maya soil classification (MSC) is a natural system based on key properties, such as relief position, rock types, size and quantity of stones, color of topsoil and subsoil, depth, water dynamics, and plant-supporting processes. The MSC addresses the soil properties of surficial and subsurficial horizons, and uses plant communities as qualifier in some cases. The MSC is more accurate than the WRB for classifying Leptosols.

The abundance of karst depressions in Yucatán has been widely recognized, but they have not been classified or quantified despite their importance in land-use planning. Our objective was to study the types and areas of the sinkholes, uvalas, and poljes and identify their patterns of spatial distribution. We used 58 topographic maps (1:50,000) from INEGI, from which we extracted the depressions and bodies of water. For typology, we used a circularity index and the shape and area of the depressions. For single-density analysis, we extracted the centroids and added an inventory of karst features (cenotes, caves). We counted 6717 depressions with a total area of 454 km 2 and 750 karst features. We identified 4620 dolines (34 km 2 ), mainly in plateaus below 30 masl. In number, they are followed by uvalas (2021) and poljes (76), occupying together a similar area (210 km 2 ) and dominating in elevations higher than 30 masl. Eighty percent of the dolines were automatically labeled. The density of depressions allowed us to identify the "ring of cenotes" and the "field of dolines" according to two main types of factors, structural and climatic. The typology and density of the depressions could be used as geomorphological differentiation criteria in the vast plateaus of central and eastern parts of the state.

In large industrialized cities, tons of particles containing heavy metals are released into the environment and accumulate on street surfaces. Such particles cause a potential risk to human health due to their composition and size. The heavy metal contamination levels, main emission sources, and human health risks were identified in 482 samples of street dust. Heavy metal concentrations were obtained by microwave-assisted acid digestion and ICP-OES. The results indicated that street dust in Mexico City is contaminated mainly with Pb, Zn, and Cu, according to the contamination factor and the geoaccumulation index. The pollution load index of the street dust was made with the concentrations of Pb, Zn, Cu, Cr, and Ni. The main sources of Pb, Zn, Cu, and Cr are anthropic, probably due to vehicular traffic. The highest levels of Cr and Pb in urban dust represent a health risk for children. Contamination limits were proposed for heavy metals in street dust of Mexico City. These limits might be useful to generate and apply public policies to decrease anthropic emissions of the heavy metals studied, particularly Cr and Pb.