『Abstract
The Mexican Geological Survey (SGM), the National Institute of
Statistics, Geography and Informatics (INEGI) and the Autonomous
University of San Luis Potosi (UASLP) have established a multidisciplinary
team with the objective of creating a national program of geochemical
mapping of soils in Mexico. This is being done as part of the
North American Soil Geochemical Landscapes Project in partnership
with the US Geological Survey and the Geological Survey of Canada.
As the first step, a pilot study was conducted over a transect
that extends from the Mexico-US border near Ciudad Juarez in the
north to the Pacific Ocean in the south. This pilot transect was
conducted in two phases, and this paper presents results from
the first phase, which sampled soils at about a 40-km spacing
along a 730-km transect beginning in Central Mexico and ending
at the Pacific Coast. Samples were collected from the A and C
horizons at each site and 60 elements were analyzed. This pilot
study demonstrates that geochemical mapping based on a 40-km spacing
is adequate to identify broad-scale geochemical patterns. Geologic
influence (i.e., soil parent material) was the most important
factor influencing the distribution of elements along the transect,
followed by the influence of regional mineralization. The study
also showed that influence by human activities over the transect
is minimal except possibly in large mining districts. A comparison
of element abundance in the A horizon with the environmental soil
guidelines in Mexico showed that the natural concentrations of
the studied soils were lower than the established threshold for
soil restoration with the exception of V and As. The former had
a median value (75 mg/kg) approximately equal to the value established
in Mexico for soil restoration in agricultural and residential
lands (78 mg/kg), and the latter had three values higher than
the 22 mg/kg threshold for soil restoration in agricultural and
residential lands. These cases demonstrate the importance of knowing
the national- and regional-scale geochemistry of Mexican soils
as a support for the decision-making process, particularly for
the proper formulation and application of soil guidelines designed
to protect human and ecosystem health.』
1. Introduction
2. Description of the Mexican pilot transect (phase 1)
2.1. Geology
2.2. Soil types
2.3. Land use and resource activities
3. Methodology
3.1. Sampling
3.2. Sample preparation and chemical analysis
3.3. Quality control
3.4. Spatial analysis
4. Results
4.1. Statistics
4.2. Spatial representation
5. Discussion
6. Conclusions
Acknowledgements
References