The continental area of Portugal is now entirely covered by a soil geochemical survey (1 site/135 km2), taking as the sampling media topsoils (upper mineral horizons, A) and organic horizons (humus, O). Standard methods for sampling, sample preparation and analysis were used in order to achieve high quality and consistent data. Each sample was analyzed for 32 chemical elements, pH, electrical conductivity and organic matter content.
The main purpose of the survey was to obtain baseline levels for various chemical elements. The compilation of all data (nearly 45,000 individual data) in an organised way, led to the production of the first Soil Geochemical Atlas of Portugal. In this Atlas it is possible to find for each chemical element a set of information statistics (basic statistical parameters, boxplots, cumulative frequency curves, etc.), maps of spatial distribution, among other information of geochemical and environmental interest. This paper gives an overview of the Soil Atlas and examples of application. The data were used to calculate reference values for 9 elements of environmental importance and to obtain empirical formulae allowing the estimation of elements in the coarse fraction of soils (＜2.00 mm) from known concentration in a finer fraction (＜0.18 mm).
Keywords: Geochemical mapping; Soils; Geochemical atlas; Geochemical baselines; Portugal』
2. The study area
3.1. Sample collection and treatment
3.2. Analysis and analytical quality control
3.3. Statistical processing and mapping
4. Results and discussion
4.1. General interpretation
4.2. Evaluation of quality standards for soils
4.3. Comparative analysis of data based on different size fractions
4.3.1. Regression models