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Zastosowanie geostatystyki i GIS do analizy wpływu czynników naturalnych i antropogenicznych na koncentrację metali ciężkich w glebach rejonu olkuskiego

Namysłowska-Wilczyńska B., Rusak K.

Roczniki Geomatyki

2005

T. 3, z. 2

115-124

The distribution and concentration of metals in soils depends on many natural and anthropogenic factors such as: the percentages of clayey, dusty and sandy fractions, the soil's pH, the lithology of surface formations, the wind directions, the kind of flora, the distance from pollution sources and the type of building and land development. The subject of the investigations was the Olkusz region where Zn and Pb ore deposits occur and are mined. The soils in the area show one of the greatest Cd-Pb-Zn anomalies in Poland, associated with ore-bearing dolomite outcrops and the historical and contemporary mining, processing and smelting of Zn and Pb ores. As part of this research an analysis of the factors affecting the distribution of heavy metals in the Olkusz industrialized area was carried out using GIS and geostatistics. The combination of these tools allowed more accurate estimation of soil Cd and Zn content averages Z and the computation of an estimation accuracy measure, i.e. standard deviation sk for averages Z. First numerical surface maps were constructed using GIS spatial analysis and the MicroStation GeoGraphics software. Topographical and geological maps at a scale of 1:50 000 were vectorized to create various thematic overlays such as: land development, building development, transport, waters and geologic structure elements. The object-oriented structure of the map elements was taken into account in the vectorization. Then geostatistical studies based on the results of geochemical analyses of soil samples taken in a regular (1 km 1 km) grid from a depth of 0.0.0.2 m within a study area of 171 km2 in the years: 2000 (50 samples) and 2001 (70 samples) were carried out. The studied area was covered by a grid of 250 100 m elementary blocks. The total number of block centres for which estimated averages Z were calculated was 7696. Prior to the geostatistical analysis basic statistical parameters were calculated. Then the empirical isotropic semivariograms were computed. The linear model combined with the nugget effect, was used to approximate the heavy metals (Zn and Cd) content semivariograms. In the last stage of the structural analysis, the cross-validation procedure was applied. For the studied sampling subpopulation (N = 120) the values of the standardized estimation error . a measure of model fit show that the adopted mathematical model represents well the empirical Cd and Zn content semivariograms. Then ordinary (block) kriging was used to estimate the averages Z of the Cd and Zn. The analyses have shown that the presence of the ore-bearing dolomites in the substratum has no significant effect on the spatial distribution of estimated Cd and Zn content averages Z. The existing high Cd and Zn concentration centre is associated with the activity of the Boles3aw Mining-Smelting Works operating in this area for several decades and with the smelting wastes accumulated in the nearby dumps and sedimentation tanks. The geostatistical studies have corroborated the geochemical Zn and Cd anomaly which is unrelated to the shape or surface extent of the current mining areas in the Olkusz region, where mining is carried on underground. The elevated Cd and Zn content subareas show similar spatial distributions of the two metals and coincide to a large extent with the location of the historical and contemporary Zn-Pb ore mining.