چكيده لاتين :
1. Introduction Heavy metals in the soil are an important indicator of global environmental contamination and constitute an important part of the pollutants, which due to toxic and aggregate properties, even at low concentrations, have high environmental significance. Therefore, the distribution of their contamination is highly noticeable. Population growth, urban expansion, industrial development and distribution without management in agricultural inputs are among the most important factors in increasing the concentration of heavy metals. To improve the management recommendations for controlling and eliminating these pollutants, it is necessary to determine the spatial pattern of pollutants. In practice, the precise separation of ground contaminated with heavy elements is difficult due to the complexity of the pattern of spatial variations, the severe changes, and the presence of local contaminants. But there are several studies for the interpolation and determination of spatial distribution of heavy metals concentration in the soil. The analysis of the spatial distribution of heavy metals in soils is of fundamental importance in a vast number of applications, including general soil surveying and characterization, delineation of potentially polluted spots at unsampled sites, or planning remediation strategies. The relevance of heavy metal soil pollution has favoured the application of advanced geostatistical techniques such as kriging in their different varieties. Kriging techniques have also been widely applied in other earth sciences applications such as mapping of precipitation, air temperature or solar radiation at different temporal and spatial scales. Vanadium is a trace element, which is widely distributed in nature. The average abundance of vanadium in the crust is approximately 0.01% Vanadium in the environment comes from :( 1) weathering of parental rocks; (2) combustion of fossil fuels; (3) mining and high-temperature industrial activities including steel-iron refining, electronics and dyeing, etc. While in the soil, vanadium is derived from parental rocks and deposits Human activities, such as the disposal of vanadium-contained waste and oil leakage, may also provide a certain amount of vanadium to the soil. Consequently, there are few countries, where standards and regulations for environmental pollution in soil with vanadium are accepted, for example, Russia, where the maximum of 150 g g−1 allowed in agricultural soil Because of industrial activities and anthropogenic emissions, the concentrations of vanadium in soil have increased significantly in recent years, and the number of people affected by vanadium pollution is also increased. The purpose of this paper were to: (i) estimate the upper baseline concentration of As in topsoils of Isfahan Province (central Iran); (ii) evaluate factors controlling the spatial distribution of soil V concentrations and (iii) delineate polluted from unpolluted areas using geostatistic methods. 2. Materials & Methods This research was conducted in Isfahan province, central Iran. Isfahan has an arid climate and is about 6800 km2 around Zayandehroud River. Mean annual precipitation and temperature are 120 mm and 14.5 oC, respectively and direction of dominant wind in study area is NW-SE (Fig 2b). the area extends from easting of 51o15' to 52o41' longitude and northing of 32o7' to 32o59' latitude. The area covers different land uses including agricultural, industrial, urban and uncultivated lands. There are several big steel factories in the study area. The underlying geology consists mainly of recent terraces, resent alluvial deposit and undifferentiated terraces, all of quaternary age. In addition, lower Cretaceous grey limestone containing Orbitalin and Jurassic shale are found in the south west and south of region. In this study, soil sampling strategy was random stratify. A total of 207 soil samples (0-20 cm) were collected. At each sampling point the coordinates were obtained using a portable GPS and its land use was recorded the distances. Soil samples were air dried and ground to pass through a 2 mm sieve. Total V concentration in the soil was determined by XRF. Statistics including mean, variance, maximum, minimum, coefficient of variation (CV) were calculated using SPSS 11.0 for Windows. Based on the land use information, data sets were grouped into three subsets: industrial and urban, agricultural and uncultivated lands. After calculation, 46.5% of the sampling locations occurred in agricultural lands, 43.5% in uncultivated lands and 10% in industrial and urban areas. The ANOVA was then used to compare the effect of land use The spatial variability analysis is a necessary step prior to applying kriging techniques In this work several theoretical variogram functions including linear, exponential and spherical forms considering nugget effects were evaluated using the VARIOWIN and WINGSLIB software. With the sets of fitted variogram functions, the next step is cross validation of the prediction models with MSE. Distribution maps of V was produced using the ordinary kriging procedure and mapped. Correlation coefficient (Pearson) computed between real and estimated data with ordinary kriging that this parameter is identifier of relatively high accuracy estimation in maps. Maps were produce with Surfer (version 10) and ILWIS (version 3.3). 3. Discussion & Results The average V concentration was 82.9 mg/kg with range of 19.2-140.1 mg/kg in Isfahan surface soils. Total V concentration was scanned for trend determination and no trend was apparent. Therefore, V concentration roughly followed a normal distribution indicating that the data is from a single statistical population. Total V concentrations in different land uses were compared using one-way ANOVA. Total V concentrations were significantly affected by land use and Total V concentrations in agricultural lands also industrial and urban areas are higher significantly. Directional variograms for V concentration computed along twelve directions of azimuth 30 degree with tolerance ± 15 degree. The best variograms fitted in directions of 90 degree and a spherical theoretical covariance model suitable for spatial fields was fitted. Present of spatial dependence (sill/ C0) indicate that distribution of V have Intermediate spatial dependence class. Distribution maps of V indicate high concentration of V in parts of east Isfahan province and industrial and mining activity are important factor to concentration of vanadium in this regions and direction of dominant wind which has affected spread of V in east of the study area. Pearson coefficient in V concentration was rather high and this parameter is identifier of relatively high accuracy estimation in maps. 4. Conclusion The overall distribution of heavy metals in surface soil can be due to local changes in rock, land use, and climatic processes. The average V concentration is 82.9 mg/kg in Isfahan surface soils and this is not higher than global average concentration. Land use did have significant effect on V concentration. Agricultural and industrial activities are probably effective factors causing increase the V concentration in the region. Vanadium is one of the impurities of earth crust deposits. Considering the wide expansion of industries such as Isfahan Iron Ore in the Lenjan and Mobarakeh Steel Area in Mobarakeh, and also the significant difference in the average concentration of vanadium in urban land-industrial areas with incult land, the role of industrial activities in these areas can be increased in extend of vanadium. Direction of dominant wind have affected in spread of Vanadium in the high concentration spot in study area.
