Spatial distribution of soil heavy metals in different land uses of an industrial area of Tehran (Iran)

Vegetation and different land uses may affect the spatial distribution of heavy metals in soils. The objective of the current article was to study the impact of industrial activities and land use type on the distribution of heavy metals in soils of Chitgar Forrest Park, located in industrial zone in the west of Tehran City. The soil samples were taken from 116 sites in a regular sampling grid (250 x 250 m) at a depth of 0-20 cm, including three different land uses, needle leaf forests, broadleaf forests and rangeland. Nitric acid-extractable form of seven metals, Cu, Cd, Fe, Mn, Ni, Pb and Zn, and DTPA-extractable form of Cu, Fe, Mn and Zn were measured. Soil texture, pH, organic carbon, carbon-to-nitrogen ratio, percentage of calcium carbonate and electrical conductivity (EC) were also determined. According to the maps and background amounts, heavy metals were affected by industrial activities and road traffic. Proximity to heavy traffic highway of Tehran-Karaj and large autoindustry plants can be considered for increasing metal concentrations. Results of statistical methods (coefficient variation and cluster analysis), besides geostatistical analysis (variogram and map), showed that total concentrations of heavy metals are controlled by intrinsic and extrinsic factors in the studied area. Although land use type did not affect the alteration in the distribution of total concentrations of heavy metals, it changed the distribution of DTPA form of heavy metals in the soils through affecting the soil organic matter.