Surveying of soil factors effects on total form and DTPA-extractable form of heavy metals in three land-Use types

Today one of the important environmental issues is soil pollution with heavy metal. Pollutants entering to soil causes the gradual elimination of beneficial organisms from this habitat, therefore Biodiversity is the original condition for dynamics, self-regulation, balance and stability of soil ecosystems, is destroyed. Total metal concentrations in the environment do not necessarily reflect its degree of toxicity or bioavailability because the bioavailability greatly depends on various environmental conditions. On the other hand, Land use impacts on many physical and chemical properties of soils. Recognition effective processes on bioavailability of metals help in modeling and understanding the environmental effects of these elements in the soil. In order to investigate the influence of soil factors on the total form and mobility and bioavailability heavy metals in different land-use, 116 samples were taken from surface soil in three land use Including Needle leaf forest, broadleaf and Rangeland in Chitgar Forest Park located in the West of Tehran city. Mean annual precipitation based on 14 years statistics of Chitgar meteorological synoptic station from 1996 to 2010 were 267 mm and annual temperature was 17.2 degree centigrade. In the laboratory amount of calcium carbonate, pH, electrical conductivity, percent organic carbon, iron, copper, zinc and manganese in two form DTPA-extractable and total form was measured. Then, using stepwise regression methods most influential factors determined in each land use and were compared with each other. According to Mean comparison, the maximum amount of carbon was in the broad-leaves forests with average 2.7 that showed significant difference with Needle leaves forest with average 1.6 and pasture with average 0.8. Soil organic Carbon had a strong positive correlation with DTPA extractable Zn(R= 0.762). This correlation was variable between the land use types. Also, the amount of carbon showed a significant positive correlation with Fe and Mn DTPA form. One way variance analysis of calcium carbonate (CaCO3) had significant difference in all studied land uses (P<0.05). On the other hand a significant negative correlation (p<0.01) Was observed Between CaCO3 and total amount of Cu (R=-0.469), Mn(R=-0.441) and Fe (R=-0.641) in the entire study area.  Results showed that soil factors play an important role in the bioavailability of heavy metals in the soil. These factors are affected by parent material, and sometimes land-use and management types and Cause different effects on the bioavailability of metals in the soil. This study contributes to the understanding of factors that affect the bioavailability of metals and also help to Model and predict available form of metal with regard to soil physical and chemical properties under different land use.‎