Thursday, 13 July 2006 - 2:25 PM
74-4

Trace Element Distribution in the Soils of Peshawar-Pakistan Using GIS.

Samina Siddiqui, Univ of Peshawar-Pakistan, National Centre of Excellence in Geology, Peshawar, Pakistan

Low metals concentrations in the soils are more likely because of natural source whereas their elevated contents were concurrence because of anthropogenic sources.  Beside these sources, their accumulation and leaching in soil pedons were controlled through soil pedogenic processes and soils physical & chemical characteristics.  Keeping in view the significance of these processes and factors on metals in the soils, it is necessary to evaluate the fate and effect of these sources in accordance with processes on metals distributions and mobility in soil pedons in order to develop best management practices.  The main objective of the study was to develop a database on total metals (Na, K, Fe, Cu, Zn, Mn, Pb, Ni) concentrations in Peshawar soil pedons according to U.S taxonomical classification.  Soil samples were collected from 22 soil pedons and were examined for soil pH (1:1 H2O methods), organic matter (L.O.I), texture (particle size distribution), metal (AAS) and mineral (XRD) contents.  Separation of metals into each horizon of soils pedon was determined with sequential extraction technique through AAS.  Significant differences in the metals contents in relation to depth and minerals contents in all of the soil pedons were explored.  Moreover, relationship between pedogenic processes (illuviation and eluviation) and metals transport in all of the soils pedons was established.  Correlation between metals and soil physiochemical characteristics was also developed.  The results of the study showed that all Peshawar soils pedons were calcareous and alkaline with low organic matter having clay loam, silt loam and sandy loam texture.  According to U.S taxonomical classification, 22 soil pedons of Peshawar were classified into Alfisols (1), Entisols (6), and Inceptisols (15).  Metals contents (Na, K, Cu, Ni, Zn, Mn, Pb, Fe) among three soil pedons were as Inceptisols ≤ Entisols<Alfisols and were in the range of about 6837.5-619375 μg/g, 9625-49875 μg/g, 1.65-39.75 μg/g, 15.21-73.47 μg/g, 15.78-153.42 μg/g, 347.5-925.5 μg/g, 3-20.4 μg/g and 30025-75762.5 μg/g, respectively.  Total metals were found not to be deficient or sufficient in any of the Peshawar soil pedons and remained within the U.S permissible limits.  The only odd soil pedons was Warsak soil (Inceptisols) in which Cu (1.65 μg/g) was found to be deficient in the upper horizon of one of the Inceptisols.  This is suggested by the observation that loss of Cu will be through agricultural runoff.  The presence of K and Na in the soils was because of the waterlogging and salinity.  Fe2O3 in all of the soil pedons was because of weathering of hematite, maghemite, and magnetite.  Similarly Pb, Mg and Ni in the Peshawar soils were concurrence because of weathering of galena, quartz, pyroxenes, olivine, amphibole and garnets.  There were significant differences (P<0.05) between metals contents and increase in depth of soil pedons.  Metals accumulation was high in Argillic and Cambic B horizon in all soil pedons and suggested by the observation that this could be due to sorption of metals with Mn or Fe oxides in the soils.  It was noted that among metals, Cu, Pb, Mn, Ni, Zn were bound to organic matter, Mn and Fe oxides and to CO3 when extracted with H2O2, NH2OH.HCl and NaOAc through sequential extraction of selected soil pedons (Entisols, Inceptisols and Alfisols).  No significant differences in the metals contents were noted among three of the soil pedons.  Clay eluviation was the main pedogenic processes noted in the B horizon of Alfisols.  XRD analysis showed that the dominant minerals in all of the soil pedons were quartz, calcite, mica, feldspar and kaolinite.  These minerals were also present in the sediments of Kabul river.  However, there were no positive relationship between minerals contents and distributions of metals in the soil pedons.  Similarly there were no significant differences between metals distributions in all of the soil pedons.  The data obtained were incorporated to develop point maps of Peshawar soils using geospatial tools (GIS, RS) in order to classify them into deficient and sufficient according to metals contents in Inceptisols, Entisols and Alfisols.      


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