جستجوی مقالات مرتبط با کلیدواژه "weathering indices" در نشریات گروه "آب و خاک"

Rivers are delivery vehicles of soluble compounds and sediments eroded from upper reach to wetlands and lakes. Therefore, evaluation of weathering intensity opens new insight into upland erosion, anthropogenic and geochemical process. Weathering indices CIA and WIP have been extensively used for the study of soil genesis. Nonetheless, little information available on the weathering indices in Iran 's soil and sediments. Therefore, this study was conducted on sediments of seven main rivers of Urmia Lake basin with objective of evaluation of two weathering indices and influence of particle size distribution on the weathering process. In this study 34 composite sediment samples have been taken from seven main western rivers of Urmia Lake basin including: Nazloo Chai, Shahar Chai, Barandooz Chai, Ghadar Chai, Mahabad Chai, Simineh Chai and Zola Chai. The physical and chemical properties of sediment were determined with routine soil testing methods. Elemental analyses of sediment samples were determined using an X-ray fluorescence (XRF) spectrometry. Major element oxides were measured by using a built-in program SUPERQ. Then the CIA and WIP indices were calculated. The analysis of data was carried out using correlation, principal component analysis (PCA) and cluster analysis. The major oxides in the studied sediments were silica, aluminum and calcium. The ratio of silica oxide (SiO2) to upper continental crust (UCC) for all the samples were less than 1 and varied between 0.57 and 0.84 indicating no dilution effect in the mineral transportation. Based on the major oxides component, the similarity among the different rivers was more than 65 and only in the Ghadar and Barandooz rivers the similarity is low because of the presence of MaO. The content of CaO had inverse significant correlation with SiO2, Al2O3, and Fe2O3 (with correlation coefficient between -0.62 to -0.67, P<0.001). The CIA and WIP values were varied between 50.1 to 82.6 and 42.4 to 66.2, respectively. Both indices had normal distribution, but WIP index had higher correlation coefficient with particle size distribution particularly D50 (r=-0.84, P<0.001). The CIA index showed lower significant correlation with D50 in comparison with WIP. High concentration CaO and MgO in the river sediments may be due to the presence of calcareous rocks such as limestone, dolomite, and calcareous shales in the watersheds. High SiO2 and Al2O3 concentration in river sediments may draw a conclusion that lower silica weathering and enrichment of potassium feldspar in river sediments. High loading value of in the river sediments may be due to the presence of calcareous rocks such as limestone, dolomite, and calcareous shales in the watersheds. Overall, the CIA and WIP weathering intensity values in upper and lower reach sediments revealed high difference. However, in some rivers such as Mahabad Chai because of construction of dam for more than half century the pattern of weathering intensity was different. Based on the A-CN-K curve. The studied river sediment indicate weathering trend in parallel with the A-CN line, indicating the elimination of silicate minerals of Ca and Na from parent material. Weathering indices in particular WIP had higher correlation coefficient with particle size distribution and D50 and we can conclude a proper index for evaluation of weathering intensity in the sediments.

This study was conducted to assess different chemical weathering indices and to evaluate the weathering rates of soils developed on volcanic (hornbelende andesite، pyroxene andesite and dacite) and plutonic (alkali granite، granodiorite، monzodiorite، syenite and pyroxene diorite) igneous rocks in the northwestern Iran. Representative soil profiles were described and soil samples were collected and analyzed for selected chemical and physical properties. Total concentrations of major elements and trace element (Zr، V، Ti and Y) were determined with ICP-OES and ICP-MS، respectively. Significant correlation coefficients were obtained between soil properties (clay percent، pedogenic iron and bulk density) and Ba، B/A، B/R، CIA، CIW، PIA، PWI and the WR chemical weathering indices. These indices are based on the ratio of a group of mobile oxides to one or more immobile oxides and are suitable for explaining the weathering rate of the soils developed on igneous rocks in this semiarid region. A-CN-K and MFW ternary plots showed that the soils developed on volcanic rocks (hornbelende andesite> pyroxene andesite> dacite) were more weathered than those on the plutonic parent rocks (alkali granite، granodiorite، monzodiorite، syenite، pyroxene diorite). Ba and CIA weathering indices predicted weathering trend such as MFW ternary plot، and it seems these two weathering indices are the most suitable weathering indices after W index (or MFW ternary plot) in this semiarid region. Ca، Na and K elements are presented in chemical weathering formulas of these two indices. These elements are in the feldspar minerals structures which are the most mineral in the earth crust.