Study of the 59 groundwater samples from Lenjanat area, central Iran, was carried out in order to assess their chemical compositions and suitability for drinking and agricultural purposes. Based on Gibbs' diagram, weathering of rocks and evaporation were found to be the dominant processes in the ion concentration of the water samples. The saturation index calculated through geochemical modeling indicates a suitable chemical environment for anhydrite, aragonite, calcite, dolomite, fluorite, and gypsum dissolution in both wet and dry seasons. All samples have the SO 4 2-? HCO 3 -more than 5 meq/l indicating that in addition to calcite and dolomite, dissolution of gypsum is the probable process in this plain. Assessment of the concentration of Mg 2? ? Ca 2? proportion to SO 4 2-? HCO 3 -demonstrates that the advanced direct and reverse ion exchange between groundwater and surrounding environment has occurred. The Chadha diagram indicates that the amount of earthalkali parameters is more than alkali ones and by considering the high value of strong acids, the dominant hydrochemical facies in both wet and dry seasons are Ca 2? -Mg 2? -Cl --SO 4 2-. According to pollution index, in the selected time domain, all samples are in safe conditions. Calculation of entropy weighted water quality index for groundwater samples demonstrates that in the wet and dry seasons, over 57 and 42 % of the samples are in the range of ''excellent'' to ''medium'' quality, respectively. The values of SI, RSC, SSP, SAR, KR, PI, MAR, and CI show that 90 and 85 % of the samples in wet and dry seasons have the good quality for agricultural purposes.

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Organic carbon is an important component of soil that influences soil fertility, biological activity, food security, and climate change. One of the important issues in soil science is the establishment of empirical relationships between different soil properties. The objectives of this research were to investigate the influence of different factors on soil organic carbon, such as total nitrogen, clay content, calcium carbonate equivalent and pH, for soils from various geomorphologic settings in the Damavand Region in Northwest Tehran, Iran. Regression models were developed for prediction of the organic carbon content of soils characteristics in this region. Lower SOC concentrations were measured for plateau soils (~4.92 g kg -1 ), associated with lower plant biomass and reduced temperatures at higher elevations. In contrast, soils from River Alluvial Plain regions, which are currently utilized for gardening, had the highest organic carbon content (~22.05 g kg -1 ). For all landform types (i.e., alluvial fan (irrigated farming lands), plateau (Rangeland), and River Alluvial Plain soils (garden)), SOC had positive and significant relationship with total nitrogen (r = 0.962, p < 0.01). Simple linear regression, multiple linear regression, and nonlinear regression models were also developed for describing the relationship between SOC and landforms physical and chemical characteristics.