Assessing the effect of land use and geomorphology on spatial variability of heavy metals and magnetic susceptibility (Case study: Kurdistan province)

The parent material and geology have a significant contribution to heavy metal contents and magnetic susceptibility in soils. Magnetic susceptibility is known as the extent of a material’s impact on the magnetic field, which depends on the concentration and the type of magnetic minerals in the soil. Magnetic susceptibility measurement is fast, easy, economically convenient, and non-destructive. Mass magnetic susceptibility and frequency-dependent magnetic susceptibility are among the conventionally used parameters. The type of land use is among the main factors influencing magnetic susceptibility distribution in soil. Besides, soil magnetic susceptibility is affected by slope position and different soil properties such as soil organic matter and carbonates. A variety of relationships have been observed between heavy metal concentrations and magnetic susceptibility across various types of soil, parent material and climatic regimes. Generally, magnetic properties have positively correlated with the type and concentration of magnetic minerals as well as the particle size of soil fractions. Besides, magnetic susceptibility has a weak negative correlation with diamagnetic components such as quartz, gypsum, calcite, and organic materials. The main objectives of this study were to i) determine the relationships between magnetic susceptibility (MS) and concentration of some heavy metals such as copper, iron, zinc, and manganese in the surface soils and ii) explore the impacts of land use and geomorphological units on the variability of heavy metals and MS in a semi-arid region in the west of Iran.

The present study was conducted in Kurdistan province located in western Iran, the area is about 110,000 ha and mean altitude of 2277m above sea level. The area has an average annual temperature of 10.20 °C and an average annual rainfall of 369.8 mm, which dominantly occurs in spring and winter. Besides, the area has soil moisture and temperature regimes of Xeric and Mesic, respectively. The lithological setting of the studied area includes reddish of sandy marls and marl sandstone, river deposits, alluvium-cultivated land, and granite. The studied area was divided into different parts in terms of geomorphology and land use. Soil sampling was done using the stratified random sampling approach. A total of 347 samples were collected from the surface layers (0-30 cm depth) of the studied area. Magnetic susceptibility at both high and low frequencies was measured using a Bartington MS2 dual-frequency sensor. The amounts of all the selected heavy metals including iron, zinc, manganese, copper, and nickel were measured using atomic absorption spectrophotometer. Soil particle sizes, acidity, SOC, CCE and electrical conductivity were measured in all soil samples. The concentration factor and Tomlinson’s Pollution Load Index were calculated. The Spearman correlation coefficient was used to examine the correlation between different parameters. The analysis of variance was used to evaluate the effects of geomorphology and land use on heavy metals and magnetic susceptibility. Spatial analysis was done conducted for some variables (Fe, Mn, Zn, Ni, Cu, and χlf) and the map of variables were created in ArcGIS v.13 software.

The results showed that the positive significant correlations were observed between heavy metals and silt content and negative significant correlations were observed between heavy metals and sand content. Fine soil fraction compared with coarse fraction has the higher specific surfaces and more susceptible to attract heavy metals. Moreover, positive and significant correlations were obtained between the SOC and heavy metals across various land use types and geomorphic units. Organic matters have a high cation exchange capacity, therefore they adsorb heavy metals and hold them on their surfaces. pH and CCE showed negative and significant correlations with heavy metals and magnetic susceptibility. The positive correlation between heavy metals and magnetic susceptibility in agricultural land, piedmont, and river plains units observed. Also, PLI and CF have a positive correlation with magnetic susceptibility. The t-test showed that a significant difference between agricultural lands and non-agricultural land types and ANOVA results in various geomorphic units of the study area indicated that the magnetic susceptibility between piedmont and mountainous areas were significantly different.

Results indicated a significant correlation between magnetic susceptibility and heavy metals. Besides, the magnetic properties of the soil are influenced by its physical and chemical properties that have large impacts on reducing or improving its magnetic field. Significant differences were observed between agricultural lands and non-agricultural lands as well as mountainous and piedmont areas that had different parent materials. These results indicate the great impact of parent materials constituting the soil on the absence or presence of diamagnetism in the region.