Document Type : Research Paper
Authors
1 Assistant Professor, Soil Protection and Watershed Management Department, Fars Agricultural and Natural Resources Research and Education Center
2 Assistant Professor, Desert Research Division, Research Institute of Forests and Rangelands, Agricultural Research Education and Extension Organization (AREEO), Tehran, Iran
Abstract
Abstract
Background and objective
The phenomenon of dust storms results from a combination of natural and human-induced factors and has serious impacts on health, agriculture, transportation, and water resources. Strong winds can detach fine particles from dry soils, leading to the formation of dust storms that transport these particles over long distances. Consequently, dust storms have become a local, regional, and global challenge. In southwestern Iran, the average number of dusty days over the past 50 years has ranged between 27 and 75 days per year. Due to its geographical and climatic conditions, Fars Province is affected by both internal and external dust sources. Land-use changes, consecutive droughts, and geological characteristics are among the key factors contributing to the expansion of this phenomenon. Considering the geological conditions of Fars Province, the presence of abandoned agricultural lands, the drying of wetlands, and land-use changes, the dust phenomenon holds particular significance. The objective of this study is to examine the distribution and introduce the physicochemical properties of surface soils in dust-producing areas through the analysis of land-use documents, meteorological and geological data, remote sensing, field visits, and laboratory investigations. Additionally, this research aims to provide a foundation for further studies and desertification control projects.
Materials and methods
In this study, dust source areas were identified and classified using maps of desert regions, geology, land use, and vegetation cover within a GIS environment. Sampling points were then determined using a 2×2 km grid method over these source areas. Two soil samples were collected from each point: a 2-kg sample from the 0 to 30 cm depth for physicochemical tests and a 20-kg sample for wind erosion testing. The physicochemical tests included measuring pH, electrical conductivity (ECe), ionic compositions, cation exchange capacity (CEC), saturated moisture percentage (SP), gypsum content, and soil texture. Additionally, a wind tunnel test was conducted to evaluate wind erosion. Finally, to examine the relationship between soil properties of the source areas and wind erosion, the data obtained were analyzed using charts and tables.
Results
Five major dust source areas have been identified in Fars Province, including Bakhtegan-Neyriz, Maharloo-Sarvestan, Shahrpir-Zarindasht, Dezhgah-Farashband, and Khonj-Larestan. These dust hotspots are located in the central, eastern, and southern parts of the province and are primarily affected by rangeland degradation, drought, and wetland desiccation. Land-use analysis in these areas indicates that 65% of the land consists of degraded rangelands, 19% comprises dried wetlands, and 16% includes abandoned agricultural lands and rainfed farms. The threshold wind erosion speed in these hotspots ranges between 8 and 10 meters per second. Moreover, the correlation between erosion intensity and increasing wind speed in most of these areas is between 80% and 99%, highlighting their high sensitivity to atmospheric changes and rising wind speeds.
Wind tunnel experiments indicate that the highest wind erosion occurred in Dezhgah-Farashband, where at a wind speed of 25 meters per second, the erosion rate reached 15.76 kg per square meter per minute. The soil texture in these dust source areas mainly consists of loam, sandy loam, and loamy sand. The soil pH varies between 7.5 and 8.5, while electrical conductivity ranges from 0.41 to 157.7 dS/m. A correlation study between soil wind erosion and parameters such as salinity, acidity, sodium content, organic matter, and soil texture (sand, silt, clay) indicates a weak correlation between wind erosion and salinity, particularly in saline soils. However, in non-saline soils, a positive and significant correlation (66.7%) exists. Conversely, a positive and significant correlation is observed between wind erosion and sand content, while a negative correlation is found with silt and clay content.
Discussion
The study reveals that the wind erosion threshold velocity varies across different locations, primarily depending on the physical and chemical properties of the soil. In areas with coarser soil textures, and relatively higher silt proportions (e.g., the Dezhgah-Farashband dust resources), a lower wind speed is required to initiate wind erosion and transport soil particles; thus, the threshold wind erosion velocity is lower. Conversely, in areas with higher clay content and lower silt content (e.g., parts of the Khonj - Larestan and the Shahrpir-Zarindasht dust resources), a higher wind speed is necessary to initiate wind erosion. The wind erosion threshold velocity across all study ranged from 7 to 10 meters per second. The Dejgah-Farashband dust resource exhibits the highest dust production due to its soil composition. Conversely, the Shahrpir-Zarindasht dust resource is more resistant to wind erosion due to its heavier soil texture. Furthermore, increased soil salinity reduces particle cohesion, potentially lowering the wind erosion threshold velocity. This study indicates that soil salinity, pH, and organic matter content can influence both the wind erosion threshold velocity and dust production.
Conclusion
The dust hotspots in Fars Province, including Neyriz-Bakhtegan, Maharloo-Sarvestan, Shahrpir-Zarindasht, Dezhgah-Farashband, and Khonj-Larestan, are influenced by a combination of environmental factors. The most significant of these include the drying of wetlands (particularly Bakhtegan, Abadeh Tashk, and Maharloo), extensive rangeland degradation, and unfavorable soil characteristics such as loamy texture, high salinity, and low organic carbon content. Although high wind speeds (with an erosion threshold of 8 to 10 m/s) play a crucial role in erosion within these areas, the extent of windborne sediment transport and dust production is significantly influenced by soil texture and the percentage of clay and silt. For instance, the Shahrpir-Zarindasht hotspot exhibits lower erosion due to its fine-grained soil texture. Therefore, a comprehensive and targeted management approach, focusing on wetland restoration, vegetation improvement, and soil rehabilitation, is essential to mitigate the adverse impacts of dust storms.
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