بررسي اثر عوامل فيزيكي ، شيميايي و آب و هوايي در توليد رسوب ناشي از فرسايش سطحي خاك هاي لسي (مطالعه موردي در استان گلستان )

The study of the effect of physical, chemical, and climate factors on surface erosion sediment yield of loess soils (Case study in Golestan province).

Loess is one of the most important quaternary sediments units. About 3000 Kmʹ of Golestan province is covered by loess deposits. Due to physical and chemical characteristics, these sediments are sensitive to erosion and sediment yield. The loess sediments of different regions show different erosional features : Gully and tunnel erosions are widespread in arid and semi-arid regions, but they are less abundant in temperate and semi-humid areas. Chemical, physical, topographical and climatic factors play important role in erodibility and sediment production of these deposits.In order to study these relationships, the maps of loess distribution and climate were prepared using satellite images (TM) and other available data with the help of Ilwis software in GIS (Geographic Information System). By combining two mentioned maps and other observations,five localities with seven replications were chosen for the investigations. 35 soil samples were taken for the analyses.Texture amount of organic matter, calcium carbonate, electrical conductivity and acidity of the soil samples were determined in the laboratory.For the measurement of sediment yield quantitatively, a small rainfall simulater was used in the field and runoff and sediment were collected. The effect of independent variables including physical (percentage of clay,silt and sand),chemical ( pH, Ec, the amount of calcium carbonate and organic matter), topographical (elevation) and climatic parameters (De-Marston aridity index) on sediment yield of loess deposits and soils was studied by stepwise regression analyses. The amount of organic matter and De-Manton aridity index show very high correlation with the amount of sediments. Accordingly, loess deposits were classified into ones having low,medium and high sediment yield. The loess deposits of humid and subhumid regions have low sediment yield and ones from arid and semi-arid regions have high sediment yield, others have medium sediment yield.