Influence of soil physical and mineralogical properties on erosion variations in Marlylands of Southern Guilan Province, Iran.

Abstract

Marls are the most talented geological formation of erosion and produce large amount of sediments that annihilate fertile soil and deduct the capacity of dams. Erosion in marls depends on external factors such as distribution of rainfall and internal factors which include soil physical and mineralogical properties. Therefore, the objective of this research was to determine the changes of physical and mineralogical properties of marls because of erosion variations in arid regions of Guilan Province (Gilevan region) of Northern Iran. The concerned soil physical properties of Marlylands were percentage of saturation, surface gravels, sands, silts, clays, fine sands, fine clays, and the level of bulk density, mean weight diameter (MWD) of soil aggregates (dry sieve), liquid limit, plastic limit, activity and ratio of fine clay to total clay. In addition, four samples from Marly soils and one sample from parent material were prepared for X-ray diffraction analysis. Comparing the average of physical factors with different type of erosion by means of Duncan multiple range test showed that the percentage of clays, fine clays, saturation, and the level of MWD, liquid limit and activity showed significant changes (p < 0.05) in some types of erosion, whereas other measured parameters had no significant effect on the form and type of erosion. Furthermore, results of X-ray diffraction showed the presence of smectitic group, double-layer clay minerals that are dispersive (2:1 clays), in badland and gully areas, while these types of clay minerals were not found in areas with rill and sheet erosion. Hence, with respect to the results of this research, it can be concluded that mineralogical properties as well as some soil physical characteristics are the main factors controlling the shape and form of erosion in Marlylands of Northern Iran.   Key words: Clay minerals, erosion types, Guilan province, physical factors.