Introduction
One of the most important sedimentary units in terms of environmental hazards, development, water management and erosion of Iran is marls, due to their physical and chemical properties, the ability to produce sediment and erosion, and their study and their separation is necessary. The nature of the grains, the size of the particle size, the elements and chemical composition of the marl, and the effect of these two issues are one of the important points about the degree of erosion. The physical and chemical properties of Marls have a significant impact on the development and spread of badlands.This study deals with the physicochemical characteristics of the marl units and their effect on various forms of erosion in Pishva-Varamin region. Although badlands are one of the known landforms in fine-grained soils in dry and semi-arid regions such as the studied area in Varamin, they are observed in different climatic conditions. Badlands typically have steep, high drainage densities; high erosion rates, unvegetated slopes, and a tendency to form dried cracks in regolith profile, making the surface puffy. In the formation of badlands, two factors of geology (land) and climate are decisive and important. Marls and loose geology, heavy rainfall and runoff, along with massive waste processes such as slipping, drift and land creep are the main factors determining how erosion landforms are formed, including badlands in slopes containing silt and clay.
Materials and Methods
In this research, after field observation and the selection of five marl units in the region based on various forms of erosion, in addition to sampling of sediments, a simulation of rain (using a rain simulator) was conducted in these five areas. In the laboratory, the runoff and sediment produced at each point were measured. Also, the electrical conductivity parameters, the amount of sodium, potassium, calcium, magnesium, gypsum, sediment content and absorbed sodium (SAR) of the samples in the laboratory were measured and analyzed by means of analysis of variance and analysis of the data in SPSS software. Due to the difference between the north and south slopes for erosion, a brief comparison was made between them.
Discussion and Results
In this research, particle size, chemical composition, mineralogy and soil geochemistry and runoff chemistry in both types eroded (south-facing) and non-eroded (north-facing) and their characteristics were determined. In the meantime, only a few grain-size parameters and silt and clay mineralogy discriminate eroded from non-eroded slope substrates. The phenomenon of erosion is more likely to occur where silt deposits are abundant in soils. This may be due to the reduction of soil permeability in these lands, because soil resistance to weathering and its permeability is another important factor in soil erosion. Pedogenetic processes on slopes with less erosion are affected by the type of clay minerals and have a direct relationship with the increase of layer minerals and other minerals. Therefore, geochemical data can more clearly distinguish between slopes with different degrees of erosion. Parameters such as acidity, sodium adsorption, total soluble salts, and sodium percent can easily explain this distinction. TDS values increase in deep sections of the soil in steady slopes and focus on erosive slopes precisely in the surface subsoil of soil. Also, on average, the slopes and eroded slopes show higher values of acidity, sodium ratio and sodium percentage. The exchangeable sodium percent also showed higher values at higher erosion ranges. In some soils, the crustal layer of the crust is less disintegrating and dispersed than the underlying layers, and sometimes the layers without erosion below act superficially. Therefore, a sharp decrease in the percentage and ratio of sodium adsorption and its exchangeable amount can increase the stability of slopes and slopes against erosion. In the text of the article, several diagrams are presented to compare and distinguish erosional marls from erosion-resistant items. In the text of the article, several diagrams are presented to compare and distinguish erosional marls from erosion-resistant items. In this case study, sodium exchangeable forms of resistant shells are isolated from soluble ones. The values of the maximum sodium absorption ratio and the total soluble salts and covariance parameters are interpreted as lowering permeability results, local increase of fine-grained grain particles. The volatility of the sodium absorption ratio is of great importance in soil erosion, and many researchers have used chemical solutions such as runoff to justify and explain soil contamination and dispersion.
Conclusions
Based on the results in different forms of erosion in Pishva area, the amount of sodium ion, its absorption ratio and the amount of silt and clay is very variable. The percentage of silt particles is the most important factor in erosion in the region. Also, the average amount of sodium ion and the ratio of sodium absorption from surface erosion to gully erosion in marl area of the region increased and the average clay percentage from surface erosion decreased to ghost erosion. Analysis of variance of different forms of erosion in the amount of sodium ion, sodium adsorption ratio and percentage of clay has a significant difference. Finally, three variables such as sodium absorption ratio, silt and clay percent and sodium ion can be considered as factors influencing the erosion of marl area and creating different forms of erosion. The study considers the mechanism of erosion in the region, including morphology, geology, climate, particle size, mineralogy, and chemical exchangeable soil processes.