Journal of Spatial Analysis

Erosion is one of the most destructive and continuous phenomena that cannot be prevented and only could be controlled by studying the chemical and physical properties of soil. Marls are one of the most important sedimentary units in Iran which have high rate in sediment production and erodibility because of their Physico-chemical characteristics. These properties caused large environmental and civil damages and so, the study of erosion and erodibility of the marl units is essential. One of the most important points about marls is grain size nature and elements in them and their effects on amount of erosion. The physical and chemical proprieties of soil are very important in the development of badlands. This study deals with Physico-chemical properties of Marl and its impact on various land forms of erosion in Lotshur-Pakdasht region. Badlands are a typical landform of greatly dissected fine-grained materials in arid or semi-arid environments like Lotshour, although they are also found in different climatic conditions. Climate and geology are several factors determining the tendency to badland formation. Runoff, rain splash, marl and loose formations together with massive wasting processes such as creep, sliding and flow, become the dominant factors determining landform genesis, resulting in the formation of badlands in Clayey-silt slopes.

In this research, in addition to sampling the soil and sediments, rain simulated (using rain simulators) in two marl, two conglomerates and two alluvium  units, in area with different forms of erosion and runoff and produced sediment amounts in each point were measured in laboratory. Also, at the same time, soil samples were taken from adjacent plot and the amount of runoff and sediment produced in the laboratory, separated and measured in the lab for all points. parameters such as Ph, electrical conductivity, content of sodium, potassium, calcium, magnesium, gypsum, chlore, carbonate, solfate, nitrate, organic carbon, CEC was measured. In analyzing the data, analysis of correlations and Pearson and Spearman comparison of means method were used in SPSS software. Also, grain size and Aterberg limits for all samples were determined in lab.

Mineralogical, geochemical and grain-size composition of soil and pore-water chemistry parameters was characterized on both eroded (south-facing) and non-eroded (north-facing). Only a few grain-size parameters and mineralogy discriminate eroded from non-eroded slope substrates. Erosion occurs where the fine fraction is abundant. This may be due to reduced permeability in the eroded soil, whereas the non-eroded one is more stable with respect to weathering, as it is more permeable. The abundance of clay minerals is affected by pedogenetic processes in the non-eroded slope, which increases in mixed layers and indirectly reduces the amounts of other minerals, making clay mineralogy a discriminating parameter in the two different types. Chemical data enable discrimination between eroded and non-eroded slopes. pH, SAR (sodium adsorption ratio), TDS (total dissolved salts), mineralogy and PS (percentage of sodium) are distinctive parameters for both eroded and non-eroded slopes. TDS increases in depth in the non-eroded slope, whereas the maximum TDS is just below the crust in the eroded one. On average, eroded substrates are higher in pH, SAR and PS than non-eroded ones. The ESP (exchangeable sodium percentage) of the eroded slope has a higher value than the non-eroded one. Crusts are less dispersive than eroded substrates, and non-eroded substrates behave as crusts. This suggests that the portion of the slope most severely exposed to weathering tends to stabilize, due to strong decreases in SAR, PS and ESP. Several diagrams reported in the literature show similarly anomalous crust samples on eroded slopes, compared with other samples coming from greater depths on eroded slopes. In the present case study, the exchangeable form of Na characterizes crusts more than the soluble form. The meaning of maximum SAR and TDS (and covariant parameters) is interpreted as the effect of decreased permeability, as suggested by a local increase in the fine-grained fraction, which coincides with maximum TDS. Variations in SAR values are of primary importance for soil erosion, because many authors have used solution chemistry (i.e., SAR, PS, TDS, EC) as a descriptor of dispersity.

            Based on results of analysis of variance in various forms of erosion are significantly different in the sodium ion, sodium absorption ratio and the percentage of clay. The average amount of sodium ion and sodium absorption ratio in marl samples of region, increase from sheet to gully erosion forms while average clay percentage decreases in this trend. Finally, three variables of sodium ions, sodium absorption ratio and clay percentage of marl samples can be significant factors in erosion and related forms in this region. This study describes the erosional mechanism, which involves morphological and geographic exposure and climatic elements, as well as grain size, mineralogy, chemistry and exchangeable processes of soils.

In analyzing the data, correlation analysis and comparison of averages by the SPSS software has been used. As well as a brief comparison between north and south facing slopes that are different in terms of erosion, was also performed. Based on statistical analysis of in various land forms of erosion are significantly different in the sodium ion, sodium absorption ratio and the percentage of silt and clay. The average of sodium ion value and sodium absorption ratio increase from surface to gully erosion form and average silt percent reduced from surface to Gully erosion in marls outcrops in this area. Also, three variables of sodium ions, sodium absorption ratio and clay percent factors can be seen in the erosion of marl and create various land forms of erosion in the region.