Classification and Determination of Erodibility Indices of Ardabil Province Marls

On the one hand, considering the zones distribution with marl formations in Ardabil province catchments, and on the other hand, capability of some natural hazards of such lands like soil erosion and high sediment yields and progress of different erosion forms (surface, rill and gully erosions), it is necessary to study of marls, from the viewpoint of physical, chemical and mechanical properties, in order to recognize the erodibility of marls. In addition to, any erosion modeling requires complete knowledge of the erodibility Indices of erodibile formations as marls. In this research, the relationship between marls erosion forms and its rate with their physical and chemical properties were investigated. By this reasoning the lithological, slope and climatic maps were prepared and then the work units map was made by overlapping of them. Then, 40 samples of soils on the marl formations that belonged to 35 erosional points were taken and for determining of amount of physicochemical variables were sent to laboratory. Also, characteristics of sampling place such as slope, geographical situation and lithology have been noted, and the seven parameters for soil surface factor were privileged. Also, 35 treatments were conducted using a drop maker rainfall simulator device (with rainfall levels of 1 m1ύΓ m) with the intensity 20 mm/ h for the duration of 30 minutes, and the start time of runoff, the amount of runoff, sediment concentration and soil loss rate were measured. Then the all data were evaluated by different statistical methods such as correlation analysis, bivariate and multivariate regression approaches, factor and cluster analysis. The result of this research show that the marl formations have Neogene age. The soils on the marl formations of area have been assigned four and three groups orderly by chemical, physical and physicochemical variables. The classification accuracy of soils on the marl formations are equivalent 97.6%΅ 87.8% and 97.6%, respectively. Investigation of soil properties and sediment yield relationship showed that only six variables are significantly correlated with the amount of soil loss. These variables include: electrical conductivity (EC), chlorine (Cl-), sulfate (SO4-2), potassium (K+), organic content percent (OC%) and silt percent. With increasing electrical conductivity, silt percent, sand percent and the plastic limit (PL) of the soils, soil surface factors (SSF) form of Bureau of Land Management (BLM) method increased. Soil surface factors (SSF) form of Bureau of Land Management (BLM) method decreased with decreasing of chlorine (Cl-), sulfate (SO4-2), the percentage of total neutralizing value (TNV%) and cation exchange capacity (CEC). The physical, chemical and physicochemical variables have been loaded on the three, four and six components by factor analysis. The results of factor analysis based on physicochemical variables show the items loading on the six factors with 21 items loading above liquid and plastic limits (LL and PL), cation exchange capacity (CEC), clay and sand percent and clay ratio on component 1, sodium ion concentration, electrical conductivity, sulfate (SO4-2) and organic content percent (OC%) items on component 2, calcium (Ca2+) and potassium (K+) ions concentration, gypsum and the amount of runoff items on component 3, slope gradient, sediment concentration, bicarbonate ion (HCO3-) concentration, total neutralizing value (TNV%) and pH items on component 4, silt percent and chlorine (Cl-) concentration items on component 5 and 6, respectively. Marl zones with different forms of erosion (surface, rill and gully) can be categorized using the slope gradient, silt percent, K factor, type of marl formations and sediment yield, with a significance value of p0.05. Marl soils in Ardabil region can be classified into four groups by cluster analysis and using chemical, physical and physicochemical properties of soils. The output of this research is a map that shows four different groups of marl soils for the Ardabil region. Means of sediment yield rates are 130.73, 355, 406.82 and 463.46 g/m2 in 1, 3, 4 and 2 clusters, respectively. The produced results will aid the planners to determine the actions for mitigating erosion rates and land use planning.