عنوان مقاله [English]
Soil erosion is a natural process that causes soil loss due to various environmental factors such as climate, soil, topography and vegetation (Abedini et al., 1402: 115). Nowadays, due to the ever-increasing population of the world, the importance of soil erosion studies as one of the most important issues in the sustainable development of agriculture and food production and its environmental effects is more obvious. Due to its environmental and economic effects, soil erosion is a serious global problem that affects many natural and human ecosystems (Abedini et al., 1401: 106).The issue of soil erosion and land degradation is one of the most important issues in natural sciences, the evaluation of its environmental and economic consequences requires quantitative data. In addition, soil erosion has long-term destructive effects on natural and human-managed ecosystems. Soil erosion causes a decrease in soil fertility and productivity, has an adverse effect on the quality and quantity of runoff, and reduces the efficiency of irrigation dams and canals and food production (Abedini, 1400: 100). One of the most important factors in increasing soil erosion is the lack of awareness of the economic value of this ecosystem gift. In recent decades, soil erosion by runoff (WSE) has become a serious problem worldwide, as the ratio of natural resources to population is drastically decreasing. The surface soil is the first part that is exposed to erosion and the amount of nutrients in the soil is greatly reduced. This reduces organic matter (nitrogen, phosphorus and potassium) and other elements needed for the growth of crops (calcium, magnesium, etc.) (Ariafar, 2014: 4).In the Alazarcha basin, the formation is sensitive to erosion, inappropriate use of land, texture, topographical conditions of the area, etc. are factors that cause erosion at the basin level, as an important issue in the development of agriculture and protection of natural resources. In this study, searches using the PSIAC model; The studies of soil erosion in Alazarchai River watershed are carried out and finally, the parts prone to erosion in different parts of the basin are separated and identified.
In order to collect the following data and information from the relevant organizations, necessary measures have been taken:
1- Topographic maps of the studied area with a scale of 1:50000.
2- Geological maps of the studied area with a scale of 1:100,000.
3- Meteorological data and statistics of the studied area (climate and meteorology of Ardabil province).
4-Excel software for preparing charts and data analysis.
5- Arc GIS and Arc view software for map preparation.
In different stages of this research, statistical and graphic software have been used to prepare and draw tables, charts, maps and data analysis. The most basic aspect of the present study was the identification of geomorphological working units of the studied basin. For this purpose, the information in geological and topographical maps was digitized using Arc Map software. In the next step, tectonic, lithology, hydrography, direction and slope maps were prepared using ArcGIS software. Due to the large volume of information and in order to increase the accuracy of work, information layers have been integrated to identify work units using Arc Map software. Other software used in this research include Surfer and Excell graphic software, which were used in the preparation of maps and specifications, tables and data analysis, respectively. The purpose of this study is to evaluate erosion and sediment production in Alazarchai watershed. For this purpose, after identifying the study basins, we estimate the amount of sediment using the PSIAC experimental model. In this method, according to the strength and weakness of each factor, a number is assigned to it. Finally, taking into account the sum of the numbers obtained for different factors, the sedimentation rate of the basin is satisfied. This method using GIS requires that an information layer be prepared for each effective factor in erosion. Therefore, in this research, using arc gis 10.2 software, we divide the watershed into 3 separate hydrological units (Figure 2) and examine the MPSIAC factors according to the hydrological units.
In the assessment of soil erosion and sediment production in Alazarchai basin, among the factors affecting soil erosion in the MPSIAC model, the land use factor with a score of 46.56 is the first priority and the land cover is the last priority with a score of 5.25. Other factors (geology, soil, topography, weather, runoff, current state of erosion and river erosion) are in the next priorities with scores (21.47, 22.18, 18.85, 17.93, 10.65, 44.75, 35.07) respectively. Also, after scoring nine factors affecting soil erosion using calculations, the specific sediment in cubic meters per square kilometer per year was obtained in each of the sub-basins of the study area using PSIAC and MPSIAC models. Finally, the level and intensity of sedimentation of the basin and its sub-basins were determined using Table (3) to determine the level of sedimentation and soil erosion level. The results showed that according to the PSIAC model, the erosion rate of the Alazar watershed is 674.60 cubic meters per square kilometer per year under the Hamza Khan basin, 434.99 cubic meters per square kilometer under the Alilah basin, and 308 cubic meters per square kilometer per year under the Quzlu basin. The main reason for the high amount of sediment in the Hamza Khanlu sub-basin is alluvial defenses and alluvial cones. which caused it to become sensitive to erosion and eventually cause the formation and accumulation of sediment in the area.
Also, the results obtained from the two models show that the specific sediment and sediment load of the basin and its sub-basins in the PSIAC model is twice the sediment load and specific sediment of the basin and its sub-basins in the MPSIAC model. The amount of specific sediment of the entire basin in the PSIAC model is 472.53, but in the MPSIAC model, it is 238.47 cubic meters per square kilometer per year. There are differences in the class and intensity of sedimentation of these two models in the entire basin and its sub-basins. In the PSIAC model, Hamze Khan sub-basin is in high sedimentation class (IV) and Alileh and Qozlu sub-basins are in medium sedimentation class (III), while this class in Alazarchai basin and its sub-basins are in sedimentation class III and II in the MPSIAC model, which The intensity of erosion and sedimentation in Hamza Khan sub-basin is moderate and in Alileh and Quzlo sub-basins it is low.
Keywords: Alazarchai watershed; soil erosion; PSIAC model; sediment