فرسایش خاک

Today, soil erosion in particular and soil degradation in general as a result of human activities have been raised as a social problem, and the role of the human factor in the emergence and acceleration of the soil degradation process has been clarified in many fields. Obtaining accurate statistics and information about soil erosion and sediment yield in the watersheds is necessary for the implementation of soil conservation programs and methods for determining the resistance to soil erosion and reducing sediment yield. Due to the lack of data about soil erosion and sediment yield in many watersheds of Iran, the use of appropriate empirical methods is inevitable to erosion estimation, sediment yield and especially sediment delivery ratio.

For this purpose, in the present study, empirical models for estimation of the sediment delivery ratio based on easy-to-measure variables and three models of SATEEC, InVEST and WaTEM/SEDEM were used in the Khamsan representative-paired watershed, western Iran. The WaTEM module of the WaTEM/SEDEM model is based on the RUSLE model for estimating soil erosion, and in the SEDEM module is based on the performance of effective physical factors in the sediment transport equation. In many sources, the 137Cs method is mentioned as the only available and reliable method for measuring the components of the sediment budget, including total erosion, total sedimentation, net erosion (sediment yield) and sediment delivery ratio, especially at the hillslope and sub-watershed scales. To evaluation of the used models, the results of calculating the sediment delivery ratio using the 137Cs method obtained from previous researches were used, which are 25.61% and 58.94% for the entire watershed and the average of 15 sub-watersheds, respectively, and its accuracy is based on the observed sediment data at the outlet of the watershed has been confirmed.

Among the studied sediment delivery ratio models, Renfro and Waldo (1983), Williams and Brendt (1972), Roehl (1962) considering one hour excess precipitation, Walling (1983), Ferro (1995), Vanoni (1975) and USDA (1972) provided the closest estimates (±10%) to the 137Cs method for the whole watershed scale and the Renfro (1975), USDA (1972), USDA-SCS (1979), SATEEC and Roehl (1962) considering one hour excess precipitation for the sub-watershed scale provided the closest estimates (±10%) to the 137Cs method for the sub-watershed scale and were selected as suitable sediment delivery ratio models for Khamsan representative-paired watershed. Also, these models can be used to estimate the sediment delivery ratio in watersheds similar to Khamsan representative-paired watershed.

In the sub-watersheds scale, the equations estimations based on easy-to-measure variables except the Roehl (1962) method - excess rainfall of 1.0 h was significantly lower than the SATEEC model, on the other hand, the estimations of all the methods except the Roehl (1962) method - excess rainfall of 0.1 h was significantly higher than WaTEM/SEDEM and InVEST models. This issue emphasizes the importance of considering excess precipitation conditions to estimation of the sediment delivery ratio in the presented equations by Roehl. Also, at the scale of the whole watershed, the estimations of the equations based on easy-to-measure variables, except for the Mutchler and Bowie (1975) method, were lower than the results of the SATEEC model. The great difference of the investigated methods performance in the two scales of the sub-watershed and the whole watershed is due to the undeniable effect of the middle plain of the Khamsan watershed in the drastic reduction of the sediment transportation from the sub-watersheds to the outlet of the watershed.

Soil erosion and sedimentation are among the major problems and environmental challenges in watersheds. The sediment load in rivers causes numerous issues, such as sedimentation in dam reservoirs, changes in river courses due to sedimentation in their beds, reduced water carrying capacity in waterways and water transfer facilities, and changes in water quality for drinking and agriculture. These problems are of great concern to researchers and water resource managers as they can investigate sedimentation, erosion, and potential effects on biological processes. Therefore, it is essential to investigate and evaluate suspended sediment concentrations to determine water quality and hydrological functions. In this regard, the use of accurate, extensive, and cost-effective techniques, such as remote sensing, is invaluable for improving sedimentation estimation and, consequently, water quality assessment. Understanding the spatial relationships between upstream vegetation and sedimentation is crucial for the effective control and optimal management of water resources and soil. The present study aimed to determine the relationship between vegetation cover and suspended sediment concentrations in the Doab Mereg and Gamasiab watersheds.

In this research, the Sentinel-2 satellite data were investigated in the first step. If there were cloudy conditions, dust particles, or other radiometric problems, they were removed from the calculations. Then, factors such as band type (visible and infrared bands), river width (higher than the image pixel - 40 meters at the Doab station and 80 meters at the Polchehr station), separation power, and sensor location (10 and 20 meters) were considered to select the appropriate image pixel for obtaining the spectral reflectance of water. The pixel corresponding to the hydrometric station and its surroundings was selected to extract the spectral reflectance. Then, the suspended sediment concentration statistics of the Doab Mereg station located in the Qarasu River and the Polchehr station located in the Gamasiab River in the five-year period (2016 to 2020) were used simultaneously to investigate the correlation between the spectral reflectance of the Sentinel-2 image bands and sediment concentration. Next, the Normalized Difference Vegetation Index (NDVI) for the two May and June seasons was extracted using Sentinel-2 images. The relationship between vegetation cover and suspended sediment concentration recorded at the station and extracted from the images was estimated separately.

The results of the correlation analysis of suspended sediment concentration showed that the best result for the Doab and Polchehr stations belonged to band 4 (R2 = 0.86) and band 5 (R2 = 0.83), respectively. The suspended sediment concentrations varied from 0.17 to 76.45 and 0.44 to 118.86 mg/liter in the Doab Mereg and Polchehr stations, respectively. In the Doab station, the depth of the power state had the highest correlation coefficient between the observational data (recorded in the station) and the data extracted from the images. In the Polchehr station, it had a high correlation coefficient in both polynomial and exponential modes. The best values of the coefficient of determination (R2) of the normalized vegetation cover difference index for the Doab and Polchehr stations were 0.98 and 0.64, respectively. This means that the amount of sediment decreases with an increase in vegetation cover. The average values of the vegetation index for the Mereg watershed (0.35) and the Gamasiab watershed (0.28) show the relatively sparse vegetation in the area. The lowest average values of vegetation cover in the studied season (spring) were respectively equal to 0.11 and 0.21 in the Mereg watershed in June and the Gamasiab watershed at the end of May. The results of the regression test showed a strong and significant relationship between the density of vegetation and the amount of suspended sediment concentration recorded in the hydrometric stations of the two basins.

The results showed that six models were extracted for the studied area, which had acceptable and suitable R2 and error values. Among the obtained models, better results were obtained in the single-band model than in the case of using the band ratio. The highest correlations belonged to bands B2, B3, B4, and B5 in the Doab Mereg station, and to B4 and B5 in the Pol Cheher station. The highest R2 values obtained for the two stations were 0.86 and 0.83, respectively, in the exponential model. The results of this study show that Sentinel-2 can be used as a suitable tool to estimate suspended sediment concentrations with acceptable accuracy in small-scale basins and flood conditions, which has been confirmed in a number of similar studies. Sediment rate refers to the positive effect of vegetation on soil protection and the reduction of sediment production and transport within watersheds. In general, the results demonstrate that vegetation has been effective in the quantity and quality of the spatial changes in the sedimentation rate of the basins. In fact, the NDVI vegetation index, as a representative of the vegetation, can be successfully used to create a statistical model of the changes in the sedimentation rate. The revitalization of vegetation should be included in development plans.

Introduction and Goal:

The implementation of watershed management practices in the country and the evaluation the conducted activities and effects investigation of these projects are essential on the governing processes at watershed. However, such an important approach has to be adequately considered.

Accordingly, the present study was planned with the simulation aim of the impact of watershed management practices on hydrological parameters using the SWAT model in the Kan Watershed in Tehran Province, Iran. Therefore, the first of the initial implementation of the model was carried out, and then it was calibrated and validated. In this research, SWAT-CUP software was used to usage of various instructions and objective functions and also to test and the model calibration and validation. In order to determination and comparison of the simulation conditions with the governing conditions on watershed applied the evaluation criteria such as the coefficient of explanation and the coefficient of efficiency.

The research results showed that the model efficiency was acceptable for the hydrological simulation of the studied watershed. So, the explanation coefficient for calibration and validation was with rates of 0.69 and 0.86 respectively. Also, the Nash-Sutcliffe index for the calibration and validation obtained with rates of 0.85 and 0.93, respectively. Then, watershed management practices simulated at the level of studied watershed. The simulated results showed that the surface runoff decreased with the practices of watershed management in the form of gabion, masonry check dam, counter trench and loose- stone check dam with the values of 25, 23, 21, and 11 percent, respectively. Also, the available water was more after the practices of watershed management in the form of gabion, masonry check dam, counter trench and loose- stone check dam with rates of 19.0, 21.3, 20.5 and 10.75 percent, respectively, compared to the absence conditions of these practices at the watershed level. Also, the maximum amount of flow changes observed in the practices conditions of masonry check dams. In addition, the evapotranspiration increased with implementation of gabion. masonry check dams, counter trench and loose- stone check dams with rates of 20.19, 20.86, 19.0 and 10.87 percent, respectively.

Conclusion and Suggestions:

Based on the results of this research in the Kan watershed, the flood possibility and the flood damages can be reduced by practices of the watershed management, management and biological programs.

Desertification is one of the most significant process of land degradation in all the world, especially in arid and semi-arid regions. In the United Nations Convention to Combat Desertification report (1994), Desertification is land degradation in dry-lands, resulting from various factors, including both climatic variations and human activities. This process is always associated with soil degradation, pollution and reduction of water resources, vegetation and other biological resources in natural and ecological conditions. Therefore, determining the main factors of this process can be very effective in proper land management. This research was conducted with the aim of zoning sensitivity areas to the desertification intensity based on ESAs model and providing management strategies based on scenario planning in Razavi Khorasan province.

In this research, five criteria such as climatic quality, soil, vegetation, erosion and management (human activities), and 20 indicators such as soil texture, soil depth, rock fragment, parent Material, vegetation density, fire risk, rainfall. drought, water and wind erosion, land use change, mining, livestock density in pasture, etc. were used. were used. Scoring and weighting of the indicators was done using a questionnaire and based on the expert opinions of specialists, executive managers and field experiments. The designed questionnaire included 21 questions, that classified in the form of 5 criteria of soil, climate, vegetation, erosion and management, which were distributed among the statistical population in two rounds. Management strategies and policies were also obtained in the Delphi method in the form of expert panels (brainstorming).

The results showed that the vegetation criteria with indicators such as the reduction of vegetation, the increase in the risk of fire in pastures and forests due to the continuous droughts of the past two decades and the increase in the intensity of wind and water erosion, with a value of 1.419, has had the greatest value and importance in expansion the intensity of desertification. After that, factors such as human activities (management), climate, erosion and soil respectively have had the greatest impact on the sensitivity areas to desertification in Khorasan Razavi province. In terms of the critical situation, the high percentage of the areas in the northwestern regions such as Quchan and Chenaran township due to the impacts of drought, severe changes in land use and water has become desertification. In the central, eastern and southern parts due to drought, land use changes, lack of optimal land management and wind erosion, main reason has been the expansion of desertification. Besides that, all the townships of Khorasan Razavi province have fragile conditions. This issue can be considered as an important and serious warning for the future management of Khorasan Razavi province. Therefore, in order to provide effective ways to deal with the intensity of desertification, based on the opinion of experts and specialists in the current research, by considering only the priority indicators of each of the criteria, the number of 10 cross matrix of the important indicators of each of the criteria, 20 scenarios, 6 strategies and more than 40 strategies were obtained. So that, by using the suggested strategies could be planned and managed according to regional and local conditions, to reduce the intensity of desertification.

The ESAs model uses four criteria of management, vegetation, soil quality and climate mainly to evaluate areas sensitive to desertification. So that, in this research, due to the importance of the erosion (water and wind erosion), for zoning map of sensitivity areas to desertification were used. In order to provide management plans (strategies and policy), to reduce and combat desertification in Khorasan Razavi province, management strategies such as; -sustainable management of vegetation, - water resources management and watershed management, - soil management, - livestock management and reduction of environmental hazards caused by human activities, -education, promotion and culture and sustainable management. Therefore, in this research, only the important strategies and policy that can provide a comprehensive vision of land management in Khorasan Razavi province, were suggested.

Today, the destruction of natural resources is one of the most important and serious challenges facing development programs. Soil erosion is among the processes that directly and indirectly threaten our country's soil and water resources. Water erosion appears on the earth in different forms, one of the advanced forms of which is the gulies. Gully erosion is one of the important processes of soil destruction, which in different climates causes significant soil losses and the production of large amounts of sediment. The purpose of the present research is to investigate the morphological characteristics of the gullies of Khuzestan province and the role of its influencing factors in the expansion of the gully areas.

 First, by collecting available data and comparing it to satellite image and other data, the province's gullies have been defined. The first field visit focused on verifying the integrity of these areas and correcting the gullies boundaries. The total area of Khuzestan province approximately is 64000 km2 in the dry desert climate, and more than 33,862 ha of it is under the influence of gully erosion. The hot semi-arid climate also covers approximately 12,1% of the province and 16,116 ha have experienced gullies erosion. After determining the area of gullies and dividing the areas above and below 500 ha, due to the difference in appearance, topography, and vegetation, 2 and 1 representative areas were selected from the hot-dry desert and hot-semi-arid climates, respectively, and 2 replicates were selected from each representative. Longitudinal and cross-sectional profiles of representative and replicated gullies were drawn and after soil sampling, all morphological features of the gullies were measured.

According to the results, most of the gullies of the province have been created in the plains with a low slope with deep soil and loamy sand texture, silt or silt loam with pasture, and sometimes agricultural land and U-shaped cross-section. Darkhazine and Sharif gullies, with 1260 and 912 cm, and Darkhazine gullies with 420 cm value have the maximum width of top, bottom and depth in the cross-section of 75%. Also, the gullies of Choghazanbil, Darkhazine and Choghazanbil with values of 30 cm have the lowest depth, top and bottom width in the cross-section area of 75%. The overall profile is scratched, and in terms of depth class, they are in the category of medium-deep gullies with a vertical top.

Intrinsic characteristics of soil, formation and geological type, climate, intensity of rainfall as natural factors, and destruction of vegetation, land use change and the lack of proper management, unprincipled road and bridge construction operations, construction and installation of oil facilities and electricity bars as human factors have played a role in the process of gully expansion. However, the diversity and change of the number and degree of influence of different factors from one point to another and the difference in their participation in the formation and expansion of the gully are based on the environmental conditions of the land. These conditions require that more research be carried out to identify as many factors as possible in the phenomenon of gully erosion and their participation in the formation and expansion of this phenomenon in different places and with different environmental conditions.

Soil erosion is a serious threat to human well-being and life, especially in arid and semi-arid regions, and is one of the important issues in land management. Rill erosion is one of the most significant events in water erosion that affect soil loss, landscape, water resources, and land degradation can cause significant loss of soil in different climates. Identifying the effective processes that lead to the creation and expansion of rill erosion is necessary, and finding effective solutions to prevent rills is essential. In the meantime, one of the management solutions is determining the prone area to rill erosion. The high sensitivity of the lands of Nehbandan city (Kaji wetland watershed) to erosion is the reason for determining the prone areas to rill erosion. The maximum entropy method was used to identify the area that is susceptible to rill erosion.

The modeling process used 9 effective factors, including height, slope steepness, slope direction, rainfall, land use, land cover, soil texture, geomorphology, and geology, based on similar research. Factors affecting the occurrence of rill erosion were analyzed as independent variables. The first step in preparing a rill erosion sensitivity map was to determine the location of rill erosions in the Kaji wetland watershed using Google Earth and then to conduct field surveys. The basin was monitored in the field using GPS and 138 cases of rill erosion were recorded. The occurrence points were divided into two groups: training and validation, with a 70:30 ratio. The total occurrence points were divided into 97 incident points that were randomly selected for model training (validation stage) and 41 incident points that were used for validation purposes. The MaxEnt model relied on the data set used for training as independent variables. In order to use the maximum entropy model to determine rill erosion, first the independent variables (factors affecting the occurrence of rill erosion) and the dependent variable (identification of points with rill erosion) was converted to the required format and introduced to MaxEnt software. To evaluate the effectiveness of the model in detecting occurrence points (rill erosion) from pseudo-non-occurrence points, the area under the ROC curve was used. The Jack Knife test was utilized to investigate the identification and prioritization of 9 influential factors (independent variables) that influence the results. The model was implemented using the remaining variables as input factors after removing the independent variables separately for this purpose. The efficiency of the model built using all independent variables was measured in comparison to the case where the model was built based on other variables. To determine its effect on the output, the contribution of the omitted independent variable was examined.

According to the validation results, the sensitivity map for rill erosion has a high efficiency. The test stage should have a ROC curve of 0.859 (very good) and the test stage should have an average curve of 0.6 (moderate). The Jack Knife test revealed that the slope's steepness was the most significant environmental factor in the predicted sensitivity map for rill erosion in the study area. Geology and land cover were also recognized as other important factors. The MaxEnt model was found to be an effective model for preparing the rill erosion susceptibility map, according to the results. According to the findings, the slope steepness factor, which is 25%, is the main factor that affects the rill erosion of the Kaji wetland watershed. The high frequency of the slope class with a slope class below 20% suggests that this slope class is a significant factor in the development of rill erosion. The geological map of the region indicates that the majority of the region is dedicated to Quaternary formations, which is crucial for the development and creation of erosion in the region. The watershed's proneness to rill erosion is caused by poor rangeland usage. Management of vegetation and rangeland is necessary to reduce the potential for soil erosion in the region. According to the results, the soil texture of the region had less effect on the development of rill erosion; because most of the soil in the area is related to sand-gravel texture, which has a low effect on rill erosion. The MaxEnt model's high accuracy in modeling the sensitivity of rill erosion is evidenced by the results of the present study.

Soil erosion reduces soil fertility, weakens vegetation, deposits sediments, deforms and fills rivers due to floods, and reduces water quality. Therefore, the precision of soil erosion estimation is essential for proper watershed management. Among all-soil erosion prediction models proposed for storm-scale, one of the most widely used is the Revised Universal Soil Loss Equation (RUSLE). Due to the importance of the LS factor in small watersheds with complex topography on the final estimation of the RUSLE model, in this current research, the soil erosion results were obtained from four different LS factor methods were investigated.

Soil erosion obtained by the RUSLE model and four methods of LS factor calculation including the Moore et al. (1991), Desmet and Govers (1996), Boehner and Selige (2006), and manual method; for 38 storm events recorded during 2011 to 2019 for the Galazchai Watershed, West Azerbaijan Province, Iran.

The results showed that the mean of the topographic factor for Moore et al. (1991), Desmet and Govers (1996), Boehner and Selige (2006), and manual methods were 9.91, 5.26, 13.29, and 6.54, respectively. Comparison analysis of the methods used by the manual method showed that the ratio of the estimated mean values varied from 0.80 to 2.03. Comparing the mean of LS maps with the manual method as the basic method and calculating error estimation found that Desmet and Govers' (1996) method was more successful in the LS factor estimation, resulting in better estimation of soil erosion for the study storm events. Despite the difference in soil erosion values, almost the same spatial pattern was observed in all methods.

Analysis of the results obtained from different LS factor methods in the Galazchai Watershed verified the significant effect of the studied methods on the estimated soil erosion. Therefore, soil erosion studies need to select an appropriate method to achieve precise soil erosion to prevent errors and minimize uncertainties. Incorrect estimation of soil erosion leads to erroneous management of watersheds and loss of money and energy. The present study is new in term of comparative evaluation of one of the sensetive factors in USLE and its different versions on the estimated storm-wise soil loss at the watershed scale. It is also innovative in viewpoint of focusing on the necessity of selection of appropriate computational methods for the local managers and experts. Extensive studies are recommended to investigate other methods of calculating LS, and even other RUSLE factors at different scales are recommended for a better conclusion.

It is the main objective of the present study to identify the factors affecting farmers’ unwillingness to convert their sloping agricultural lands into orchards. The study is a descriptive and survey one using a statistical population of 250 farmers in Galikesh County, Golestan Province, who rejected the idea of changing their sloping crop lands to orchards. For this purpose, 150 farmers were selected using the multi-stage random sampling method and the Krejcie and Morgan Table and a questionnaire was used to collect data in 2021. The content and face validities of the questionnaire were confirmed using the opinions of extension, soil protection, and horticulture experts at Golestan Agricultural Jihad Organization. The validity of the questionnaire was determined using Cronbach's alpha method to obtain a coefficient of 0.85 and data analysis was performed using SPSS19. Based on the results obtained, the following 12 factors affected farmer unwillingness listed in a descending order of significance: non-availability of production tools, farmers’ subculture, complex cultivation operations, lack of government support, investment cost, lack of confidence in experts, lack of knowledge, non-compliance behavior, non-observable operation results, sparsely distributed agricultural lands, uneconomical results, and lack of confidence in responsible government agencies. These parameters explained about 75.189% of the total variance among the factors involved. Also, the results indicated that extending low-interest loans, high-quality and high-yield seedlings, water availability, and tools and implements to farmers as well as communication with influential local leaders and trustees to solicit their opinions during the various stages of protection operations may be suggested as helpful in convincing farmers to accept the conversion.

Fingerprint method determines the contribution of sediment in the land units. In this method, a suitable composite (set) of diagnostic properties and a multivariate mixing model are employed to estimate the relative contribution of sediment sources to sediments transported to watershed outlet. The purpose of this study was to determine the contribution of different sediment sources in the Beheshtabad watershed with 308 km2 area. For this purpose, 36 soil samples were taken from sedimentary sources (0-5 cm depth) and 10 sediment samples from watershed outlet. In each of the sources, initial traces were evaluated by Kruskal-Wallis test. In the second stage, an optimal combination of tracers for each source was obtained using diagnostic analysis functions, and finally, in the next step, the contribution of each user in sediment production for each sampling method was determined using Collins et al. model. The contribution of agricultural, rangeland, rainfed and residential land use was equal to 67.88, 7.63, 19.40, and 5.10 %, respectively. Results showed agricultural has maximum share in sediment with 67.88percent. Due to the fact that the contribution of sediment in agricultural lands in the study area is high, special attention should be paid to the way of agricultural operations.

Water erosion causes as loss of quality and environmental issues problems. The best methods of soil management are prevention of soil erosion, control of runoff and sediment, and maintenance of soil quality.

This research was conducted in order to investigate the effect of compost and vermicompost on physical and chemical properties of soil (based on a completely randomized blocks) and runoff and sediment (factorial based on a completely randomized blocks). For the experiment 9 plots were used, (3 plots include of compost, 3 plots include of vermicompost and 3 plots control) in an average 5 percent slope area. 18 ton/ha compost and vermicompost were added to each plot and mixed it with soil 30 cm deep. Soil erosion was estimated by runoff and sediment by 2 natural rain and 1 rainfall simulator with 3 Repetition in each rain. Some physico chemical and biological properties of soil, as pH, EC, MWD, BD, NPK, OM, Sp, CaCO3 were measured.

The results showed that Vermicompost and Compost fertilizers significantly increase the total N, available k, available P, organic matter, Mean weight diameter (MWD) and saturation percentage more than the control plot. Soil bulk density decreased in plots of Vermicompost and Compost compare to the control. The compost and vermicompost in the level of 1 percent reduce significantly the runoff volume in the first natural rainfall 68.5 and 82.6 and the second natural rainfall 62.56 and 74.2 and the simulator 30.3 and 45.45. The compost and vermicompost in the level of 1 percent reduced significantly sedimentation the compare to the control. Vermicompost treatments had the least and control treatments had the most of runoff volume and sedimentation. The compost and vermicompost in the level of 1 perecent reduce significantly sedimentation the compare of control. Vermicompost treatments had the least and control treatments had the most of runoff volume and sedimentation.

Thus, it seems Using the fertilizers such as compost and vermicompost can significantly effect on the soil nutrition preservation and improve soil properties and can be found useful in the development of erosion control programs.

One of the functions of rangeland ecosystems is to prevent soil erosion and increase nutrient retention capacity. The present study was conducted to highlight the effect of Rangelands degradation on the preservation of Mg, Ca, N, P, and K elements in the soil and emphasize the role of rangeland plants in preventing the wastage of these elements in the rangelands of the Salman watershed in Qom. For this purpose, a sample was taken from the soil of the habitat in each work unit, in the classes of poor and good rangeland conditions, representing degraded and non-degraded rangeland, respectively. Then, the amount of eroded soil was determined from each unit using the modified PSIAC (MPSIAC) model. In the following, the amount of loss of nutrients using the results of soil analysis and related relationships, was calculated and based on the replacement cost method; by estimating the alternative fertilizer, the monetary value of maintaining nutrients by the ecosystem was calculated. The results showed that the destruction of the rangeland ecosystems of the region causes erosion equivalent to 35.68 tons per hectare per year, which damages the functional services of the ecosystem at an annual cost of 11.6 billion rials (11606427781 rials) by reducing the nutrients of the soil. Also, each hectare of good rangelands in the region can prevent the loss of nutrients with an approximate value of 335.6 thousand rials. The results indicate the effective role of the rangeland ecosystem in controlling erosion and preventing the loss of soil nutrients. What is certain to emphasize more the role of rangeland ecosystems in soil erosion control; it is recommended that are also estimated the amount of soil erosion by other common methods, such as the global model of soil erosion (USLE), EPM, etc., and the results are compared with each other in future research.

Gully erosion affected by many factors causes the destruction and loss of large volumes of soil along with great economic and social damage. The variability of diversity, the number and size of the influence of different factors from one point to another and the difference of their participation in the formation and expansion of gullies is based on the conditions of the land. Such conditions have caused more researches to be carried out to identify as many factors as possible in the phenomenon of gully erosion and the extent of their participation in the formation and expansion of this phenomenon. In this regard, the present study has been planned with the aim of monitoring and evaluating the effective factors in the development of gullies in the Haddam and Sharif watersheds of Khuzestan province. Modares Shushtar watershed, having Sharif and Hadam subwatersheds, as one of the important and typical basins of the province, every year a large area of its agricultural land is threatened by gully erosion.

In order to carry out this research, first, the parts with gullies in the study area were identified on the topography map with a scale of 1:250,000 during the 20-year period (1993-2012). Then, 15 gullies have been identified and investigated from each climate class of hot-dry desert and hot-semi-arid. Features such as the slope of the initial point of creating a gully and the slope of the front of the gully were calculated by the field method and using a tape measure, level and inclinometer measuring device and the mirage area of the gully front in the Google Earth softwave. Also, the physical and chemical characteristics of the soil of each gully were tested.

The results showed that the average percentage of bare soil above the head cut of selected gullies in Haddam and Sharif watersheds is 99.8% and 97.26%, respectively. Based on soil characteristics, the main cause of soil instability and erosion in gullies in both watersheds is EC. The morphometric characteristics of the gullies showed that in the Haddam watershed, all gullies are V-shaped in terms of cross section, and in the Sharif watershed, only gullies are B12, V-shaped and the rest are U-shaped. The Haddam watershed has the highest depth, width, and top of the gully compared to the Sharif watershed. The total volume of soil loss in Sharif and Haddam watersheds is 23000 and 51579 m3, respectively. Gullies A18 and B1 in Haddam watershed have the highest and lowest soil loss volume, at 11599 and 1612 m3, respectively. In the Sharif watershed, the maximum and minimum soil loss volume of gullies related to gullies A2 and B4 are 5282 and 369 m2, respectively.

Conclusion and Suggestions  :

The most important factors in the volume of soil loss and expansion of gulies are the characteristics of the watershed located upstream of the gully front (such as the extent and slope of the watershed) as well as the fineness of the geological formation (silt) and high soil salinity. Due to the excessive bareness of the soil, increasing the roughness of the soil surface with the establishment of vegetation is one of the compatible and low-cost methods in protecting soil resources. In order to control the spread of gully erosion, it is necessary to increase soil organic matter, modify saline and sodium soils with the use of modifiers, and also divert the runoff from the gully front.

Iran is one of the countries that soil erodibility is becoming one of the acute environmental problems and every year millions of tons of fertile soil are left unusable due to lack of proper management.  In order to effectively protect and prevent the adverse effects of soil erosion, it is necessary to identify the factors affecting soil erosion and provide an appropriate estimate of their amount in the country. In this regard, the present study was conducted to estimate soil erodibility (K-factor) for a soil depth of 0-30 cm in Iran.

For this purpose, two database were used, including the Harmonized World Soil Database (HWSD) and global gridded soil information (SoilGrids), as well as RStudio and ArcGIS software. First, SoilGrids data was prepared at four depths of 0, 5, 15 and 30 cm and averaging was done. Also, the HWSD database was received in vector format for a depth of 0 to 30 cm. Finally, these data have been used to estimate the erodibility factor based on the soil content of organic carbon, clay, sand and silt using the EPIC equation. Finally, Relative Error (RE), Median Absolute Deviation (MAD) and Root Mean Square Error (RMSE) were calculated to compare two databases.

Assessments indicate that the average percentage of clay particles in the sub-basins of Iran varies between 15 and 32% and the average for the whole country is 23%. On the other hand, the average percentage of silt particles in the sub-basins of Iran varies between 19 and 45%, and the average for the whole country is 32%, among which the maximum and minimum percentage of silt particles are in the sub-basins of Qarasu-GorganRoud and Kavir Lut, respectively. Also, the average percentage of sand particles in the sub-basins of Iran varies between 28 and 65, and on the other hand, the average for the whole country is 44%, the minimum of which is related to the sub-basin of Karkheh and the maximum is related to the sub-basin of Kavir Lut. In Gavkhouni and Kavir Lut sub-basins, the reason the low soil erodibility factor is the high percentage of sand in these sub-basins, so that the percentage of sand in the Lut and Gavkhouni basins is 65 and 47% of the total soil particles, respectively. Considering that the average percentage of organic carbon in the sub-basins of Iran varies between 0.3 and 3.9, respectively, these values are related to the sub-basins of Hamun-e-Hirmand and Sefidroud-Haraz, so it can be said that the majority of the country's sub-basins are in poor conditions in terms of the percentage of organic matter. The results show that the southwestern, western and northeastern parts of the country have the maximum amount of soil erodibility factor, and the central Iran and desert parts of Iran have lower erodibility due to having a higher percentage of sand particles. Also, the results show that the lowest average amount of soil erodibility at the sub-basin scale using SoilGrids data with a value of 0.033 (ton*h/Mj*mm) is related to Lut Desert and also its maximum value is 0.045 (ton*h/ Mj*mm) related to it is the sub-basin of Haleh. In addition, the maximum and minimum values of the erodibility index with the HWSD data as an average of the basins of Iran are corresponding to the Mand and Gavkhouni sub-basins, respectively, with values of 0.042 and 0.033 (ton*h/ Mj*mm). So, the results showed that the average soil erodibility factor in Iran using two the HWSD and SoilGrids databases was 0.036 and 0.038 (ton*h/ Mj*mm) respectively.

Conclusion and Suggestions:

The study of soil erodibility with the data of SoilGrids and HWSD at the sub-basins scale showed that the maximum and minimum RE in Atrak and South Balochestan sub-basins are 21 and 1 percent, respectively, and the amount of RE is about 5% for the country average; Therefore, it can be concluded that although the RE between the two databases is not high, SoilGrids data is a more suitable source for soil and water resource modeling due to its continuity and better spatial resolution. Finally, it should be said that although this database is modeled using a larger number of profiles (about 150,000 soil profiles in the world), so they have appropriate accuracy. However, it is necessary to state that investigating the uncertainty of these data in order to improve the results of this database in order to improve the results of that in different parts of the country is recommended to researchers and researchers. Also, it is noteworthy that the EPIC model was used to estimate soil erodibility in this study, while its evaluation and comparison with other soil erodibility estimation models in the country is suggested to other researchers and experts.

Proper management of water and soil resources in a watershed requires recognition the potential of sediment production and runoff. In addition, every year thousands of tons of fertile soil from different lands of the country are unavailable due to soil erosion, and due to the wastage of water and accumulation in sedimentation areas, causes considerable damage. In this regard, the control of soil erosion and flood refers to the ability of ecosystems to conserve soil and water. Therefore, the current research is planned with the aim of evaluation the effectiveness of implementing watershed projects (1376- 1397) on the amount of soil erosion and flood discharge in Chehlkhaneh watershed. Soil erosion and flood discharge were estimated respectively using the MPSIC SCS method. The results showed that the implementation of watershed projects has led to the reduction of soil erosion and sediment (4.30 and 1.80 ton/h) compared to before the implementation of watershed operations (6.05 and 2.30 ton/h). Also, with the increase of the return period of floods, the effectiveness of watershed projects in controlling of watershed flood and reduction of discharge and flood volume increases.

One of the most critical environmental problems globally is soil erosion, which leads to several problems in the field of economy and sustainable development. This study aims to use new methods in soil science studies of the paired sub-catchments to update service descriptions in Dehgin, Hormozgan Province. For this purpose, to select sampling sites of pedons and soil samples, the conditional Latin Hypercube sampling (cLHS) method was used using environmental covariates (digital elevation model), which derivate from unmanned aerial vehicles (UAV), phantom4 pro, and multirotor. The results showed two main land types in the study area, including hills, plateaus, and high terraces. Soil development in the region is mainly influenced by elevation, and the soils of the hill lands are directly related to the type of parent material and slope percentage. In the areas containing wooded pasture and areas with silt loam texture class, the aggregate stability values are higher, which are auxiliary covariates essential and influential parameters in the aggregate stability map. The RMSE and R2 values are 0.32 and 0.26, respectively, for the evaluation map criteria. The values of cation exchange capacity (CEC) and nitrogen in both control and sample sub-catchments are small and the maximum amounts of soil organic carbon in the sample sub-catchment are higher than in the control sub-catchment. The use of new methods including UAV, accurate sampling methods using high-resolution environmental covariates, and digital soil mapping can reduce the number of soil samples, increase the accuracy of output maps, and provide more accurate erosion estimation results, which has reduced time and cost compared to the old methods.

Different forms of water erosion can be observed in many parts of Iran, and the specific role of each factor in sediment delivery can be presented. This research was conducted to investigate the effect of geological formations and topographic features on creating important forms of water erosion in the Golidagh watershed in the Golestan Province.

At first, we used the Google Earth images, aerial photos, maps, and field surveys of the area, so that the forms of erosion and their quality were determined. Lithology, elevation, slope, and aspect were selected as independent variables, and each form of water erosion, including sheet erosion, rills, gullies, and badlands, were determined as dependent variables. After, independent variables information layers were overlay with a layer of erosion forms in the ArcGIS and the relationship between them was obtained through Chi-square (ϰ2 ) distribution using SPSS software.

Overlay analysis of the maps showed that the advanced forms of water erosion, including gully erosion and badlands, are dominant as the loess formations in altitudes less than 800 meters, and were more than expected. Also, an area of all forms of erosion is low at the slope of 0-10 percent and their area increases at the slope of 10 percent and higher. investigation of forms of water erosion in relation with the aspect showed that advanced erosion of the gully and badland had more in southwest area and were more than expected, while the surface lacks erosion predominates in the north, northwest and northeast areas. The relationship between variables with different forms of erosion in the area was determined through the chi-square test. The results showed that the relationship between the studied variables and forms of water erosion in the area is significant at 1%. The intensity of the relationship based on the contingency coefficient indicates the more importance of elevation (0.631) and geological formations (0.461) in the region.

The created forms of erosion are dependent on elevation and lithology in the area, and these variables can be used in selecting appropriate methods and executive strategies for managing forms of erosion and controlling their intensity.

Iran, is located in the arid and semi-arid regions of the world, so due to geological and topographic conditions, has various and extensive limitations in soil resources and lands. These restrictions, along with unprincipled and intensive exploitation over the past few decades, have posed many challenges to these resources and thus endangered food security and public health. In this article, while briefly stating the importance and functions of soil, the current situation, and the most important challenges and limitations of soil resources in the country are explained. According to available information and data, soil water and wind erosion is the most important cause of soil degradation in Iran, which has many economic, social and environmental consequences. The lowest soil erosion estimated in the country is much higher than its tolerable (average amount of soil formation). The most important cause of soil degradation in agricultural lands, especially irrigated farms, is soil salinity. At least 50% of the country's irrigated lands are facing an increasing problem of salinity. Land use change can be considered as the most important and urgent challenge of the soil resources, especially fertile lands, which also has negative economic, social, cultural and security consequences. Lack of organic carbon and loss of soil fertility, especially agricultural lands, are important limitations of soil quality that severely threaten food security and health. The degradation of soil resources has not only affected its productive function, but has also drastically reduced the capacity of lands and territories to cope with climate change, drought and floods. Occurrence of floods with a frequency greater than the return period of rainfall events, as well as hydrological and agricultural droughts, more severe than climatic droughts, are signs of this degradation.

Rangeland suitability for livestock grazing is assessed by scoring criteria for vegetation, water resources and soil erosion. In this study, the suitability of Lar Absar rangeland in Mazandaran province for grazing domestic animals and herbivorous wildlife grazing from the rangeland was investigated. Many researchers have examined pasture suitability for grazing cattle, sheep, goats, and camels; But very little research has been done on grazing for wildlife (along with livestock). The purpose of this study is to calculate the actual rangeland suitability for livestock grazing so that high efficiency and more effective management can focus on the rangeland. This has not been done in the research mentioned.

The present study was conducted in a part of Haraz river basin, Mazandaran province, Amol city, Larijan section, Lower Larijan village, Lar Absar rangeland. In July 1398, sampling was carried out in the area representing plant types in a systematic random method with the establishment of two 100-meter transects and 10 plots of one square meter in each plant type; Production of grazable plant species was measured by cutting and weighing. Type and statistics of wildlife were received from Mazandaran Environment Department. The type of plants used was also determined by asking the shepherds. Plant species palatability was determined for wildlife using different sources. The recommended coefficients for appetizer class I were> 0.50, for class II was 0.30 and for class III was 0.20. The list of plant species was written in each type and after applying the coefficient of palatability, the percentage of palatability was obtained for each animal in each type. In the above-mentioned guidelines, vegetation criteria, water resources and soil erosion were examined.

According to the list of plant species in Lar Absar rangeland, 76 plant species from 24 families were identified; Of these, Poaceae and Asteraceae families with 13 and 12 plant species, respectively, have the highest abundance. The results show that wheatgrass and chicory families are predominant among other plants. These plants are important for livestock (35); And provide a large portion of livestock feed (10). The results of this study showed that after the wheat and chicory families, the mint and legume families are abundant in the rangeland. The results showed that the suitability of different plant types for livestock grazing is different and the factor that reduces grazing suitability (domestic livestock and wildlife) is the slope. Plant type 7 is good for grazing livestock and plant type 2 (Fe.ov-On.co) is good for grazing sheep and for other types of livestock.

According to the results of this study, it seems that Lar Absar rangeland is suitable for grazing domestic animals and wildlife. Pasture grazing wildlife is not limited to wild goats and whole rams and wild ewes; Other animals, such as deer, deer, etc., may also graze in the pastures. The difference is the slope, which is a topographical and environmental factor. Therefore, it can be concluded that grazing of livestock and wildlife is possible together and management can provide a correct planning with high efficiency by classifying pasture slope.

Accelerated soil erosion and high sediment production are important issues in many parts of Iran. The identification of high erosion risk regions is necessary for the planning of soil and water conservation measures in order to reduce erosion damages. Empirical models are required for estimating soil erosion and sediment yield in the absence of gauged small watersheds. The Erosion Potential Method (EPM), originally developed in Croatia, is a popular erosion estimating model in Iran; however, its efficiency across the country has not been thoroughly assessed. Therefore, a calibration study was carried out by comparison between the model the estimated and measured sediment yields through sediment survey for 63 reservoirs at the outlet of small catchments in the Semnan, Markazi, Isfahan, Chaharmahal va Bakhtiari, West Azarbaijan, Lorestan, Fars, Golestan, and the Khorasan Razavi Provinces. All required maps and information of the study basins for estimating the EPM sediment yield were produced via field survey as well as data analysis. Comparison of the results showed that in most cases, the model estimates (0.19 to 9.71 tons per square kilometer per year) are lower than the measured sediment yields ​​at the reservoir inlets (0.44 to 459.64 tons per square kilometer per year). Thus, we calibrated the EPM by modifying its original tables and evaluated the results using the Nash‐Sutcliffe efficiency coefficient in two scenarios, a, all basins, and b, after dividing into three geographical zones, which significantly improved the estimates. The Nash ‐ Sutcliffe efficiency coefficient for scenario a was 0.66, and 0.68, 0.50 and 0.89 for the Central, Zagros, and Northeast zones, for scenario b respectively. Based on the results, it is strongly recommended to use the modified EPM instead of the original model.

Acidic rainfall is one of the complications of industry life that a point of view geographically in recent years spread widely and the attention of many researchers has been found. These rains have significant effects on the different ecosystems of earth. In this study, in order to investigate the sensitivity of erosion and sediment yield of Gachsaran Formation to acidic rainfall and its density change, parts of the Kuhe Gach watershed area in Izeh Township are selected with the area of 1202 hectares. This investigation in order to determine productivity runoff and sediment in 8 points and with 3 replicates in Gachsaran formation in different intensities 1, 1/25 mm in min and in the intensities of distilled water and 4, 5 acidic water in four aspects of northern, southern, eastern, western with using kamphorst rain simulator was done. In order to analyze statistical was used SPSS and EXCEL packages. The highest of runoff and sediment rates in Gachsaran formation in 1, 1/25 mm in min are related to 4 acidic rainfalls. The rainfall of 5 acidic also runoff and sediment are more than the rain of distilled water. The infiltration rates in rainfall different intensities also showed a significant difference.