نشریه آب و خاک
سال سی و هفتم شماره 3 (پیاپی 89، امرداد و شهریور 1402)

IntroductionWheat (Triticum aestivum L.) has become very important as a valuable strategic product with high energy level. The importance of investigating environmental stresses and their role in predicting and evaluating the growth and crops yield is essential. A wide range of plant response to stress is extended to morphological, physiological and biochemical responses. Considering the rapid advancement in computer model development, plant growth models have emerged as a valuable tool to predict changes in production yield. These growth simulation models effectively incorporate the intricate influences of various factors, such as climate, soil characteristics, and management practices on crop yield. By doing so, they offer a cost-effective and time-efficient alternative to traditional field research methods. Material and MethodsThis research was conducted in the research farm of Varamin province, which has a silty loam soil texture. The latitude and longitude of the region are 35º 32ʹ N and 51º 64ʹ E, respectively. Its height above sea level is 21 meters. According to Demarten classification, Varamin has a temperate humid climate. The long-term mean temperature of Varamin is 11.18 ° C and the total long-term rainfall is 780 mm. In this study, in order to simulate irrigated wheat cv. Mehregan growth under drought stress, an experimental based on completely randomized blocks (CRBD) including: non-stress as control (NS), water stress at booting stage (WSB), water stress at flowering stage (WSF), water stress at milking stage (WSM) and water stress at doughing stage (WSD) with three replications during growth season 2019-2020 was carried out in Varamin, Iran. Crop growth simulation was done using SSM-wheat model. This model simulates growth and yield on a daily basis as a function of weather conditions, soil characteristics and crop management (cultivar, planting date, plant density, irrigation regime). Results and DiscussionBased on the results, the simulation of the phenological stages of irrigated wheat cv. Mehregan under water stress condition using SSM-wheat model showed that there was no difference between observed and simulated values. Summary, the values of day to termination of seed growth (TSG) were observed under non- stress, stress in the booting stage, flowering, milking and doughing of the grains, 222, 219, 219, 221, 221 days, respectively andsimulation values with 224, 221, 220, 221, respectively. However, with their simulation values, there were slight differences with 224, 221, 220, 221, respectively. Acceptable values of RMSE (11.7 g.m-2) and CV (3.5) indexes showed the high ability of the SSM model in simulating the grain yield of irrigated wheat cv. Mehregan under water stress conditions. Grain yield values were observed in non-stress conditions of 5783, water stress in booting, flowering, milking and doughing of the grain stages in 5423, 5160, 5006 and 5100 kg. h-1, respectively. While the simulated values were 5630, 5220, 4920, 4680 and 4880 kg. h-1, respectively. Based on the findings, observed and simulated values of leaf area index (LAI) were observed under water stress condition in the booting, flowering, milking and doughing of the grain stages (4.3 and 4.47), (4.33) and 4.46), (4.4 and 4.57) and (4.4 and 4.58) cm-2, respectively. Evaluation of the 1000-grain weight of irrigated wheat cv. Mehregan under the water stress showed that the SSM model was highly accurate. RMSE (4.6 g.m-2) and CV (1.8) values indicate the ability of the SSM model to simulate the 1000-grain weight of irrigated wheat cv. Mehregan. Also, the simulated values of the harvest index were 34.7 % in non-stress conditions, which decreased by 6 % compared to the observed value. Harvest index values were observed under water stress conditions in the in the booting, flowering, milking and doughing of the grain stages in 30.2, 29.3, 29.9 and 29.5 %, respectively. Compared to its observed values, it was reduced by 3, 3.5, 5, and 5.5 %, respectively. ConclusionBased on the findings, the slight difference between the observed and simulated values demonstrates the SSM model's capability to accurately capture water stress impacts on the phenological stages, grain yield, and yield components of irrigated wheat cv. Mehregan during critical growth stages, including booting, flowering, milking, and doughing. The results indicate that the SSM model is effective in simulating wheat growth under water stress conditions, showcasing its potential as a valuable tool for modeling irrigated wheat growth. The model's ability to account for water stress and its effects on various growth parameters makes it a reliable and efficient tool for predicting crop performance in water-limited environments.

IntroductionDevelopment of reservoirs helps to meet food and energy needs by supplying water for agriculture and hydropower plants. Efficient management of water resources is important and vital to overcome the problems of water leakage and meet agricultural, industrial and drinking needs. Each of these requirements creates limitations in the way the reservoir is operated, which requires accurate information on the changes in the reservoir storage and other influential components during the operation period. In order to manage and plan water resources at country scale, using reservoir simulation models as a suitable tool in simulating processes related to dams, such as the operation of water reservoirs, will be very effective. Reservoir simulation models such as the HEC-ResSim model provide the opportunity to simulate the natural and hydrological processes related to the water resources system and the relationships between the supply and demand sectors by implementing a schematic structure of a real reservoir. Two scenarios of water savings of 20 and 30 percent were used in the current investigation.  Additionally, using this method, the objectives of water resource management can be assessed.Materials and MethodsIn the present study, the use of the Latian reservoir in real conditions was simulated using the HEC-ResSim model. The simulation was carried out according to the river's inflow from 1968 to 2018, downstream water needs, energy production capacity by turbines, physical characteristics and reservoir building. The implementation of the HEC-ResSim model is summarized in three steps. The Watershed Setup module is used to introduce the general outline of the watershed. In this module, the shape and geographical location of the basin and related elements such as rivers, reservoirs, hydrometric stations and other projects in it should be specified. The Reservoir Network module is used to introduce the desired reservoir network and to enter the physical characteristics and how to use them. The Simulation module is designed to introduce the simulation period and display the model outputs.  In this module, the simulation time and period and the operation pattern should be determined.Results and DiscussionAccording to the results obtained from the reservoir simulation model, the average storage capacity of Latian dam for the simulation period was estimated to be 41 million cubic meters, which shows a significant drop of 49% compared to the normal level (83 million cubic meters). Additionally, for the same period, it was estimated that the average discharge was equivalent to 5.4 cubic meters per second and the average inflow to the reservoir of the Latian dam was equal to 5.7 cubic meters per second. This is in contrast to the period's average demand, which for the area downstream of the Latian Dam is 12.1 cubic meters. The findings indicate that the reservoir of the dam frequently, and particularly at the conclusion of the simulation period, is unable to satisfy the needs of the downstream. Additionally, according to the findings of the current study, the Latian dam power plant's (Kalan) average annual hydro-electric energy production was projected to be 68,000 MWh, and the results show that in accordance with the policy of operating the Latian dam in the majority ofthe years, the Kalan power plant is able to supply the electricity required in the study area. According to the results, the average reservoir volume of Latian dam for the entire period in the first and second scenario was estimated to be 49 and 63 million cubic meters, respectively. Also, by applying the first and second water saving scenarios, the Latian dam reservoir will be able to generate 66,000 and 63,000 MWh of energy annually.ConclusionIn this study, the functioning and operation of the Latian dam reservoir was used by applying the Hec-ResSim reservoir simulation model. After entering data such as the elevation and length of the dam, surface-volume-elevation curve, evaporation from the surface of the reservoir, elevation and uncontrolled outlet coefficient, dam storage areas, rule curve, were simulated by the model. In the present study, the values of inactive volume and conservation volume of Latian Dam were estimated as 28 and 83 million cubic meters, respectively. The average water release of Latian dam for the first and second 25 years of operation was equal to 6.1 and 3.7 cubic meters per second, respectively, which met 50 and 32% of the downstream demand on average. The results indicate that the success rate of Latian dam in supplying drinking, industry and downstream environment for the period of operation is 42%. Also, 16 years out of 50 years of operation, Kalan hydropower plant has fully met 100% of the needs. On average, the large power plant is able to provide 80% of the energy needs of the study area for the entire simulation period.

 Rill erosion is one of the main factors of soil degradation, especially in rainfed lands in semi-arid regions. These soils have relatively lower organic matter content with weakly-aggregated units, which increases their susceptibility to water erosion processes. Conventional tillage systems are adversely affect on soil structure and surface soil cover in rainfed lands. Raindrop energy and flow shear stress are the main erosive factors in the slope lands. The raindrop impact destroys soil structure and changes it to erodible unites; micro-aggregates and single particles, and so makes them to more detachment. A few studies have been done on the role of raindrop impact to soil erosion by water. Nevertheless, there is no sufficient information on the effect of raindrop impact on soil loss in the rills particularly in semi-arid regions. Therefore, this study was conducted to investigate the role of raindrop impact on soil loss from rills in various soil textures under different rainfall intensities.
 

 A laboratory experiment was performed on two soil textures (clay loam and sandy loam) under four rainfall intensities (30, 50, 72 and 83 mm.h-1) in two rainfall conditions (under raindrops impact and without raindrops impact). Soil samples (0-30 cm) were taken from a semi-arid region in Zanjan province in 2020. The experiments were set up in an erosion flume with 100 cm long and 60 cm width and 15 cm depth which were exposed to simulated rainfalls for 30 min duration. Runoff and soil loss were measured at three rills under slope gradient 10% in the two rainfall conditions for each rainfall intensity. Soil loss from rills was determined as the mass of sediment collected from rill outlet per rill surface area (g.m-2). Under raindrop impact, the soil was exposed directly to raindrop impact and under without raindrop impact, a metal mesh sheet was used to eliminate raindrops impact to soil surface. The role of raindrops impact to runoff and soil loss was computed from the difference of runoff and soil loss under raindrops impact and without raindrops impacts. A t-test was used to assess the role of raindrops impact between the two rainfall conditions for the soils and rainfall intensities.  
 

 Results indicated that runoff production and soil loss were significantly affected by the soil texture and rainfall intensity. Runoff and soil loss under raindrops impact increased in the soils with increasing rainfall intensity. Clay loam showed more runoff production and soil loss than sandy loam which was associated to lower aggregate stability and hydraulic conductivity. Runoff and soil loss in the two soils and four rainfall intensities were significantly affected by raindrops impact. Runoff production and soil loss except to 72 mm.h-1 rainfall intensity were very higher under raindrop impact than without raindrop impact. It seems under 72 mm.h-1 rainfall intensity, raindrops impact varied the rill’s morphology and prevent more runoff production. Runoff production in clay loam and sandy loam under raindrop impact were increased by 44 and 36 percent, respectively (p< 0.01). Soil loss resulted by raindrop impact in clay loam and sandy loam increased by 53 and 62 percent, respectively (p< 0.01). Raindrops impact had more importance in soil loss rather than runoff production. This result is related to the role of raindrops impact in destroying aggregates and producing more erodible soil particles and closing soil macrospores and declining water infiltration. The role of raindrop impact in runoff production and soil loss varied among the rainfall intensities. A slight reduction in the role of raindrop impact in runoff and soil loss was occurred with increasing rainfall intensity, especially in sandy loam.
 

 The role of raindrop impact in runoff production and soil loss was significantly affected by soil type and rainfall intensity. Raindrops impact has more important in runoff and soil loss in the soils having higher aggregate stability and more hydraulic conductivity. The role of raindrop impact in runoff and soil loss in these soils declines with increasing rainfall intensity. In general, maintain soil surface cover is essential to control raindrops impact and decrease runoff and soil loss in semi-arid areas. The importance of soil surface cover is most obvious under different rainfalls in weakly-aggregated soils which are dominant in many slope lands. Also, soil surface cover has important role in controlling runoff and soil loss under heavy rainfalls in soils with more water-stable aggregates. Prevention from intensive tillage and using conservation tillage systems such as minimum tillage are effective strategies in controlling raindrop impact in rainfed lands in semi-arid regions.

Changing land use may have a major influence on physical, chemical, and biological soil properties with a consequence for soil functioning and productivity. Abandonment of agricultural lands is actually a kind of restoration of these lands to their original natural conditions, which is often done through human intervention. Soil restoration after land abandonment is a complex phenomenon. The pastures of our country are typically cultivated in rainfed methods, and the use of agricultural inputs such as animal manure, poisons, and chemical fertilizers is not very common. Therefore the continuous cultivation of a product and the lack of use of agricultural inputs causes a gradual decrease in fertility and increase erosion. Hence, after years of cultivation, the production potential decreases, and the land is abandoned.
This study was conducted to determine the effects of land abandonment on some physical, chemical, and biological soil properties in the 0-20 and 20-40 cm depth at three different sites including Lal Abad, Qaleh Kohneh and Chalab-e Pain, using 2×2 factorial layout arranged in a completely randomized design (CRD) with three replications. The physical, chemical, and biological characteristics of the soil were measured by conventional laboratory methods. Electrical conductivity of saturated paste extract (ECe) with electrical conductivity meter device in saturated paste extract, pH of saturated paste with pH meter device, and bulk density by cylinder method were determined in the samples. The amount of dispersible clay (DC) was determined by the method of Gee and Bauder and the Mean Weight Diameter (MWD) was determined by the method of the wet sieve. The amount of absorbable phosphorus by extraction method and total soil nitrogen by Keldahl method were measured in the samples. The amount of soil organic carbon (OC) in the samples was determined by the method of Walkley and Black. Mineralization of organic carbon (soil respiration) (Cmin) and metabolic quotient (qCO2) were obtained by validated and conventional methods.
 The results showed that the abandonment of agricultural lands significantly increased the MWD and reduced the amount of dispersible clay. Bulk density also decreased due to the abandonment of agricultural land in all areas except the Qaleh Kohneh area. The results of the analysis of the chemical characteristics of the soil indicated a decrease in soil pH in all areas and depths, except in the Qaleh Kohneh area. The biological results also showed that the abandonment of agricultural lands caused the change in biological characteristics. Abandonment of agricultural lands in all three regions led to an increase in microbial biomass carbon and soil microbial respiration. High microbial respiration in abandoned lands is probably related to more organic carbon in these soils. Loss of soil organic matter due to cultivation and improper soil management is often the main reason for reducing soil respiration in agricultural lands compared to abandoned lands.
Changing land use from agriculture to abandonment improved the physical, chemical, and biological indicators of soil quality, especially the surface layer of the soil, which ultimately led to the improvement of soil quality in all the studied areas. It can be concluded that the release of agricultural lands has increased soil health by increasing the carbon input into the soil, improving the soil aggregates, and improving the microbial activity of the soil.

Introduction Changes in soil properties depend on factors such as climate, topography, landscape features, altitude, parent material, and vegetation. The quantity and quality of soils obtained from different rocks (igneous, sedimentary and metamorphic rocks) depend on the minerals that make up the rock, as well as weather and other factors. Soil parent material is one of the primary and important issues in soil classification in terms of physical quality and also one of the most important effective factors in soil erodibility. The topographical factor of each region is one of the important and influential features on the soil quality of that region. The present research was conducted with the aim of understanding the spatial changes of soil properties in different slopes and different types of rocks. Material and Methods The studied area is located in Razavi Khorasan province in the cities of Mashhad, Chenaran, Sarakhs and Torbat-Haidarieh. The geographic location of the region ranges from 58 degrees and 52 minutes to 60 degrees and 40 minutes east longitude and 35 degrees and 38 minutes to 36 degrees and 25 minutes north latitude. This research was carried out on seven types of rocks: granite, Sarakhs paleogene limestone, Chenaran jurassic limestone, marl, shale, sandstone and ophiolite from relatively pure rocks of Razavi Khorasan province. In the present study, two factors of rock type and slope were investigated as effective factors of soil properties. Soil samples were taken from the surface layer (0-20 cm) and from three slope classes ie., less than 10%, 10-25% and more than 25%, as well as all soil samples from the southern slopes. Tree soil samples were taken from each slope and a total of 63 samples were taken and the samples were transfered to the laboratory for physical and chemical tests. In this study, the soil particle size distribution (texture) was measured by hydrometer method, organic carbon and calcium carbonate were determined by wet oxidation and titration with HCl 6 M, the mean weight diameter of soil aggregates and surface crust factor were calculated by related equations. To measure soil cohesion and penetration resistance were used pocket vane test and pocket penetrometer, respectively. Comparison of means was done through Duncan test in spss software. Results and Discussion The results showed that all the studied variables in different types of stones had a significant difference at the level of 1%. There was no significant difference in the variable of surface level in different slopes. Also, the variables of calcium carbonate percentage and saturated conductivity at 5% level had significant differences in different slopes. Other characteristics of soil, including percentage of organic matter, the mean weight diameter of soil aggregates, the number of drops impact, and soil cohesion and penetration resistance in different slopes had a significant difference at the level of 1%. Althoug the soil texture class was not significantly different in different slopes, the percentage changes of clay, silt and sand had a lot of difference along the slope. The highest and lowest parameters of organic matter percentage, Soil cohesion and penetration resistance were observed in granite and shale, respectively. The highest percentage of calcium carbonate was observed in Chenaran limestone (40.41%) and the lowest in granite (14.72 %). The mean weight diameter of soil aggregates was the highest in ophiolite (1.005 mm) and the lowest in marl (0.403 mm). The mean weight diameter of soil aggregates in the medium slope was significantly higher than the other two slopes. The parameter of the number of drops impact was the highest in granite (47.14 number) and the lowest in marl (27.70 number). The highest value of saturated conductivity variable was observed in marl rock and the lowest value was observed in Chenaran limestone. Conclusion The results showed that all the investigated variables had significant differences in different types of stones. Also, some of the investigated variables such as percentage of organic matter, percentage of equivalent calcium carbonate and the mean weight diameter of soil aggregates had significant changes along the hillside. As a general conclusion, given that the physical and chemical properties of the soil are partly under the influence of the parent material and the slope, and also with the presence of good geological information in the country, it can be suggested to provide suitable management solutions to prevent soil erosion and degradation by comprehensive examination of soil properties under different slope and types of stones.

IntroductionThe contamination of agricultural soils with heavy metals is considered as a fundamental problem of industrial and non-industrial societies all over the world, which is increasing significantly with technological advances and is considered a serious threat to the environment, soil and human health. One of these heavy metals is cadmium, which has entered the environmental cycle due to various industrial activities such as metal smelting, battery manufacturing, paints, and plastic production. One of the suitable methods for cleaning the soil contaminated with heavy metals is to stabilize the elements by adding a modifier to the soil, which leads to a decrease in their mobility and bioavailability during the processes of absorption, oxidation and reduction, complexation or deposition. The use of iron nanoparticles is a new generation of environmental cleaning technology that can be an economic solution to some problems caused by pollutants, unlike traditional methods. Considering the importance of soil as a plant food holder and its special role in the food chain and the harmful effects of pollutants such as heavy metals in the soil, this research seeks to explore the potential of magnetic iron nanoparticles in remediating cadmium-contaminated soil. The study aims to investigate the effectiveness of these nanoparticles in reducing cadmium levels and their impact on the distribution of cadmium in different soil components. Materials and MethodsThe experiments were carried out in the chemical and biological research laboratory of the Department of Soil Science and Engineering of Maragheh University. To conduct the experiment, a soil sample from Ajabshir city with a geographic location of 54 degrees 46 minutes 51.7 seconds east longitude and 37 degrees 24 minutes 34 seconds north latitude located in East Azarbaijan province with an altitude of 1451 meters above sea level, with this The target of extractable cadmium less than 1.16 mg/kg of dry and textured soil (loam) was selected. This experiment is factorial based on random design with two factors of heavy metal cadmium from cadmium sulfate source including cadmium concentrations at three levels of zero, 6 and 12 mg/kg of soil and the factor of magnetic iron nanoparticles at three levels of zero, 1 and 2% in The time was four weeks after the addition of cadmium treatments and it was implemented in three repetitions. After measuring some physical and chemical properties of soil, cadmium concentrations in different species and ionic fractions were measured according to the method provided by Tisser. Finally, the obtained data were analyzed using SPSS and MSTATC software and the means were compared with Duncan's multiple range test at the level of five and one percent probability and the results were interpreted. Discussion and ConclusionBy increasing the amount of cadmium treatment levels from 6 to 12 mg/kg, the amount of cadmium absorption in the exchange phase decreased. Therefore, the increase in the amount of cadmium levels in different levels of iron nanoparticles reduced the absorption of cadmium in the exchange phase, which in turn reduced the ability of the plant to absorb cadmium and removed cadmium from the plant. By increasing the amount of cadmium in the soil by 1%, nanoparticles increased the amount of cadmium extracted from the carbonate phase. Increasing the amount of cadmium added to the soil at different levels of nanoparticles, the amount of cadmium absorption extracted from the carbonate phase increased, and at the level of 12 mg cadmium/kg, the amount of cadmium extracted from the carbonate phase increased compared to the level of 6 mg cadmium/kg. In cadmium treatments at the level of 12 mg/kg, the amount of cadmium extracted from the phase of iron and manganese oxides were increased compared to cadmium at the level of 6 mg/kg, and in the same treatments at the level of 12 mg/kg, the amount of cadmium extracted was increased with the increase in the amount of nanoparticles. The results showed an increase in the phase of iron and manganese oxides, which may reduce the amount of cadmium available to the plant. In cadmium treatments at the level of 6 mg/kg at the level of 1% of nanoparticles, compared to the other two treatments, an increase in the amount of cadmium extracted from the oxide phase was observed. In the treatment of cadmium at the level of 12 mg/kg, the amount of cadmium extracted from the phase of organic matter increased compared to the treatment of cadmium at the level of 6 mg/kg. Indeed, the research findings reveal an interesting trend in the impact of increasing iron nanoparticles at both cadmium levels of 6 and 12 mg/kg. Specifically, the changes in the amount of cadmium extracted from the organic phase of the soil follow a consistent pattern. Initially, as the iron nanoparticles were introduced, the cadmium extraction from the organic materials decreased. However, at higher levels of nanoparticles, the cadmium extraction started to increase again.This trend suggests that the presence of a higher concentration of nanoparticles may play a role in stabilizing cadmium in the organic matter of the soil. As a result, it may reduce the accessibility of cadmium to plants. In the treatment of cadmium at the level of 12 mg/kg, the amount of cadmium extracted from the residual phase increased compared to cadmium at the level of 6 mg/kg. In the examination of cadmium extracted from the residual phase, it was found that, unlike other phases, the difference between treatments at zero cadmium level and other treatment levels of cadmium in the remaining phase was less compared to other phases, so that the amount of cadmium absorbed in the remaining phase 6 and 12 mg of cadmium per kilograms of soil have the lowest values among different absorption phases. Also, another noteworthy point about this examination was the trend of changes in extracted cadmium according to the levels of nanoparticles in all three levels of cadmium, so that with the increase of nanoparticles from zero to 1% in all levels of cadmium, there was a decreasing trend and with the increase of non-particles to two percent, an increasing trend was observed. ConclusionThe results showed that in general, with increasing the level of iron nanoparticles, treatment of 12 kg of cadmium, the amounts of residual cadmium, carbonate, organic and oxide phases increased. Increasing the level of cadmium in different levels of iron nanoparticles reduced the absorption of cadmium in the exchange phase, which reduces the ability of the plant to absorb cadmium and removes cadmium from the plant, so that in the treatment with cadmium at the level of 12 mg/kg, the amount of cadmium extracted from the exchange phase reduced. Also, in the cadmium treatment at the level of 6 mg/kg with increasing the amount of nanoparticles, the amount of cadmium extracted from the exchange phase first increased and then a slight decrease in the amount of absorbed cadmium was observed, while at the level of 12 mg of cadmium, the amount of cadmium increased, absorption reduced, and thus removing cadmium from the plant.

Soil erosion is considered as one of the critical threats to the conservation of water and soil resources. However, until now, its various components, including its spatial changes, have yet to be given due attention. In order to implement soil erosion control and conservation programs in the watershed, it is essential to have basic information leading to know and accurately identify the factors affecting the degradation of soil and water resources. Meanwhile, the CORINE model has been considered as one of the practical models for estimating soil erosion and displaying the spatial distribution of soil erosion with easy and accessible inputs. The CORINE model developed based on the Universal Soil Loss Equation (USLE) was therefore employed in the present study in the GIS environment to determine the potential and actual erosion risks of the Brimvand Watershed in Kermanshah Province, Iran.
 

The main associated factors of soil erosion, viz. soil erodibility and erosivity, such as slope, vegetation, depth, texture, and percentage of gravel, were collected, compiled, and ultimately classified in the ArcGIS software. The Fournier index (FI) and FAO-UNEP drought index (DI) were used to prepare the input maps. The Fournier index reflects the performance of the soil erosive agent. In other words, it shows the role of rainfall on soil erosion. The FAO-UNEP drought index shows the simultaneous performance of evaporation and precipitation on soil erosion of a region. The potential soil erosion risk was obtained by combining slope, erodibility, and erosivity layers. In addition, the actual soil erosion risk map was determined by combining the vegetation map and potential soil erosion risk.
 

Based on the results of the vegetation distribution in the region, the use of rainfed and abandoned lands had the largest area in the watershed, with an occupation percentage of 65.48%. Furthermore, the rangeland and forest areas, with respective coverage of 29.65 and 4.87%, stood in the second and third priority from the viewpoint of the area. The region has varying slopes, but more importantly, it has a low slope. Soil texture, depth, and gravel content significantly affect the area's erosion. The soil depth in a large part of the watershed, especiallywith a slope of less than 4% is more than 65 cm where it is mainly covered by abandoned and rainfed lands. In the studied area, the depth of the soil decreases with height increase, which indicates that the high slopes of the area are dominantly outcrops. Most of the area has gravel contents between 10 and 40%. The erosion potential of the region is not that much high because of the desired features of the affecting factors. According to the potential soil erosion risk, it was determined that about 65.57, 23.62, and 10.81% of the area were classified as intermediate, low, and high erosion potential, respectively. Further, the actual soil erosion risk was categorized as low, intermediate, and high with respective areal coverage of 53.83, 15.53, and 30.64%. It is therefore implied that the amount of erosion and sediment transfer will increase if the land cover in the watershed is declined.  This indicates that the erosion rate was highest in hilly areas due to lack of vegetation and soil with loamy texture. Accordingly, to curb soil erosion and prevent its associated adverse effects in the Brimvand watershed, it is strongly suggested to use lands based on their capability and potential, maintain the present cover status, and carry out management plans to restore vegetation.
 

Soil erosion remains one of the most critical challenges in watersheds, and its neglect can lead to various problems for the beneficiaries. In light of this, the present study aimed to address this issue by employing the CORINE model to assess potential and actual soil erosion in the Brimvand Watershed of Kermanshah Province, Iran. The research findings reveal the pivotal role of vegetation in mitigating soil erosion. Notably, areas with gentle slopes, which are inherently susceptible to erosion, benefit significantly from vegetation cover, leading to a noticeable reduction in erosion. However, the loss of this protective cover can trigger a rapid increase in soil erosion and subsequent loss of valuable soil resources. By shedding light on the spatial distribution of soil erosion, this study emphasizes the importance of preserving and promoting vegetation in the watershed to ensure its long-term sustainability and safeguard the well-being of those who depend on it. Therefore, land utilization should be planned based on capacity and potential of the land to curb erosion and avoid its detrimental impacts in the Brimvand Watershed. In addition, not only the current cover situation has to be maintained but also the vegetation conditions have to be improved through the implementation of managerial and reclamation plans leading to managing soil erosion.

In recent years, soil contamination with potentially toxic elements (PTEs) has become a major problem in most parts of the world. PTEs are naturally generated from the pedogenesis in the soil and are formed mainly by rock weathering. Nevertheless, the natural content of metals, i.e., Cr, Zn, Ni, Pb, Cd, used to be low in the soil, but due to anthropogenic activities such as industrial emissions, atmospheric transportation, sewage irrigation, and application of pesticides and fertilizers, there is an increase in the content of PTEs. PTEs in soil are one of the most important environmental pollutants due to their toxicity, durability, easy absorption by plants and long half-life. Therefore, the assessment of soil health is very important for the sustainable development of agriculture and the rehabilitation of soils contaminated with PTEs. The present study was conducted to quantify PTEs pollution for soil environmental assessment using a flexible approach based on multivariate analysis and using pollution indicators in a part of the central lands of Khuzestan province.
 
For this purpose, in February 2021, 200 surface soil samples (0-10 cm) were taken using stratified random sampling. The collected soil samples were cleaned by removing plant materials and other pebbles, and air dried, powdered, and sieved by using a 2 mm sieve size. The interest in soil's physical and chemical properties i.e., pH was determined with a digital pH meter. Soil textural particles were measured by the hydrometer method, soil organic carbon (SOC) content was estimated by following Walkley and Black method, bulk density (BD) was measured by the Clod method, and total metal content was determined using the aqua-regia solution digestion method and analyzed using Inductively Coupled Plasma-Optical Emission spectrometry (ICP-OEC). The level of Pb, Ni, Zn, Cr pollution was estimated based on environmental indicators including contamination factor (CF), enrichment factor (EF), geo-accumulation index (Igeo), pollution index of individual metals (PI), and modified pollution index of individual metals (MPI). Multivariate statistical methods including correlation analysis, cluster analysis (CA), and principal component analysis (PCA) were used to find the source of metals in the soil. All statistical methods were performed using SPSS (26 version) software.
 
Measurement of soil pH showed that the soil of the studied area tends to alkalinity. Also, the soil texture in this area is loam. The results showed that the SOC in these soil samples is 0.71%, and the range of EC (between 0.18 and 60.5 dS/m) indicates the distribution of saline and non-saline soils in the studied area. The total average concentration of Zn, Ni, Cr, and Pb were 60.26, 50.96, 50.38, and 12.67 mg/kg, respectively. The order of average for heavy metals was Zn> Ni> Cr> Pb. The highest amount of standard deviation and concentration changes were observed in Zn and Pb elements. These two elements also showed a high degree of variation coefficient in the studied area, which can indicate the high impact of human activities on the content of these elements. The results obtained from the application of multivariate statistics showed that there is a positive correlation between the elements such as Zn, Ni, and Pb in the study area, indicating that these metals probably have the same source. Whereas the absence of correlation of Cr with these elements indicates a separate source for this element compared to Pb, Zn, and Ni. There was also a strong relationship among these elements based on the PCA and CA classification. Based on the multivariate statistical analysis the source of pollution for the metals studied was mainly from both anthropogenic and geogenic activities. The results showed that the soil samples taken from the study area are in the low pollution category based on the individual element indices of CF and Igeo, but in the moderate pollution class based on the EF index. In addition, the evaluation based on the cumulative and multi-element indices of PI and MPI showed that 100% of samples have high pollution.
 
The present study concludes that the average values of Zn, Ni, Cr, and Pb were found to be below the guidelines set by the IEPA (Iran Environmental Protection Agency) as well as the Earth's crust values. The results indicate existing relationships among the studied variables, revealing that the heavy metals Zn, Ni, and Zn share the same source in the study area. Additionally, it was observed that the source of Cr is primarily geogenic in nature. These findings highlight the significance of utilizing multivariate statistical methods and pollution indicators in tandem, as they prove to be valuable tools for evaluating and quantitatively determining the potential pollution risk.

Drought is a costly natural hazard with wide-ranging consequences for agriculture, ecosystems, and water resources. The purpose of this research is to determine the characteristics of drought and its types in Iran during the last four decades. Drought turns into different types in the water cycle and imposes many negative consequences on natural ecosystems and different socio-economic sectors. According to International Disaster Database (EM-DAT), drought accounts for 59% of the economic losses caused by climate change. Many parts of the world have experienced extensive and severe droughts in recent decades. In Iran, droughts have occurred frequently during the last four decades and have become more severe in the last decade.
In this research, we used precipitation, temperature, wind speed, and sunshine hours of 49 synoptic meteorological stations during 1981-2020. Drought has been investigated with The Standardized Precipitation-Evapotranspiration Index (SPEI) in four scales of 3, 6, 12, and 24 months, which represent meteorological, agricultural, hydrological, and socio-economic droughts. To calculate the SPEI, the precipitation variable (P) is analyzed with the cumulative difference between P and potential evapotranspiration (PET). In other words, surplus/deficit climate water balance (CWB) is considered. The FAO Penman-Monteith method was used to calculate PET. Then, using the RUN theory, the characteristics of drought, including its magnitude, duration, intensity, and frequency, were determined for all four investigated scales.
The results showed that the frequency of drought events fluctuates from a minimum of 12.13% to a maximum of 18.13% in different regions of the country during 1981-2020. The climatological study of drought characteristics shows that the most frequent drought events occurred in the west, southwest, and southern coasts of the Persian Gulf and northwest of Iran compare to other regions of the country. This is while the duration of the drought period is longer in the eastern and interior regions of Iran. Examining the types of droughts shows that more than 60% of the droughts occurring in Iran are moderate droughts. Moderate and severe droughts are mostly seen in the west, southwest, and northwest of Iran. The duration of Iran's drought varies from at least 3 months in meteorological drought to more than 8 months in socio-economic drought. Therefore, droughts are more frequent in the western regions and longer in the eastern regions. The intensity of drought is also higher in the eastern and interior regions than in the western and northwestern regions of Iran. The decadal changes of drought show that the duration and magnitude of drought in Iran have increased and the severity of the drought has decreased during recent decades.
The intensity, magnitude, and duration of the drought period in Iran increased with the increase of the investigated scales from 3 months to 24 months. Examining the average frequency of drought showed that as we move from meteorological drought to socio-economic drought, the frequency of drought increases, which confirms the previous findings. The eastern and southeastern parts of Iran have experienced a longer duration and larger magnitude of drought than the western and northwestern Iran, which can be caused by the climate conditions of this region, i.e., high temperature and evapotranspiration and less precipitation, and seasonality.
The maximum magnitude of drought in Iran is related to socio-economic drought (SPEI-24) followed by hydrological drought (SPEI-12). This characteristic has increased especially in the last two decades (2001-2020) compared to the previous decades (1981-2000). This is while the magnitude of meteorological (SPEI-3) and agricultural (SPEI-12) droughts do not increase much in the last two decades compared to the previous decades.
Anthropogenic activities play a more prominent role in increasing the magnitude of socio-economic (SPEI-24) and hydrological (SPEI-12) droughts than natural forcing. With the construction of many dams and the digging of countless deep wells, as well as changing the direction of rivers, the water cycle has been completely affected by human activities during the last four decades in Iran. Obviously, anthropogenic activities play an important role in increasing the magnitude of hydrological and socio-economic droughts. In contrast, meteorological and agricultural droughts have not shown many changes in Iran.
The results of the decadal average of drought intensity showed that this characteristic of drought in the last decade (2011-2020) has decreased compared to previous decades (1981-2010). On the other hand, as mentioned earlier, the magnitude and duration of drought, especially for hydrological and socio-economic droughts, have increased in the last two decades (2001-2020). Therefore, the reason for the decrease in the severity of the drought has a statistical explanation before it has a climatic reason because the severity of the drought is calculated by dividing the magnitude of the drought by its duration.

Achieving food security in the future with sustainable use of water resources will be a big challenge for the current and future generations. Population increase, economic growth and climate change intensifythe pressure on existing resources. Agriculture is a key consumer of water, and it is necessary to closely monitor water productivity for it and explore opportunities to increase its productivity. Systematic monitoring of water productivity through the use of remote sensing techniques can help identifying the gaps in water productivity and evaluate appropriate solutions to address these gaps.
 
Qazvin plain is known as a hub of modern agriculture by providing about 5% of the country's agricultural products. Therefore, estimating water demand and water productivity in agricultural management in the region is considered important and necessary. In order to monitor water productivity through access to various data across Africa and the Middle East, the WaPOR database provides the possibility to examine the rate of evapotranspiration, biomass and gross and net biomass volume productivity based on the land use map in the period of years 2009 to 2021. In this database, it is possible to check the mentioned items at three levels with different spatial resolution, which according to the scope of the study, it is possible to check values with a spatial resolution of 250(m). In order to determine the efficiency and accuracy of the land cover classification map of the WaPOR database, the results obtained are examined and compared with the Dynamic World model, which represents a global model with high accuracy. For this purpose, the latest land use map related to 2021 Using the WaPOR database and Dynamic World in the GEE system, it was prepared and based on the classification of the region in order to check the accuracy of the user map of the WaPOR database and to determine the percentage of each class compared to each other. Finally, all estimable indicators were calculated and checked by the WaPOR database during the years 2009 to 2022.
 
The amount of evapotranspiration of the plants covered by the irrigation network in the period of 2009 to 2016 has been associated with a relatively stable trend, but this trend has decreased in 2017 onwards, which is one of the reasons for the decrease in the amount of evapotranspiration in this the period of time and can refer to the lack of water available to the plant due to the limited water resources in recent years. The investigation of the total amount of biomass in different lands shows that during the years 2009 to 2022, this index has been accompanied by a gradual increase in all uses, so that the amount of TBP index in 2020 was 17% more than in 2009. It shows the amount of biomass in different lands. The amount of biomass in the lands covered by the water network is 5 to 6 times higher than that of the rainfed lands. Among the influential parameters in estimating the TBP index, we can mention the amount of evaporation, transpiration, and transpiration, the increase or decrease of each of these parameters will have a significant impact on the estimated amount of biomass. The results showed that the amount of biomass production in the areas covered by the irrigation network largely depends on the high transpiration rate in these areas. From the beginning of 2009 to 2016, the gross amount of biomass water in the lands covered by the irrigation network has been accompanied by an increase, but in 2017, drastic changes in the process of underground changes will decrease the area of the lands covered by the network and many of these lands. It has been turned into fallow and rainfed lands. The analysis of NBWP index also showed that the amount of net productivity in rainfed lands is strongly dependent on the annual increase rate, and much of the crop yield in rainfed lands is dependent on the amount received. Among the influential parameters in estimating the total amount of biomass, we can mention the amount of evaporation, transpiration and transpiration, the increase or decrease of each of these parameters will have a significant impact on the amount of estimated biomass.
 
WaPOR database data can play an important role in estimating the rate of delayed transpiration and parameters related to water productivity in the region due to its ten-day spatial resolution and the absence of data gaps. In general, the WaPOR database can be used as a guide in the reliable determination of evapotranspiration values and planning related to water resources in the agricultural sector.