فصلنامه پژوهش های فرسایش محیطی
سال ششم شماره 3 (پیاپی 23، پاییز 1395)

In the arid and semi-arid areas of Asia, dust storms occur frequently. Much progress has been made in the monitoring modeling and prediction of Asian dust storms. Dust emission is caused by wind erosion in the sensitive areas. Wind erosion is described as the transportation of soil particles by means of the wind. Soil Surface moisture is one of the most important factors that affects wind erosion. Soil Surface moisture is very low in deserts; consequently, appropriate land surface module must be used for accurate soil moisture and dust simulation. The difficulty in the initialization of soil moisture fields over mesoscale or regional domains and the inability of simple soil moisture models to track realistically the long-term evolution of soil moisture fields suggest the need for some kind of data assimilation for the dynamical adjustment of soil moisture fields. The key elements of the land surface model include soil moisture and evapotranspiration based on the ISBA model. The surface model includes a two-layer soil model with a 1-cm surface layer and a 1-m root-zone layer.
THEORETICAL FRAMEWORK: Efforts have been made to develop integrated dust modelling systems which couple the models for atmospheric, land-surface, and aeolian processes, real-time dust observations and databases for land-surface parameters, so that the dust-storm dynamics and the environmental control factors are adequately represented. The modeling component comprises an atmospheric model and some modules for the land-surface processes, dust emission, transport, and deposition. Land-surface data are required for the atmospheric model as well as for the land-surface, dust-emission, and dust-deposition schemes. In this study, Pliem Xiu and NOAH land surface modules were used and their dust simulations were compared.
Land surface models are becoming increasingly common components of mesoscale meteorological models. The Pleim–Xiu land surface model has been incrementally improved by the addition of an alternative indirect data assimilation technique. The soil moisture assimilation technique developed for this model differs from the techniques used with the ISBA model in two ways. First, instead of the incremental periodic adjustments to the soil moisture, the continuous Newtonian relaxation or “nudging” was used. Second, nudging coefficients were defined according to the model parameters rather than statistical analysis. The nudging soil moisture tendencies were
.Soil moisture tendencies were evaluated every model time step using the current forecast values of T and RH as compared with the “observed” values interpolated from periodic (usually 3 hourly) objective analyses. When the deep soil moisture w2 exceeded the field capacity, further moistening through nudging was not permitted but drying was allowed. In a similar way, when w2 fell below the wilting point, only nudging in the moistening direction was allowed. These restrictions prevented runaway moistening or drying when model biases did not respond to the soil moisture adjustments.
Results indicated that the Pliem Xiu module simulated low levels of soil surface moisture and accurate dust concentrations. The soil surface thickness of the Pliem Xiu was 1 cm and the soil surface thickness in the NOAH was 10 cm.
CONCLUSIONS AND SUGGESTIONS: Land surface models are becoming increasingly common components of mesoscale meteorological models. It seems that lower thickness in Pliem Xiu caused faster response of the soil surface moisture to atmosphere forces and more accurate soil surface moisture. The third level of soil moisture was daily used to assess the data schema produced from the radar satellite.

Atmospheric aerosols, solid and liquid particles in the atmosphere, play a crucial role in the atmospheric radiation equilibrium. These particles have an influence on the scattering and absorption of short wavelength radiation, and on the other hand, affect radiation absorption and emission in long wavelengths. Dust particles are among the important aerosols affecting the air quality and human health. Variation on the amount of dust in the atmosphere results in radiation equilibrium, hence changes the surface temperature. Dust particles can also alter the global climate condition through changing precipitation, wind intensity, regional humidity equilibrium. Wind erosion is a complicated process which leads to the rise of dust particles from the surface. This process is under the influence of different factors such as atmospheric condition (wind, precipitation and temperature), land properties (topography, surface humidity, roughness length and vegetation), soil condition (texture, compound and density), and land use (agriculture). Numerical models using the wind erosion schemes for better understanding of dust impact on the atmosphere are developing. Although their results have improved, they still suffer from uncertainties for the estimation of dust emission. Therefore, it can be anticipated that the estimated values of different models for dust emission with different surface conditions (such as soil texture and vegetation) would be different.
In the present study, temporal and spatial distribution of surface flux of aerosols were calculated through coupling three dynamic wind erosion models within the numerical Weather Research and Forecasting model coupled with Chemistry (WFR-Chem). This study addressed a more realistic investigation of temporal-spatial properties of dust emission in the Middle East. To this end, first, the necessary physical condition for the wind erosion event was investigated in the study region. Then, the main structure of the wind erosion models along with the effective parameters was explained. In addition, the wind erosion schemes were introduced and described, and finally, the results were discussed.
THEORETICAL FRAMEWORK: Depending on their size, aerosol particles have different moving modes during the wind erosion. According to the field observations in the wind tunnel, particles movement can be classified into three modes: suspension, saltation and creep. In the suspension mode, as dust particles have small final velocity after their entrance into the atmosphere, they can remain suspended. Due to the turbulence of the boundary layer, they can easily diffuse in long distances. As the time of dust particles’ lasting in the atmosphere depends on their final velocity, dust particle suspension can be divided into long-term and short-term suspension modes. In the saltation mode, an intense movement of the sand along the surface happens during the wind erosion. This is the main mechanism for the huge amount of dust transfer in the wind direction which results in the formation of sandy lands and sand hills. In the normal condition, the particles with the diameter of higher than 1000 micron cannot be elevated from the surface; these particles can only move on the surface as a result of the wind or saltation beats which is called creeping. Wind erosion schemes are used to determine the type of aerosol movements, and also to estimate the vertical and horizontal flux. In this study, three schemes of Marticrana-Bergumetti (1995), Lou and Shao (1999), and Shao (2004) are employed. The aim of this study is to investigate the performance of the wind erosion schemes through WRF-Chem model to simulate the dust emission over the Middle East region.
In this study, first, 3 dust schemes, including Marticorena-Bergametti, Lu-Shao and Shao 2004 were introduced and studied. Then, through WRF-Chem model, the results of dust emission simulation through these three schemes were compared with 4-9 July 2009 dust event in the Middle East. For simulation, new surface data, including topography, soil texture and vegetation were used instead of the available data in WRF-Chem model. The advantage of these data is their higher resolution in comparison with WRF-Chem data, in a way that it can detect the existing dust sources of the region with higher accuracy playing a significant role in the dust emission simulation in the region.
Results of simulated dust emission with WRF-Chem and Marticrana-Bergumetti (1995); Lou and Shao (1999), and Shao (2004) were investigated for the storm period of 4-9th of July in 2009 in the Middle East. Results show that all the three schemes revealed the beginning of dust emission at 6:00 in July 4th, 2009 in the southeastern deserts of Africa. These three schemes also showed the same emission sources for this event. At the beginning of the storm event, Marticrana-Bergumetti scheme indicated more extensive and intense dust sources, when compared with Lou-Shao and Shao schemes. Source regions continue their activities during the storm but the amount of emissions were different by the application of different schemes. Simulated dust flux show the same spatial distribution for all the three applied schemes, since the parameterization processes of horizontal flux were the same in the three schemes. However, the simulated values of the vertical flux were different.
Difference in the vertical dust flux reflects the complexity of the soil texture and friction velocities. Marticrana-Bergumetti estimated larger dust emission for the studied storm in comparison with Shao’s (2004) scheme. At the beginning of the dust storm, the highest difference in the estimated dust emission between Marticrana-Bergametti and Shao (2004) was observed in the southeastern regions of Africa. By the advancement of the storm from west to east, the maximum difference was observed in Saudi Arabia desert followed by the central and eastern regions of Iran. Regions with maximum difference in the estimated values of the two schemes at the beginning of the event had loam or silty-loam soil, whereas the regions with the least difference had clay soil.
CONCLUSIONS AND SUGGESTIONS: The results showed that all the three wind erosion schemes estimated the same emission resources for these dust events, while, at the beginning of the event, Marticorena-Bergametti scheme showed a wider and more intensified dust emission source in comparison with the two other schemes. Examining the spatial distribution differences of the simulated dust emission revealed that Marticorena-Bergametti and Lu-Shao resulted in spatial distribution ranges several times larger than that of Shao’s (2004) scheme.

In the regions with the active tectonics, the geometry and evolution of the river systems are sensitive to the surface uplift rate. The simply-folded belt of Zagros has been developed during the late Cenozoic era, and is still active as it is affected by the tectonic activity of the Arabian-Iranian shortening processes pertaining to plate boundary, since the widespread seismic activity in this region is an evidence. In a tectonically active region, geomorphic markers, such as alluvial fans, multiple river terraces and some other geomorphic features are essential as a reference frame for the gauge deformations. Stream profile analysis is a more stable parameter in the tectonic studies than the river terraces. By using digital elevation models (DEMs), such analyses would become easier, faster, and more precise. The study area is located in the southwestern Zagros Simply-Folded Belt (ZSFB) in southwestern Iran.
THEORETICAL FRAMEWORK: Geomorphometric analyses were done by using Digital Elevation Model in this study and some parameters such as concavity and drainage steepness were calculated. The Tectonic Uplift rate of the main stream of the catchment was calculated based on the geomorphometric analysis. The hypsometry curve showed that this catchment is an old one, so erosion is more progressive than the tectonic activity. The uplift rate in the middle of the catchment is higher. Also, the isobase maps were analyzed to yield more accurate understanding about the erosional condition of the catchment in its history. The spatial distribution of the stream height (isobase map) is a useful proxy for investigating the geologic or tectonic processes. Drainage networks are commonly organized according to the Strahler stream order. Streams of similar orders are of similar geological age, and are related to similar geological events. Hence, the interpolation of the isobase lines, connecting streams with a similar order, produces a surface resulting from the same erosional events.
The hypsometric curves have been used to infer the developmental stage of the drainage network and also it is a powerful tool to differentiate between the tectonically active and inactive areas. The curve is created by plotting the proportion of total basin height against the proportion of total basin area. Convex hypsometric curves characterize the young slightly eroded regions; The S shaped curves characterize the moderately eroded regions; concave curves point to the old, highly eroded regions. Streams of similar orders are of similar geological age and are related to similar geological events. Hence, the interpolation of isobase lines, which connects streams with a similar order, produces a surface resulting from the same erosional events. Isobase lines represent the erosional surfaces formed due to the recent tectonic and erosional events. Studies suggest that the isobase maps are prepared by interpolating the elevation at the location of the 2nd and the 3rd order streams. Sharp changes in the isobase map indicate the possible location of the faults and/or lithological contrasts.
Results show that the Khayzi anticline is a flat part in the isobase map, meaning that this anticline is younger than the other parts of the study area. The quantitative SL indices linked to the relative rock resistance described above with field observations suggest that, along the southern part of the Maroon River, the values of the SL index show a variable distribution. The highest and perhaps the most anomalous values of the index are along the Maroon River on its pass from Khayiz anticline. Hypsometry analysis is based on investigating the shape of the basin hypsometric curves which is convex. The hypsometric integral of the Maroon river basin is about 0.22, which means that this basin is an old one. The analyses suggest that as the basin is in the old stage, so the erosion processes are more influent that the tectonic ones. The incision map or the local relief is used to identify the regions of high gradients. The Maroon River is studied using the stream power law. This is a three-segment stream. The two knickpoints show the tectonic activity.
CONCLUSIONS AND SUGGESTIONS: As the stream goes down, the sharp change in the geomorphic indices shows gradual changes in the lithology and tectonic activity. The northern part of the region has low steepness values and because the steepness is directly related to the uplift rate, it means that the region has undergone less deformation processes on the northern section, compared to the other parts.

Nowadays, environmental aspects of soil erosion are specifically considered by researchers. In this regard, secondary (aggregate) particle size distribution (SPSD) is so important in different issues such as nutrient loss, pollutant transport and carbon cycle. Aggregate size distribution is known as the representative of soil structure, which is by itself regarded as a dynamic soil feature. The type and application method of plant residues have a significant influence on the aggregate size distribution. Therefore, the accurate utilization of plant residue management after the harvesting procedure is of crucial environmental issues. However, farmers in some parts of the country, burn plant residues remaining after harvesting; this leads to the destruction of soil structure, greenhouse gas emissions and environmental damages. Therefore, the purpose of the current study was to investigate the effects of the type and different managements of plant residues on the aggregate size distribution indices.
THEORETICAL FRAMEWORK: Several studies around the world and in Iran have been conducted on the impact of different management methods of crop residues on the aggregate size distribution. In this context, it has been found that through mixing and/or keeping crop residue after harvesting, the mean weight diameter (MWD) of the aggregates increased significantly in both wet and dry cases as compared with the control. On the other hand, due to the positive effects of these two methods of management on the structural stability compared to burning, the formation and development of the surface crust decreases. Compared to the favorable effects of mixing and keeping plant residues in farm on aggregate size distribution, some destructive operations such as burning have negative influences.
To obtain the objectives, a field experiment was done as factorial based on RCBD with three replicates. The first factor was the residue type including barely straw and alfalfa residue, and the second factor was different management practices including 1) incorporating one percent of the plant residues into the soil, 2) incorporating 0.5 percent of the plant residues into the soil, 3) surface retention­­ of plant­ residues, 4) burning of plant residues and 5) control. After nine months, the aggregate size distribution indices including the mean weight diameter (MWD) and the geometric mean diameter (GMD) both at two cases of wet and dry and also water stable aggregates (WSA) and dry stable aggregates (DSA) were measured.
Results of the variance analysis showed that the influence of plant residue type was just significant on MWD and GMD in wet case, whereas, the effect of plant residue management was significant on all the studied indices. This indicates that the management of plant residues is more important than the type of residues. Also, barley straw was more effective than alfalfa residue in improving the aggregate size indices, which was attributed to higher content of carbon and greater C:N ratio in the composition of barley straw. Also, in all cases, mixing one percent of plant residues with soil showed greater role in improving the soil structure than the other application methods of residues. The incorporation of one percent barely straw led to the highest influence on the improvement of aggregate size distribution, so that due to the application of this treatment as compared with control, MWD and GMD increased respectively by 87% and 68.6% (under wet conditions) and by 33.6% and 21% (under dry conditions), while WSA and DSA were enhanced by 86.4% and 23.7%, respectively. Moreover, the surface application of residues resulted in aggregate size improvement, however, its effectiveness was less than the incorporation method. In contrast, the burning of residues reduced almost all the indices compared to the control.
CONCLUSIONS & SUGGESTIONS: In general, the priority of residue application methods regarding the improvement of aggregate size distribution was determined respectively as: burning.

Soil erosion is one of the most important problems of the environment, natural resources, and agriculture in the world. Soil structure stability is the key element of soil health, the main factor in the improvement or degradation of soils, and the important point in evaluating the effects of land management and the operations practices to control soil erosion. Bioengineering systems and soil stabilizers such as chemical polymers are applied to increase the soil structural stability and resistance against degradative agents, and to control soil erosion.
THEORETICAL FRAMEWORK: Although many researches have been carried out to study the effect of PAM on soil strcutursl stability and soil erosion, most of them were conducted in the lab condition, and also the mixture of PAM with the bioengineering techniques, especially in field condition and semi-arid regions such as Khorasan Razavi province, was not studied. Regarding the potential of vetiver in soil conservation, it seems that the vetiver has been well adapted in most regions of Iran, and can decrease soil erosion. Therefore, this research was performed to investigate the effect of the vetiver cultivation system, as a valuable bioengineering technique, and polyacrylamide (PAM) on soil structure and aggregate stability indices and soil erosion characteristics in a loamy soil under field condition.
The study was conducted in a loamy soil on slope of 5% in Agriculture Campus, Ferdowsi University of Mashhad. To apply the treatments, experimental plots (1 m × 1 m) were prepared in the given area. Experimental treatments include vetiver cultivation (VP0), PAM (20 (P2) and 40 (P4) kg ha-1), simultaneous application of vetiver and above PAM concentrations (VP2, and VP4. In addition, P0 (no PAM and vetiver) was regarded as control treatment. The undisturbed samples were collected to measure the structure indices before and after simulating the rainfall test. Structural stability indices including wet and dry mean weight diameter of aggregates (MWDwet and MWDdry), aggregate stability (AS), structural stability index (SI), and the percentage of aggregate degradation (PAD) were determined. The simulated rainfall intensity of 30 mm h-1 during 30 minutes was applied on the treated soils, and runoff and sediment volume were collected. This study was performed based on the randomized complete blocks design and a factorial arrangement with 3 replications. The data pertaining to soil structural stability and erosion indices were analyzed using SPSS software.
RESULTS & DISCUSION: The results showed that vetiver and PAM increased the soil structural stability indices i.e. MWDwet, MWDdry, AS, and SI, and decreased PAD. However, vetiver enhanced the stability indices more than PAM. Also, vetiver and PAM decreased soil erosion indices, and the decrease in soil loss, runoff, and runoff coefficient was more due to the vetiver. The higher aggregation and structural stability, and as a result, the considerable reduction of aggregate degradation in the vetiver plots is due to the effect of high density of fine roots biomass and microbial activity associated with the rhizosphere of the vetiver grass. On the other hand, when the aggregate stability increases, the water infiltration will increase and runoff will decrease. Consequently, particle detachment and aggregate degradation, and transport of soil particles due to the rain drop impact and runoff decrease. Also, vetiver increases soil resistance against raindrops; soil erosion decreases runoff probably through binding soil particles, aggregation and creating the macro pores. Adsorption of the long chains of PAM polymer on the surfaces of soil particles and aggregates, flocculating the soil particles and binding them by PAM ledad to increase aggregation and aggregate stability, creates continuous and stable macropores in soils, and decreases aggregate degradation. Therefore, PAM increases water permeability and as a results decreases the runoff, coefficient of runoff and soil loss. However, the efficiency of PAM to decrease the runoff and soil loss depends on the concentration and viscosity of the dissolved PAM.
CONCLUSIONS AND SUGGESTIONS: Generally, the results of this research indicated that the vetiver system can be recommended due to the very low cost and long-term bioengineering technique to improve the soil structure; it increases aggregate stability, and decreases runoff and soil loss in thesemi-arid regions such as Iran.

The contribution of crop cover to reducing runoff and erosion depends on the type, height, density and stage of plant growth. The literature review indicates that because of the different life forms, the effect of plants on the reduction of runoff and erosion are different at different growth stages [13]. However, no comprehensive studies have been conducted in Iran in this field. Therefore, the aim of this study was to investigate the changes of runoff and sediment production during the growing season and in different densities of lentil dry farming in the soil conservation research station of Tikmeh in eastern Azerbaijan.
This study was carried out in nine experimental plots (4.8 × 40 m2 in size), with three treatments including three levels of sowing densities (30, 35 and 40 kg of seed per hectare) of Kimiya cultivar of lentil (Culinaris L.), in three blocks. For this reason, in spring, plots were plowed and sowed on 8 April 2013. The amount of runoff in each plot during the growing season after each rainfall was measured through volumetric method and the amount of sediment in the runoff was determined. Moreover, some agronomical characteristics of lentil such as the canopy cover and plant height were measured. The results were analyzed as split-plot design in time by MSTATC and SPSS softwares.
In this study, only in three growth stages, rainfall resulted in runoff and sediment. The first stage of sampling in this research was consistent with the stage of the plant establishment; the second stage was in accordance with plant growth; and the third stage of sampling was consistent with the plant ripening. Results showed that the amount of runoff decreased from the first event to the last one. In other word, after the lentil germination, its efficiency in soil conservation dramatically increased, so that the amount of runoff at the stage of plant growth and ripening stage respectively was 44.71% and 54.31%, and the amount of sediment was 67.10% and 75.20% less than the plant establishment. During the growing season, through increasing the density of lentil dry cultivation from 30 to 40 kg of seed per hectare, the amount of sediments declined significantly. The total amount of sediment resulting from a density of 30 kg seed per hectare was almost two times more than the density treatment of 40 kg of seed per hectare.
The results showed that, over the time, the difference between the treatments in the weeds increased, so that, at the stage of the plant establishment, although there was no significant difference between the treatments, the treatment of 30 kg per hectare had the highest percentage of weed density at ripening stage.
CONCLUSIONS AND SUGGESTIONS: Reducing the runoff and sediment at the end of the growing season can occur due to the reduction in the amount and intensity of rainfall in the above three events, and also due to the increased canopy density of the lentils during the growing season. In addition, results showed that during the growing season, the lentil role in reducing soil loss was more effective than the runoff.
Since in the dry farming of lentil in the study area, crop density of 40 kg per hectare resulted in a minimum amount of runoff and sediment compared to the other treatments; therefore, the sowing rate of 40 kg per hectare is recommended to the farmers of this region.