Ariyan Matboo; Vahedberdi Sheikh; Ali Mohammadian Behbahani; Arash Zare Garizi
Abstract
Introduction
The hills surrounding the international wetlands of Almagol and Ajigol in the Golestan Province are exposed to severe erosion and every year a large amount of sediments from these hillslopes discharge into these wetlands. Whilst a large extent of these surrounding hills, covered with Biological ...
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Introduction
The hills surrounding the international wetlands of Almagol and Ajigol in the Golestan Province are exposed to severe erosion and every year a large amount of sediments from these hillslopes discharge into these wetlands. Whilst a large extent of these surrounding hills, covered with Biological Soil Crusts (BSC), has been destroyed due to lack of awareness of their values, sensitivity and ecological functions. Improving soil properties, preventing direct contact of raindrops with the soil surface, all indicate the important role of BSC in hydrological processes and soil loss control.
Materials and methods
In this study, the role of BSC in the hydrological processes of dry areas was investigated using a rain simulator. After a field survey and evaluation of the area, different treatments including biological crust with a dominant lichen cover, biological crust with a dominant moss cover, an area covered with vascular plants, an area without cover and areas covered with a combination of moss and lichen were selected to perform rain simulation and compare their effects on the hydrological processes of the selected region. Rain simulation was done in 2×1 meter plots for 30 minutes and intensity of 82 mm per hour. The start time of runoff and the volume of produced runoff at the outlet of the plot were measured and recorded. Also, at five-minute intervals from the beginning of the simulation process, 500 ml runoff samples were collected and transferred to the laboratory for testing in order to estimate the sediment concentration and mass. In addition, the depth of the wetting front caused by the infiltration of rain was measured at the beginning, middle and end sections of the plots.
Results and discussion
The results of rainfall-runoff simulations at a 2×1 m2 plot scale with a rainfall intensity of 82 mm.h-1 and a duration of 30 minutes plots, showed that the average mass of sediments from plots with the dominant cover of moss (104 g), lichen (91 g), lichen-moss combination (176 g) and bush (99 g) was significantly higher than bare soil (1133 grams). Therefore, in case of destruction of the existing BSC and the formation of bare lands, the sedimentation rate will increase by more than 5 times. A significant decrease in water infiltration into BSC causes a significant increase of 30-40% in runoff generation compared to the treatment covered with bushes and a significant increase of 8-18% compared to the bare soil treatment.
Conclusions
by reducing soil loss and sediment concentration, BSC cause the production and transfer of high-quality runoff to the wetlands and as a result maintain the ecological function and health of the region’s wetlands. The results of this research show the positive influence of BSC on the hydrological and ecological performance of arid areas in the north of Gorgan Plain and protection of Ramsar-listed wetlands in the region.
yasin salehi; Alireza vaezi
Abstract
IntroductionSoil erosion is the most important aspect of land degradation and one of the most important environmental, agricultural and food production problems in the world. More than half of the agricultural lands in semi-arid regions are under rainfed cultivation, and the tensions caused by erosion ...
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IntroductionSoil erosion is the most important aspect of land degradation and one of the most important environmental, agricultural and food production problems in the world. More than half of the agricultural lands in semi-arid regions are under rainfed cultivation, and the tensions caused by erosion and destruction of land are important in terms of the effects within the field of erosion, such as soil fertility, and the effects outside the field, such as soil pollution. Information about the size distribution of eroded particles is a substantial step for managing the loss of nutrients and the transfer of pollutants from the soil. For this purpose, this study was conducted to investigate the particle size distribution of sediments resulting from interrill erosion under the influences of slope gradient and soil texture in some soils of the semi-arid region of Zanjan Province. Materials and methodsToward this, four hillslopes having different soil textures (sandy loam, silty loam, sandy clay loam and clay loam) in four north-south slope percent (five, 10, 15 and 20%) were investigated using a simulated rainfall with an intensity of 60 mmh-1 for 60 minutes. In order to monitor the runoff and sediment samples from the beginning of the runoff until reaching a stable state, were taken at 5-min intervals from the initiation of runoff. The particles size distribution of sediment was determined by the method of particle separation using a series of sieves with diameters of 75, two, one, 0.5, 0.25, 0.1 and 0.05 mm. Also, the percentage of finer particles (silt and clay) was calculated by hydrometer method. Then the sediment particles are divided into eight categories: gravel (1-75 mm), very coarse sand (1-2 mm), coarse sand (0.5-1 mm), medium sand (0.25-0.5 mm), fine sand (0.1-0.25 mm), very fine sand (0.05-0.1 mm), silt (0.002-0.05 mm) and clay (<0.002 mm) were categorized. Results and discussionThe results showed that, with the increase in the slope of the land surface, the size distribution of sediment particles changed in all soils. So that, the transport of particles larger than 0.1 mm (including very coarse sand, coarse sand, medium sand and fine sand) increased with increasing slope. While the percentage of silt particles (0.002-0.05 mm) decreased in all textures. Also, particles with the size class of medium sand and fine sand formed between 40 and 50% of the sediment particles for each texture and did not change significantly with the increase of the slope. The highest ratio of particles in the sediment to the main soil was related to silt particles and in silty loam texture (4.33 times) and the lowest was related to clay particles and in silty loam texture (0.26 times). Sand and silt particles in different textures, had high transmission ratios. Silt particles in three textures of sandy loam, clay loam and silty loam had a ratio of more than one and clay particles less than one. Except in clay loam soil, sand particles changed in the range of 0.83 to 1.24 times compared to the main soil and the overall average ratio of its availability in sediment to original soil was 0.98 times. ConclusionIn general, this research showed that with increasing slope, the selectivity of fine particles decreases and the share of coarse particles increases. The effects of these changes are more visible in fine-textured soils. Due to the increase in the destruction of aggregates and flow rate with the increase of the surface slope, it is very important to prevent the removal of vegetation and observe the principles of tillage in order to reduce the direct impact of raindrops on the soil surface and reduce the transportability of particles by the flow. Also, the results show that the ratio of particles in the soil texture and the characteristics of soil structure (abundance and stability of aggregates) are the determining factors of particle transport and it is necessary to consider these characteristics in choosing soil conservation methods.
Ramyar Aliramayee; Abdulvahed Khaledi Darvishan; Mahmood Arabkhedri
Abstract
Various factors such as rainfall intensity and slope affect hydrological processes such as infiltration and runoff. Study on rainfed soils is very important because of intense degradation and sensitive ecosystem. The present research was conducted to investigate the effect of rainfall intensity and slope ...
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Various factors such as rainfall intensity and slope affect hydrological processes such as infiltration and runoff. Study on rainfed soils is very important because of intense degradation and sensitive ecosystem. The present research was conducted to investigate the effect of rainfall intensity and slope gradient on infiltration and surface runoff using rainfall simulator in rainfed lands of Kalaleh region, Golestan Province. To achieve the study purposes, four rainfall events with the intensities of 33, 64, 80 and 110 mm hr-1 and duration of 15 min were simulated. Three slope gradients of 6, 12 and 25% were selected and infiltration and surface runoff were measured in four 25×25 cm2 plots. The results showed that the infiltration average rate and runoff average coefficient were increased with increasing rainfall intensity and slope gradient. The main and interaction effects of rainfall intensity and slope gradient on infiltration and surface runoff were significant (p≤0.01). The results of subgroups of rainfall intensity and slope gradient using Duncan test showed that two turning points in hydrological response of plot are distinguishable, one between rainfall intensities of 64 and 80 mm hr-1 and another between slope gradients of 12 and 25%. In other words, at the rainfall intensity more than about 70 mm hr-1 and the slope gradient more than about 15%, average infiltration rate and average runoff coefficient were significantly decreased and increased, respectively. These results emphasized on land use management via avoiding change from rangeland to rainfed land especially when the slope is more than 15%. Agricultural and land cover management was also emphasized especially in high rainfall intensities (more than 70 mm h-1).
Aghdas Sotoudehnia; Majid Mahmoodabadi; Majid Fekri
Abstract
Due to low plant cover in arid and semi-arid regions, surface gravel cover (SGC) plays an important role in soil erosion control. The aim of this study is to investigate the effect of SGC and slope gradient on splash as well as interrill erosion in two contrasting soils. For this purpose, a constant ...
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Due to low plant cover in arid and semi-arid regions, surface gravel cover (SGC) plays an important role in soil erosion control. The aim of this study is to investigate the effect of SGC and slope gradient on splash as well as interrill erosion in two contrasting soils. For this purpose, a constant rain was simulated on two soils namely sandy and cropland with different aggregate size distributions at four slope gradients including 0.5, 2, 5 and 10 % and five levels of SGC including 0, 5, 10, 20 and 40 % each at three replicates. Through producing a rain intensity of 35 mm/h for 35 min duration on a 0.35 m by 0.35 m test area, both splash (downward, upward and the total splashed material) and interrill erosion rates were measured. Result showed that with increasing SGC in both soils, the downward, upward and the total average splash increased, significantly. However, the downward splash rate was higher than the upward splash rate. With increasing SGC from 0% (control) to 5, 10, 20 and 40 %, the downward splash rate decreased for the sandy soil by 12.9%, 25.3%, 35.7% and 47.7%, and for the cropland soil by 13.9%, 25.4%, 37.0% and 49.4%, respectively. Regarding the interrill erosion rate, the corresponding reduction percentages for the sandy soil were 13.5%, 26.4%, 33.3% and 46.4% and for the cropland soil were 12.9%, 30.7%, 37.3% and 45.9%, respectively. Moreover, nonlinear increases in the interrill and splash erosion rates were found at steeper slopes. Due to lower cohesion and greater detachability of sandy soil, it exhibited higher erosion rates than those for the cropland soil. The findings of this study revealed that in the presence of SGC, both splash and interrill erosion rates will reduce, significantly.
Leila Gholami
Abstract
In severely eroded areas, especially steep slopes, establishment of vegetation cover is not possible. The application of organic and inorganic amendments can therefore improve the conditions leading to establish vegetation cover through playing an effective role in runoff control. Accordingly, in the ...
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In severely eroded areas, especially steep slopes, establishment of vegetation cover is not possible. The application of organic and inorganic amendments can therefore improve the conditions leading to establish vegetation cover through playing an effective role in runoff control. Accordingly, in the present study, woodchips as a soil organic amendment was applied to control runoff variables including time to runoff, runoff volume and coefficient. For this purpose, three levels of woodchips treatment of 0.5, 1.0 and 1.5 kgm-2 were used in three replications at in 1 m2- plot scale. The plots were located in 30% slope in accordance with field conditions under simulated rainfall of 60 mmh-1 and duration of 15 min. The results showed that application of woodchips in 0.5, 1.0 and 1.5 kgm-2, time to runoff increased 97.50, 192.38 and 203.31%, respectively. The runoff volume decreased 35.23, 55.11 and 60.43% and runoff coefficient also decreased 42.43, 67.40 and 72.14% in three levels of woodchips treatments, respectively. The results of GLM showed that woodchips treatment had a significant increasing effect on time to runoff (p≤0.01) as well as a significant decreasing effect on runoff volume and coefficient (p≤0.05). The application of woodchips as a conservation treatment on the soil surface showed that this amendment can be used for runoff control especially where large quantities of woodchips are simply available.
Mahbobeh Kiani Harchegani; Seyed Hamidreza Sadeghi; Hossein Asadi
Abstract
Water erosion comprises major processes of the detachment, entrainment, transport and deposition. Sediment washed out from the watershed is composed of different particle sizes. The particle size distribution of sediment is a significant factor influencing detachment and transport processes. However, ...
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Water erosion comprises major processes of the detachment, entrainment, transport and deposition. Sediment washed out from the watershed is composed of different particle sizes. The particle size distribution of sediment is a significant factor influencing detachment and transport processes. However, the changeability variables of particle size distribution under different flow conditions have been less considered. Accordingly present study was therefore planned to evaluate the changes in particle size distribution of effective sediments by laser diffraction in initial unsteady and mature steady flow conditions in laboratory scale for a type of soil that was collected from Koudir region in Mazandaran Province. Towards this attempt, rainfall simulation experiments with intensities of 30, 60, and 90 mm h-1were conducted in a set of 1 × 6 m plot with varying slopes of 5, 15 and 25% based on governing condition in the north region of the a soil type and in three replications. The results showed that the sediment concentration is influenced by the slope more than by the rainfall intensity in runoff different conditions. In addition, the results explained significant levels of (p<0.05) for particle of 10 in slope of 5% and in rainfall intensities of 60 and 90 mm h-1 in steady and unsteady flow conditions. While particle of >2 micron had a significant different (p<0.05) in slope of 5% and in rainfall intensity of 30 mm h-1. In this regard, variable of D50 had very complex behavior in slopes and different rainfall intensities but D90 was not influenced by slopes and rainfall intensities in confidence level of 90% in steady and unsteady flow conditions because of inability flow in moving particles of >63 micron and especially variable of D90.
Seyed Hamidreza Sadeghi; Zeinab Karimi; Zahra Hashemiarian
Abstract
Annually, high amount of soil is washed out by erosion from the watershed. Implementation of appropriate management methods to control soil erosion is therefore essential. Application of economically-effective and environmentally friendly amendments to soil is one of the solutions and new technologies ...
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Annually, high amount of soil is washed out by erosion from the watershed. Implementation of appropriate management methods to control soil erosion is therefore essential. Application of economically-effective and environmentally friendly amendments to soil is one of the solutions and new technologies to control soil erosion. However, the comprehensive assessment of the impact of commonly used soil amendments on soil erosion has not been conducted. The present study therefore aimed to assess the performance of combined application of polyacrylamide powder (6 gm-2) and vermicompost (24 gm-2) in comparison with individual application of the polyacrylamide and vermicompost as well as control (without amendments) condition to control runoff and soil erosion under laboratory condition and on a clay-loamy soil. The study variables of runoff, soil loss and sediment concentrations were measured under a simulation rainfall intensity of 80 mm.h-1 and duration of 8 minutes. The results indicated a statistically significant effect (p=0.00) of all study treatments on the reduction of runoff, soil loss and sediment concentration from the study small plots. The combined effect of polyacrylamide and vermicompost on runoff and sediment concentration was also found greater than that recorded for soil loss.
Vafa Homayounfar; Abdulvahed Khaledi Darvishan
Abstract
Laboratory plots and rainfall simulators are useful tools for erosion studies, but transferring soil and consequent preparation steps which leads to damage soil structure, are among the disadvantages of laboratorial soil erosion studies yet. In other words, soil preparation steps can cause considerable ...
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Laboratory plots and rainfall simulators are useful tools for erosion studies, but transferring soil and consequent preparation steps which leads to damage soil structure, are among the disadvantages of laboratorial soil erosion studies yet. In other words, soil preparation steps can cause considerable errors in the results of runoff and erosion in laboratorial conditions. On the other hand, measuring splash erosion, as the first ability to detach and move the soil particles, is very important in soil erosion studies. Knowing the uncertainties of splash results due to soil preparation methods is therefore essential to improve the accuracy of laboratory results. The present study has been therefore conducted to measure and compare the amount of splash in a sandy-clay-loam soil in both undisturbed and disturbed conditions in a hillslope in the southern part of Alborz Mountains under three rainfall intensities of 40, 60 and 80 mm h-1. The results showed that disturbing soil in erosion laboratory studies could significantly increase the upslope, downslope, gross splash (p<0.01) and net splash (p<0.05). The effects of soil disturbance on the ratio between upslope and downslope splash was not significant. According to the results, the increasing rates of upslope, downslope, gross and net splash due to soil disturbance were 216, 241, 234 and 257%, respectively.
