جستجوی مقالات مرتبط با کلیدواژه « deposition » در نشریات گروه « آبخیزداری، بیابان، محیط زیست، مرتع »

Due to the increase in the consumption of fossil fuels and chemical fertilizers, especially nitrogen-containing fertilizers, the entry of nitrogen into the cycle of ecosystems has been more than normal.Nitrogen deposition as a consequence of increasing nitrogen input to the atmosphere, can be a threat to ecosystems. It can affect soil properties, soil microorganisms and their activities, vegetation and animals. The aim of the present study is to investigate the effects of deposition of different rates of atmospheric nitrogen on the biochemical properties of a summer rangeland's soil.

For this purpose, the seeds of Medicago sativa were planted in 36 pots containing rangeland soil in a completely randomized block design.  Two months after seed germination in pots, six Nitrogen treatments included control,30, 60,90,120 and 150 kg ammonium nitrate/ha which dissolved in water were applied in 6 replications during a period of 75 days. At the end of experiment, some soil biochemical properties (acidity, electrical conductivity, absorbable phosphorus, total nitrogen, organic carbon and exchangeable potassium along with biomass and microbial respiration) and Root weight and depth factors were measured.  Data analysis was done using analysis of variance method and mean comparison was done using Duncan's test.

The results demonstrated that increasing the level of ammonium nitrate deposition to 60 and 90 kg per hectare per year, despite the significant increase (p < 0.05) of organic carbon and total soil nitrogen, causes a significant decrease in other measured biochemical properties of the soil (p < 0.05). An increase in nitrogen deposition in the early stages may be partially responsible for root growth, but with nitrogen saturation in the soil and the occurrence of nitrate leaching, as well as the loss of soil fertility, unfavorable conditions for root growth are provided. With the increase of nitrogen deposition in the soil, up to the level of 60 kg /ha, the average respiration and microbial biomass increased, But at higher levels of  nitrogen deposition, respiration and microbial biomass decreased.

In case of an increase in mineral nitrogen deposition in the studied area, it is recommended to use the Medicago sativa in the improvement of vegetation restoration projects of summer rangelands to absorb the deposed mineral nitrogen in excess of the soil holding capacity, its alleviate negative consequences and creating a suitable root zone for the the  activity of soil microbial.

Introduction Water erosion is one of the most important factors in land degradation in large parts of Iran destroying fertile soils and agricultural land. The impact of soil erosion and related sediments decreases significantly water quality and reservoir capacity. Especially in semiarid areas like in the Menderjan watershed in the west Isfahan province sheet and rill erosion contributes to the sediment dynamics in a significant way. Particularly, sheet and rill erosion processes and related forms and features are very common in this region. Hence, this study is aimed at identifying and quantifying the major erosion process dynamics. Therefore, we applied an integrated approach combining the USPED and RUSLE models with data mining, remote sensing, and GIS methods.
Materials and methods The study area is Menderjan watershed locating at east Isfahan and has an area of about 21,100 hectares. In this study, the USPED and RUSLE was used. The USPED model is based on the assumption that soil erosion depends on the detachment capacity and the sediment transport capacity of surface runoff. However, the USPED models do not consider the sediment yields from gullies, stream banks, and stream bed erosion. In the USPED model erosion and deposition (ED) are computed as the change in sediment flow in the direction of flow.
ED=d×(T×cosa)/ dx d×(T×sina) /dy
Where a is the aspect of the terrain surface, dx, dy is the grid resolution, and T is the sediment flow at transport capacity. ED can be positive, indicating soil deposition, or negative, indicating soil erosion. Transport capacity (A) is expressed as: A=R×K×C×P×L m×(sin S) n
Where A: Average yearly soil erosion (t ha-1 y-1), R: yearly rainfall erosivity factor (MJ mm ha-1 year-1h-1), K: the soil edibility factor, LS: Slope Length and Steepness factor, C: cover management factor and P: Support Practice Factor, S is the slope, L is the upslope contributing area, and m and n are constants. For prevailing rill erosion m = 1.6, n = 1.3, while for prevailing sheet erosion, m = n = 1. The USPED and RUSLE model was applied using Arcmap10. In this study, the Landsat satellite images 8 (OLI) and rainfall data, soil properties and digital elevation model (DEM) were used, and GIS plays a major role in preparing thematic layers and estimating soil erosion.
Result The range of obtained R factor values range was from 82 to 118 MJ mm/ ha h year. The average values for the Menderjan watershed amount to 265.2 MJ mm/ ha year-1. According to the soil laboratory analysis soil texture is dominated by silt clay loam and clay loam and thus is highly susceptible to soil erosion. The amount of organic matter in all samples was 2 %. Soil organic matter reduces the erodibility of soil. In many arid and semiarid areas soil organic matter is low due to scarce vegetation, and hence, soil is more susceptible to erosion. The annual average soil erodibility of this basin 0.04 (t h MJ-1 mm-1). The amount of topography for RUSLE varies from 0.001 to 16.7 and USPED varies 0.01 to 30 Support Practice Factor of the study area is variable from 0.1 to 1 and C factor value varies was 0.2 to 0.5. According to result more than 35 % of the area is affected by high to very high erosion and deposition process intensities. The stable areas and low erosion and deposition zones cover about 15 % of the area. However, some of the mapped and predicted sheet and rill processes are located in the stable and low intensity soil erosion classes. The extreme values are characterized by steep slopes in ridge positions in the northern and southern parts of the watershed.
Discussion and Conclusions During recent years, the role of water erosion as one of the land degradation factors in arid and semi-arid areas of large parts of Iran has increased. In our study we applied a combined approach using the RUSLE and USPED models rill/inter-rill (sheet) erosion processes, and deposition processes. To the knowledge of the authors, this is the first attempt integrating different erosion processes and deposition dynamics in Iran. In the study area soil loss is concentrated especially in the abandoned bare land areas. The protection of bare soil to reduce soil loss should be ensured by appropriate cultivations. According to the results a large part of severe erosion occurs in the steep areas in the north and southwest of the study area. Agricultural cultivations may change the land cover, leading to poorer vegetation cover or bare land, especially after harvest and thus increase erosion processes and land degradation. Thus, control of soil erosion targeted to the area not only reduces direct costs of soil erosion; however, it also it diminishes the implementation costs of control operations for decreasing soil erosion.

Information on erosion and capacity of sediment carrying condition in various basins is one of the subjects that in each of hydrology and river engineering projects should be considered. In the present study HEC-RAS model was applied to evaluate and predict the sedimentation and erosion in the reach of Talar River with 12 km length. For doing this study 40 cross section which was surveyed in 2006 is applied in the simulation and 4 cross section which was surveyed in 2011 applied for calibration of the model. Model calibration and verification showed that the Meyer Peter Muller sediment transport equation has a better fit with the observed results. In order to predict the erosion and sedimentation trend, using recorded data of dischrges in Shirgah hydrometric station during last 30 years and using SAMS Statistical model, the amounts of monthly stream flow was predicted for the next 10 years and then sedimentation model was executed. Variations in the longitudinal profile of river in all profiles showed that the most changes will occurs within the middle reach area and the beginning of the river reach with the length of about 1000m and with having the mild slope is stable. Also predicted amount of sediment outflow from the studied reach is about 348534 tones for the next 10 years.

Construction activities on the river branches and the middle areas of the watersheds can lead to changes on the river bed morphology of down streams. Understanding the river bed morphology changes and its effects on the lands next to river is essential to rehabilitate and stabilize the bed and banks. This study aim to identify the river bed morphology changes over the past five decades in Zarrinehrud River. In this research a range of 25 km at the end of Zarrinehrud River in West Azerbaijan province was studied using aerial photos of year 1334 and 1346, topographic maps of year 1375 and SPOT satellite image of year 1382. Results showed that morphological changes of the river bed and the surface area of adjacent lands were reduced from 561.1 ha to 221.3 ha. The sand dam area at river bed in 1346 was 13.8 ha and at 1382 was 2.7 ha, this result represents a large discharge fluctuations and changes in the hydrological and hydraulic conditions of the river. Meander form of River morphology also has been changed. Number of Meanders reduced from 4 to 3. The effective factors on the morphological changes were, changes in the hydrological regime due to dam construction, runoff reduction and sediment deposition in the river bed.

In Iran due to the lack of long experience in the implementation of Soil Conservation and Watershed Management Plans, these measures have not been evaluated quantitatively and specific methods for this purpose have not been provided. In this research effort is to investigate the effect of watershed management operations performed in Can Basin in 1379, on the amount of erosion and sedimentation and rate of project success or failure and its causes. So after providing the required information and statistics and being sure about the authenticity and accuracy of statistics and statistical reconstruction of defects with conventional methods, to investigate the effect of implemented projects on erosion and sedimentation rates, average of suspended sediments in the period before project implementation (1986-2000) and in the period after project implementation (2001-2008) was calculated using sediment rating curves through intermediate technique class, and using daily water discharge, watershed erosion and deposition were also calculated using MPSIAC model. Specific erosion and deposition map was provided in the period after project implementation using Arc GIS software and finally the amount of efficiency and effect of this operation on the amount of erosion and deposition rates was judged. The results of studies showed that due to operating this plan, the average amount of suspended sediment has changed from 47892 tons per year during the statistical period before the plan to 22365 tons per year during the eight-year statistical period after it. The amount of erosion and sedimentation has shifted from 66758 tons to 50549 tons, which shows the positive effect of plan on reducing the amount of suspended sediment and the lack of effective role in reducing the rate of erosion. The main reasons for the low efficiency of Watershed Management Plan implemented in relation to decreasing the amount of erosion are: lack of suitable biological operations in the basin (less than 25 percent of the volume of the proposed action), focusing on mechanical operations, weaknesses in project monitoring and evaluation During all stages of its implementation, failure to observe the standards and technical points such as non-conforming structures built between locations and proposed locations, lack of standards in building the necessary structures and inappropriate dimensions of structures, destruction of floor section in mortar stone structures and etc.

In the network of floodwater spreading and artificial recharge system, deposition is the main obstacle of infiltration water in the soil and reaching of water to the groundwater. Soil infiltration reduction depends on suspended material, the infiltration rate, soil physical characteristics and quality of the floodwater spreading. Fine-grained sediment enters into the network during the flood; reduce the efficiency of these projects and in long time of operation to actually lose its effectiveness. The main objective of this study is the effect of sediment deposited on the variation of infiltration rate by the floodwater spreading. In this study, double rings with triangular surface soil infiltration rate were used and the relevant data were entered into the Excel software. The analysis and comparison of the effects of the floodwater spreading on soil infiltration rate in comparison to control was evaluated using the statistical method of factorial completely randomized design. The effects of floodwater spreading on soil infiltration rate were evaluated using the statistics factorial method in completely design. Duncan mean comparison test was applied to compare rate of infiltration on spreading area with ditches between them. It is necessary to mention that the control values in the first year were compared with the results of reminder years. In general, the analysis of variances show the difference between rates of infiltration in depth of soil is significant at level %5 but the level signiticant for floodwater is %1. There is no significant difference for interaction of these two factors.

The deposition of transported materials by flood water on soil surfaces in warm and arid region causes some changes in texture, structure, depth and fertility of the soil. According to the study of flood water spreading effect on physical and chemical characteristics of the soil, the study field of flood water spreading of Jajarm in North Khorasan province was chosen. This area has located on alluvial fan with 0.75- 1%slop, 146.3 millimeter mean annual rainfall, arid and extra arid climate. For the period of 4 years (1995-1999), the soil samples were collected from recognizable A and C horizons and the depth of 0-30 centimeter (plow layer) from 7 profiles at three primary strips. The quantity of effective parameters on soil characteristics was determined in laboratory. This process was repeated after three times flood water spreading. Obtained data were analyzed: I) by t-student test to compare different properties of soil before and after flood spreading. II) by split plot procedure with three replicates to compare the whole effects at flood water spreading. The samples variance analysis showed that flood water spreading was effective on sand ratio, clay, organic matter, bicarbonate (p<0.05) and was effective too on Ca, Mg, Cl, Na, SAR and EC (p<0.01). There was a significant difference between the samples before and after spreading of flood water. Comparing the average mean of factors including soil salinity, Ca and Mg on A, C and plow layer before and after flood water spreading showed only different between plowing layers, also results showed that the sand to clay ratio and silt in a horizon were decreased. Flood water spreading had no more effect on the other soil characteristics.