نشریه خشک بوم
سال دوم شماره 2 (پاییز و زمستان 1391)

Soil erodiblity or detachability is one of the most important and applicable index in wind and water erosion studies. Grain size distribution curve plays key role in estimating soil (wind and water) erodiblity. Two approaches of dry and wet sieve methods, are often used for determining of soil grain size distribution. Hydrometer and pipette methods are based on Stoke's law and free falling of soil particles in fluid (water). In wet sieving or hydrometer method, mechanical and chemical approaches have been applied to disperse the aggregates to finer particles. Whereas, in dry sieving method, texture indices are different in compare to wet methods, because aggregates dispersion doesn’t occur. In this research, 20 soil samples were taken from fine grain plains of Yazd. After preparing of soil samples, dry and wet sieving methods were applied in eight sieve classess (32μm < d < 2000 μm). Using G.R. Graph software, the important indices of grain size distribution including mean diameter, median diameter, skewness and sorting were calculated. Results show a significant different between all of the grain size distribution indices in 5% level. It can be concluded that in wind erosion and water erosion studies, using dry sieving and wet sieving are recommended, respectively that for describing the wind erosion phenomena it is prefer to use the dry sieving method as well as wet sieving for water erosion. The results also show that the average of mean diameter and median diameter in dry sieving, is approximately 2.5 times more than form average diameter of wet sieving.

Base flow is an important part of river flow, which shows stream response to precipitation. Separation of base flow through hydrograph analysis provides useful information about characteristics of water storage, which drains into rivers. Base flow is usually related to the evacuated water from underground water reserve. It is useful to understand base flow in order to measure water quality and conditions of low flow that can be utilized for calibrating and validating of hydrologic models. There are several methods for hydrograph separation. In this research, Recursive Digital Filters of one and two parameters, PART and Local Minimum methods were used in order to separate hydrograph of flow into two parts (direct runoff and base flow) in four hydrometric gauging stations, located in Hablehroud basin. Results indicated that Local Minimum method show the best estimation of base flow index in all stations, except of Namrood. Meanwhile, in Namrood station, Recursive Digital Filters method with α value of 0.975 provided the most accurate estimations.

Iran has covered a wide range of vegetation is sagebrush, which determine the rate of exploitation sagebrush cover the management operation is necessary. This study is among the first efforts to determine susceptibility or resistance of key species in the grazing area has been done Khoshkrood Saveh. The treatments included four of the 25, 50 and 75% of control (no harvest) were. In each treatment 10 replicates were used as the basis of the species that depend on each variable is evaluated. Three years and each year to measure or estimate the visual characteristics of vigor and vitality, mortality, and the height of production was based. Results in a split plot design in time, in the three years (2008 to 2010) were analyzed using SAS software. Production of forage species Ar.sieberi showed that the effect of year, different intensities of harvest and their interaction is statistically significant at one percent. The intensity of the lowest in 2010 in 75 percent and its highest in 2008 has been in control. The average production (2008 to 2010) the decline has vitality and the intensity of the 50 and 75%, about 20 percent mortality was observed. Due to environmental changes affecting the management and pasture species, livestock grazing can be stated that 30 percent guarantee of survival in this region will A.sieberi.

In this study, it has been tried through using wind shelter angle index to consider the changes in roughness of land surface across the piedmont longitudinal transects in Khezr Abad – Rostaqh of Yazd Ardakan Plain. By using roughness pin meter and based on Putter et al. method, the wind shelter angle was measured across 35 cm of longitudinal transects. Data of elevation points was imported to Minitab & Excel software and necessary calculation for relative & cumulative abundance was carried out. Comparison between variance analysis (duken method) of pediments shows significant difference in statistic level of below 1%. Meanwhile the eroded pediment has the highest vegetation cover with wind shelter angle. In eroded pediment as an average 18.11 ± 9.27% of the land surface with an angle more than 12 degree will trap the particles. However in appendage piedmont drops to 8.44±7.73%. The deposit piedmonts in the study area lacks significant roughness and only 0.28±0.58% of the land surface with a 12 degree wind shelter angle is covered which makes the lands of this piedmont more sensitive to wind erosion. The results showed that the indicator for accumulative abundance percentage for the wind shelter angle with more than 12 percent is able to express the roughness in different pediment. The above mentioned indicator is showing that with moving down wards from across the piedmont, while decreasing the roughness of the particles, the wind erosion will be increases.

The aim of the present study is the environmental impact assessment of tilapia (Tilapia nilotica) farming project in brackish water of Bafgh, with goals to achieve localization of technology and knowledge of tilapia fish production, employment and the possibility to controlled development in other areas. Total area used for the project includes three indoor areas for breeding operation, nursery (juvenile breeding) and growing. In order to achieve sustainable development of breeding this fish, impact assessment of this project development in which, environmental and socio-economic effects are considered, it seems essential and project will be accomplished more confidently. So, after considering the technical characteristics of the project, the immediate, direct and indirect impact area were determined and environmental aspects of area identified. Simple matrix method was utilized for the environmental impact assessment. Based on investigation, accessibility of the region, compatibility with the other land uses, lack of sensitive land uses in the area, not covered with the sensitive habitats range, the lack of permanent river flow, low quality of underground water and end up underground water flows in downstream desert and evaporated which result in impossibility of escaping introduced fish from the farm and the use of existing spaces in the first half of the year to product lead to make fewer infrastructure costs and increase revenue, are the main criteria for the sustainable development of this species culture in the area. Considering the executed studies and results of the matrix assessment construction and operation phases, it was concluded that there is no considerable destructive impacts related to the project. Therefore due to the fact that 50% of means in rows and columns of the matrix were not less than -3.1, so, we proposed execution of it with rehabilitation plans. Therefore, some strategies and plans to consider reducing the negative effects and enhance positive effects of the project, including monitoring programs, were proposed.

This research carried out in order to compare some socio-economic problems in different utilization methods in point of view of responders at Yazd province in year 2011. Reference population in this study according to the grazing license, was divided to private exploitation, collective exploitation and conciliar exploitation. In this regard 16 ranches in the three exploitations methods were selected. According to the objectives and hypotheses, 38 questionnaires via direct interviews with exploitation (grazing license holders) have been completed in this region. The findings indicate that ownership’s sense factor in private exploitation is higher than collective exploitation and in collective exploitation is higher than conciliar exploitation(p<0.05). Rivalry in utilization and tendency to increase of animal in collective exploitation is higher than conciliar exploitation and private exploitation (p<0.05). there is no significant differences in Encounter to offenders by government between different utilization methods(p>0.05). Also the rate of tendency of stock holders to ranch division in collective exploitation is higher than conciliar exploitation (p<0.05).

Agricultue is an occupation which because of its nature, is confronted with a set of hazards. This study was conducted to analyze sources sense of job’s risk in the central district of Bahabad County in Yazd province. The Method of the research is descriptive-analytical on the base of survey. The Statistic Society of research is 1186 farmer that is employed in agriculture. Using Cochran's formula Cochrane formula, the sample size of 134 persons was estimated that randomly and with combination of both cluster sampling and accessibility sampling were selected the required. Data was collected through interview and a questionnaire. The opinions of experts, farmers and local agricultural experts were provided by questionnaire. Results indicated that most farmers (about 74 percent) feel their jobs are at risk. Using factor analysis of sources of job alarmed farmers in the four factors was summarized. These include: financial and credit risks, climate risks, technical and managerial risk and combined risks. These factors could to explain in 7/72 percent of the variation. 27/3 percent of the residual variance was related to other factors that their prediction in this study is not possible. The research findings show that most farmers Feelings job’s risk is due the financial and credit risks. These four factors, multi-dimensional nature of risk management practices in agricultural employment shows. That requires systematic and comprehensive approach in managing these risks.