نشریه مرتع و آبخیزداری
سال شصت و دوم شماره 2 (تابستان 1388)

Recognition of rangeland species with the maximum efficiency and the minimum water usage is very important, since major parts of rangelands in Iran are located in arid and semiarid climate. In addition, the rangeland improvement and management on the basis of transpiration rate of rangeland species in different climatic conditions has great importance. The goal of this research is comparison and measurement of transpiration rate in four important species of Medicago sativa, Trifolium repens, Sanguisorba minor and Trifolium pratens as well as the assessment of their efficiency in dry matter production under semi natural conditions in College of Natural Resources and Marine Sciences, Tarbiat Modares University, during spring and summer of 2005. The rates of daily transpiration of the mentioned species were measured in small vases with upper area of 50.27cm2 in 5 replications and adjacent to five control vases during 85 days using weighting method. The results of the study showed that the maximum and minimum rate of transpiration per dry matter is related to Trifolium pratens and Medicago sativa with the values of 498.253 and 59.274 ml, respectively. The applications of such type of result facilitates the determination of water requirement of rangeland ecosystems under improving operations and also lead to select the most suitable improvement method and rangeland species as well.

Knowledge on animal requirement, available forage and its quality is fundamental for successful livestock and range management. Since sheep is dominant grazing animal of rangelands in Iran and there are over 27 sheep breeds and each breed has special body size, physiological condition and consequently different daily nutrition requirement, animal unit should be determinated for dominant breed of sheep in every region to be calculated the forage requirement based on body weight, daily energy requirement and quality of available forage. In this study, two herds of Kermanshah's Sanjabi breed have been weighted including 50 animals in each herd (15 heads three years old ewe, 15 heads four years old ewe, 5 heads three years old ram, 5 heads four years old ram, 5 heads three months old lamb and 5 heads six months old lamb) in three stages. The body weight of Sanjabi breed (based on average body weight of three and four years old ewe) was 60.68 ±0.56 kg. Animal unit equivalent (AUE) for ewe, ram and lamb were 1.29, 1.88 and 0.63 kg, respectively. The results of analysis of variance indicated that there are significant differences between weight of ewes and rams (P

The most precise and simple method of evaporation measurement is application of pans in which class A pan is used in Iran. In contrast, there are many empirical methods which are used for estimating the evapotraspiration. In this study, Thornthwaite method was used due to the simplicity of its parameters and then we tried to use it for evaluating evapotranspiration by changing it's parameters. Because of its unproper estimation in Iran's climatic conditions in comparison with pan data we concluded that a considerable percentage of monthly evaporation with thornthwaite method with corrected alfa in different stations, have a good conformity with monthly evaporation measured with class A pan in the error range of 30% and in we added 0.5 unit to the exponent of Thornthwaite formula to having acceptable results for arid and semi arid region. In fact, the formula is not efficient in measurement of evapotranspiration without correction.

This study was carried out to investigate the effective environmental factors in the distribution of vegetation in Zirkouh rangelands of Qaen. After delimitation of the study area, sampling of soil and vegetation were performed using randomized- systematic method. Vegetation cover was recorded by using Braun-Blanquet combined abundance-cover scale in each sample. Within each sample, one profile was dug and soil samples being taken at 0-20 cm and 20-100 cm depths. Physical-chemical characteristics were determined include texture, lime, organic matter, soil moisture content, saturation moisture, EC and pH. Five vegetation groups were identified after the application of TWINSPAN method and were named after the characterizing species as follows: Salsola richteri-Aelorupes littoralis; Zygophyllum eurypterum-Haloxylon ammodendron; Artemisia sieberi-Zygophyllum eurypterum; Ammodendron persicum-Stipagrostis pennata; Artemisia aucheri-Amygdalus scoparia. The results of PCA showed that environmental factors best related with the distribution of this vegetation are texture, lime, organic matter, soil moisture content, saturation moisture, elevation and slope.

In Iran, fine grained formations (Neogene's units) are very susceptible to erosion. Also, they are the units producing runoff and causing soil loss in watersheds. The objectives of this study is to assess the effect of physical - chemical and mechanical properties of these formations on sediment and runoff rates at different rainfall intensities, based on using field simulator in Taleghan Basin. For this purpose, Neogene's units were separated into five sub-units including Halite siltstone (NgSiH), Siltstone (NgSi), Mudstone (gy1C), Gypsum mudstone (gy1CG) and Halite clay stone (gy2CH), based on physical and chemical properties. Then, runoff and sediment rates were determined in each sub-units at two different intensities (30 and 60 mm/h) using rainfall simulator. Analysis of variance and Duncan's tests showed that NgSiH sub-unit has produced the highest amount of runoff and sediment rates and then the runoff and sediment rates of other subunits in decreasing order are as follows: NgSi, gy2CH, gy1CG and gy1C are 5% significant level. The trend of induced runoff and sediment rates at different times showed that in NgSiH and NgSi sub-units, runoff amounts were fixed rapidly at second ten minutes. Also, on the other sub-units, runoff amounts were fixed at third ten minutes but sediment yield was increased rapidly at third ten minutes.

Stabilization of river terraces and natural soil slopes in rangelands by means of tree roots as a reinforcement agent is an environmental adopted method which needs to be developed. In this research a series of tests was carried out on soil blocks containing willow roots and without roots using a large scale in situ direct shear test apparatus. The results were analyzed based on direct shear theory to calculate the cohesion and internal friction angle of rooted and non-rooted soil. The results reveal that in spite of a slight decrease of 8% in the internal friction angle, the appearance cohesion of lean clay soils increase significantly up to 130%. The results of this research are presented in forms of linear and logarithmic relations between increased shear strength and root density at different depths of soil.

The system analysis plays an important role in natural resources, water resources and industrial engineering. In recent years, most parts of Iran like Golestan province, due to the lack of integrated river basin management, have been suffered numerous losses in variant environmental, social and economic aspects. In this paper an application of system analysis has been applied to optimal pattern of various resources in Gharmabdasht Watershed situated in Golesten province, Iran. To achieve an optimal allocation of natural resources in this area, firstly a linear programming algorithm has been used to maximize the benefits. Then its results have been compared with an optimal allocation of resources using a goal programming. This comparison shows if a single objective optimization (LP) be formulated correctly, it can be that the proposed pattern, has been acceptable outputs in which be compared to goal programming(GP). The allocation natural resources based on LP method, in addition to reducing %10 of sediment from admissible amount effected by safety flood abatement criterion, has also maximized the beneficiary incoming with %5 plus needful along satisfied all of the goals.

Correct estimation of suspended sediment transported by a river is an important practice in water structure design, environmental problems and water quality issues. Conventionally, sediment rating curve used for suspended sediment estimation in rivers. In this method discharge and sediment discharge or concentration related using regression relation that generally is exponential model. Respect to uncertainty and nonlinear relation between discharge and sediment concentration, sediment rating curve has not enough efficiency for this purpose. In this study using Artificial Intelligent (Fuzzy Logic and Artificial Neural Network), suspended sediment in Karaj River was estimated. First, various neural network and fuzzy logic models established. For neural network and fuzzy logic, models with four neuron in hidden layers and FIS (Fuzzy Inference System) with four Gaussian membership functions, respectively were selected as the best structure. Finally, the results showed that fuzzy logic estimates the suspended sediment loud better than the other techniques and therefore is suggested for estimation of suspended sediment load.

Estimation of river sediment load is one of the most important issues in design of hydraulic structures, investigating water quality, conserving fish habitat, estimating erosion and determining watershed management effects. There are two methods for estimating sediment load: empirical and hydrological methods. Existence of numerous empirical methods for estimation of river sediment load and a wide range of calibration coefficients shows that a suitable analytical or empirical method does not yet exist to accurately estimate the sediment load. Also, hydrological methods are not able to recognize and separate the specific data measuring conditions and they can not show the temporal variation of sediment loads. In spite of these problems, nowadays, researchers are using Artificial Intelligence methods such as Fuzzy Logic. In this study, the measured suspended sediment load at hydrometric station of Sarcham located on Zanjanroud river is analyzed using USBR and FAO methods (common hydrological methods). Furthermore, suspended sediment load are estimated with a model developed based on Fuzzy Logic rules. In order to estimate suspended load using fuzzy method, one method named Supervised Fuzzy C- mean Clustering Method, is used. Then the results of hydrological and fuzzy methods are compared. The results showed that the temporal variation of sediment loads can be analyzed using a fuzzy method. Also the results obtained using the fuzzy method in comparison with the corresponding values obtained using the usual hydrological methods shows a better correlation with the observed values.

Sustainable exploitation of land resources is directly affected by considering soil quality which finally will also conclude environmental protection. Therefore, assessing different soil quality aspects which are sensitive to various land management practices seems too important. In this study, some selected soil quality indicators have been compared in five land use systems including untouched rangelands, semi degraded rangelands due to grazing, rangelands that converted to rainfed agriculture, abandoned rainfed agriculture and an irrigated wheat farm in eastern Qazvin province, Iran. Samples were taken from the surface layer (A horizon) of soils in a completely randomized design with four replications. Statistical comparisons of the results revealed highest decrease in soil organic matter and total nitrogen owing to abandoned rainfed agriculture that showed 74% and 70% decline, respectively. Eventually the abandoned rainfed agriculture meets the sharpest slump in some soil properties such as cation exchange capacity (CEC), available phosphorous, total porosity and thickness of A horizon. Meantime the most increase in bulk density was also in recent land use. According to the results, the negative effects of inappropriate land use changes were led to soil productivity decline and will cause undesirable consequences in soil quality. So maintenance of soil quality is critical to environmental sustainability and this should be done on the basis of recognition all features that reduce its quality.