فصلنامه حفاظت منابع آب و خاک
پیاپی 4 (تابستان 1391)

Design and optimum selection of the hydraulic structures characteristics, plays very important role in water resources management in agricultural sector. In this study, ski jump of triangular flip bucket is investigated. To process the project, a physical model including a flume and an ogee weir were designed and constructed. Three flip bucket including a flip bucket with 45 degree angle and 2 cm length, flip bucket with 45 degree angle and 7 cm length and a flip bucket with 22.5 degree angle and 2 cm length. Four discharges and their corresponding Froude number were considered. The length of trajectory, upper and lower limits of jet flow were then measured and the required data were collected. The results indicated that increasing of bucket angle causes the thickness of jet trajectory increases. It is shown that Flip bucket with 45 degree angle and 7 cm length of the approaching canal is more effective than the others. It is further shown that the length of approaching canal has no significant role on the jet trajectory. Moreover, it is revealed that the angle of the bucket plays a significant role on the jet trajectory's characteristics. Increasing Froude number from 4.44 to 6.42 lead to upper and inferior of jet trajectory to be increased to 72.5 and 77.7 percents, respectively.

The intensify process of lowering Urmia lake level has led to reduce water quality, making it brackish and unusable in wells of Lake Marginal Lands. The present study investigated changes in groundwater salinity in Urmia plain using geostatistical models, and compares the results of the mapping in three time periods. To assess salinity of the groundwater, data from 57 wells in the period of 1380, 1384 and 1387 were analyzed, using Kriging in GIS, GS+ and ARCVIEW8 softwares. The results indicated that application of Kriging, experimental semi-variogram with spherical model provided better predictions with correlation coefficient of 0.99. According to the obtained groundwater salinity maps, land area with more than 2 dS/m groundwater salinity in 1380 was equal to 1924 hectares that has increased to 8331 hectares in 1387. During these years, in the study area the groundwater salinity with less than 1 dS/m was decreased about 14675 hectares. The observed maximum salinity value in 1380 has increased from 1.91 to 5.8 dS/m in 1387.

Amelioration of saline–sodic soils by means of different amendments is a subject of interest for soil and water conservation in arid and semi-arid regions. The general concept of "precision agriculture" is in contrast with traditional research methodologies, which are based on trial and error in some fields of agricultural sciences, and are time-consuming, expensive and produce uncertain/unreliable results. For this reason, recently, most researchers suggest another method, namely, the socalled "adaptive research", to overcome the mentioned weak points. The recent methodology has shown its advantages at national, local, and international levels and it only needs to be modified for specified environmental conditions. Most recently, a promising methodology is introduced as "integrated research plans", to clarify several questions in a single research project. But, at the same time, they do not ignore the other optimum conditions for such a finding. In research projects related to soil and water sciences, when plant is considered within the system, the study subject will be more complicated. In present article, it is pointed out that except some documented field experiments carried out for reclamation of salt-affected soils, the side effects of amendment applications such as ionic imbalances, plant nutrient availability, improvement of soil physical conditions (enhancing permeability and aggregate stability) did not taken into consideration. These impacts are acting due to their chemical influences on physical soil properties, but have not been adequately studied for salt- affected soils of the country.

Preservation of forest habitats has been shown to improve soil properties, rehabilitation and overall environmental quality. Soil enzymatic activities as indicator of biological activity of the soil are used for assessment quality and soil fertility. Little work has considered the effects of management in forest ecosystem. The objectives of this study were to quantify the seasonal changes in enzyme activity (alkaline phosphatase, acid phosphatase, dehydrogenase and urease) of soils at areas under canopies and intercanopy at a preserved Juniperus excelsa habitat and to compare the results with a non preserved neighbor one in Chahartagh, Iran. Soil required samples were taken on May and September, 2009. Soil enzyme activities showed seasonal variation with higher activity in September in both areas. The activity of studied enzymes was significantly higher in soils under junipers at both preserved and non preserved areas. The more enzyme activity at areas under juniper may be related to a larger microbial community especially fungi under trees. The results indicated that preservation will induce changes in soil enzyme activities which affecting the functioning of soil processes such as organic matter decomposition and nutrient cycling.

Heavy metals are the most important soil and environmental pollutants. Phytoremedation is one of the environmental oriented technologies that use plants to clean up contaminated soils from heavy metals. The objective of this study was to assess the capability of some native plants to phytoextract some heavy metals from the contaminated soils. Consequently, after preparing and stabilization of the contaminated soils, the seeds of some native plants (Arabis arenosa, Amaranthus retroflexus, Agropyron repens) were seeded, grown and harvested in a designed pot experiment. The soil and plant samples were taken and dried out in an oven at 85 Qc for 48 hours. The mean concentration of each heavy metal in the samples was determined using Atomic Absorption Spectrometry apparatus. The results indicated that Pb and Cd concentration in plant roots were more than shoots. Lead concentration in plant underground portion and Zinc concentration in aboveground portion were higher. The results further indicated that the maximum Zinc concentration in Agropyron repens aboveground portion was 262.65 Mgkg-1 and the maximum Pb concentration in amaranthus retrofleus underground portion was 71.25 Mgkg-1. From the plant extraction of this study we discovered that pb and cd concentration in soils are considered to become higher in root than shoots of plants. Pb concentration in underground portion and zinc concentration in aboveground portion is higher. Finding of this research show that Zinc concentration maximum in Agropyron repens aboveground portion is 262.65 mgkg-1 and Pb concentration maximum in Amaranthus retroflexus underground portion is 71.25 mgkg-1.

Reasonable estimation of soil physical properties is very important for optimal management of soil and water resources. Estimation of soil physical properties is usually time consuming and expensive. Geostatistical methods can be used as suitable tools to estimate such properties. In order to analyze spatial variability of soil properties in Dareh Viseh rangelands, a number of 78 soil samples from 0-30cm soil depth were taken and transferred to laboratory. Some soil properties including clay, silt, sand and bulk density were measured in laboratory. After normalizing the data, the semivariograms were obtained and evaluated. The Kriging, inverse distant weighting and radial basis function methods were then evaluated for the obtained data. To compare these methods, the cross validation method was used by statistical parameters of Mean Absolute Error (MAE) and Mean Bias Error (MBE). The results showed that the Kriging method can provide more reseanable predictions for silt, sand and bulk density, while the radial basis function provides better estimate to predict clay content in the study area.

Conservation of quality of the available water resources is very important in arid and semi-arid regions. Using constructed wetlands system for treatment of municipal, industrial and agricultural wastewater has attracted many attentions worldwide. Thus the direct discharge of wastewater contamination into water resources via chemical nutrients is prevented. Given the aquatic plants grown naturally in agricultural open drains, the aim of this study was to investigate the role of the open drains as the natural wetland systems for reducing nitrogen and phosphorus from the agricultural return flows. In this study, first in a laboratory scale, removal efficiency of nitrogen and phosphorus (in three replicates with concentration levels of 30 and 10 mg/l for both N and P) and four retention times (0.75, 1.5, 3.5 and 7 days) in constructed wetland systems containing two aquatic plant species (Phragmites australis and latifolia Typha) were studied and compared to a control system. The results showed that the system containing Phragmites australis has highest N and P removal efficiency. In the second stage in a field surveying in the range of 1000 m length of open drainage path and 200 m intervals, both drainage N and P concentrations were measured. The results indicated that concentrations of these two pollutants were reduced along with the open drain.

Large areas in Iran are located in arid and semi-arid regions and imposed to serious water shortage. In such areas, not only the available water resources are restricted, but the climatic conditions that are influencing evaporation acting more intensively. The objective of this study was to estimate evaporation from bare soil at presence and absence of impervious layer, water table and free drainage. The amount of evaporation is also estimated using the parametric model proposed by Zarei et al., (2009) based on Campbell’s retention model. For this purpose, some PVC constructed lysimeters were filled with soil samples and packed carefully. The amount of evaporation was measured three times a day by weighting the lysimeters. The proposed model of Zarei et al.,(2009) based on Campbell’s retention model was further verified against the collected experimental data to estimate evaporation from water table drawdown. Model verification indicated that the maximum (98.8) and minimum (84.8) efficiencies belong to 150 and 75 centimeters of water table depths, respectively. The results, with slightly underestimation, indicated a reasonable agreement between the measured and model output data. The small underestimation between measured and predicted values can be attributed to moisture loss as vapor, soil shrinkage and errors in digital scale measurements. The predicted instantaneous evaporation values provided better agreement with the experimental data as the water table depths were increased.