Desert
Year:2003 | Volume:8 | Issue:1|Papers Count:11

Global climatic changes due to increased- greenhouse gas concentration are likely to increase temperature, change precipitation patterns and probably raise the frequency of extreme events. Global climate models currently can not simulate with accuracy the short-duration, high-intensity and localized heavy rainfall and a change in mean monthly rainfall may not be representative of a change in short-duration rainfall. In this study, due to the importance of precipitation in dry and semi-dry regions and role of rainfall components in sustainable development, the rainfall intensity-duration relationship for Northeastern Iran was investigated. The rainfall intensity-duration relationship with different reoccurrence period has some applications including dam building, watershed management and urban waste water design. Complete statistical tests including statistical credibility of data, homogeneity, independence tests were done on data collected from rain gauge network. The rainfall intensity average for 5- and 10- year periods, 1994-1998 and 1989-1998, respectively, were compared with long-term period data. The results showed that rainfall intensity with short durations of 10, 20 and 30 minutes was enhanced as compared to the long-term period data. In addition, the Gamma distribution had a better fitting from five selected distributions.

Physiological effect of five levels of water stress (0, -0.3, -0.6, -0.9 and - 0.1.2 MP) was studied on seed germination and plumule and radicle growth lengths in three different Salsola species: S. dendroides, S. rigida and S. richteri. Polyethylene glycol (PEG) was used to prepare appropriate water potentials. A total of 25 seeds were sawn from each Salsola species. Experimental design was factorial with complete randomized design. Maximum germination rate was obtained at -0.3 MP. Germination rate and plumule and radicle lengths declined with decreasing water potential level. S. dendroides was found to be the most resistant to water stress compared to other species.

In this study, the distribution map of different metal and non-metal materials was explored based on the data from the Mine and Industry Organization, Semnan province and field as well as laboratory studies. Final reserve, possible reserve, grade and geographic situation were also obtained. The results showed that mineral deposits have a better economic situation and more qualified for investment on permanent development than ore deposits. Further, applications of ore material exploitation, generation, recovery optimization and other important factors were analyzed.

The main objective in this study was to determine seed germination rate and seedling growth of Agropyron desertorum and A. cristatum using factorial complete randomized block design with six salinity treatments of 0, 100, 200, 300, 400 and 500 mM NaCl . Seeds were incubated at 4°C for a few days and then surface-sterilized with 5% (v/v) sodium hypochlorite. The experiment was carried out in a germinator with 50% relative humidity at 25°C with a photoperiod of 8:16 hrs light/dark. Percent germination, plumule and radicle lengths and seed germination rate were measured and the data were analyzed using ANOVA and Duncan"s multiple comparison test. The results showed no significant differences between A. desertorum and A. cristatum with respect to seed germination rate and radicle and plumule lengths. The interaction effect between species and salinity and the replication effect on germination and lengths of radicle and plumule were neither significant. The effect of various salinity levels on seed germination and radicle and plumule lengths was significant at 1%. Growth of radicle and plumule and seed germination were stopped at 200 and 300 mM NaCl, respectively. Salinity levels at 0, 100, 200 and 300 mM had significantly different effects on seed germination. Salinity levels of 0, 200 and 300 mM had significantly different effects on plumule and radicle growths. Overall, seed germination rate, percent germination, lengths of plumule and radicle declined with increasing salinity concentration.

Kuh-e-Sorkh is located in Southwestern Semnan, Iran. The bedrock of this region is formed from upper red formation and includes fine and evaporative grain. Due to water erosion, various erosion shapes have been developed. One of the most interesting and rarest erosions is tunneling erosion or piping. Among these, pseudokarsts have a simple structure with V-shaped holes in various dimensions. In addition, there is an underground drainage network that is connected to the surface drainage network. Although the appearance of these structures is simple, their formation mechanism seems to be complex. Factors influencing their formation are as follows. Bed rock: lithology, aggregation (compounds) diagnosis, concentration and salts, clay types and mechanical attributes of the bed rock as follows. Soil: texture, structure, amount of salts, leaching, pH, electrical conductivity (EC), sodium absorption ratio (SAR) and exchangeable sodium percentage (ESP). Physiography: slope, aspect, elevation and hydraulic gradient slope. Climate: precipitation, temperature, precipitation and climatic changes. Biotic: human impact, livestock trampling and vegetation destruction. The effects of the above factors are not identical in formation of pseudokarsts, rather the two most effective ones are soil texture and chemical properties such as pH, EC, ESP, SAR that were subject of this investigation. In addition, field observations were taken into account in studying pseudokarst formation. The results showed that development of pseudokarsts is primarily affected by soil texture where percentage of silt particle is greater than clay and sand particles and pseudokarsts are more expanded. Thus, salts and chemical formation were considered secondary to pseudokarst formation. Further, there was a relationship between EC and SAR. Field samples revealed higher SAR content and variable amounts of EC. This indicates the important role of SAR in pseudokarst expansion without considering EC.

Populus euphratica is a woody plant that grows naturally along riverbanks in arid and semi-arid regions. Its natural stands exist mainly in Asia and North Africa. Iran is considered one of the main distribution areas of this species having around 20,000 hectares of Euphrates poplar forests. P. euphratica plays a significant ecological role along Tedzhen riverbank. Tedzhen river flows about 90 Km along Iran-Turkmenistan border. The vast habitats of Euphrates poplar forests in Khorasan province can be found along Tedzhen riverbank. Euphrates poplar forests are one of the main ecological barricades that prevent river enlargement and its geographical changes. They are also natural belts protecting arable lands against wind hazards. Euphrates poplar forests in the area were studied using topographic maps as well as land surveying. Three habitats were identified and selected for this study. Transects with various lengths were laid down systematically and 33 random plots (10x10 m) were plotted perpendicularly off the riverbank. Biophysical properties of Euphrates poplar and physico-chemical properties of soil were studied at three different depths (0-30, 30-60 and 60-90 cm) within 19 plots. Soil factors such as texture, saturation percentage (SP), CaCO3, CI, Mg, Ca, Na, pH, electrolyte conductively (EC) and sodium absorption rate (SAR) were measured in the laboratory. Relationship between biophysical factors of Euphrates poplar and soil factors were evaluated using PCA and correlation analysis. Results showed that among physical properties of soil, percentage of clay lower than 60 cm had a strong positive relationship with Euphrates poplar density. Soil chemical substances particularly Mg, Na, Cl and EC were negatively correlated with Euphrates poplar performance. Ecological analyses showed that soil salinity, pH and chloride toxicity were the main limiting factors of Euphrates poplar density. Soil acidity and lime percentage were not considered as limiting factors. Ecological analyses also revealed that soil physical factors such as light soil texture and lack of clay layer in depth of root expansion could limit natural distribution of Euphrates poplar in some parts of the region.

Field experiment was conducted in order to evaluate redroot pigweed (Amaranthus retroflexus) competition effects on soybean yield. The experiment was carried out as a factorial in randomized complete block design with three replications. Different emergence times (Ve: redroot pigweed was planted at the same time as soybean; Vc: redroot pigweed was planted at the second trifoliate leaf stage of soybean; V2: redroot pigweed was planted at the second trifoliate leaf stage of soybean) and densities (10, 20 and 40 plants m-1) of redroot pigweed were studied. Controls included redroot pigweed, soybean and soybean with natural weeds planted as separate treatments. Soybean plant height, harvest index, biological yield and grain yield were statistically significant at various times of emergence and densities of redroot pigweed. Harvest index, biological yield and grain yield decreased with increasing redroot pigweed density. Harvest index, biological yield and grain yield were at minimum when redroot pigweed and soybean emerged simultaneously and redroot pigweed density was 40 plants m-1. When redroot pigweed emerged at the third trifoliate leaf stage of soybean, soybean plant height, harvest index, biological yield and soybean grain yield were unaffected by redroot pigweed density.

Today, desertification is a major concern in most developing countries including Iran in particular. Many studies have been carried out to assess and map desertification in the world and as a result several local and regional models have been developed. ESAs model is one of the best and most recent methodology introduced by the European Commission in 1999 and evaluated by most European as well as Middle Eastern countries. ESAs has recently drawn especial attention among Iranian researchers and is more advantageous than other methods because of its accuracy, particular weighing of layers, use of geographical information systems in overlaying of maps, use of geometric mean over arithmetic one or sum in computing indices and final desertification map. In addition to a higher precision and speed of evaluating and preparing desertification map, there is a very little error using ESAs.

The processes associated with sand transport have been studied intensively in recent years based on laboratory simulation, direct measurements and field observations. In addition to stimulation of wind-blown sand transport processes, efforts have been made to design an empirical/analytical model based on simple principles of moving-sand transport due to turbulent stress near the surface. In this study, surface momentum flux at the boundary of sand-air, which is the main element of sand transport was parameterized. Here, we report the development and use of a numerical model based on volume of fluid (VOF) method to estimate the threshold velocity for moving-sand motion. Typical value for moving-sand in this model was found to be in the range of 20-25 Kg m-1hr-1. Such a model could be used to study sand transport and predict sand motions in desert areas such as the central Iran.

Segmented fans are one of the arid morpho-climatic system landforms that have drawn a significant attention among many researchers. Various results have been reported by workers studying landforms across the globe. Segmented fans are identified by different specifications such as topographic position, drainage pattern, incision depth, nature of soil profile and desert varnish to other alluvial fans. The goal of this study was to assess effective factors controlling the evolution of segmented fans. In this study, aerial photographs and topographic and geological maps in various scales were used. In addition, mountain front sinuosity, valley floor width to valley height ratio and NUVEL 1 a model were used to assess tectonic activity. The results showed that the evolution of segmented fans in Sirjan playa depended upon tectonic activity as well as climatic changes in which the role of the former seems to be much more important than the latter. In fact, continued down-lift and up-lift of Urumyeh-Dokhtar mountainous region has created the segmented fans in Sirjan playa. Despite this situation, climatic changes during arid and humid periods had a second role in the evolution of alluvial fans. Surface is considered, much more important factor than change of location of sediment assimilation thus creating new fans.

Haloxylon plantation was done due to sand dune stabilization, reclamation of degraded lands and reduction of wind erosion damages to Hossein Abad-e-Mishmast region of Qom province. The objective of the research was evaluation of Haloxylon plantation effects on soil characteristics and vegetation cover. At first, four key areas were determined in each plantation and control regions. Sampling was performed with randomized-systematic method. Three transects with length of 500 m were established in each, key area and 10 plots were selected in each transect. Floristic list, cover percentage and number of plants were recorded within each plot. Also, yield, density, frequency and species composition were determined. A profile was dug in each transect due to survey of soil characteristics. The measured soil variables included texture, organic matter, electrical conductivity (EC), acidity (pH), phosphorous, nitrogen, sodium and potassium. T-test (paired sample t-test) was used to compare the soil characteristics between two regions. The results showed that cover percentage, yield and homogeneity of vegetation increased and species composition were better in plantation lands than the control region. Also, there were significant differences between soil characteristics except of soluble sodium in plantation and control region. Organic matter, potassium, phosphorus and nitrogen in plantation lands were more than the control region. In addition, in plantation lands, alkalinity and salinity were increased more than the control region.