بررسی مورفولوژیکی ریزگردهای حاصل از فرسایش بادی خاک‌های ساحل شرقی دریاچه ارومیه در تونل باد

امروزه عوامل مختلفی دریاچه ارومیه را در معرض خشکی قرار داده و به طوفان های نمک و پخش ریزگردها منجر شده است. در این پژوهش برای شناسایی ماهیت و کنترل ریزگردهای حاصل شده از این امر، سه سایت با سه لایه براساس ارتفاع از سطح آب های آزاد انتخاب و نمونه برداری خاک‌ها از عمق 10-0 سانتی متری به روش تصادفی انجام شد. نمونه ها در لایه 1 به علت نزدیکی به آب حذف شد و با انتخاب دو نمونه تصادفی از هر لایه در سطوح ارتفاعی دیگر، در مجموع دوازده نمونه تصادفی از عمق صفر تا ده سانتی متری برای اجرای آزمایش ها و مطالعات در تونل بادی از بین 153 نمونه انتخاب شد. این نمونه ها در سینی هایی به ابعاد 3×40×30 سانتی متر در فاصله 160 سانتی‌متری از قسمت مولد باد قرار گرفت و فرسایش بادی با سرعت 45 متر در ساعت بر آنها اجرا شد، سپس برای مطالعه ویژگی های مورفولوژیکی، رسوبات حاصل شده با دستگاه sem جمع آوری و بررسی شد. نتایج مربوط نشان داد که اثر سایت بر دو ویژگی درجه مدور بودن و استحکام ذره، در سطح احتمال پنج درصد معنی دار بود و اثر ارتفاع قرارگیری در تونل باد نیز تنها بر ویژگی درجه گردآوری ذرات در سطح احتمال پنج درصد معنی دار بود. براساس نتایج تحقیقات پیشین، دلیل اصلی گردشدن ذرات ناشی از طی مسیر طولانی بود و مورفولوژی نیمه مدور اغلب ذرات نیز می تواند شاهدی بر وجود منبع محلی با کانی شناسی غالب کلسیت، کوارتز و هالیت و معرف ذرات آلومینوسیلیکاتی رسی و کوارتز در ذرات باشد. همچنین نتایج ارتباط بین قطر ذرات و فواصل طی شده نیز بیانگر این است که ذرات با قطر کمتر از یک میکرون، تا مدت ها در جو باقی می ماند که یکی از مشکلات اساسی در ساحل شرقی است و ممکن است انتقال ذرات ریزتر استان های مختلف را تحت تاثیر قرار دهد و مشکلات متعددی به وجود آورد.  

morphological investigation of dusts resulting from wind erosion of the eastern shore soils of urmia lake in the wind tunnel

1- introductionurmia lake, which has been located in the northwest of iran, is the largest saltwater in the middle east. unfortunately, nowadays various factors have exposed it to dryness and wind erosion, the result of which is the increase in soil salinity, the thinning of solute crystals, and the occurrence of dust storms. if this lake becomes dry, the climate of the area will change to hot climate and salt storms will start. therefore, we must find new ways to control and prevent the occurrence of wind erosion. identifying the nature of these dusts, especially their morphology, is important in providing solutions to deal with the crisis. investigating the characteristics and morphology of dusts in the region is also useful in predicting ways and controlling factors to reduce their damages, and dust morphology is a practical method to determine their origin. investigation of the properties and characteristics of rising dusts from this area can be useful in predicting and controlling ways to contrast/withstand their damages.2- methodologyfor this purpose, three flat sites without vegetation and prone to fine dust production were selected from the eastern shore of urmia lake. each site was divided into 3 layers based on the height from sea level, but the first layer was omitted from the studying areas because of the high soil moisture due to low distance to lake, which results in decreasing dust production by this layer, and eventually 2 random samples (0-5 cm) were picked up from each layer. this research study was carried out based on 12 selected soil samples from 3 sites and their layers. the soil samples from 0 to 5 cm depth, as a surface soil of layers, were transferred to trays with dimensions of 3 x 40 x 30 cm in the wind tunnel of agriculture faculty of tabriz university, with 370cm length, 50cm width and 70cm height. subsequently, wind erosion was simulated by applying the maximum wind speed of 45 meters per second for 15 minutes at each height. then, the dust particles released at 2 heights of the wind tunnel (10 and 30 cm from the floor of the device) and the control soil sample were sent to sem to get their images. after processing these row images, the quantitative amounts of morphological properties were obtained. finally, the statistical analyses were performed on these properties. using a nested design to find the effect of factors such as the location, layer and height of the wind tunnel on the morphological characteristics of soils in the windblown dust.3- results the images which had been adopted from sem were analyzed in image j application and 5 parameters (perimeter, circularity, roundness, accept ratio and solidity) were calculated for each particle in samples and the average of these parameters for each soil sample was listed. the presented data were analyzed in minitab application by using the fully nested method and for conducting these analyses, the test of normality of data was performed on data list. the results for each parameter were presented in a table which showed the effect of site, layer and location height of the sediments in wind tunnel.4- discussion & conclusionsthe obtained results in this research (table 3) revealed the significant effect of site (5%) on circularity and solidity properties. also, the effect of height in wind tunnel from floor was significant in 5% just on roundness, and the effect of other factors on morphological properties were not significant. in other words, the size of particles, the area and their parameter in soil samples did not have significant differences and even the wind erosion with given speed in explained time duration didn’t act optional on the size of particles. there were no significant differences between size of diameter, area and parameters of particles before and after the wind erosion. the reason of these results can be dependent on the preparing method of samples for sem study, in which the samples were rubbed on pin of device and the great grains were separated. also, the effect of site and height of wind tunnel on roundness and circularity were significant, respectively. as for other morphological properties, the effects of site, layer and the wind tunnel height were not significant and there were no significant differences between the samples.