بررسی خصوصیات کانیشناسی ریزگردهای حاصل از فرسایش بادی خاک های ساحل شرقی دریاچه ارومیه با استفاده از تونل باد مدار بسته.

Background and Objectives Urmia Lake is the largest saltwater in the Middle East, which has been located in the northwest of Iran. 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. Identifying the nature of these dusts specially the mineralogy of them is important in providing solutions to deal with the crisis. Investigating the characteristics and mineralogy of dusts in the region are useful in predicting and controlling ways to reduce their damages, and dust mineralogy is a practical method to determine their origin. In other words, the deposition of dust in different areas can affect the nearby ecosystems by making changes in the texture, composition of elements and even the acidity of the soils of the affected areas. The source of dust is very important in the mineralogy of sedimentary particles and depends on various factors such as geology and soil characteristics as well as climatic conditions. Also, the height of atmosphere which the dusts are there, can be useful in studying the effect of mineralogy in this height. Methodology For this purpose, three flat sites without vegetation and prone to fine dust production were selected from the eastern shore of Urmia Lake, and 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 work 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, and wind erosion was simulated by applying the maximum wind speed of 45 meters per second to it was done 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 subjected to XRD analysis and the obtained diffractions were interpreted using High Score software. Finally, statistical analysis was performed using a nested design to find the effect of factors such as the location, layer and height of the wind tunnel on the content of minerals in windblown dust. Findings The obtained results showed that the dominant minerals in the most dust samples, were quartz, calcite, halite and gypsum with the highest average percent of quartz, because of the widespread occurrences of this mineral in the earth crust. The statistical analysis results revealed the significant effect of layer on quartz at the p<0.01 level, but the effect of site on calcite was significant at the p<0.05 level and the maximum amount of quartz appeared in layer 2 of site 2, while its minimum amount has observed in layer 2 of site 1. The maximum and minimum amount of calcite was found in site 2 and 3 respectively, but predominance of quartz in the dust samples can be attributed to the wind blow within a short distance. Also, the differences can be related to the nature of the parent materials of sites from which soils were derived. Conclusion In general, the presence of calcite as the main mineral in samples is due to study area temperature and precipitation increase and decrease respectively, which cause lake dryness, while gypsum and halite are produced in result of chemical equilibrium process and distribute in salty soils. Gypsum also can be produced during the reaction of calcite and sulfates of sea salts. The dryness of the lake also results in rising the gypsum minerals from dried floor of Lake and the presence of halite is affected by Urmia Lake salts that remain after water evaporation in dried land as a main mineral in soil and dust samples of affected lands. [ABSTRACT FROM AUTHOR]