Evaluation of salt dust occurrence potential in the North east Zone of Urmia Lake

Extended abstract 1- Introduction Urmia Lake as the largest domestic lake in Iran is drying. Climate change in the northwest of Iran, rainfall reduction and evaporation, due to the increase in average temperature in the Northwest of the country accompanied with the involvement of human factors such as dam construction, have caused an irreparable environmental hazard in the northwestern of Iran. Undoubtedly, extending the frequency of events and expanding the range of salt dust originating from the bed of Urmia Lake is the most important consequence of the lake’s dryness (Zarasavandi, 2014). There have been various ideas about the risk of salt dust caused by the dryness of Urmia Lake. It seems that some of them do not have an exact scientific basis. In this article, the north-eastern zone of Urmia Lake is divided into different parts in terms of texture and sediments and has been investigated for the potential of salt dust generation.  2- Methodology In this research, the determination of producing the potential of salt dust is carried out through four steps including: collecting information, field and laboratory studying, checking meteorological data, and determining the winds speed and direction in regions. Different physical and chemical tests have been carried out on samples taken. Sampling and evaluating of the texture and structural properties of surface sediments, such as determining the horizons that makes sediment in each area, thickness of salt shells, type of salt shells, presence of sand cover at sediment surface to integrate with the results of wind tunnel tests, meteorological information (climate region and wind speed and direction), grain size which determine the production of salt dust potential in the area has been studied. The sampling was done according to the texture changes and the types of sediments in studied areas. Wind tunnel was used to study the evaluation of erosion of the sediments of the study area. At first, the samples were dried to be placed in the most suitable condition for wind erosion. Subsequently, samples were poured into test trays and its surface was carefully flattened and then weighed.  Afterwards, it was placed inside the wind tunnel channel. 3-  Results The results of the research were obtained from satellite images, field studies, meteorological studies, sampling, and laboratory experiments and local inquiries. Satellite images of the 15 past years have been surveyed and the lake’s drying process has been investigated. Based on the survey of satellite images in the northeast of the lake between the Sharaf- Khaneh port and the Islamic island, it has dried up over 500 square kilometers and has come out of the water. In order to investigate the prevailing winds in the region, according to the weather data of Tabriz station, wind rose-diagram has been drawn. Due to the fact that low-speed winds are not capable of producing dust storms, winds were eliminated at speeds less than 8 m/s and wind rose-diagram was drawn. The direction of most winds is to eastward. In studied areas, samples from soil or saline sediments were removed from a few points on each substrate and transferred to the laboratory. Different physical and chemical tests have been carried out on samples taken. The most important experiments including grading tests, morphometric soil particle studies, salt content determination, XRD and wind tunnel testing. To study of the sediment potential for dust generation as well as sediment erosion threshold speed has been used of wind tunnel. The experiment began with low wind speed and gradually increased the wind speed to determine the speed of erosion threshold. At low speeds, there was no effect in wind erosion, but with increasing the speed for each sample at a rate of speed (threshold speed), erosion began. This experiment was performed on samples from different subzones. At low velocities, any erosion was not observed in sediments. Also were tested salt samples in wind tunnel. The samples were placed for 15 minutes in wind tunnel at different speeds up to 30 m/s. Its weight did not change before and after being placed in the tunnel, this is a sign of a lack of wind erosion impact on the salt shells. Sharaf- Khaneh and Sheikhvali area sediments have the most erosion modulus because of the coarse size of the sediment grains compared with the sediments of the Islamic island. The wind erosion modulus of the studied sediments at speeds of about 22 m/s, the equivalent of 80 km/h increased. 4- Discussion &Conclusions Based on satellite images studies and field studies, and types of sediments, the North East Zone of Urmia Lake is divided into four subzones. Subzones separated outwards from the old coast of lake to center of lake that contains, loose soil subzone, soil saltyferous subzone, salt soilferous, subzone and pure salt subzones. The area of these subzones are about 160, 220, 170 and 58 square kilometers, respectively. Each of these subzones has special sedimentary texture.  According to the results of wind tunnel testing, the module of sediment erosion of northern area of the Islamic island is 1157  and for Sharaf-Khaneh sediments is 1948 . The lowest threshold speed of wind erosion belongs to the saline sediments of the northern shore of the Islamic island. The size of sediments in this area is smaller than other areas and the amount of salinity of sediments in this area is more than other areas too. The amount of erosion for the coastal deposits of Sheikhvali and Sharaf-Khaneh areas has been high, which is due to the coarser size of these sediments grains than the northern shore of the Islamic island. The size of sediments grains in these areas was more sand and at a very low rate silt and clay and therefore, they had low dusting potential.  According to the results of sediment grading tests, wind tunnel and field investigations, it was found that the area near the Islamic island has a higher dust potential than the northern parts of the Sharaf-Khaneh shore and the Sheikhvali shore. Wind tunnel tests showed that the soil moisture plays a major role in preventing wind erosion. Fortunately, the results of this research show that the salt storms did not have considerable impact on agriculture and gardening of area so far.