تعيين حساسيت رسوبات درياچه‌اي به فرسايش بادي و نقش آن در ايجاد گردوغبار (مطالعه موردي: درياچه خشك‌شده پريشان، استان فارس)

هدف از اين پژوهش بررسي رسوبات درياچه پريشان و نقش آن در وقوع پديده گرد­و­غبار مي­باشد. بدين ‌منظور 24 نمونه خاك سطحي از بستر درياچه و 9 نمونه خاك از اراضي كشاورزي اطراف آن جمع‌آوري و خصوصيات فيزيكي و شيميايي نمونه‌ها اندازه­ گيري شد. دانه­بندي نمونه‌ها به روش الك خشك با 5 طبقه روزنه­اي، بافت خاك به روش هيدرومتري بايكاس تعيين و درصد رطوبت اشباع، درصد گچ، درصد آهك، سديم تبادلي، كلسيم و منيزيم تبادلي، pH و EC براي هر يك از نمونه‌هاي خاك اندازه‌گيري شد. نتايج نشان داد بافت خاك نمونه‌هاي كشاورزي و درياچه تقريباً مشابه بوده و در تمامي نمونه­ها ماسه بيشترين درصد، و به­طور ميانگين 62% مواد تخريبي رسوبات درياچه را تشكيل مي‌دهد. درصد رطوبت اشباع در تمامي نمونه­ها بيشتر از 50 و قليائيت نمونه­هاي سطح درياچه بيشتر از نمونه­ هاي كشاورزي است. مورفومتري نمونه‌هاي برداشت‌شده از سطح درياچه و زمين­ه اي كشاورزي با استفاده از نرم­افزار G.R.Graph تعيين گرديد. مقدار ميانه و ميانگين تقريباً مشابه هم بوده كه علت آن نزديكي به منشأ و مسافت حمل‌ونقل كمتر مي‌باشد. ذرات داراي جور شدگي خيلي ضعيف، نامرتب و چولگي زياد به سمت ذرات درشت‌دانه مي­باشند. عوامل مؤثر در فرسايش بادي شامل فرسايندگي باد و فرسايش‌پذيري خاك مي‌باشد، بررسي نتايج آزمايشگاه خاك نشان مي­دهد كه خاك منطقه نسبت به فرسايش­پذيري در برابر باد مقاوم است. نكته مهمي كه از بررسي بادهاي منطقه حاصل مي­شود اين است كه سرعت بادهاي غالب منطقه با بيشترين فراواني كمتر از 5/3 متر بر ثانيه است و نقش مؤثري در جابه ­جايي ذرات خاك از سطح درياچه ندارد.

Introduction Soil erosion is a widespread environmental problem threatening environmental sustainability. It is one of the significant factors in both water and wind erosion. Understanding the physical and chemical characteristics of lakes and wetlands sediments is essential to study sedimentology and erosion. Drying up the wetlands around the world is one of the worst experiences of human life that has had many adverse effects. Large wetlands are drying because of changes in water use patterns, due to land-use changes and water constraints due to climate changes. Methodology Systematic random sampling was carried out from lake sediments. Then the texture of deposits was determined using triangle soil texture. The velocity and direction of the dominant and erosive winds were determined by drawing the wind and storm rose. Thirty-three soil samples were taken from the lake surface and the agricultural lands around the lake by random sampling from 0-30 cm depth, and the location of each sample was recorded using GPS. Sorting was done by dry sift technique. GR graph 3.0 software was used to determine sedimentological indices such as Median Diameter, Median, Kurtesis, and Skewness of the samples. According to Kazeroon synoptic station's wind data, the wind condition of the area was studied in the form of a wind rose. The erosion rate threshold of the lake surface sediments is needed to calculate the storm rose. For this purpose, wind data from the study area and sampling were used to determine the wind erosion threshold velocity, based on soil properties and experimental formula. Results The soil texture results showed that the sand had the highest percentage of material degradation in all samples, and the average sand content of lake sediments was about 62%. Clay and silt are less abundant, respectively. Soil texture in the study area was almost similar to agricultural land and the lake area, only with slight changes in texture due to increasing treatment intervals. According to the soil chemical analysis results, the electrical conductivity of all samples taken from the study area was less than four dSm-1 indicating that the soil was ordinary. Soil sodium content was low, thereby increasing aggregate resistance to dissemination and making the soil more resistant. In all samples, saturated moisture content was more than 50%, having high moisture content, resulting in fine particle adhesion. Based on the Kazerun station results, the frequency numbers of distribution of the annual wind class show that 50.97% of the winds are calm, and 49% of the winds have direction and velocity. The direction of the prevailing wind is westward. The Kazerun station annual storm results (2006-2016) show that 99.8% of the winds are calm, and only 0.2% of the winds have direction and velocity. This value is not visible in the flowchart diagram of the storm rose, so they can be ignored. Discussion & Conclusions Parishan Lake is one of several lakes in Iran that has dried up in recent years. In this study, we tried to show whether this event as a dust storm source, can be an environmental threat for residents living in urban and rural areas around the lake. The results showed that the sand had the highest percentage of material degradation in all samples. Therefore, due to the low abundance of silt particles in Parishan Lake's sediments, lake sediments cannot be considered a potential origin for Iran's dust storm. According to the samples taken from the Lake Surface and agricultural land, the calculated morphometric values showed that the particles have irregular Kurtesis and a high skewness towards coarse grains. The results of soil physical and chemical property analysis show that the soil is resistant to wind erosion. The important thing to conclude from the wind rose is that the prevailing winds of the region are located in the classes of velocities less than 3.5 m/s, which do not play a major role in generating dust storms, which are more abundant in the basin. The problem does not threaten the rural areas around the lake and the city of Kazerun in terms of dust. If the dust is observed a few days a year, it may be due to external sources.