تأثیر خواص فیزیکوشیمیایی مارن‌ها بر میزان فرسایش‌پذیری آن‌ها با استفاده از دستگاه شبیه‌ساز باران در منطقه نوبران، ساوه

نویسنده

چکیده

مارن‌ها یکی از مهم‌ترین واحدهای رسوبی در ایران می‌باشند که به لحاظ ویژگی‌های فیزیکی- شیمیایی از رسوب‌زدایی و فرسایش‌پذیری زیادی برخوردار هستند. ماهیت دانه‌بندی و عناصر موجود در آن‌ها و تأثیر این دو موضوع در میزان فرسایش مارن ها بسیار مهم می‌باشد. در پژوهش حاضر به بررسی ویژگی‌های فیزیکی- شیمیایی واحد‌های مارنی و تأثیر آن بر اشکال مختلف فرسایشی در منطقه نوبران ساوه پرداخته‌شده است. بدین منظور علاوه بر نمونه‌برداری از رسوبات، آزمایش شبیه‌سازی باران (به کمک دستگاه شبیه‌ساز باران) در سه واحد مارنی منطقه بر اساس اشکال مختلف فرسایشی انجام شد و میزان رواناب و رسوب تولیدشده در هر نقطه در آزمایشگاه تفکیک و اندازه‌گیری شد. همچنین در آزمایشگاه پارامتر‌های هدایت الکتریکی، میزان عناصر سدیم، پتاسیم، کلسیم، منیزیم، گچ، درصد ذرات رسوبی و سدیم قابل‌جذب (SAR) نمونه‌ها اندازه‌گیری گردید. در تجزیه‌وتحلیل داده‌ها از روش تجزیه واریانس و مقایسه میانگین‌ها در نرم‌افزار آماری SPSS استفاده‌شده است. همچنین مقایسه‌ای اجمالی بین دامنه‌های روبه شمال و جنوب که ازنظر فرسایش متفاوت می‌باشند، نیز انجام شد. بر اساس نتایج تجزیه واریانس اشکال مختلف فرسایشی در میزان یون سدیم، نسبت جذب سدیم و میزان درصد رس، دارای اختلاف معنی‌دار می‌باشند. میزان میانگین یون سدیم و نسبت جذب سدیم از فرسایش سطحی به فرسایش خندقی در مارن‌های منطقه افزایش‌یافته و میزان میانگین درصد رس از فرسایش سطحی به فرسایش خندقی کاهش می‌یابد. همچنین سه متغیر یون سدیم، نسبت جذب سدیم و درصد رس نمونه‌ها را می‌توان عواملی تأثیرگذار در فرسایش مارن‌های منطقه و ایجاد اشکال مختلف فرسایشی دانست. بنابراین بین نوع لندفرم و خواص فیزیکی و شیمیایی مواد سازنده و نحوه و میزان فرسایش‌پذیری آن ارتباط وجود دارد.

کلیدواژه‌ها


عنوان مقاله [English]

Effects of physicochemical properties of marls on their erodibility using rainfall simulator in Nowbaran, Saveh

چکیده [English]

Introduction: According to the physicochemical characteristics and high rate of erodibility, Marl is one of the most important sedimentary units are in Iran. These properties caused large environmental and civil damages and so, the study of erosion and erodibility of the marl units is essential. One of the most important points about marls is grain size nature and elements in them and their effects on amount of erosion. The physical and chemical proprieties of soil are very important in the development of badlands. This study deals with the physicochemical characteristics of the marl units and their effect on various forms of erosion in Nowbaran Saveh region. Badlands are a typical landform of greatly dissected fine-grained materials in arid or semi-arid environments like Nowbaran, although they are also found in different climatic conditions. Badlands typically have steep, unvegetated slopes, high drainage densities, high erosion rates and a tendency to form a regolith profile with dried cracks, making the surface puffy. Climate and geology are several factors determining the tendency to badland formation. Runoff, rain splash, marl and loose formations together with massive wasting processes such as creep, sliding and flow, become the dominant factors determining landform genesis, resulting in the formation of badlands in Clayey-silt slopes.
Methodology: in this research, in addition to sampling the soil and sediments, rain simulated (using rain simulators) in three marl units in area with different forms of erosion and runoff and produced sediment amounts in each point were measured in laboratory. Also, parameters such as electrical conductivity, content of sodium, potassium, calcium, magnesium, gypsum, sedimentary particles agglomerate and SAR percent (SAR) was measured. In analyzing the data, analysis of variance and comparison of means method were used in SPSS software.
Result and Discussion: Mineralogical, geochemical and grain-size composition of soil and pore-water chemistry parameters was characterized on both eroded (south-facing) and non-eroded (north-facing). Only a few grain-size parameters and clay mineralogy discriminate eroded from non-eroded slope substrates. Erosion occurs where the fine fraction is abundant. This may be due to reduced permeability in the eroded soil, whereas the non-eroded one is more stable with respect to weathering, as it is more permeable. The abundance of clay minerals is affected by pedogenetic processes in the non-eroded slope, which increases in mixed layers and indirectly reduces the amounts of other minerals, making clay mineralogy a discriminating parameter in the two different types. Chemical data enable discrimination between eroded and non-eroded slopes. pH, SAR (sodium adsorption ratio), TDS (total dissolved salts) and PS (percentage of sodium) are distinctive parameters for both eroded and non-eroded slopes. TDS increases in depth in the non-eroded slope, whereas the maximum TDS is just below the crust in the eroded one. On average, eroded substrates are higher in pH, SAR and PS than non-eroded ones. The ESP (exchangeable sodium percentage) of the eroded slope has a higher value than the non-eroded one. So, clay minerals include sodium result high rate of soil erosion with gully landforms in this study area. Crusts are less dispersive than eroded substrates, and non-eroded substrates behave as crusts. This suggests that the portion of the slope most severely exposed to weathering tends to stabilize, due to strong decreases in SAR, PS and ESP. Several diagrams reported in the literature show similarly anomalous crust samples on eroded slopes, compared with other samples coming from greater depths on eroded slopes. In the present case study, the exchangeable form of Na characterizes crusts more than the soluble form. The meaning of maximum SAR and TDS (and covariant parameters) is interpreted as the effect of decreased permeability, as suggested by a local increase in the fine-grained fraction, which coincides with maximum TDS. Variations in SAR values are of primary importance for soil erosion, because many authors have used solution chemistry (i.e., SAR, PS, TDS, EC) as a descriptor of dispersivity.
Conclusion:
Based on results of analysis of variance in various forms of erosion are significantly different in the sodium ion, sodium absorption ratio and the percentage of clay. The average amount of sodium ion and sodium absorption ratio in marl samples of region, increase from sheet to gully erosion forms while average clay percentage decreases in this trend. Finally, three variables of sodium ions, sodium absorption ratio and clay percentage of marl samples can be significant factors in erosion and related forms in this region. This study describes the erosional mechanism, which involves morphological and geographic exposure and climatic elements, as well as grain size, mineralogy, chemistry and exchangeable processes of soils.

کلیدواژه‌ها [English]

  • Erosion
  • Rainfall Simulator
  • Physicochemical properties
  • Nowbaran
  • Saveh