شناسایی و بررسی خصوصیات مورفومتریک و خاک دولین‌ها در شمال ایران (مطالعه موردی: منطقه گرازبن از جنگل آزمایشی خیرود کنار، نوشهر مازندران)

دولین‌‌ها فرورفتگی‌های شاخص مناطق کارستی شناخته می‌شوند و آب جاری در سطح زمین را از طریق این فرورفتگی‌ها به سیستم زهکشی زیرزمینی انتقال می‌دهند. پژوهش حاضر مطالعه‌ای میدانی مبتنی بر تکنیک مورفومتری است که هدف آن، شناسایی دولین‌ها، اندازه‌گیری‌ ابعاد و تحلیل و توصیف شکل دولین‌ها در منطقه مورد مطالعه است. ویژگی‌های مورفومتری مثل طول, عرض و عمق دولین‌ها اندازه‌گیری شد و برای تشخیص میزان تراکم و طبقه‌بندی نوع شکل دولین‌ها از شاخص‌های مورفومتریک استفاده شده است. همچنین برای بررسی خصوصیات فیزیکی و شیمیایی خاک از سه قسمت بیرونی، دیواره و کف دولین‌ها در عمق 15 سانتی‌متری نمونه خاک برداشت شد و نمونه‌ها برای اندازه‌گیری پارامتر‌های بافت خاک، میزان آهک و ph در آزمایشگاه مورد بررسی قرار گرفتند که نتایج آن نشان دهنده تفاوت معنی داری بین پارامترهای بافت و آهک خاک در سه موقعیت متفاوت دولین‌ها است. نتایج بدست آمده از شاخص‌های مورفومتریک حاکی از توزیع نامنظم دولین‌ها در منطقه مورد مطالعه است محورهای طولی و عرضی دولین‌ها عدم تقارن خاصی را نشان می‌دهد و شکل دولین‌ها بیشتر نیمه مدور و بیضوی بوده و حفره‌های کف دولین به خوبی توسعه نیافته و در منطقه شاهد دولین‌های انحلالی هستیم. ارزیابی ویژگی‌های و تراکم بالا و انحلالی بودن دولین‌های منطقه مورد مطالعه نشان‌دهنده توسعه یافته بودن ژئومورفولوژی کارست منطقه گرازبن است.

Doline morphometric analysis and soil characteristics in northern Iran (case study: Gorazbon district of the Kheyrud kenar experimental forest)

Abstract A doline consists of a superficial enclosed depression in karst areas, similar to a crater with one or more cavities in the bottom landform, which permit underground drainage of water. We also used the morphometric parameters collected in the fieldwork to analyze and characterize the shape of dolines in the study area. Different soil samples were collected from 3 locations (out wall bottom of4 doline) at 15 cm depth. We conducted several chemical and physical analyses that allowed us to compare soil properties in the two different doline sections. And the samples were evaluated in the laboratory for measuring soil texture parameters, lime content and ph. Soil analysis showed the different characteristics of soil in the different place of dolines. The dolines were more sub elliptical and elliptical and may not be a welldeveloped swallow hole. The results show an irregular distribution in the study area. The doline density differed within the plots in our study area, as results showed. The axes of length and width show a certain asymmetry. The dolines were more sub elliptical and elliptical and may not have a welldeveloped swallow hole, at the bottom of the doline. Evaluation of the characteristics and high density and of solution dolines in the study area indicate the development of karst geomorphology in the Gorazbon region.Keywords: Doline, Karst, Morphometry, Karst landscapes, Gorazbon.IntroductionThe motivation for such research comes from the strong belief that in this region the geomorphic systems were developed under the influence of various natural processes in the oldgrowth forest. The identification and prevent from hazards of dolines collapse and karst evolution in the region is now necessary. The major aim of this study is the identification of dolines and to describe their morphometric and soil characteristics in the different place of dolines.MethodologyThe morphometric study of these karst landforms enables quantitative analysis of karst environment (Bondesan et al,1992). In what concerns the morphometric analysis, the main problem is the lack of suitable maps with sufficient resolution. For this reason, we used morphometric parameters in fieldwork to obtain information. Data collection and field inventories took place during the summer of 2018 °..Among a great number of morphometric parameters proposed by various karst geomorphologists, only those that are possible to be measured or calculated by data from fieldwork based on the available data were included in this study. Morphometric measurements (length, width, area, perimeter, density, pitting index, circularity index, length/width ratio, diameter /depth ratio) were performed on each expression using Morphometric Index. Soil samples were collected from 3 locations (out, wall and bottom of the doline) at 15 cm depth. Our initial assumption is that the soil characteristics must be different in three different parts of the doline. In order to test this hypothesis, sixteen dolines at different plots were chosen randomly within the study area. Prior to laboratory analysis, living roots and rocks were removed, and samples were airdried and sifted through a 2mmmesh steel sieve. We conducted several chemical and physical analyses that allowed us to compare soil properties in two different dolines sections. We focused on soil texture, Ph, lime.Results and discussion Each discussed the display of parameters with graphs and maps, basic calculation of statistical values, control of morphtectonics doline development in determining the factors and the area studied provides important clues in explaining development. The doline characteristics differ within our plots. The soil texture is relatively heterogeneous at walls and bottoms, but the clay ratio in walls is greater than in the bottoms. Solution dolines commonly have clayrich residual deposits on their floor (Gutiérrez, 2016), but on the opposite, in samples of the study area, there is less clay content in the bottom of the dolines, which is probably due to evident fissures, fractures and cavity that were visible there.ConclusionThere are hundreds of dolines in the Gorazbon and in some cases, the dolines are design valleys, and they are located in an along directed line position. The application of GIS and remote sensing technology allows the analysis, and presentation of morphometric and spatial distribution parameters of the dolines. Despite the accurate, rapid, and objective data processing of GIS, it should be kept in mind that dolines may have been underrepresented because of the constraints of map resolution, the small dimension of dolines, as well as the thick vegetation and sediment cover. Comparing the results obtained from the fieldwork method with remote sensing methods and using the GIS method, it was found that the results of fieldwork are more reliable. Some of the dolines were small and close to each other and were not detected in topographic map 1:25000 Kheyrud kenar and DEM with resolution 10 M. for the spatial distribution of the doline, a regular grid of sampling points was randomly selected using a systematic random sampling technique. The dolines density differed within the plots in our study area. In this study, a set of shape parameters is specified, different methods (lengthwidth ratio, lengthdepth ratio) have been examined and applied to determine the doline shape which showed as results that axes of length and width show a certain asymmetry. The dolines were more sub elliptical and elliptical and may not be a welldeveloped swallow hole, in the bottom of the doline. Some dolines are shallow, a few little Doline funnelshaped with very steep sides. Also, soil analysis showed the different characteristic of soil on the out, bottom and wall dolines.