بررسی اثرات تغییرات کاربری اراضی بر فرسایش خاک در سطح شهرستان مشکین‌شهر

فرسایش خاک، مشکل جهانی است که به طور جدی منابع آب و خاک را تهدید می‌کند و تغییرات کاربری اراضی از عمده عوامل دخیل در افرایش پتانسیل فرسایش می‌باشد. شهرستان مشکین‌شهر، با نظر به شرایط محیطی از دیرباز تحت تاثیر وقوع فرسایش بوده است، امّا در طی سال‌های اخیر، با توجه به روند رو به‌رشد جمعیّت و تغییرات غیراصولی کاربری اراضی، پتانسیل رخداد این مخاطره در سطح شهرستان افزایش یافته است. بر این‌اساس، هدف پژوهش حاضر بررسی اثرات تغییرات کاربری اراضی بر فرسایش خاک، در سطح این شهرستان می‌باشد. در راستای دستیابی به اهداف پژوهش، نقشۀ طبقه‌بندی‌شدۀ کاربری اراضی برای دو سال 2002 و 2024 با استفاده از روش طبقه‌بندی شی‌ء‌گرا استخراج گردید. به‌منظور پهنه‌بندی خطر فرسایش، بعد از تهیۀ لایه‌های اطّلاعاتی عوامل موثر بر فرسایش در محیط gis، مدل‌سازی نهایی با بهره‌گیری از روش ترکیب خطی وزن‌دار صورت پذیرفت. نتایج نشان داد که در هر دو دورۀ زمانی مورد مطالعه کاربری‌های مراتع ضعیف و زراعت دیم بیشترین مساحت شهرستان را پوشش می‌دهند و بیشترین تغییر کاربری شهرستان به صورت تبدیل مراتع ضعیف به زراعت دیم بوده است. با نظر به نقشه پهنه‌‌بندی فرسایش نیز در سال 2002 مساحت طبقه بسیار پرخطر و پرخطر، 216.308 و 779.068 کیلومترمربع بوده است که مقدار این طبقات در سال 2024 به ترتیب؛ به 600.248 و 820.228 کیلومترمربع افزایش یافته است. با نگاهی به نتایج حاصل از تحلیل تغییرات کاربری اراضی و انطباق آن با نقشه‌های پتانسیل خطر فرسایش، می‌توان کاهش سطح مراتع، باغات و پوشش جنگلی و در مقابل افزایش مساحت اراضی زراعی (آبی و دیم) و نواحی مسکونی را به عنوان مهم‌ترین دلایل افزایش پتانسیل فرسایش خاک در سطح شهرستان مشکین‌شهر مطرح نمود.

investigating the effects of land use changes on soil erosion in meshkinshahr county

1- introductionerosion is a factor that severely threatens soil productivity and is one of the greatest obstacles to achieving sustainable development in agriculture and using natural resources. land use changes can change the physical properties of the land surface and expose the soil to erosion by affecting the type of land use and its spatial patterns. meshkinshahr county (located in ardabil province), due to its environmental characteristics, has a high potential for erosion risk. however, in recent years, due to the growing population and unprincipled land-use changes, the potential for this risk to occur at the county level has increased. therefore, given the importance of the subject, in the present study, the study of land use changes and their role in the occurrence of erosion risk has been studied in the period between 2002 and 2024.2-methodologyin this study, to investigate land use changes, first, landsat satellite images from (oli-tm) sensors for the years (2002 and 2024) were obtained from the us geological survey. then, to prepare the images, geometric and atmospheric corrections were made to the images using the flash method and envi5.3 software. in the next stage, using the object-oriented classification method and the nearest neighbor algorithm by ecognition software, land use maps were extracted in the two study periods. in the next stage, by identifying the effective factors involved in the erosion of the region (including; land use, slope, lithology, soil, distance from road, distance from river, and precipitation) and preparing information layers for each criterion in gis, the valuation and standardization of the layers were carried out using the fuzzy membership function and weighting of the criteria, using the critic method. finally; final analysis and modeling were performed using the wlc multi-criteria analysis method.3- results the results show that in the two time periods studied, the largest area of the area is covered by poor pastures and rainfed agriculture, and the lowest level of land use is related to snow-covered lands and water areas. according to the results of the study, during the period studied, the area of land used for irrigated agriculture, rainfed agriculture, residential areas, and water areas has increased. so in 2024, compared to 2002, rainfed agriculture increased by 203.78 square kilometers, irrigated agriculture by 63.06 square kilometers, residential areas by 54.48 square kilometers, and areas with water cover by 1.19 square kilometers. in contrast, the area of garden and forest land uses, good pastures, poor pastures, and snow-covered lands has decreased in 2024 compared to 2002. the results show that during the study period, the area of poor and good pastures has increased by: 180.95 and 118.59 square kilometers have decreased. the area of garden and forest lands in the county has decreased by 22.47 square kilometers in 2024, and snow cover has also decreased by 0.5 square kilometers.according to the results of weighting the criteria, in 2002, the criteria of slope, land use, lithology, and soil have the highest weight coefficients, respectively, and in 2024, the criteria of land use, slope, lithology, and soil have the highest weight coefficients. according to the erosion zoning map, in 2002, the area of the very high-risk and high-risk categories was 216.308 and 779.068 square kilometers, and the amount of these risk categories has increased to 600.348 and 820.228 square kilometers in 2024, respectively.4- discussion & conclusionsthe high extent of the very high-risk and high-risk classes in both periods of study indicates the very high erosion potential of this county, given the environmental conditions prevailing in the area. looking at the results of the analysis of land use changes and their compliance with the erosion risk potential maps, in addition to environmental conditions (such as the presence of loose soils, sensitive and erodible formations, high slope, rainfall, and abundance of the waterway network), the reduction in the area of pastures, orchards, and forest cover, and the increase in the area of agricultural lands (irrigated and dry) and residential areas can be stated as the most important reasons for the increase in soil erosion potential in meshkinshahr county. finally, according to the research results, to manage the land use of the county systematically, measures such as strengthening and restoring the vegetation cover of pastures, reducing the pressure of pasture exploitation by providing alternative jobs, converting low-yielding rainfed lands to forage crops, raising public awareness about the consequences of converting pasture lands to rainfed lands, familiarizing farmers with protective measures on sloping lands and how to cultivate them, and training them on methods of combating soil erosion are suggested.