شبیه‏سازی دینامیک کربن آلی خاک تحت تأثیر سناریوهای مختلف فرسایش آبی و مدیریت چرا در مراتع نیمه‏خشک باجگاه با استفاده از مدل Century

نوع مقاله : مقاله کامل علمی پژوهشی

نویسندگان

1 دانش دانشجوی دکتری گروه احیاء مناطق خشک و کوهستانی، دانشگاه تهران، آموخته کارشناسیارشد مدیریت مناطق بیابانی، بخش مهندسی منابع طبیعی و محیطزیست، دانشگاه شیراز

2 استادیار بخش مهندسی منابع طبیعی و محیطزیست، دانشگاه شیراز

چکیده

سابقه و هدف: بیشتر مطالعات یک ارتباط قوی بین فرسایش آبی و هدر‏روی کربن آلی خاک را گزارش کرده‏اند، به طوری که جابجایی و تغییر مکان کربن ناشی از فرسایش آبی یک فاکتور مهم تأثیر گذار بر غلظت CO2 در اتمسفر بیان شده است. بنابراین فهمیدن اثر فرآیند فرسایش آبی بر کربن آلی خاک اکوسیستم ضروری است. با توجه به اینکه ارزیابی اثرات فرسایش آبی بر ذخیره کربن آلی خاک در طولانی مدت بدون ابزار مدل‏سازی مشکل هست، مطالعه دینامیک کربن آلی خاک از طریق استفاده از مدل‏های شبیه‏سازی در ترکیب با داده‏های اندازه‏گیری شده توصیه شده است. با توجه به اینکه مراتع ایران مساحت بزرگی از کشور را فراگرفته، مدل‌سازی اثر فرسایش آبی بر دینامیک کربن آلی خاک در مراتع می‌تواند راهکارهای مدیریتی شایسته‌ای در اختیار سازمان‌های مرتبط قرار دهد. تاکنون در ایران مدل‌سازی کربن آلی خاک تحت تأثیر فرسایش آبی انجام نشده است و این بررسی می‌تواند زیربنای آینده مدل‌سازی کربن آلی خاک باشد. بنابراین تحقیق حاضر با هدف 1) بهبود اعتبارسنجی مدل Century به عنوان پرکاربردترین مدل در مطالعات کربن خاک با استفاده از خروجی سه مدل فرسایش آبی GLEAMS، WEPP و ANSWERS و 2) شبیه‏سازی دینامیک ذخیره کربن آلی خاک تحت تأثیر دو سناریو فرسایشی در مراتع نیمه خشک باجگاه انجام گرفت.
مواد و روش‏ها: برای انجام این تحقیق تعداد 60 نمونه خاک به روش نمونه‏برداری تصادفی از عمق 20-0 سانتی‏متری از سطح مراتع نیمه خشک باجگاه برداشت شد. جهت تعیین وزن مخصوص ظاهری خاک دو نمونه سیلندر در کنار هر گودال خاک (به طورکلی 120 نمونه) برداشته شد. پس از تعیین حجم نمونه‏گیری پوشش گیاهی (تعداد پلات)؛ بیومس بالازمینی، لاشبرگ و بیومس زیرزمینی موجود در 17 پلات جمع‏آوری و به آزمایشگاه منتقل شدند. ببا استفاده از 43 سال داده‏های هواشناسی ایستگاه هواشناسی، داده‏های ویژه سایت و همچنین مقادیر پارامترهای فیزیولوژیکی و اکولوژیکی مرتع، پارامتریابی و کالیبره کردن مدل Century انجام شد. سپس میانگین میزان دراز مدت فرسایش آبی شبیه‏سازی شده توسط سه مدل‏ فرسایشی WEPP، GLEAMS و ANSWERS به عنوان ورودی در مدل وارد گردیدند. در نهایت یک مدل فرسایش آبی که میزان فرسایش شبیه‏سازی شده توسط آن موجب بهبود نتایج اعتبارسنجی مدل Century شد، انتخاب گردید و سپس اثر دو سناریو فرسایش آبی بر تغییرات کربن آلی خاک برای دو دوره مدیریت چرای دام مورد بررسی قرار گرفت.
یافته‏ها: نتایج شبیه‏سازی نشان داد که استفاده از خروجی مدل GLEAMS باعث شده که مدل Century، ذخیره کربن آلی خاک را به طور دقیق‏تری پیش‏بینی کند. بنابراین از خروجی مدل فرسایشی GLEAMS برای شبیه‏سازی تغییرات ذخیره کربن آلی خاک تحت تأثیر فرسایش آبی داستفاده شد. نتایج شبیه‏سازی‏های مدل Century نشان داد که ذخیره کربن آلی خاک در مراتع باجگاه طی دوره II با مدیریت چرای متوسط دام از 3496 تا 93/3260 (گرم بر سانتی‏مترمربع) و از 3496 تا 90/3243 به ترتیب در سناریوهای بدون فرسایش و فرسایش کاهش یافته است و تفاوت معنی‏داری (05/0 p <) بین آنها مشاهده نشد. همچنین طی دوره III با مدیریت بدون چرای دام، ذخیره کربن آلی خاک از 30/3245 تا 04/3356 (گرم بر سانتی‏مترمربع) و از 37/3227 تا 42/3350 به ترتیب در سناریوهای بدون فرسایش و فرسایش کاهش یافته بود. به طورکلی فرسایش آبی ذخیره کربن آلی خاک را در مراتع نیمه‏خشک باجگاه در مقایسه با سناریو بدون فرسایش به ترتیب به میزان 52/0 درصد و 16/0 درصد در پایان دوره‏های II و III کاهش داده بود. فرسایش موجب کاهش ناچیز ذخیره کربن آلی خاک در مراتع نیمه‏خشک باجگاه در مقایسه با سناریو بدون فرسایش شده بود. برمبنای نتایج این مطالعه می‏توان گفت نقش مدیریت چرای دام در مراتع نیمه‏خشک باجگاه بیشتر از فرسایش در هدرروی و تغییرات ذخیره کربن آلی خاک مشهود بوده است.

کلیدواژه‌ها

عنوان مقاله [English]

Simulating soil organic carbon dynamics as affected by different water erosion scenarios and grazing management in semi-arid rangelands of Bajgah using the Century model

نویسندگان [English]

  • Bijan Azad 1
  • Sayed Fakhreddin Afzali 2
1 Shiraz University
2 Assistant prof. of Department of desert regions management, shiraz university
چکیده [English]

Background and Objectives: Most studies have reported a strong relationship between water erosion and soil organic carbon (SOC) losses, so that carbon displacement caused by water erosion stated as an important factor affecting the concentration of CO2 in the atmosphere. Therefore, understanding water erosion processes effect on SOC within an ecosystem is essential. Since evaluating the impacts of water erosion on SOC stock dynamic in long-term is difficult without modeling tool, studying of SOC dynamic through use of simulation models in combination with measured data is recommended. Considering that rangelands of Iran have taken a large part of the country, modeling the effect of water erosion on SOC dynamics in rangelands can provide appropriate management solutions for related organizations. The SOC modeling has not been conducted under the influence of water erosion, and this study could be basis for the future of SOC modeling. Therefore, the present study aims to: 1) improve the validation of the Century model as the most widely used model in the soil carbon studies, by using the output of three water erosion models of GLEAMS, WEPP, and ANSWERS, and 2) simulating the SOC stock dynamic under the influence of two erosion scenarios in the semi-arid rangelands of Bajgah.
Materials and Methods: To conduct this research, 60 soil samples were taken by randomized sampling methodfrom a depth of 0-20 cm of soil in the semi-arid rangelands of Bajgah. To determine the soil bulk density, two cylinders were collected beside each soil puddle (120 samples). After determining the volume of vegetation sampling (number of plots); aboveground biomass, litter and belowground biomass were collected in 17 plots then transferred to the laboratory. Parameterization and calibrating the Century model was performed by using 43 years of weather data, site specific data, as well as physiological and ecological parameters of rangeland. Then, the long-term average of water erosion rate simulated by WEPP, GLEAMS and ANSWERS erosion models entered as input in the Century model. Finally, a water erosion model, that its simulated erosion rate improves the validation results of the Century model, was selected then illustrated the effect of two water erosion scenarios on the changes of SOC stock for two periods of grazing management including period of nationalization of rangelands with moderate grazing management.
Results: The simulation results showed that use of the GLEAMS model output made the Century model more accurately predict SOC stock. Therefore, the GLEAMS erosion model output was used for simulate the SOC stock variations under the influence of water erosion. The simulation results of the Century model showed that the SOC stock in the Bajgah rangelands during the II period with moderate grazing management, decreased from 3496 to 3260.93 (g cm-2) and 3496 to 3243.90 (g cm-2) in the no-erosion and erosion scenarios, respectively and there was no significant difference between them (p < 0.05). Also during the III period with no grazing management, SOC stock decreased from 3245.30 to 3356.04 (g cm-2) and 3227.37 to 3350.42 (g cm-2) in the no-erosion and erosion scenarios, respectively and there was no significant difference between them (p <0.05). Generally, water erosion decreased the SOC stock in the semi-arid rangelands of Bajgah compared with the non-erosion scenario by 0.52% and 0.16% in the end of periods II and III, respectively. The erosion resulted in a slight reduction in SOC stock in the semi-arid rangelands of Bajgah compared to the non-erosion scenario. Based on the results of this study, it can be state that the role of grazing management than the erosion in the changes and losses of SOC stock was more evident in the semi-arid rangelands of Bajgah.

کلیدواژه‌ها [English]

  • Global Warming
  • Carbon Sequestration
  • Soil Organic Carbon Stock
  • Soil Carbon Modeling
  • Water Erosion Models

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مجله مدیریت خاک و تولید پایدار
دوره 9، شماره 4
اسفند 1398
صفحه 69-87

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