بررسی شدت بیابان زایی در اراضی آبیاری شده با پساب تصفیه شده شهر یزد و مقایسه آن با اراضی طبیعی با بهره گیری از معیار خاک در مدل IMDPA

نوع مقاله : مقالات پژوهشی

نویسندگان

1 اداره کل منابع طبیعی و آبخیزداری استان اصفهان

2 دانشگاه یزد

3 دانشگاه یزد و مرکز آموزش عالی علمی کاربردی ملاصدرا یزد

چکیده

از مهم ترین مسائلی که بر کیفیت محیط زیست جهان فشار زیادی وارد می آورد، پدیده بیابان زایی است. از آن جایی که آبیاری با پساب بیشترین تاثیر را بر روی خواص فیزیکی و شیمیایی خاک دارد، در این تحقیق با استفاده از مدل ایرانی ارزیابی پتانسیل بیابان زایی IMDPA)) شدت بیابان‌زایی اراضی آبیاری شده با پساب تصفیه‌خانه فاضلاب شهر یزد و اراضی طبیعی منطقه با در نظر گرفتن معیار خاک مورد بررسی قرار گرفت. شاخص های مورد بررسی شاخص بافت ، درصد سنگریزه عمقی، عمق خاک و هدایت الکتریکی بود. به این منظور اراضی آبیاری شده و اراضی طبیعی به عنوان واحدهای کاری انتخاب و نقشه های مربوط به هر شاخص تهیه شد. در پایان از میانگین گیری هندسی شاخص ها، نقشه حساسیت بیابان زایی منطقه به دست آمد. نتایج نشان داد که در اراضی آبیاری شده با پساب، شاخص بافت خاک با میانگین وزنی 74/3 در کلاس بیابان زایی خیلی شدید و شاخص های هدایت الکتریکی، عمق خاک و درصد سنگریزه عمقی به ترتیب با میانگین وزنی 23/1، 1 و 1 در کلاس شدت بیابان-زایی کم قرار می گیرند. در نهایت معیار خاک با میانگین وزنی 21/1 در کلاس شدت بیابان زایی کم قرار می گیرد. در اراضی طبیعی منطقه نیز شاخص درصد سنگریزه عمقی با میانگین وزنی1 در کلاس کم، شاخص عمق خاک با میانگین وزنی 06/3 در کلاس شدت بیابان زایی شدید و شاخص های هدایت الکتریکی و بافت خاک به ترتیب با میانگین وزنی 4 و 93/3 در کلاس خیلی شدید قرار می گیرند. در این اراضی معیار خاک با متوسط وزنی 89/2 در کلاس شدت بیابان زایی شدید قرار دارد. نتایج نشان می دهد که در اراضی آبیاری شده با پساب شاخص بافت خاک و در اراضی طبیعی منطقه شاخص هدایت الکتریکی موثرترین شاخص در افزایش شدت بیابان زایی است. همچنین با در نظر گرفتن تمامی محدوده معیار خاک با میانگین وزنی 8/2 درکلاس شدت بیابان زایی شدید واقع شده است.

کلیدواژه‌ها


عنوان مقاله [English]

Comparison of Desertification Intensity in the Purified Wastewater Irrigated Lands with Normal Lands in Yazd Using of Soil Criterion of the IMDPA Model

نویسندگان [English]

  • M. Yektafar 1
  • M. Zare 2
  • M. Akhavan Ghalibaf 2
  • S. R. Mahdavi Ardakani 3
1 Natural Resources and Watershed Management Organization of Isfahan Province
2 Yazd University
3 Yazd University-e University of Applied Sciences, Mulla Sadra
چکیده [English]

Introduction: Desertification, is a complex phenomenon, which as environmental, socio-economical, and cultural impacts on natural resources. According to the United Nations Convention to Combat Desertification defination, desertification is land degradation in arid, semi-arid, and dry sub-humid regions, resulting from climate change and human activities. Because of limiting access to qualified water resources in arid lands, it is necessary to use, all forms of acceptable water resources such as wastewater. Since irrigation with sewages has most effects on soil, in this research, desertification intensity of lands irrigated with sewages and natural lands of the area, where located near Yazd city, has been analyzed considering soil criterion of the Iranian Model for Desertification Potential Assessment (IMDPA). Several studies have done in Iran and in the world in order to provide national, regional or global desertification assessment models. A significant feature of the IMDPA is easily defining and measuring criteria, indicators, and ability of the model to use geometric means for the criteria and indicators.
Materials and Methods: In first step, In first step, in a random method, soil samples were taken in each of the defined land units with considering of the size of area. Next, all indices related to the soil criterion such as soil texture index, soil deep gravel percentage, soil depth, and soil electrical conductivity were evaluated in each land use (both irrigated lands and natural lands) and weighted considering the present conditions of the lands. Each index was scored according to the standard table of soil that categorized desertification. Then, geometry average of all indices were calculated and map of the desertification intensity of the study area were prepared. Thus, four maps were prepared according to each index. These maps were used to study both quality and effect of each index on desertification. Finally, these maps were integrated to prepare the final map that shows current status of desertification in the region by calculating geometric mean of all indices based on following formula:
QS = [EC * STI * SDI* SGI]1/4
Where:
QS: Soil criteria score; EC: Electrical Conductivity index; STI: Soil texture index; SDI: Soil depth index and SGI: Soil deep gravel percentage index.
Integrating of thematic databases and spatial analyst and mapping were done using ESRI Arc GIS v.10 software. Statistical analyses such as Mann-Whitney and t-statistic were done using SPSS v.21 software for comparing land irrigated with wastewater and natural land area.
Results and Discussion: Results show that in the land irrigated with wastewater, soil texture index with weighted average of 3.74 classified in severe desertification intensity class, and soil depth gravel percent, soil depth, and soil electrical conductivity indices with weighted average of 1.23, 1, and 1, respectively were classified in low desertification class. In general, soil criteria with weighted average of 1.21 classified in low desertification class. In natural lands of the area, soil depth gravel percent index (1) classified in low intensity class, soil depth index (3.06) grouped in severe class, and soil electrical conductivity (4) and soil texture (3.93) indices with were classified in very high desertification intensity classes.
Conclusion: In natural lands, soil criteria with weighted average of 2.89 classified in severe desertification class. General results show that in the lands irrigated with sewages, soils tissue index and in the natural lands, soil electrical conductivity index are the most effective indices in increasing of desertification intensity. Totally, soil criteria with the weighted average of 2.8, which are grouped in the very high desertification intensity class, are the main factors affecting desertification in total study area. Totally, soils tissue index is the most effective index of increasing in intensity of desertification in the total study area. However, the intensity of desertifcation in the land irrigated with wastewater is lower than the desrtification intensity in the natural lands of the study area, but this issue caused by losing of large amounts of good quality purified wastewater and converting of a large part of the area to wetland which can craates numerous environmental problems in the region in future. Finally, it can be concluded that the natural land of the study area, are not suitable for afforestation and agriculture in present condition, and if the land is irrigatted, salinity of the soil depths transferred up to the surface and can be cause some environmental problems in thi region.

کلیدواژه‌ها [English]

  • Desertification Intensity
  • IMDPA Model
  • Soil Criterion
  • Purified Wastewater
  • Yazd
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