ارزيابي شدت بيابان‌زايي مبتني بر تغييرات زماني-مكاني آب زيرزميني حاصل از توسعۀ اراضي كشاورزي در دشت درگز خراسان رضوي

Spatio-temporal Monitoring of Groundwater Changes on Desertification Intensity in Agricultural Areas in Dargaz Plain, Khorasan Razavi Province

اين تحقيق با هدف بررسي تغييرات كمّي و كيفي آب زيرزميني ناشي از توسعۀ كشاورزي در شدت بيابان‌زايي دشت درگز در شمال خراسان رضوي انجام شد. براي آناليز كمّي، از شاخص افت سطح تراز آب و براي بررسي كيفي، از شاخص‌هاي هدايت الكتريكي آب، نسبت جذب سديم و كلر استفاده شد. مبناي اطلاعات آماري، داده‌هاي بيش از 124 حلقه چاه پيزومتر بود كه براي مدت زماني 20ساله از 1375 تا 1395 و در چهار دورۀ 5 ساله، به روش زمين‌آمار كريجيگ در محيط نرم‌افزاري GIS پهنه‌بندي و طبق مدل ايراني ارزيابي پتانسيل بيابان‌زايي (IMDPA) طبقه‌بندي شدند. نتايج نشان داد ميزان افت سطح آب در بخش‌هاي غربي و شمال غربي منطقه، بيشترين مقدار بوده كه علت آن حفر چاه‌هاي عميق غيرمجاز و برداشت بيش ‌از حد آب است. از بُعد تغييرات كيفي هدايت الكتريكي، بخش‌هاي شرقي در كلاس شديد و گاه خيلي شديد بيابان‌زايي قرار دارد؛ به‌طوري كه در مدت 20 سال گذشته، از 14 به 23درصد رسيده و اين نشان‌دهندۀ وضعيت هشدار در مقدار شوري آب آبياري و به‌تبع آن، افزايش شدت بيابان‌زايي است. به نظر مي‌رسد در شرايط فعلي، مديريت منابع آب زيرزميني دشت درگز بايد به‌عنوان يك اولويت مديريتي مورد توجه قرار گيرد.

Introduction: A lot of part of Iran is covered by dry and semi-arid climate. In these regions, due to the lack of rainfall, agriculture is heavily dependent on groundwater resources. The continuing drought in recent decades and the excessive withdrawal of groundwater aquifers for agricultural development, has led to more land degradation and desertification. Understanding the quality and quantity of groundwater as one of the most important and most vulnerable sources of water supply in recent decades which is so necessary. For optimal groundwater management, it is necessary to collect sufficient information from a set of quantitative and qualitative characteristics of aquifers in different regions and to be evaluated in appropriate ways. Therefore, due to the importance of this issue (non-systematic use of water resources for agricultural activities), the present study aims to assess the process of ground water changes due to the agricultural activities in Dargaz county of Khorasan Razavi province along with the presentation and proposal of management plans for risk reduction Desertification was carried out. Demir et al. (2009) investigated the spatial variation of depth and salinity of groundwater in agricultural areas in northern Turkey using the statistical method of the earthquake. The results of their research showed that the eastern part of agricultural lands in the middle parts of the Black Sea, which has poor drainage, has the highest salinity risk. Akbari et al. (2009), using the Geographic Information System, studied the groundwater level in Mashhad Plain during the twenty years and estimated the average annual loss of 60 centimeters. Their results indicated that the increase in the number of wells in the area and drought, were the main causes of groundwater subsidence decline. Methodology: The study area is located in northeastern part of Iran and in the north of Khorasan Razavi province. Dargaz County has an area of about 376459 ha. Dargaz Plain is considered as one of the agricultural poles in Khorasan Razavi province. In order to study the process of water change, two sub-criteria of groundwater quantity such as the groundwater table index, and quality indices were used such as water conductivity, sodium adsorption ratio, and chlorine index. For evaluation and zonation of quantitative indices of groundwater level, 124 wells and 111 aqueducts were used and the analyzed using geo-statistical interpolation such as Kriging method in GIS software environment. In addition, groundwater quality criteria has evaluated during the 20 years period of 1996-2016 and in the 5 years’ time period.