Iranian Jornal of Watershed Management Science&Engineering

fa بررسی تغییرات مکانی- زمانی ویژگی‌های کیفی آب مورد استفاده در بخش کشاورزی دشت ملایر Spatial-Temporal Assessment of Groundwater Quality Characteristics for Agricultural Use in Malayer Plain تخصصي Special پژوهشي Research آب زیرزمینی از مهمترین منابع تأمین آب کشاورزی در مناطق خشک و نیمه‌خشک است. استخراج بی‌رویه آب از سفره‌های آب زیرزمینی، منجر به تخریب کیفی و کمی آبخوان‌ها و کاهش پتانسیل آن‌ها برای تأمین آب می‌شود. این پژوهش با هدف بررسی تغییرات مکانی و زمانی کیفیت آب زیرزمینی در دشت ملایر استان همدان طی دوره آماری پنج‌ساله 1395 تا 1399 انجام شد. با توجه به نقش حیاتی آب زیرزمینی در کشاورزی مناطق خشک و نیمه‌خشک و تهدیدهای ناشی از بهره‌برداری بی‌رویه، از روش‌های درون‌یابی زمین‌آمار شامل کریجینگ (معمولی، عام و ساده) و IDW در محیط نرم‌افزار ArcGIS 10 برای تهیه نقشه‌های پهنه‌بندی پارامترهای کیفیEC، pH، HCO3،  CLو SAR در دو مقطع زمانی خرداد و شهریور استفاده شد. داده‌های مورد نیاز از 31 حلقه چاه تأمین و دقت روش‌ها با شاخص‌های آماری مانند میانگین خطا و ریشه میانگین مربع خطا ارزیابی شد. نتایج نشان داد که دقت روش‌ها بسته به پارامتر و زمان متفاوت است، به‌گونه‌ای که در ماه خرداد، روش کریجینگ معمولی برای اکثر پارامترها بهترین عملکرد را داشت، در حالی که در شهریور ترکیبی از کریجینگ و IDW بهینه بود. با استفاده از شاخص ویلکاکس، کیفیت آب برای کشاورزی در چهار کلاس ارزیابی و نقشه‌های طبقه‌بندی‌شده با زبان برنامه‌نویسی پایتون تولید شد. تحلیل تغییرات نشان داد که کیفیت آب در پارامترهایی چون EC،  HCO3و CL در دوره انتهایی نسبت به ابتدای دوره کاهش داشته و غلظت آن‌ها افزایش یافته است، در حالی که تغییرات pH و SAR کمتر بوده‌اند. همچنین مساحت مناطقی با کیفیت "خوب" به‌ترتیب در خرداد و شهریور به میزان 9/4 و 3/12 درصد کاهش یافته است. هیچ‌یک از مناطق در کلاس "نامناسب" قرار نگرفتند، اما بخش‌هایی از نواحی مرکزی و جنوب‌شرقی در کلاس "متوسط" قرار گرفته و مستعد بحران هستند. نتایج بیانگر کارایی بالای روش‌های درون‌یابی در پایش و مدیریت منابع آب زیرزمینی بوده و استفاده مستمر از آن‌ها برای حفظ پایداری منابع آب کشاورزی منطقه پیشنهاد می‌شود.   Abstract Abstract Introduction  Groundwater is a vital resource for agricultural water supply, particularly in arid and semi-arid regions. Overextraction of groundwater aquifers has led to both qualitative and quantitative degradation, reducing their potential for sustainable water supply. Monitoring spatial and temporal variations in agricultural water quality is essential for efficient utilization and aligning water quality parameters with agricultural usage. Geostatistics has emerged as a powerful tool across various disciplines, especially for interpolation and estimation tasks. Numerous methods are available for studying and mapping groundwater quality variations, with their accuracy depending on regional conditions and data availability. Previous research highlights the reliability of interpolation methods in generating groundwater quality maps. Thus, creating groundwater quality maps using local data and appropriate spatial analysis methods is vital for water resource management. This study evaluates geostatistical methods to analyze spatial and temporal variations in groundwater quality parameters for agricultural purposes in Malayer Plain, Hamadan Province. Methodology  The study area encompasses the main aquifer of Malayer Plain in Hamadan Province, with an area of 518.63 km². Data from 31 wells, provided by the Hamadan Regional Water Company, were used to analyze groundwater quality parameters. These parameters included EC, pH, HCO₃, CL, and SAR, measured during June and September over a five-year period (2016–2020). Zoning maps were created using Inverse Distance Weighting (IDW) and Kriging (Ordinary, Universal, and Simple) methods with exponential, Gaussian, and spherical variograms in ArcGIS 10. The accuracy of the zoning methods was evaluated using statistical metrics such as Mean Error (ME), Root Mean Square Error (RMSE), and Root Mean Square Standardized Error (RMSSE). The best interpolation method for each parameter was selected based on these metrics. Temporal variations in groundwater quality parameters were assessed by generating algebraic maps using the Raster Calculator tool, dividing the parameter values for June and September 2020 by those from 2016. Continuous classified maps were created using the Wilcox agricultural water quality index implemented via Python scripting in ArcGIS 10. Results and Discussion  In June, the most suitable interpolation methods for each parameter were Ordinary Kriging, Universal Kriging, IDW, and Ordinary Kriging, respectively. In September, the preferred methods for EC, pH, HCO₃, CL, and SAR were Ordinary Kriging, Universal Kriging, IDW, Ordinary Kriging, and IDW, respectively. Groundwater quality was classified into four standard classes—excellent, good, medium, and poor—based on EC and SAR. Maps of agricultural water quality standards were developed for June and September. The SAR parameter exhibited a stable trend in June but showed significant fluctuations in September, particularly in 2017. For EC, despite an increasing trend in both months, values were consistently lower in June compared to September. According to the Wilcox index, areas classified as "good" quality decreased by 4.9% from 2016 to 2020 in June and by 12.3% in September. Conclusion  This study utilized GIS tools to determine the quality standards for agricultural water and analyze spatial-temporal variations in groundwater quality parameters in the saturated aquifer of Malayer Plain. Python scripting was employed to produce classified raster maps based on the Wilcox index. The results indicated that the geostatistical methods used were sufficiently accurate for the study area. Kriging and IDW provided the best interpolation accuracy. The analysis covered five years of data for June and September, focusing on EC, pH, HCO₃, CL, and SAR. The results showed declining groundwater quality, with increased concentrations of CL, HCO₃, and EC over time, while slight reductions were observed for pH and SAR. None of the areas were classified as "poor" according to the Wilcox index, but central and southeastern parts of the aquifer fell into the "medium" class, indicating vulnerability to critical conditions. Given the importance of groundwater quality for agriculture, the environment, and the economy, the continued application of interpolation methods can serve as a fast and effective approach for groundwater quality monitoring in Malayer Plain. .   ملایر, آب‌زیرزمینی, خشک‌سالی, زمین‌آمار, ویلکاکس Malayer, Groundwater, Drought, Land statistics, Wilcox 78 92 http://jwmsei.ir/browse.php?a_code=A-10-1654-1&slc_lang=fa&sid=1 Samira Alsadat Hedayati سمیراالسادات هدایتی s.hedayti@basu.ac.ir 100319475328460018946 0009-0008-7945-3948 No Department of Water Science and Engineering, Boali-Sina University, Hamadan, Iran. Omid Bahmani امید بهمنی omid.bahmani@basu.ac.ir 100319475328460018947 100319475328460018947 Yes Department of Water Science and Engineering, Boali-Sina University, Hamadan, Iran. Peyman Tahmasebi پیمان طهماسبی p.tahmasebi@agr.basu.ac.ir 100319475328460018948 0009-0003-1316-2260 No Department of Water Science and Engineering, Boali-Sina University, Hamadan, Iran. Fatemeh Dalvand فاطمه دالوند fatemedalvand7499@gmail.com 100319475328460018949 0009-0008-7347-975X No Department of Water Science and Engineering, Boali-Sina University, Hamadan, Iran. Seyed Abolfazl Hosseini سید ابولفضل حسینی nemayeh22@gmail.com 100319475328460018950 0009-0008-0082-7768 No Department of Water Science and Engineering, Boali-Sina University, Hamadan, Iran.