بررسی کارایی شاخص کیفیت آب زیرزمینی (gqi) به منظور ارزیابی بلندمدت تاثیرات انتقال آب بین حوضه‌ای با کمک روش‌های ناپارامتری و gis (مطالعه موردی آبخوان یزد- اردکان)

بررسی روند زمانی و تغییرات مکانی کیفیت آب زیرزمینی متاثر از انتقال آب بین حوضه‌ای در مدیریت منابع آبی نقش مهمی دارد. هدف از این پژوهش، بررسی روند زمانی پارامترهای کیفی آب‌زیرزمینی با استفاده از آزمون من‌کندال و تخمین‌گر شیب سن و بررسی تغییر مکانی کیفیت آب زیرزمینی و تاثیرات انتقال آب بین‌حوضه‌ای می‌باشد. بدین‌ منظور از پارامترهای کل جامدات محلول، کلر، سولفات، سدیم، کلسیم و منیزیم مربوط به 43 چاه در دوره زمانی 1399-1379جهت بررسی روند زمانی و مکانی استفاده شد. نتایج بررسی روند زمانی نشان داد، پارامترهای سولفات، سدیم و کل جامدات محلول در بیشتر چاه‌ها روند کاهشی داشته است، اما شاخص‌های کلسیم، منیزیم و کلر دارای روند افزایشی بوده است و همه پارامترها به جز tds، در دوره زمانی مورد بررسی بر اساس طبقه بندی سازمان بهداشت جهانی در حد مجاز قرار داشتند. نتایج رتبه‌بندی پارامترها نشان داد، tds، کلر و منیزیم بیشترین تاثیر را بر کیفیت منابع آب زیرزمینی آبخوان داشته‌اند و همچنین پارامتر منیزیم بیشترین و tds کمترین تغییر را در بین سال‌های 1379 تا 1399 دارا بود. کاربرد شاخص کیفیت آب زیرزمینی (gqi) در این پژوهش نشان داد که کیفیت کلی آبخوان یزد اردکان، حتی با توجه به افت نسبتا زیاد آب‌زیرزمینی، در ابتدا و انتهای دوره زمانی مورد بررسی در رده‌ی متوسط (8060) و قابل قبول قراردارد و کاهش کیفیت در این دوره بسیار کم و قابل چشم‌پوشی است. نتایج نهایی پژوهش حاضر نشان‌ داد،آب انتقالی با کیفیت مناسب توانسته افزایش میزان کل جامدات محلول، سولفات و سدیم را کنترل کند و موجب افزایش کلر در این مناطق شود. در انتها مشخص شد، تغییرپذیری مکانی آلاینده‌های مختلف و طیف گسترده پارامترهای اندازه‌گیری شده و  به‌طورکلی توصیف کیفیت آب،امری دشوار است؛ بنابراین استفاده ازشاخص‌های کیفیت آب می‌توانند شرایط کلی کیفیت آب را به‌طورخلاصه و قابل‌درک ارائه کند.

Study of the Efficiency of Groundwater Quality Index to Evaluate the Long-term Effects of Inter-Basin Water Transfer Using Non-Parametric Methods and GIS (Case Study Yazd-Ardakan Aquifer)

Introduction: Interbasin water transfer affects the environment, culture and economy of donor and recipient basin. In this regard, one of the most important aspects are the positive and negative effects on the quality of groundwater in the recipient basin.  Spatiotemporal changes of groundwater quality as the results of interbasin water transfer, plays an important role in water resources management. Thus, this study attempts to investigate the temporal trends of groundwater quality parameters using MannKendall test and Sen’s slope estimator. In addition, spatial changes of groundwater quality and the effects of interbasin water transfer were studied.Materials and Methods: In this study, nonparametric methods and interpolation models were used to evaluate the  spatiotemporal patterns of groundwater quality parameters in the YazdArdakan plain. MannKendall nonparametric test and Sen’s slope were used to examine the temporal trends in the span of 2000 to 2020. The interpolation models and groundwater quality index (GQI) were used to study the spatial patterns and classify the quality of groundwater. The assessment of quality parameters of all studied wells including Ca2+, Mg2+, Cl, Na+, SO42 and TDS were studied in equal time periods. Groundwater quality measurements were performed twice a year using a volumetric method, one in spring and the other one in autumn. The World Health Organization (WHO) standard was considered to compare values of different parameters in the plain.Results and Discussion: A decreasing trend was observed in SO42, Na+ and TDS parameters in most wells and there was an increasing trend for Ca2+, Mg2+ and Cl parameters. Considering WHO classification standard, all the studied parameters were in the allowable ranges except TDS. The parameter ranking showed that TDS, Cl and Mg2+ had the greatest impact on the quality of aquifer groundwater. The Mg and TDS parameters had the highest and the lowest changes, respectively during 2000 to 2020. Results of the GQI showed that the total quality of the YazdArdakan aquifer was in the moderate class and acceptable because of relatively large decrease in the groundwater in the span of the studied period. However, the decrease in groundwater quality was negligible. Changes of the quality map showed that the most negative quality changes were related to the Yazd, Taft, Meybod, Ardakan and northern regions (ChahAfzal desert). This indicates high groundwater pumping in these areas and being located near the desert area. The most positive quality changes belonged to the central and southern part of the aquifer.Conclusion: Comparison of the interpolation models showed that the geostatistical methods can show better results than the definitive methods in zoning groundwater quality parameters. The Kriging and IDW models were the best models and consistent with the results of the research. The quality of groundwater was acceptable, while the reduction in quality was very low and negligible in the YazdArdakan aquifer during the studied period. The temporal trends of SO42, Na+ and TDS had either a negative significant trend or no trend in the Yazd area. Considering ranking maps, TDS, Cl and Mg2+ had high impacts on determining the GQI. These trends were positive in Yazd city and consequently the GQI maps could not confirm the negative temporal trend and zoning maps. This finding showed that the use of qualitative indicators could neutralize the effects of the parameters on each other and provide a better and acceptable result. In all, the transfer water with appropriate quality could control the increase of the TDS, SO42, Na and caused an increase in Cl in these areas. There are many effective factors to study water quality, so its description seems to be difficult. Therefore, using water quality indicators can provide total water quality conditions in a concise and understandable way.