كليدواژه :
انتقال آب , شاخص كيفيت آب زيرزميني , شيب سن , من‌كندال , يزد- اردكان
چكيده فارسي :
بررسي روند زماني و تغييرات مكاني كيفيت آب زيرزميني متاثر از انتقال آب بين حوضه‌اي در مديريت منابع آبي نقش مهمي دارد. هدف از اين پژوهش، بررسي روند زماني پارامترهاي كيفي آب‌زيرزميني با استفاده از آزمون من‌كندال و تخمين‌گر شيب سن و بررسي تغيير مكاني كيفيت آب زيرزميني و تاثيرات انتقال آب بين‌حوضه‌اي مي‌باشد. بدين منظور از پارامترهاي كل جامدات محلول، كلر، سولفات، سديم، كلسيم و منيزيم مربوط به 43 چاه در دوره زماني 1399-1379جهت بررسي روند زماني و مكاني استفاده شد. نتايج بررسي روند زماني نشان داد، پارامترهاي سولفات، سديم و كل جامدات محلول در بيشتر چاه‌ها روند كاهشي داشته است، اما شاخص‌هاي كلسيم، منيزيم و كلر داراي روند افزايشي بوده است و همه پارامترها به جز TDS، در دوره زماني مورد بررسي بر اساس طبقه بندي سازمان بهداشت جهاني در حد مجاز قرار داشتند. نتايج رتبه‌بندي پارامترها نشان داد، TDS، كلر و منيزيم بيشترين تاثير را بر كيفيت منابع آب زيرزميني آبخوان داشته‌اند و همچنين پارامتر منيزيم بيشترين و TDS كمترين تغيير را در بين سال‌هاي 1379 تا 1399 دارا بود. كاربرد شاخص كيفيت آب زيرزميني (GQI) در اين پژوهش نشان داد كه كيفيت كلي آبخوان يزد- اردكان، حتي با توجه به افت نسبتا زياد آب‌زيرزميني، در ابتدا و انتهاي دوره زماني مورد بررسي در رده‌ي متوسط (80-60) و قابل قبول قراردارد و كاهش كيفيت در اين دوره بسيار كم و قابل چشم‌پوشي است. نتايج نهايي پژوهش حاضر نشان داد،آب انتقالي با كيفيت مناسب توانسته افزايش ميزان كل جامدات محلول، سولفات و سديم را كنترل كند و موجب افزايش كلر در اين مناطق شود. در انتها مشخص شد، تغييرپذيري مكاني آلاينده‌هاي مختلف و طيف گسترده پارامترهاي اندازه‌گيري شده و به‌طوركلي توصيف كيفيت آب،امري دشوار است؛ بنابراين استفاده ازشاخص‌هاي كيفيت آب مي‌توانند شرايط كلي كيفيت آب را به‌طورخلاصه و قابل‌درك ارائه كند.
چكيده لاتين :
Introduction: Inter-basin 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. Spatio-temporal changes of groundwater quality as the results of inter-basin water transfer, plays an important role in water resources management. Thus, this study attempts to investigate the temporal trends of groundwater quality parameters using Mann-Kendall test and Sen's slope estimator. In addition, spatial changes of groundwater quality and the effects of inter-basin water transfer were studied.
Materials and Methods: In this study, non-parametric methods and interpolation models were used to evaluate the spatio-temporal patterns of groundwater quality parameters in the Yazd-Ardakan plain. Mann-Kendall 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 Yazd-Ardakan 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 (Chah-Afzal 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 Yazd-Ardakan 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.
