تجزیه و تحلیل روند تغییرات زمانی کیفیت منابع آب زیرزمینی با استفاده از آزمون ناپارامتری منکندال و روش تخمینگر شیب سن نمونه‌ پژوهش: دشت یزد- اردکان

چکیده 1آب زیرزمینی از مهم‌ترین منابع تامین‌کننده‌ آب مورد نیاز کشاورزی، شرب و صنعت به‌ویژه در مناطق خشک فلات مرکزی ایران است؛ بنابراین بررسی روند تغییرات کیفی آن اهمیت فراوانی در مدیریت پایدار منابع آب دارد. در همین زمینه پژوهش حاضر روند تغییرات کیفی آب زیرزمینی را در دشت یزد اردکان با استفاده از روش ناپارامتری من‌کندال و تخمین‌گر شیب سن بررسی کرده است. برای این منظور از آمار و اطلاعات 25 محل اندازه‌گیری (چاه، چشمه و قنات) در بازه‌ زمانی 83-84 تا 93-94 مربوط به دوره‌ تغذیه و تخلیه استفاده شد. پارامترهای بررسی‌شده شامل میزان اسیدیته، هدایت الکتریکی، غلظت املاح محلول، نسبت جذب سدیم، بی‌کربنات، کلر، سولفات، پتاسیم، منیزیم، کلسیم، سدیم و درصد سدیم محلول بوده است. در این انتخاب تلاش شده است منابع برداشت (چاه، چشمه و قنات) پراکنش مناسب در کل سطح دشت و آمار استفاده‌شده ازنظر طول دوره‌ آماری نواقص کمتری داشته باشد. نتایج به‌دست‌آمده از این پژوهش نشان داد روند تغییرات تمامی متغیرهای کیفی بررسی‌شده در این دشت رو به افزایش بوده است و در طول دوره‌ تغذیه 49.2 درصد و در طول دوره‌ تخلیه 50.8 درصد، روند منفی معنا‌دار را در سطح اعتماد 90 درصد نشان دادند. حال آنکه روند مثبت معنا‌دار در طول دوره‌ زمانی تغذیه، 45.3 درصد و در طول دوره‌ تخلیه، 54.7 درصد را در سطح اعتماد 90 درصد نشان داد. با توجه به مثبت‌بودن شیب خط روند برای متغیرهای کیفی موثر در منابع آب زیرزمینی می‌توان نتیجه گرفت که روند تغییرات کیفی آب زیرزمینی در این دشت رو به کاهش بوده و این روند در زمان‌های تخلیه یا برداشت نسبت به زمان‌های تغذیه بیشتر بوده که ناشی از کاهش بارش‌ها و پیرو آن کاهش کیفیت منابع آب زیرزمینی بوده است.

Analysis of temporal trend of groundwater quality using nonparametric Mann-Kendall and Sen’s methods (Case study: Yazd-Ardakan Plain)

Extended abstractIntroductionAs one of the vital components of life, water is essential for many economic activities. The assessment and monitoring of groundwater quality has always been a major challenge associated with special problems. Taking into account the decline in the level of groundwater in most of Iran’s plains including YazdArdakan plain, and its effects on groundwater quality, the present study uses a nonparametric MannKendall test to investigate the trend of changes in the vriables of groundwater quality in YazdArdakan plain and to estimate the slope of trend line by Sen’s slope estimator. MethodologyYazdArdakan Plain is one of the widest plains in Iran. In this research, the statistics and information about 25 sources including 12 wells, 12 qanats and 1 spring during a 10year statistical period (20042014) has been used. To study the trend in time series, many parametric and nonparametric statistical methods have been developed and widely used by various researchers. MannKendall method was initially developed by Mann (1945), and then by Kendall (1970). The null hypothesis in MannKendall test implies randomness and lack of trend in data series, and confirmation of hypothesis one (rejection of the null hypothesis) indicates the presence of a trend in the data series. A very useful index in Mann Kendall test, Sen’s slope estimator shows the linearity of trend. DiscussionGroundwater is considered as one of the important biological parameters; therefore, the monitoring and evaluation of groundwater quality change is a significant issue. Overall, of all the studied parameters, the parameters of total dissolved salts, sodium absorption ratio and electrical conductivity had very large positive slopes compared with other parameters. This represents a significant increase in the concentration of sch parameters during the period of investigation. ConclusionIn this study, the trend of changes in some groundwater quality parameters in YazdArdakan plain in Yazd province was studied by using MannKendall’s nonparametric test and the magnitude of this trend was measured by Sen’s slope estimator. The results show that the quality of groundwater in this plain has declined over the studied period. The biggest slope changes in the trend line (micromhos on cm  EC= 550)  was related to the electrical conductivity indicating groundwater salinity, Moreover, the noticeable changes in electrical conductivity in recharge and discharge months indicate drastic changes in the groundwater quality due to precipitation. 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