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

Abstract

Groundwater is the most important water resource for agriculture, industry, and drinking, and therefore qualitative changes in program planning and sustainable management of water resources are necessary. This study aimed to evaluate the trend of groundwater quality parameters of some selected stations in Yazd province by using non-parametric Mann-Kendall and Sens Methods. For this purpose, the water quality data were gathered in 25 stations of Yazd-Ardakan plain during 2005-2014. The quality parameters used in this study were TH, Cl-, K+, Mg++, Ca++, Na%, TDS, SAR, Na+, HCO3-, SO42-, EC, pH, the total sum of cation and anion. Before analyzing the data, the effect of significant first-order autocorrelation was investigated from the data set. The results showed most water quality parameters tend to rise. 50.8% and 49.2% of groundwater quality time series show meaningful positive trends during wet and dry seasons, respectively. Also, 54.7% and 45.3% of groundwater quality time series show meaningful negative trends during wet and dry seasons, respectively. Due to the positive slope of the trend line for most quality parameters, water quality in this region tends to decreases. The maximum positive slope of the trend line belongs to EC, where observed downstream of the plain. The loss of groundwater level due to an increase in consumption can be one of the main reasons for decreasing the groundwater quality and salinity.