Investigating spatial and temporal trend of groundwater quality in relation to water balance components (A case study of Chaharmahal va Bakhtiari Province, Iran)

Abstract

One of the problems of water resources in Iran is excessive drop in groundwater level, in which Chaharmahal va Bakhtiari province, located in this country, is no exception․ In this study, the trend of spatial and temporal changes in groundwater quality and water balance and the relationship between them in this province were investigated. The WetSpass-M distribution model was used due to the capability of distribution models in simulating watershed hydrological processes. The results showed good accuracy of the model in simulating runoff and basal flow of the study basin. The trend of water quality changes was investigated by calculating the IRWQI index and preparing its zoning maps. For this purpose, 132 samples of well water in different areas of the study were prepared in 2007 to 2017. Spatial distribution maps showed that the groundwater quality in the north and northeast of the region was lower than in other parts. Also, groundwater quality had declined over time. In rangeland, groundwater quality was better and nitrate level was lower than in agriculture and buildup land uses. Also, the relationship between nitrate and drought with water quality was seen due to the similar color pattern in their zoning maps in the region. The correlation between groundwater quality parameters and water balance components also showed a weak correlation on an annual scale and a strong correlation between some parameters in some wells on a monthly scale.