Evaluation of groundwater quality in an evaporation dominant arid environment; a case study from Al Asyah area in Saudi Arabia

Saudi Arabia is an arid country with very limited surface water resources and over dependence on the available nonrenewable groundwater reserves in the deep-seated aquifers especially for agricultural production. The over abstraction of groundwater has led to the decline in water levels and deterioration of groundwater quality. The present study was carried out in the Al Asyah region in the Qassim Province of Saudi Arabia which experiences a typical arid climate with annual average precipitation of less than 100 mm and very high evaporation rates. Twenty-one groundwater samples were collected from agricultural bore wells and were analyzed for major ions including nitrate and fluoride. The striking feature is the high total dissolved solids (TDS) content which is a result of the evaporation dominant environment in the region. Ion exchange, reverse ion exchange, gypsum dissolution, calcite, and K-Feldspar weathering are the other natural factors controlling the groundwater chemistry in the region. Piper diagram reveals SO4-Cl type of groundwater. The plot of sodium absorption ratio (SAR) vs electrical conductivity (EC) shows that the water is highly saline with medium to high alkalinity and is not very suitable for irrigation. Principal component analysis resulted in the extraction of three principal components pointing mainly toward natural processes. However, the high concentration of nitrate which shows a high factor loading in PC3 is due to the application of nitrate fertilizers on agricultural farms. Fluoride is also a source of major concern in the study area and is attributed mainly to the geogenic sources.