Deriving Mathematical Relationships Between Electrical Conductivity and Concentrations of Some Minerals in Groundwater: A Case Study in the Mediterranean Region of Turkey

OpenAlex İngilizce

The quality and quantity of water varies from place to place and time to time. Therefore, supply of fresh water is a limiting factor for irrigated agriculture in arid and semi-arid regions of the world, including Mediterranean region although irrigation and fertilizers are two of the major inputs of modern agriculture in the region. Pollution from anthropogenic sources or activities degrades the quality of freshwater, lessening its usefulness. In this regard, irrigated agriculture has negative impacts on surface and groundwater resources. Staple objectives of this study are two-fold: a) to derive mathematical forms of relationship between electrical conductivity and concentrations of some minerals in groundwater, b) to bring those relationships into the use in areas where shallow water table with poor quality is dominant and only EC measurements are available. In line with those objectives, the study was conducted in an irrigated catchment, covering an area of 9 495 ha, located in the Lower Seyhan Plain irrigation project area, in the Mediterranean region of southern Turkey. A total of 362 groundwater samples were collected from 105 drainage observation wells with the depth of 4-m in winter, spring and autumn in 2016 and 2017. Electrical conductivity (EC, dS m-1) and concentrations (meq L-1) of major ions, i.e. calcium and magnesium (Ca+Mg), sodium (Na), potassium (K), chloride (Cl), carbonate (CO3), bicarbonate (HCO3) and sulfate (SO4), were determined in the lab by following standard methods. Then, total dissolved solids (TDS in mg L-1) concentration in each was calculated by summing up the major ion concentrations considered. Correlation and regression analysis was performed to derive mathematical forms of relationship between EC and TDS, and other ion concentrations. Analysis results showed that a strong linear mathematical relationship existed between TDS and EC, and Na with the determination coefficient (R2) greater than 93 percent (r≥0.95). Surprisingly the relationship between EC and Cl was found to be in the form of quadratic (R2=0.97). On the other hand, although the association between EC and Ca+Mg was linear and weak (R2=0.71), ANOVA results lead us to conclude that the relationship was statistically significant (α=0.05). Contrary to the expectations, no statistically significant relationship existed between EC and the remaining ion concentrations. Mathematical forms of the relationships between EC and mineral ion concentrations may be used to derive additional information regarding groundwater quality in agricultural areas where drainage observation wells are available and EC measurements are taken for granted.