Evaluation of pollution indicators and transported sediment content in agricultural drainage waters for reuse as irrigation, Harran Plain, Turkey.

Abstract

The aim of this study is to determine the variation of certain pollution indicators and the level of sediment carried within drainage channel discharge waters following irrigation of fields on the Harfran Plain during the irrigation season. In this context, water samples were taken from 27 stations in total, including 26 drainage channels and 1 irrigation water channel (reference point), for 6months between May 2020 and October 2020, and determined parameters were measured. Areal distribution maps were prepared with the ArcGIS program in order to better visually present the pollution level across the plain with the obtained data. The monthly changes of the analysis parameters and the significance level of the differences between the stations were determined using ANOVA analysis and the correlations between the measured parameters were determined using the Pearson correlation matrix SPSS package program. Evaluated on the basis of these areal distribution maps, it can be seen that the agricultural drainage waters of the Harran Plain are not suitable for irrigation in terms of five pollution indicators (pH, conductivity (EC), turbidity (Turb), sodium (Na+), and nitrate (NO3-)). Some sampling points in terms of pH (D9, R), conductivity (D10, D20), turbidity (all points) and Na + (as sodium adsorption rate) (D20) are in the "high usage restriction" category. In terms of conductivity, five points (D12, D13, D14, D15, D18); all points in terms of bicarbonate (HCO3-); and three points (D10, D12, D18) in terms of Na+ (as SAR) are classified as "low-medium usage restriction". According to the One-way ANOVA test performed to determine the differences between the points, there is a significant difference (p < 0.05) between the sampling points for all the following values: EC, dissolved oxygen (DO), Turb, Na+, HCO3-, chloride (Cl-), sulphate (SO42-), NO3-, pH, and transported sediment (TS), within the 95% confidence interval. In the test performed to determine the differences between the months, at the 95% confidence interval there is a significant difference (p < 0.05) between the months for parameters such as water temperature (WT), pH, DO, Turb, HCO3-, NO3-, and TS. There is a strong positive correlation between EC and Na+, Cl-, and NO3- (r = 0.785-0.915) and Turb and TS (r = 0.725). With regard to sustainable agricultural practice for the plain, it is thought that the obtained results will contribute to administrative decision-making at a variety of management levels.