Hydrochemical Assessment of the Rivers Adada and Obinna in Enugu, Nigeria, for Irrigational Application

Waters from Rivers Obinna and Adada, located in Enugu, Nigeria, were assessed for their potential for irrigational purposes. Forty-eight water samples were collected from four sampling points during the early dry season and late dry seasons (when these river waters are used for irrigation) from both rivers. Physicochemical parameters were analyzed using standard methods, and seven irrigation water quality indices were applied in ascertaining the suitability of the river waters for irrigation. Mean pH results revealed that the river waters were slightly acidic (6.7). All physicochemical parameters analyzed were within the international standard irrigational water limits, indicating the suitability of the river waters for irrigation. The cations and anions analyzed in the river water were observed to follow the trend ${\mathrm{Ca}}^{2+}{>\mathrm{Mg}}^{2+}{>\mathrm{K}}^{+}{>\mathrm{Na}}^{+}$ and ${\mathrm{Cl}}^{-}{>\mathrm{SO}}_4^{2-}{>\mathrm{NO}}_3^{-}>{\mathrm{PO}}_4^{3-}{>\mathrm{HCO}}_3^{-}{>\mathrm{CO}}_3^{-}$, respectively. Results showed calcium and chloride ions as the most dominant cation and anions, respectively. Piper plots of the anions and cations showed that alkaline earth metals surpassed alkali metal, whereas the weak acids also exceeded the strong acids, with the exception of one sample, which showed dominance of strong acids over weak acids. The observed prevalence of the ${\mathrm{Ca}}^{2+}{-\mathrm{HCO}}_{3-}$ facies was attributed to the large presence of carbonate rocks such as dolomite and calcite, a good indicator of the occurrence of freshwater in both rivers. Positive correlations among the physicochemical parameters was reported, indicating the likelihood of ion exchange between the river waters and surrounding soils. All irrigational water quality indices revealed the suitability of Adada and Obinna Rivers for irrigation applications.