Determination of irrigation water quality of surface and groundwater in Luvuvhu catchment in Limpopo, South Africa
Rapid economic expansion and intensive irrigation activities constitute significant threat to groundwater depletion. This study emphasized on the surface water quality and groundwater quality for irrigation purpose by adopting multivariate statistical methods and the hydrochemical processes and on the probable groundwater contamination in the Luvuvhu catchment Limpopo province. Groundwater samples were collected from 41 wells during 2015 and 2016; and seven samples were collected from Luvuvhu River. The physical parameters pH, EC, TDS, temperature and ORP were measured in the field. Major ion Ca2+, Mg2+, Na+, K+, Cl-, HCO3- and nitrate were analyzed. The pH values indicate that groundwater is acidic in nature during 2015 and 2016. TDS values indicate that groundwater is fresh in nature. The dominant sequence of cations is presented as Ca2+ > Mg2+ >Na+>K+ while that of anions as HCO3- > Cl- > SO42_ in the year 2015 and 2016. The Piper and Chadha plots show that the dominant water types are Ca2+-Mg2+-HCO3- and Ca2+–Mg2+–Cl-. Gibbs plot reveals that the chemistry of water was influenced by rock-water interaction. Bivariate plots indicate the dissolution of carbonate and silicate minerals, reverse ion exchange and anthropogenic activities influenced the water chemistry in the study area. Groundwater was saturated and oversaturated with respect to calcite and dolomite and undersaturated with gypsum and halite. High nitrate concentration resulted from agricultural and farming activities and leakage of sewage system. Temporal groundwater fluctuations indicates that recharge processes decrease the concentration of ions in groundwater by mixing of infiltrated fresh water with groundwater. Factor analysis revealed that the two main factors of 80.68% and 79.95% of total variance for both years. These factors indicate the impact of irrigation return flows, human disposals and usage of K+ and NO3- fertilizers. Electrical conductivity, pH and the concentration of Na+, Ca2+, Mg2+, K+, Cl- exceeded the drinking water quality standards prescribed by the DWAF on few samples. DWQI classification results show that 1% and 2% of samples indicate excellent, 49% and 49% specify good, 27% and 29% shows poor, 7% and 10% of very poor, 16% and 10% of unsuitable during 2015 and 2016, respectively. Sodium percentage, residual sodium carbonate and permeability index reveals that surface water and groundwater is suitable for irrigation. USSL diagram suggests that surface water and groundwater is suitable for irrigation with low alkali hazards which represents excellent water quality for irrigation purpose. This study results revealed the divergent methods are significant for the combined evaluation of the natural processes and groundwater contamination. It contributes a technological basis for the strategic future development where broad organization will be useful for public. However, the study suggest for intensive monitoring to detect the anthropogenic and other contamination elements in the groundwater and surface water to produce quality yield.
irrigation --water quality --groundwater --catchment areas --South Africa
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