Groundwater quality assessment and application of multivariate statistical analysis in Luvuvhu catchment, Limpopo, South Africa
Introduction
Groundwater is a precious natural resource that flourishes the base flow for the river system and influences the characteristic of the aquatic ecosystem (Lerner and Harris, 2009). Groundwater is an inevitable water resource in urban Africa for domestic and drinking uses (MacDonald et al., 2011; Lapworth et al., 2017; Kawo and Karuppannan, 2018; Vetrimurugan et al., 2019). In South Africa, there is a high demand for potable water due to limited surface water resources and unpredictable climatic conditions. Due to imbalance between the available water resources and population growth, groundwater is over utilized and demand for potable freshwater has rapidly increased (Foster, 1995). Despite demand groundwater is less contaminated than surface water (Niu et al., 2017; Kazakis et al., 2017). Groundwater is rechargeable which could be contaminated from natural and anthropogenic sources. The chemical constituents in groundwater are the ideological representations of groundwater quality. Complexity in natural factors such as lithology, geochemical processes and the anthropogenic activities such as intensive irrigation practices, inappropriate waste disposal, urbanisation and industrial expansions, population growth and over exploitation of groundwater are identified as the major sources of groundwater contamination influencing groundwater quality (Vetrimurugan et al., 2013). Using agrochemicals for longer periods can possibly affect the portability of groundwater due to increased concentration of ions and poor flushing (Vetrimurugan and Elango, 2007). Correlation of K with SO4 and NO3 indicates nitrification due to wastewater infiltration and irrigation return flow (Vhonani et al., 2019). Nitrate contamination has been studied worldwide and was identified as the principal pollutant in groundwater due to extensive irrigation. The pollutants released from different land use activities are being carried by water which percolates through soil, mix with splintered rocks and weathered materials before finding its way to reach the saturated zone. (Busico et al., 2017; Ascott et al., 2017). It has become a fact that municipal landfills, waste generated from industries and mining activities causes surface water and groundwater contamination in many countries (Vetrimurugan et al., 2017a; Wu et al., 2019). The WHO (2011) reported that consumption of contaminated groundwater leads to high rate of deaths in many countries.
Geochemical analyses and multivariate statistical analyses are the important tools to understand the characteristic and behaviour of the aquifer along with its association to groundwater quality (Ma et al., 2014). Numerous studies have been carried out worldwide through hydrogeochemical analyses and multivariate statistical analysis to understand the relation between groundwater quality and processes responsible for groundwater contamination (Qian et al., 2016; Rajmohan et al., 2017; Vetrimurugan et al., 2017b; Yidana et al., 2018; Busico et al., 2018, 2020; Nnorom et al., 2019; Pan and NgRichter, 2019). In Luvuvhu sub-catchment in Limpopo province of South Africa, groundwater is a highly dependent resource for agriculture and drinking uses, as it is the most reachable resource compared to Luvuvhu River which is flowing nearby. Domestic water supply in rural areas are relatively low limiting 25 l/day per person from which it could be foreseen that groundwater could be the only possible resources in furture (Busari, 2008). Poor management of untreated domestic sewage and agricultural runoff are the major factors controlling groundwater chemistry (Molekoa et al., 2019). Mineral weathering caused by nitrification, wastewater infiltration and irrigation return flow has been reported in Luvuvhu catchment (Vhonani et al., 2019). Continued discharge of untreated waste water effluents from wastewater plants into downstream contaminates the freshwater and makes it unsuitable for human consumption. Higher concentration of nitrate causes eutrophication and favours growth of harmful algal blooms. Schistomiasis infections are common in human consuming contaminated freshwater (Gumbo et al., 2016). However, spatial extent on the suitability of groundwater and water quality for various purposes was seldom studied. Hence, the aims of the current study were: (i) to study the groundwater quality and its suitability for drinking and irrigation uses (ii) to analyse the spatial variation in its chemical constituents and (iii) to understand the groundwater evolution using multivariate statistical techniques.
Section snippets
Description of the study area
The research was performed in the upper part of Luvuvhu catchment which falls under Vhembe District in Limpopo province of South Africa (Fig. 1). The temperature of the study area varies from 25 °C to 40 °C in summer and 22 °C to 26 °C in winter. The climate is semi-arid coupled with mean annual rainfall varying from 350 to 450 mm. The rainfall is extremely periodical at a rate of 95% during October and March (Mmarete, 2003) experienced seasonally. Heavy precipitation is also experienced during
General hydrochemistry
Chemical parameters are the key factors to understand general hydrogeochemistry of the study region. The minimum, maximum and mean values of chemical constituents are given in Table 1. Groundwater in this region is acidic to neutral in nature with pH ranging from 5.4 to 7.6. Calcium is the dominant cation in the groundwater. The order of dominance of cations are identified as Ca2+ > Mg2+ > Na+ > K+ while the order of anions is identified as HCO3− > Cl− > SO42−. EC varied from 81 to 1206 μS/cm
Conclusions
The study was carried out to assess the groundwater quality and its suitability in the upper part of Luvuvhu catchment, Limpopo. The groundwater is slightly acidic to alkaline and fresh in nature. The Ca–Mg–Cl and Ca–HCO3 are the major hydrochemical facies in the study area. Drinking water suitability assessment suggests that groundwater quality is suitable for drinking and all the parameters are within the permissible limits of WHO and SANS. Irrigation suitability assessment was carried out
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
Authors from the University of Zululand express their gratitude to National Research Foundation (NRF), South Africa (NRF/NSFC Reference: NSFC170331225349 Grant No: 110773) for providing grants and Department of Research and Innovation, the University of Zululand for support in buying Ion Chromatography instrument for this research. The department of Hydrology for their support in the successful completion of this research work.
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