Assessment of groundwater quality in the buffer zone of Limpopo National Park, Gaza Province, Southern Mozambique

Many areas in the Southern African Development Community are data-poor and poorly accessible. Water quality assessment in these areas therefore has to rely on the limited available data, coupled with restricted field sampling. This paper documents the first evaluation of the main geochemical processes and impact of anthropogenic and natural sources of contamination on the groundwater quality of the aquifer system used for domestic and agricultural purposes in Limpopo National Park, Gaza Province, Southern Mozambique. Twenty-five groundwater and surface water samples were collected during two field campaigns, one in October 2016 (the end of the arid period) and the other in March 2017 (the end of the wet period). In the field, the researchers analysed chemical–physical parameters such as temperature, pH and EC. In the laboratory, the major ions (boron, Na+, Ca2+, K+, Mg2+) and anions (Cl−, SO42−, NO3−, HCO3−, CO32−) were determined, and almost all groundwater samples fall into the brackish water category. The B/Cl ratio and δ11B concentrations were then measured to better understand the origin of these brackish waters. The direct relationship between boron and chlorine and δ11B concentrations above 40‰ suggests the presence of fossil water in the aquifer. The groundwater in this area was found to be above the limits stated as desirable by the Department of Water and Sanitation (DWS) and the World Health Organisation for domestic and irrigation purposes. The suitability of the groundwater for drinking purposes was also evaluated, with the results indicating that it is not suitable. The values of the sodium absorption ratio, sodium percentage and electrical conductivity show that most of the groundwater samples are also not suitable for agricultural purposes. However, the surface waters have higher quality for both domestic and irrigation purposes. The water of Massingir Lake turns out to be the most suitable resource for a possible rural development plan for the area.