Assessment of Potential Temporal Impacts of “Land use Activities on Water Quality of the Luvuvhu River “Catchment, South Africa

Abstract

River health is crucial to benefit from the full resource potential of surface water bodies. This benefit becomes compromised when there’s high water quality degradation in the system. Considering the South African context, the use of untreated river water for domestic uses such as laundry, recreation, and crop irrigation, is a common practice in various urban and rural communities. The Luvuvhu River Catchment (LRC), in Limpopo Province, South Africa, serves as an essential water resource for the communities within the catchment. Thus, the main focus of this study was to assess the impacts of land use activities on the water quality of the Luvuvhu River Catchment (LRC). This was achieved by analysing the spatiotemporal variation of river water, sediment quality and the potential ecological as well as human health risks associated with the river water and sediments. Sediment and water “samples were collected from 22 sampling sites along” the Luvuvhu River Catchment between November 2020 and October 2021. Water samples were analysed for physicochemical parameters, nutrients, major metals and heavy metals, while sediments were analysed for heavy metals only. Physicochemical and nutrients data analysed consisted of pH, total dissolved solids (TDS), turbidity, temperature, dissolved oxygen (DO), salinity, biological oxygen demand (BOD), chemical oxygen demand (COD), electrical conductivity (EC), nitrate (NO3⁻), chloride (Clˉ), sulphate (SO4 2ˉ), and phosphate (PO₄³⁻). Samples were digested “using microwave acid digestion (EPA 3051) and analysed using inductively coupled plasma-optical emission spectroscopy (ICP-OES) and inductively coupled plasma mass spectrometer” (ICP-MS) for major metals (Na, Mg, K, and Ca) and heavy metals (Mn, Fe, Al, Cr, Cu, Zn, As, Co, Ni, Mo, Ba, Hg, Cd, and Pb), respectively. The study examined the spatial distribution of these parameters using the Interpolated Distance Weighted (IDW) method on Esri ArcGIS Pro software. The findings were compared to South African Water Quality Guidelines and the World Health Organization. The results show that the water quality fluctuated during the sampling period. Some parameters such as turbidity, EC, nitrate, Al, Mn, and Fe exceeded the drinking water standards. The findings also show spatiotemporal differences in water quality. The upstream catchment of the river is predominantly covered by agricultural activities and land use becomes more naturally vegetated in the downstream catchment inside the Kruger National Park. Further, the study reveals that the Luvuvhu River Catchment receives a significant amount of pollutants from the upstream and midstream reaches as well as upstream rivers in the Limpopo River before the confluence of the Luvuvhu River. The quality of water further degrades towards the downstream catchment along the gradient as the river flows through various land use activities. It is therefore, concluded that upstream activities and other tributaries of the Limpopo River have a significant impact on the river’s water quality. The quality of water in some sampling sites are not suitable (higher than the Department of Water Affairs and Forestry guidelines) for agricultural use and protection of aquatic ecosystems due to elevated concentrations of some parameters such as Hg, Cu, Mn, Fe, and Al. Generally, about 72% of the metals in “sediments and water are higher during the wet season than the” dry season. It is also found that high runoff during the wet season act as a transporting mechanism for pollutants though some parameters are not seasonally influenced. The statistical tools used were able to analyse the water quality data of the river and provided meaningful and relevant information about the river. Multivariate Principal Component Analysis (PCA) revealed substantial anthropogenic contributions of metals in sediment and Cluster Analysis (CA) revealed three classes indicating three major anthropogenic (land use activities) contributions. While the “Pollution Load Index (PLI), Enrichment Factor (EF), Contamination Factor (Ci f) and Geo-accumulation Index (Igeo) indicate that the level of contamination is low to moderate in most of the” sediment samples. In consideration of “the potential ecological risk, the LRC sediments show low potential ecological” risk. Also, chronic daily intake of metals because of ingestion was below the recommended guidelines. The overall hazard index for children and adults did not exceed the recommended limit (HI < 1) indicating no or low health risk (non-carcinogenic). The carcinogenic risks of As, Pb and Cd at various sampling sites via ingestion were lower than 10-6 indicating no or low risk to develop cancer. This study recommends further studies to be conducted in specific time frames to limit heavy metal content and to prevent further pollution of catchment ecosystems including Kruger National Park by future industrialisation and urbanisation processes upstream of the catchment.