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.