Abstract:
Freshwater ecosystems in South Africa are losing their quality and quantity over time
due to pollution mainly from mining, agriculture, industries, deforestation, sewage
systems, construction of dams, channel modification and over extraction of water. The
Dwars River, a tributary of the Olifants River, is of no exception, as recent studies
indicated an increase in nutrient input possibly from agriculture. The Dwars River is an
important source of water for nearby communities (Ga-Mampuru). The aim of the study
was to assess water and sediment quality of the Dwars River using
macroinvertebrates as bioindicators of pollution. Water and macroinvertebrates
sampling were done seasonally from July 2017 to May 2018. The water quality results
indicated that non-toxic constituents such as salinity and EC (Electrical Conductivity)
were above permissible limits stipulated by the DWAF (1996) guidelines.
More sensitive taxa were found upstream, despite high concentrations of some
nutrients and metals in the water column. The high abundance and distribution of
macroinvertebrates observed upstream was confirmed by the Canonical
Correspondence Analysis (CCA), South African Scoring System (SASS5) and
Average Score Per Taxon (ASPT) results during the study. Site 1 was dominated by
the most sensitive taxa and this could be due to high dissolved oxygen content and
increased heterogeneity of the area. Site 4 was dominated by the most tolerant taxa,
according to the CCA, SASS score and ASPT results. This could possibly be due to
the nutrients and heavy metals washed from upstream, which get adsorbed by the
sediment. The results for species abundance, diversity and richness indicated that
Ephemeroptera was the most abundant, while Diptera was the most diverse.
Ephemeropterans are known to be indicators of good water quality. Site 1 had the
highest number of families and orders while site 4 had the least families and orders.
Ephemeroptera, Plecoptera and Tricoptera (EPT) taxa richness and Shannon diversity
(H’) index values are high upstream and decrease downstream. Overall, the SASS5
indices, CCA and physicochemical results indicated that the water quality in the Dwars
River is deteriorating in most impacted sites
