Aquatic health assessment of the upper Olifants River Catchment, Mpumalanga Province, South Africa

Abstract: Water quality deterioration in South Africa is a common problem. The Olifants Water Management Area (WMA) covers about 54 570 km2 and has three distinct zones, which are the upper Olifants, middle Olifants and lower Olifants. The total mean annual runoff in the Olifants WMA is approximately 2400 million cubic meters per year. Land use activities within the upper Olifants River catchment include coal mining, agriculture, wastewater treatment works, power generation, chemical manufacture and metal smelters. Crop irrigation and intensive livestock farming (piggeries and cattle feedlots) also take place in various parts of the catchment. The aim of this study was to conduct an aquatic assessment using biological indictors and water quality parameters and determine the anthropogenic impacts within the vicinity of the study sites in the upper Olifants River catchment. The objectives were to 1) determine the Present Ecological State (PES) of the upper Olifants River catchment, 2) identify possible sources of pollution and 3) assess the impacts of human activities on in-situ water quality. Biomonitoring was conducted at selected sampling locations in the Bronkhorstspruit and Elands rivers, which are tributaries of the upper Olifants River main stem. The methods that were used for the study included the South African Scoring System (SASS5) for macroinvertebrates, sampling in-situ water quality parameters and data analysis using Eco- Status Models. Results indicate changes in the drivers of the aquatic system (i.e. water quality and flow), with resultant negative responses of sensitive biota. Changes in macroinvertebrate community composition from sensitive to tolerant taxa indicate impaired conditions. Flow modification and water quality pollution were considered the main sources of impairment during field sampling. Monitoring site B3ELAND-DETWE recorded the highest number of taxa, with 26 taxa recorded during the dry season. The lowest number of taxa was recorded at monitoring site B2BRON-MOOIF, with 7 taxa recorded during the dry season. The SASS5 scores ranged from 22 at monitoring site B2BRON-MOOIF during the August 2019 survey period to 180 at B3ELAND-DETWE during the June 2019 survey...M.Sc. (Aquatic Health