Assessing the sensitivity of aquatic macroinvertebrates to acid deposition in South African headwater streams
Date
2019
Authors
Khuzwayo, Londiwe Mandisa
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Abstract
GIS was used to identify three study regions in south Africa susceptible to acidification. These regions namely, Mpumalanga (HV), Waterberg (WB) and the south-western Cape (SWC) were identified and categorised to represent high, medium and low acid deposition loads respectively based on the distribution of coalfired power stations and acid sensitive soils and waters. A total of 80 headwater streams representing 84 sampling sites were identified, 21 in Mpumalanga, 33 from the Waterberg and 30 for the south-western Cape and measured for water chemistry. The project tried to identify sites that had no direct human influences on the water quality (i.e. mining and intensive agriculture) within their catchments in order to focus the study on impacts related entirely to atmospheric deposition. Macroinvertebrate samples were collected from a subset (n = 56) of these sites due to habitat suitability, and species response to changes in environmental variables were investigated. Geographically the three study regions differed significantly from each other and this difference was most apparent with the difference in altitude, biomes, ecoregions and species composition.
When compared to the other study regions the Mpumalanga region had very high pH (Mean = 7.24, Minimum = 5.32, Maximum = 9.52) and electrical conductivity (Mean = 180, Minimum = 14, Maximum = 1827) that appeared to be mostly anthropogenically impacted, which meant that a large portion of the streams from this region were unsuitable for the purposes of this study. Furthermore, the region has been subjected to a high degree of environmental degradation attributed to coal mining, agricultural activity and general industrialisation that has led to abstraction from and deterioration of many aquatic ecosystems. During the course of this study the Waterberg experienced a major drought which appears to have influenced species assemblages. The naturally acidic streams of the south-western Cape as well as the overall heterogeneity of the three study regions made comparing species presence/absence across regions unfavourable. Thus, developing a national South African scoring system for acidification became equally implausible. Furthermore, in-depth analysis of species response to seasonal drought from the Waterberg and alkalinity of streams in the Mpumalanga region may have been feasible had other taxonomic Orders been included. However, for the purposes of this study taxonomic groups primarily associated with acidification were chosen and thus further investigations were only limited to these groups. Nonetheless several mayfly species were found to show acid intolerance or be moderately intolerant.
Description
A thesis submitted in fulfilment of the requirements for the degree of Doctor of Philosophy to the Faculty of Science, University of the Witwatersrand, Johannesburg, 2019