Response of estuarine and freshwater macroinvertebrate assemblages to habitat, water quality, flow and land use change in the lowland Amatikulu/Nyoni catchment.

Abstract

Water has become a scarce commodity in Sub-Saharan Africa and in drought prone South Africa. Due to the extensive utilization of water resources in South Africa, management and monitoring of our rivers and estuaries is required by law to achieve a balance between use and protection. Macrobenthic invertebrates of estuaries and freshwater macroinvertebrates have played a large role as indicators of ecosystem health. The lowland Amatikulu/Nyoni catchment in the province of KwaZulu-Natal is relatively poorly understood and baseline information about the ecology of the ecosystem is required. This therefore advocates more research into the Amatikulu/Nyoni catchments ecological wellbeing is needed to inform best management practices. The overall aim of this study was to utilize aquatic macroinvertebrates as ecological indicators to evaluate the current biological condition of the Amatikulu/Nyoni River/Estuary. Freshwater and estuarine invertebrates were evaluated separately in the study with two main lines of evidence including: (1) the use of valid statistical methods to determine how water quality, habitat and sediment composition affected estuarine and freshwater macroinvertebrates community structure, abundance and distribution, and (2) the use of an established community metric measure or biological index namely the South African Scoring System (SASS) Version 5 to evaluate the wellbeing of the freshwater invertebrate communities. The application of these lines of evidence are detailed in chapters two and three. Chapter one is a general introduction for the thesis and a comprehensive literature review of how and why macroinvertebrates have been used as a bio indicators of freshwater and estuarine integrity. Chapter two describes the collection of freshwater macroinvertebrates from four freshwater sites and their assessment using the SASS5 community metric measure during the high and low flow seasons in 2017. In addition, multivariate statistical analyses were performed on the data to test the significance of macroinvertebrate community shifts and correlations with changes in temperature, conductivity, dissolved oxygen, percentage dissolved oxygen, pH, South African Scoring System Version 5 Scores, Average Score Per Taxa (ASPT), the number of individuals for each survey and flow periods and between sites. The lowland Amatikulu River catchment sites showed that there was a change in the ecological condition of freshwater macroinvertebrate assemblages as well as along a longitudinal gradient with upstream sites having better conditions to support more sensitive species. In the third chapter, estuarine benthic macroinvertebrates were collected from four estuary sites using a Van Veen grab during two sampling surveys in 2017. To analyse the data, Conoco version 4.5 was also used to test the significance of benthic invertebrate community shifts and correlations with environmental, spatial and temporal variables. Estuarine benthic invertebrate assemblages varied between sampling sessions in accordance with estuary mouth conditions, nutrient concentrations, sediment grain size distributions and total organic content levels compared with other environmental parameters. By identifying the relationship and drivers between aquatic macroinvertebrates with water quality, habitat, flow and anthropogenic land use change, insight has been gained into the structure and function of the Amatikulu/Nyoni Catchment, its ecosystem health and some management and monitoring recommendations derived to contribute to the sustainable management of the system.