Using riparian vegetation responses in the Mooi River catchment within an ecological water requirement framework

Abstract

Riparian zones are generally the boundary between aquatic and terrestrial systems which provide several ecosystem services such as an ecological corridor that acts as a migration corridor for animal, birds and even plants. They also provide a natural habitat, useful for riverbank stabilisation and assist with organic matter provisioning, which is used as food for aquatic macro invertebrates. The root systems of riparian vegetation filter sediments and nutrients that discharge of surface slopes and therefore protect and improve the water quality of river systems. Many studies have been conducted on the changes in riparian zones, however, no study has been conducted to determine the ecological status of riparian vegetation in the Mooi River Catchments in South Africa. This study’s aim was to determine how the riparian zone within the Mooi River Catchments has responded in the past 10 years, based on changing land use. The study examined the riparian vegetation cover and established modifications in vegetation composition and the spatial extent of the riparian zone. The study area was within the Mooi River Catchments in the Potchefstroom area where six sites were sampled within the catchment to assess and compare the different responses of the riparian vegetation over time. Different sites were sampled to determine the present ecological status of the riparian vegetation which was compared with the reference condition for the Mooi River Catchments. The riparian vegetation was assessed in terms of the Vegetation Response Assessment Index (VEGRAI) assessment methodology and a scoring system of generic ecological categories for EcoStatus components. The results showed that the riparian vegetation of this area is moderately to largely modified. This indicated that a loss and a change of the natural environment and biota have occurred but that the basic ecosystem functions were adversely altered and a large loss of natural habitat, biota and basic ecosystem functions have not occurred. It was established that the Mooi River catchment falls within C/D ecological category, i.e. a moderately to largely modified status. Therefore, critical mitigation measures to safeguard the riparian zone and the river system of the Mooi River Catchments should be implemented before it deteriorates further.

Maps were also used to determine the different responses for different species composition within the Mooi River riparian zone over time, using aerial photographs of the study area covering a period between 2009, 2014 and 2019.