Increased abstraction of water in the catchment results in a reduced or altered pattern of river flow
and this holds serious consequences for the downstream estuarine ecosystem. In South Africa this
is a serious concern because freshwater is in limited supply and the demand for freshwater can be
expected to increase in the future.
A large multi-disciplinary consortium of South African scientists are working on projects to
determine the freshwater requirements of estuarine ecosystems. As part of this, this thesis reports
on research undertaken to develop mathematical models to determine the freshwater requirements
of estuarine macrophytes. Three key macrophytes are selected. The macrophytes are Zostera
capensis Setchell, Ruppia cirrhosa Grande, and Phragmites australis. They are common
macrophytes in South African estuaries. Zostera and Ruppia are submerged macrophytes and
Phragmites is an emergent macrophyte. They have different freshwater environments and
therefore respond differently to alterations in freshwater flow.
A first order differential equation model is used to determine the effect of different combinations
of open and closed mouth conditions of the estuary on Zostera and Ruppia. The scenarios are
selected to determine whether achieving a switch in states from a Zostera-dominated estuary to
a Ruppia-dominated estuary is possible.
To predict encroachment rates and colonisation patterns, a cellular automaton of the vegetative
spread of existing Zostera beds is developed. After analysing various scenarios accounting for
both an increase and a decrease in freshwater supply, the cellular automaton is extended to include
interactions between Ruppia and Phragmites. The multi-species model is applied to the Kromme
estuary, South Africa and the Great Brak estuary, South Africa. Various freshwater scenarios are
examined from the natural runoff condition to the situation of no freshwater inflow.
A sensitivity analysis of the spatial model with Zostera, Ruppia and Phragmites is conducted. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1998.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ukzn/oai:http://researchspace.ukzn.ac.za:10413/4767 |
| Date | January 1998 |
| Creators | Wortmann, Joanne. |
| Contributors | Hearne, John W. |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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