An integrated modelling approach to the management of freshwater inflow to South African estuaries.
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Date
1998
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Abstract
Estuaries are recognised for their biological diversity and productivity, as well as the vital role
they play in providing habitat for organisms which utilise them as nurseries and feeding
grounds. In many parts of the world concern has been expressed that the important functions
and values of estuaries are being increasingly impacted upon by human activity. In South Africa
diminishing freshwater inflow is a particular concern as this has led to an increase in the
frequency and duration of mouth closure, which together with other factors has resulted in a
marked deterioration in the condition of many estuaries.
Global environmental imperatives require an approach to ecosystem management that is
defensible and sustainable in the long term. Current approaches to estuary management in
South Africa do not meet these criteria, and consequently, this study set out to develop
methodologies to address these shortcomings. Three modelling approaches are presented,
which can be used independently, or conjunctively, in defining the freshwater requirements of
estuaries. The models assess the consequences of change in freshwater inflow for (i) juvenile
fish which utilise estuaries as nurseries, (ii) the availability of intertidal and species specific
habitats, and (iii) the population structure and production of a common estuarine invertebrate
(Upogebia africana), endemic to the region.
These techniques are applied in a case study of the Great Brak estuary (Western Cape, South
Africa). The results indicate the utility of the approach and are supported, in part, by the
findings of a long-term monitoring programme. The study also recognises the need for resource
management to occur in the context of an integrated framework, which includes the explicit
definition of ecological goals. Such a framework is presented, and is consistent with the
Ecological Society of America's guidelines on sustainable ecosystem management.
As this approach has been devised to be applicable to South African estuaries, characterised
by poor data availability, it is anticipated that methodologies will be equally applicable to
estuaries in other developing countries with a similar lack of data. The methodologies also
extend current international approaches to the management of estuary freshwater inflow, and
would therefore be of value to estuaries in the United States of America, Australia and other
regions where diminishing freshwater inflow has been raised as a concern.
Description
Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1998.
Keywords
Estuaries--South Africa., Estuarine ecology., Estuarine biology., Ecosystem management--South Africa., Natural resources--Mathematical models., Theses--Environmental science.