The St Lucia estuarine lake system in South Africa is part of a UN-
ESCO World Heritage site and a Ramsar wetland of international
importance. Like many estuarine systems worldwide St Lucia has
experienced signi cant anthropogenic impacts over the past century
including catchment land use changes, water diversions/abstractions
and inlet manipulation. In addition, the system has recently su ered
losses in species diversity and abundance following unprecedented hy-
persaline conditions and desiccation. Questions regarding its sustain-
ability have motivated a reevaluation of management decisions made
in the past and of options for the future. To understand the func-
tioning of the system, it is necessary to analyse it holistically in terms
of the physical processes and their interaction with the biology. This
study focusses on aspects of the biophysical interactions in the estu-
arine complex, and aims to provide new knowledge to underpin the
development of improved models for predicting the response of the
system to anthropogenic interventions.
A model for the water and salt budgets was used to investigate what
if scenarios in terms of past anthropogenic interventions, in particular
the e ects of diverting the Mfolozi River from St Lucia. Furthermore,
the risks of hypersalinity and desiccation were assessed for each sce-
nario. Integrating these modeled scenarios with observed biological
responses to physicochemical changes suggested that large long-term
changes in the ecological structure can be expected in the di erent
management scenarios. To validate this, the ecosystem response to
changing environmental responses was quantitatively assessed using
ecological network analysis.
Long-term simulations show that the separation of the Mfolozi and
St Lucia mouths had a signi cant impact on the functioning of the St
Lucia system. The Mfolozi plays a pivotal role in maintaining a more
stable mouth state regime and provides a vital source of freshwater
during dry conditions. The con guration of the Mfolozi/St Lucia inlet
plays a key role in the physico-chemical environment of the system and
in
uences the system's susceptibility to desiccation and hypersaline
conditions. Ecosystem indices revealed that the water level, salinity
and mouth state have a signi cant impact on species abundance and
diversity as well as the ecological structure and functioning of the
system. In addition, ecosystem indices show that the system recovers
rapidly during favourable conditions. The arti cial separation of the
St Lucia and Mfolozi inlets underpins the most signi cant impacts on
the water and salt budget of the lake and its reversal is key to the
sustainability of the system. / Thesis (Ph.D.)-University of KwaZulu-Natal, Durban, 2013.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ukzn/oai:http://researchspace.ukzn.ac.za:10413/10408 |
| Date | January 2013 |
| Creators | Chrystal, Robynne Angela Lawrie. |
| Contributors | Stretch, Derek D. |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
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