Abstract
The evolution of the St Lucia estuarine lake basin and the other coastal lakes in Maputaland bears testimony to the cyclical environmental changes operating across a range of temporal scales during the past 2.6 million years (Ma) of the Quaternary Period. The lake environment is constantly changing in response to fluctuating discharge and sediment flux from the five main catchments, evaporation from the shallow lake, groundwater level change, and the influence of the littoral marine environment on the estuary. The impact of these factors during the Quaternary Period can be interpreted from the geological record in the surrounding dunefields and sediments below the lake bed. Sedimentary deposits show that the St Lucia lake has been subjected to frequent marine transgressions and regressions and that the present shoreline morphology was only achieved within the past ~1000 years. The system has evolved in response to cyclical fluctuations of marine base level and the shifting confluence of the fluvial systems with the Indian Ocean. This has led to the St Lucia lake basin alternating between an open marine embayment or shallow continental shelf environment during sea-level highstands and a subaerially exposed shallow valley lowland incised by river channels during sea-level lowstands (Orme, 1973; Wright et al., 2000; Green and Uken, 2005; Botha and Porat, 2007; Porat and Botha, 2008). The St Lucia lake basin was elevated above sea level as a terrestrial ecosystem for longer periods during the Pleistocene and Holocene than it was inundated to levels similar to its present lacustrine morphology.The resilience of this environment and its biota to short-term changes such as periodic salinity increases has been influenced by the evolution of the system over geological temporal scales. The system has, in addition, been subjected to anthropogenic stresses over the past few centuries imposed by catchment degradation, rapidly increasing fluvial sediment load, canalization of the lower river channels, dredging of the narrow marine interface and rising sea level.
Original language | English |
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Title of host publication | Ecology and Conservation of Estuarine Ecosystems |
Subtitle of host publication | Lake St Lucia as a Global Model |
Publisher | Cambridge University Press |
Pages | 47-62 |
Number of pages | 16 |
ISBN (Electronic) | 9781139095723 |
ISBN (Print) | 9781107019751 |
DOIs | |
State | Published - 1 Jan 2011 |
Externally published | Yes |
Bibliographical note
Publisher Copyright:© Cambridge University Press 2013.