Geological history

Greg A. Botha, Sylvi Haldorsen, Naomi Porat

Research output: Chapter in Book/Report/Conference proceedingChapterpeer-review

6 Scopus citations

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 languageEnglish
Title of host publicationEcology and Conservation of Estuarine Ecosystems
Subtitle of host publicationLake St Lucia as a Global Model
PublisherCambridge University Press
Pages47-62
Number of pages16
ISBN (Electronic)9781139095723
ISBN (Print)9781107019751
DOIs
StatePublished - 1 Jan 2011
Externally publishedYes

Bibliographical note

Publisher Copyright:
© Cambridge University Press 2013.

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