Browsing by Author "van Niekerk, L"

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    A multidisciplinary study of a small, temporarily open/closed South African estuary, with particular emphasis on the influence of mouth state on the ecology of the system
    (2008) Whitfield, A K; Adams, J B; Bate, G C; Bezuidenhout, K; Bornman, T G; Cowley, P D; Froneman, P W; Gama, P T; James, N C; Mackenzie, B; Riddin, T; Snow, G C; Strydom, N A; Taljaard, S; Terörde, A I; Theron, A K; Turpi, J K; van Niekerk, L; Vorwerk, P D; Wooldridg, T H
    In 2005/2006 a multidisciplinary research programme that included studies on the hydrodynamics, sediment dynamics, macronutrients, microalgae, macrophytes, zoobenthos, hyperbenthos, zooplankton, ichthyoplankton, fish and birds of the temporarily open/closed East Kleinemonde Estuary was conducted. Particular attention was given to the responses of the different ecosystem components to the opening and closing of the estuary mouth and how this is driven by both riverine and marine events. Using a complementary dataset of daily estuary mouth conditions spanning a 14-year period, five distinct phases of the estuary were identified, including closed (average = 90% of the days), outflow (<1%), tidal (9%) and semi-closed (<1%). The open-mouth phase is critical for the movements of a number of estuary-associated fish (e.g. Rhabdosargus holubi) and invertebrates (e.g. Scylla serrata) between the estuary and sea. The timing of this open phase has a direct influence on the ability of certain estuaryassociated fish (e.g. Lithognathus lithognathus) and invertebrates (e.g. Palaemon peringueyi) to successfully recruit into the system, with a spring opening (October/November) being regarded as optimal for most species. The type of mouth-breaching event and outflow phase is also important in terms of the subsequent salinity regime once the berm barrier forms. A deep mouth breaching following a large river flood tends to result in major tidal inputs of marine water prior to mouth closure and therefore higher salinities (15–25). Conversely, a shallow mouth breaching with reduced tidal exchange during the open phase often leads to a much lower salinity regime at the time of mouth closure (5–15). The biota, especially the submerged macrophytes, respond very differently to the above two scenarios, with Ruppia cirrhosa benefiting from the former and Potamogeton pectinatus from the latter. River flooding and the associated outflow of large volumes of water through the estuary can result in major declines in zooplankton, zoobenthos, hyperbenthos and fish populations during this phase. However, this resetting of the estuary is necessary because certain marine invertebrate and fish species are dependent on the opening of the estuary mouth in order to facilitate recruitment of larvae and post-larvae into the system from the sea. Slight increases in the numbers of certain piscivorous and resident wading bird species were recorded when the estuary mouth opened, possibly linked to increased feeding opportunities during that phase.
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    A status quo, vulnerability and adaptation assessment of the physical and socio-economic effects of climate change in the Western Cape
    (2005) Midgley, G F; Chapman, R A; Hewitson, B; Johnston, P; de Wit, M; Ziervogel, G; Mukheibir, P; van Niekerk, L; Tadross, M; van Wilgen, B W; Kgope, B; Morant, P D; Theron, A; Scholes, R J; Forsyth, G G
    The South African Country Study on Climate Change, carried out in the late 1990’s, identified the Northern and Western Cape Provinces as being most at risk from projected climate change-induced warming and rainfall change (results of this study are summarized in South Africa’s initial National Communication, prepared in accordance with Article 12 of the United Nations Framework Convention on Climate Change: www.environment.gov.za/Documents/Documents/2005Feb22/NatCom_Nov%202003%20(b). doc ). However, this study was based on a limited set of model projections of climate change that have now been superseded by projections using more advanced techniques. In this study we have carried out a broad reassessment of the vulnerability of the Western Cape to climate change impacts, using a wider range of climate scenarios from more sophisticated climate models, and for a range of sectors (with the exception of agriculture and fisheries, according to our brief). We also identify some key adaptive strategies that might alleviate or avoid the worst impacts of climate change in some sectors. We conclude that further detailed study of some of the implications of these findings will be necessary to explore these and further strategies in order to guide policy development.