Salt marsh elevation and responses to future sea-level rise in the Knysna Estuary, South Africa

Raw, Jacqueline L.; Riddin, T.; Wasserman, Johan; Lehman, T.W.K.; Bornman, Thomas G.

doi:10.2989/16085914.2019.1662763

Cited by 34 publications

(13 citation statements)

References 63 publications

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“…Compared to other tidal gauges around the world, a significantly higher growth is observed in the Bay of Cádiz. The 3.5 mm annual rise in mean sea level in this environment contrasts with, for example, the 2.7 mm recorded by Hartig et al (2002) in New York in the USA or the 2.19 mm observed by Raw et al (2020) in the Knysna estuary in South Africa. However, contrary to what might be expected, the result of the calculation in this research is slightly more optimistic than in the literature used (Fraile et al, 2018).…”

Section: Discussioncontrasting

confidence: 68%

“…In general, the authors agree that predictions of mean sea-level rise should be reflected in cartography using the Geographic Information Systems, with ArcMap being the most recurrent software (Hartig et al, 2002;Bornman et al, 2016;Raw et al, 2020). Also, the projections tend to conform to the models disseminated by the IPCC, both those published by the Special Report in Emissions Scenarios (SRES) and the RCP.…”

Section: Discussionmentioning

confidence: 76%

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Territorial impacts of sea-level rise in marsh environments. The case of the Bay of Cádiz, Spain

Pinillos

Marchena-Gómez

2021

CIG

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How can sea-level rise affect territory? Has territorial planning adjusted to this new situation? This paper analyses the possible ramifications of changes in tidal recurrence over the course of this century in a potentially vulnerable marsh environment, such as the Bay of Cádiz, in southern Spain, where sea-level rise is already a fact. For that purpose, the regionalisation criterion is used as a basis for adjusting the magnitude of global problems to subregional scale. Geographic information systems are applied to portray the forecasted territorial changes according to the RCP4.5 and RCP8.5 scenarios presented by the Intergovernmental Panel on Climate Change (IPCC) for the years 2050 and 2100. Projections of sea-level rise show that the tide is travelling farther inland, not just invading unoccupied areas of marshes and beaches but also reaching urban and productive areas. Estimates indicate that the floodable area could expand by more than 20% in 2050, with a further 2,000 ha of flooded areas added in 2100 for either of the two scenarios used. The occurrence of these changes, regardless of the model used, would therefore entail an alteration of the environmental, social, cultural and economic values and elements of the Bay of Cádiz, with the Natural Park being the most affected area. In response to these consequences, the need to apply the resulting projections to other variables is insisted on, with a view to introducing territorial management tailored to this new and already present reality. Application of the regionalisation criterion to study repercussions of the climate crisis in the Bay of Cádiz could serve as a precedent for the development of adaptation strategies in other marsh environments at subregional or local level.

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Section: Discussioncontrasting

confidence: 68%

Section: Discussionmentioning

confidence: 76%

Territorial impacts of sea-level rise in marsh environments. The case of the Bay of Cádiz, Spain

Pinillos

Marchena-Gómez

2021

CIG

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“…The axial main channel provides the only subtidal habitat within the Knysna estuarine bay, but it does not support the only intertidal area of seagrass. There is an extensive block of seagrass-covered mudflats and creeks within the sheltered, saltmarsh-lined eastern half of the marine embayment, between Thesen and Leisure Islands and the mainland (see Raw et al 2020). These seagrass beds support a qualitatively and quantitatively different faunal assemblage (Barnes 2013a).…”

Section: Discussionmentioning

confidence: 99%

Do beds of subtidal estuarine seagrass constitute a refuge for macrobenthic biodiversity threatened intertidally?

Barnes

Claassens

2020

Biodivers Conserv

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Biodiversity differentials between macrobenthic assemblages associated with adjacent intertidal and subtidal areas of a single seagrass system were investigated for the first time. Assemblage metrics of conservation relevance—faunal abundance and its patchiness, faunal richness, and beta diversity—were examined at four contrasting dwarf-eelgrass localities in the Knysna estuarine bay, part of South Africa's Garden Route National Park but a system whose intertidal areas are heavily impacted anthropogenically. Faunal assemblages were significantly different across all localities and between subtidal and intertidal levels at each locality although their taxonomic distinctness was effectively constant. Although, as would be expected, there were clear trends for increases in overall numbers of species towards the mouth at all levels, few generalities relating to the relative importance of the subtidal seagrass habitat were evident across the whole system—magnitude and direction of differentials were contingent on locality. Shore-height related differences in assemblage metrics were minor in the estuarine and lagoonal zones but major in the marine compartment, although the much greater subtidal faunal abundance there was largely consequent on the superabundance of a single species (the microgastropod Alaba pinnae), intertidal zones then displaying the greater species diversity due to greater equitability of species densities. Along its axial channel, the Knysna subtidal seagrass does not support richer versions of the intertidal polychaete-dominated assemblages fringing it; instead, it supports different and more patchily dispersed gastropod-dominated ones. At Knysna at least, the subtidal hardly constitutes a reservoir of the seagrass biodiversity present intertidally.

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“…Sea level rise can either counteract the reduction in runoff to an estuary or exacerbate the effect depending on the size of the estuary, sediment availability, and wave energy near or at its mouth. Significant research effort is currently underway to understand the impact of sea level rise on estuary habitats [49] with a key requirement being the identification of habitat accommodation space using models such as the Sea-Level Affecting Marshes Model (SLAMM) (Warren Pinnacle Consulting, Inc., Waitsfield, VT, USA, e.g., [50]. However, many of these models neglect or underestimate processes such as marsh accretion and subsidence.…”

Section: Ocean Forcingmentioning

confidence: 99%

Advancing the Science of Environmental Flow Management for Protection of Temporarily Closed Estuaries and Coastal Lagoons

Stein

Gee

Adams

et al. 2021

Water

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The science needed to inform management of environmental flows to temporarily closed estuaries and coastal lagoons is decades behind the state of knowledge for rivers and large embayments. These globally ubiquitous small systems, which are often seasonally closed to the ocean’s influence, are under particular threat associated with hydrologic alteration because of changes in atershed land use, water use practices, and climate change. Managing environmental flows in these systems is complicated by their tight coupling with watershed processes, variable states because of intermittently closing mouths, and reliance on regional scale sediment transport and littoral processes. Here we synthesize our current understanding of ecohydrology in temporarily closed estuaries (TCEs) and coastal lagoons and propose a prioritized research agenda aimed at advancing understanding of ecological responses to altered flow regimes in TCEs. Key research needs include agreeing on a consistent typology, improving models that couple watershed and ocean forcing at appropriate spatial and temporal scales, quantifying stress–response relationships associated with hydrologic alteration, improving tools to establish desired conditions that account for climate change and consider cultural/indigenous objectives, improving tools to measure ecosystem function and social/cultural values, and developing monitoring and adaptive management programs that can inform environmental flow management in consideration of other stressors and across different habitat types. Coordinated global efforts to address the identified research gaps can help guide management actions aimed at reducing or mitigating potential impacts of hydrologic alteration and climate change through informed management of freshwater inflows.

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Salt marsh elevation and responses to future sea-level rise in the Knysna Estuary, South Africa

Cited by 34 publications

References 63 publications

Territorial impacts of sea-level rise in marsh environments. The case of the Bay of Cádiz, Spain

Territorial impacts of sea-level rise in marsh environments. The case of the Bay of Cádiz, Spain

Do beds of subtidal estuarine seagrass constitute a refuge for macrobenthic biodiversity threatened intertidally?

Advancing the Science of Environmental Flow Management for Protection of Temporarily Closed Estuaries and Coastal Lagoons

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