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Vertical accretion versus elevational adjustment in UK saltmarshes: an evaluation of alternative methodologies
Cahoon, D.R.; French, J.R.; Spencer, T.; Reed, D.; Möller, I. (2000). Vertical accretion versus elevational adjustment in UK saltmarshes: an evaluation of alternative methodologies, in: Pye, K. et al. (Ed.) Coastal and estuarine environments: sedimentology, geomorphology and geoarchaeology. Geological Society Special Publication, 175: pp. 223-238
In: Pye, K.; Allen, J.R.L. (Ed.) (2000). Coastal and estuarine environments: sedimentology, geomorphology and geoarchaeology Geological Society Special Publication, 175 The Geological Society: London. ISBN 1-86239-070-3. 435 pp., more
In: Hartley, A.J. et al. (Ed.) Geological Society Special Publication. Geological Society of London: Oxford; London; Edinburgh; Boston, Mass.; Carlton, Vic.. ISSN 0305-8719, more
Peer reviewed article  

Available in  Authors 
    VLIZ: Geology and Geophysics [5917]
Document type: Conference paper

Keywords
    Marine; Brackish water

Authors  Top 
  • Cahoon, D.R.
  • French, J.R.
  • Spencer, T.
  • Reed, D.
  • Möller, I.

Abstract
    Simultaneous measurements of vertical accretion from marker horizons and marsh-elevation change from sedimentation-erosion tables (SET) were made in selected marshes along the East Anglian coast of the UK in order to address the following objectives: (1) to ascertain the validity of treating accretion measurements obtained within tidally dominated, minerogenic saltmarshes as equivalent to surface elevation changes; (2) to explore the implications, in terms of physical and biological processes, of discrepancies between separately measured vertical accretion and elevation change within contrasting marsh types. Data were collected from several marsh environments at Scolt Head Island and Stifikey on the North Norfolk coast and at an experimental managed realignment project near Tollesbury, Essex. Scolt Head Island was selected for its long-term datasets of marsh accretion, Stifikey for its contrasting open coast-back barrier settings, and Tollesbury for its experimental management, in order to illustrate the potential application of the SET method and evaluate the relationship between vertical accretion and elevation change in a variety of marsh settings. The relationship between vertical accretion and elevation change varied widely among marsh settings of different age and height (within the tidal frame) at Scolt Head Island and Stifikey. Rates of vertical accretion and elevation change were similar in the older and mid-height settings on Scolt Head Island, indicating control of elevation change by surface accretionary processes (e.g. sediment deposition). However, subsurface processes controlled elevation at three of the marsh sites. Spartina Marsh, the youngest and lowest of the back barrier settings at Scolt Head Island, exhibited continuous shallow subsidence (vertical accretion greater than elevation change) over a 4-year period, implying that compaction controls elevation change. In the upper part of Hut Marsh and the interior of the Stifikey marshes, elevation change exceeded vertical accretion suggesting that subsurface processes (e.g. organic accumulation) controlled elevation in these settings. Surface accretionary processes control elevation change in both the highly dynamic, outer marsh at Stifikey and the low, restored marsh at Tollesbury. Despite the occurrence of shallow subsidence, all sites gained elevation at an annual rate comparable to that of sea-Ievel rise. In summary , the SET provides the means to critically evaluate the influence of vertical accretion measures on elevation and represents an improved method by which to evaluate the vulnerability of a marsh to sea-Ievel rise.

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