Geostatistical Analysis of Sediment Deposition In Two Small Tidal Wetlands, Norfolk, U.K.

J. R. French, T. Spencer, A. L. Murray, N. S. Arnold


Attempts to assess the sedimentary status of coastal wetlands have typically utilized either residual sediment transport via major drainage channels ('creeks') or the rate of vertical substrate accretion. The first method neglects the interaction between channel and surface sedimentation and may be inappropriate where significant water movement occurs across wetland margins. The second method requires areal interpolation from a limited number of cores, sediment traps or marker horizons, yet the effects of different spatial and temporal sampling strategies are rarely considered.

This paper presents an analysis of spatial patterns of sediment deposition within two tidal wetlands on the eastern coast of England. Extensive deployments of surface-mounted sediment traps over individual tidal cycles provide new insights into the spatial scales over which particle settling varies. Sedimentation is appropriately considered as a regionalized variable and estimation of 2-dimensional semivariograms allows the spatial scale of variability to be incorporated into interpolated 'sedimentation surfaces'. This enables more accurate estimation of mass fluxes than is possible from conventional arithmetic averaging or measurements of mass flux via drainage creeks. Rapid particle settling during lateral and apical overtopping of the creeks results in coherent patterns of sedimentation at spatial scales of the order 20200 m, depending on the developmental stage of the wetland surface-channel system. Comparison of these findings with vertical accretion averaged over several years indicates an increasing dependence of sedimentation rate upon inundation frequency (and therefore elevation) as the time-averaging period is lengthened.

Failure to consider these spatial and temporal sampling requirements may result in misleading assessments of wetland vulnerability to future accelerated sea-level rise or to changes in sediment supply.


Tidal wetlands; sedimentation; geostatistics; sea-level; Norfolk; U.K.

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