Spatial patterns, rates and mechanisms of saltmarsh cycles (Westerschelde, the Netherlands)

Saltmarsh development was studied in a spatial context, in order to understand the mechanisms involved in saltmarsh cycles. A 30-y time-series of very high resolution false colour aerial photographs was studied for eight saltmarsh sites in the Westerschelde estuary (southwest Netherlands). Detailed maps of vegetation cover were produced for each year, based on a supervised classification, and changes in vegetation cover were analysed in a geographical information system. The results of the vegetation change maps and complementary series of topographic surveys have shown evidence of saltmarsh cycles, but without spatial synchrony in these cycles for the Westerschelde. For each saltmarsh, a different status of net erosion or accretion was found. Within each saltmarsh, there were both areas with vegetation loss and with vegetation expansion in each period. Most saltmarshes showed a simultaneous expansion of Spartina anglica by tussock growth, and a lateral retreat of the saltmarsh plateau through undercutting of a cliff at the edge of this plateau, resulting in saltmarsh rejuvenation. The rate of lateral retreat of the saltmarsh plateau decreased with the establishment of pioneer vegetation in front of the cliff (probably through dissipation of wave and tidal energy caused by the friction associated with the pioneer vegetation), and was generally not related to the frequency of high magnitude tides and high magnitude onshore winds. For the saltmarsh site that showed severe lateral erosion, a relationship with the mudflat topography was found, with lateral retreat of the saltmarsh plateau being compensated by an increase in mudflat elevation, eventually slowing down the erosion rate, and facilitating the subsequent expansion of pioneer vegetation in front of the cliff. The study demonstrates the significance of intrinsic processes in saltmarsh development, and the necessity to consider the local feedback mechanisms between plant growth, morphology and hydrodynamics of both the saltmarsh and the mudflat, when assessing the status of saltmarshes. It also shows the importance of assessing the changes in saltmarsh area in a spatial context, rather than looking at changes in total area of saltmarsh vegetation.

[1]  A. Thomson,et al.  Long-term changes in salt marsh extent affected by channel deepening in a modified estuary , 2003 .

[2]  Aaron M. Ellison,et al.  Saltmarshes: Morphodynamics, Conservation and Engineering Significance , 1993 .

[3]  J. Hubbard.  Spartina marshes in southern England. 6. Pattern of invasion in Poole Harbour. , 1965 .

[4]  A. Swales,et al.  Influence of wave and sediment dynamics on cordgrass (Spartina anglica) growth and sediment accumulation on an exposed intertidal flat , 2004 .

[5]  N. Cooper.  Wave Dissipation Across Intertidal Surfaces in the Wash Tidal Inlet, Eastern England , 2005 .

[6]  Iris Möller,et al.  Wave dissipation over macro-tidal saltmarshes: Effects of marsh edge typology and vegetation change , 2002, Journal of Coastal Research.

[7]  R. Davidson‐Arnott,et al.  Hydrodynamics and sedimentation in salt marshes: examples from a macrotidal marsh, Bay of Fundy , 2002 .

[8]  K. Pye,et al.  Controls on Long-term Saltmarsh Accretion and Erosion in the Wash, Eastern England , 1995 .

[9]  Iris Möller,et al.  Quantifying saltmarsh vegetation and its effect on wave height dissipation: Results from a UK East coast saltmarsh , 2006 .

[10]  Richard P. Stumpf,et al.  The process of sedimentation on the surface of a salt marsh , 1983 .

[11]  P. Cranford,et al.  Observations on the ecological importance of salt marshes in the Cumberland Basin, a macrotidal estuary in the Bay of Fundy , 1985 .

[12]  D. Reed.  Sediment dynamics and deposition in a retreating coastal salt marsh , 1988 .

[13]  D. Wal,et al.  Long-term morphological change in the Ribble Estuary, northwest England , 2002 .

[14]  Patrick Meire,et al.  Modelling estuarine variations in tidal marsh sedimentation: response to changing sea level and suspended sediment concentrations , 2004 .

[15]  D. Ranwell.  World resources of Spartina townsendii (sensu lato) and economic use of Spartina marshland. , 1967 .

[16]  D. Johns,et al.  The Salt Marshes of the Dovey Estuary , 1916 .

[17]  John Robert Lawrence Allen,et al.  Morphodynamics of Holocene salt marshes: a review sketch from the Atlantic and Southern North Sea coasts of Europe , 2000 .

[18]  Paul L. Knutson,et al.  Wave damping inSpartinaalterniflora marshes , 1982, Wetlands.

[19]  J. Izco,et al.  Primary colonisation of mudflat estuaries by Spartina maritima (Curtis) Fernald in Northwest Spain : vegetation structure and sediment accretion , 2001 .

[20]  D. Wal,et al.  Patterns, rates and possible causes of saltmarsh erosion in the Greater Thames area (UK) , 2004 .

[21]  A. Pringle,et al.  Erosion of a cyclic saltmarsh in Morecambe Bay, North‐West England , 1995 .

[22]  J. Pethick,et al.  Shoreline adjustments and coastal management: physical and biological processes under accelerated sea-level rise , 1993 .

[23]  R. Marrs,et al.  Spatial and temporal changes in salt marsh distribution in the Dee estuary, NW England, determined from aerial photographs , 2004, Wetlands Ecology and Management.

[24]  W. Wolff,et al.  Expected Effects of Climatic Change on Marine Coastal Ecosystems , 1990, Developments in Hydrobiology.

[25]  S. Long,et al.  An assessment of saltmarsh erosion in Essex, England, with reference to the Dengie Peninsula , 1986 .

[26]  W. H. Patrick,et al.  The relationship of smooth cordgrass (Spartina alterniflora) to tidal datums: A review , 1988 .

[27]  M. Best,et al.  Developing a saltmarsh classification tool for the European water framework directive. , 2007, Marine pollution bulletin.

[28]  T. Bouma,et al.  Morphological variation and habitat modification are strongly correlated for the autogenic ecosystem engineerSpartina anglica (common cordgrass) , 2007 .

[29]  L. Leonard,et al.  The effect of standing biomass on flow velocity and turbulence in Spartina alterniflora canopies , 2006 .

[30]  R. Schwimmer.  Rates and Processes of Marsh Shoreline Erosion in Rehoboth Bay, Delaware, U.S.A. , 2001 .

[31]  E. Houwing.  Morphodynamic development of intertidal mudflats: consequences for the extension of the pioneer zone , 2000 .

[32]  Urs Neumeier,et al.  The influence of vegetation on turbulence and flow velocities in European salt‐marshes , 2006 .

[33]  S. Silvestri,et al.  Mapping salt-marsh vegetation by multispectral and hyperspectral remote sensing , 2006 .

[34]  A. Hastings,et al.  Mapping marshland vegetation of San Francisco Bay, California, using hyperspectral data , 2005 .

[35]  A. Cooper,et al.  The distribution of Spartina anglica on estuarine mudflats in relation to wave-related hydrodynamic parameters. , 2002, Journal of Coastal Research.

[36]  D. Marshall,et al.  A Century of Evolution in Spartina anglica , 1991 .

[37]  B. E. Feist,et al.  Expansion rates and recruitment frequency of exotic smooth cordgrass, Spartina alterniflora (Loisel), colonizing unvegetated littoral flats in Willapa Bay, Washington , 2000 .

[38]  J. Thompson.  The biology of an invasive plant : what makes Spartina anglica so successful? , 1991 .

[39]  Johan van de Koppel,et al.  Self‐Organization and Vegetation Collapse in Salt Marsh Ecosystems , 2004, The American Naturalist.

[40]  Peter G. Appleby,et al.  Accretion of a New England (U.S.A.) Salt Marsh in Response to Inlet Migration, Storms, and Sea-level Rise , 1997 .

[41]  Donald R. Cahoon,et al.  Coastal Land Loss in Louisiana , 1990 .

[42]  Richard A. Wadsworth,et al.  Short-term vegetation succession and erosion identified by airborne remote sensing of Westerschelde salt marshes, The Netherlands , 2004 .

[43]  Peter M. J. Herman,et al.  Spatial flow and sedimentation patterns within patches of epibenthic structures: Combining field, flume and modelling experiments , 2007 .

[44]  J. Gosselink,et al.  Estimation of primary production using five different methods in a Spartina alterniflora salt marsh , 1990, Wetlands Ecology and Management.

[45]  C. Lambert,et al.  General description of the Scheldt estuary , 2004, Hydrobiologia.

[46]  S. Temmerman,et al.  Vegetation causes channel erosion in a tidal landscape , 2007 .