Seasonal and annual variations in the volumetric sediment balance of a macro-tidal salt marsh |
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| Institution: | 1. Benthos Laboratory, Center for Marine Studies, Federal University of Paraná, Brazil;2. Laboratory of Coastal Oceanography and GIS, Center for Marine Studies, Federal University of Paraná, Av. Beira Mar, s/n, 83255-976, Pontal do Sul, PR, Brazil;1. State Key Laboratory of Estuarine and Coastal Research, East China Normal University, Shanghai 200062, People''s Republic of China;2. Section of Environmental Fluid Mechanics, Faculty of Civil Engineering and Geosciences, Delft University of Technology, PO Box 5048, 2600, GA, Delft, The Netherlands;3. School of Marine Science and Engineering, University of Plymouth, Drake Circus, Plymouth, Devon PL4 8AA, United Kingdom;4. HR Wallingford, Howbery Park, Wallingford OX10 8BA, United Kingdom;5. Department of Geography, Environment and Earth Sciences, University of Hull, Hull HU6 7RX, United Kingdom;1. University of Trento, Department of Civil, Environmental and Mechanical Engineering, via Mesiano 77, Trento 38123, Italy;2. Queen Mary, University of London, School of Geography, Mile End Road, London E1 4NS, United Kingdom;3. University of Padova, Department of Civil, Environmental and Architectural Engineering, via Marzolo 9, Padova 35131, Italy |
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| Abstract: | This paper examines the spatial and temporal variability in the volumetric sediment balance of Allen Creek marsh, a macro-tidal salt marsh in the Bay of Fundy. The volumetric balance was determined as the balance of inputs of sediments and organic matter via accretion on the marsh surface and outputs of sedimentary material primarily due to erosion of the marsh margin. Changes in marsh surface elevation were measured at 20 buried plates and 3 modified sediment elevation tables from 1996–2002, and detailed margin surveys were conducted in 1997, 1999 and 2001 using a differential global positioning system. Changes in surface area were calculated using GIS overlay analysis and used in conjunction with accretion and erosion data to derive volumetric estimates of gains and losses of sedimentary material in the marsh system.Currently the volumetric sediment balance at Allen Creek marsh is positive. However the processes of erosion and accretion demonstrate seasonal, annual and spatial variability. Inputs to the system include deposition on the marsh surface from sediment laden waters and from ice rafting of sediments. Sediment is deposited onto the marsh surface year round, even during the winter when vegetation cover is sparse, and the amount of deposition in general is not significantly correlated with the frequency of tidal inundations. Based on the data from 1996 to 2002, the mid and high marsh zones experience mean accretion rates of approximately 1.4 cm year? 1 whereas accretion rates in the low marsh region are statistically significantly lower (0.8 cm year? 1). The absolute amount of accretion varies between seasons and from year to year. The main loss to the marsh is through erosion of the marsh margin cliffs which can remove a comparatively large volume of sedimentary material in one mass wasting event and which also decreases the vegetated surface area available for deposition from sediment laden waters. The volume of material removed from the marsh margin almost tripled between 1997 (169 m3) and 2001 (502 m3) following breaching of the side of a tidal creek channel, altering the patterns of margin erosion and deposition in the marsh system. During this time, however, other sheltered areas of the marsh system, such as along the tidal creek banks, showed evidence of new vegetation growth, increasing the amount of vegetated surface area available for deposition.The processes of erosion and deposition on the marsh surface exhibit considerable spatial variability, with different regions of the marsh being more or less sensitive to seasonal variability in the dominant controls influencing sediment deposition and erosion in this system, namely wave activity, vegetation, ice and water depths. A key factor in predicting how a marsh will evolve and respond to a number of different controls, e.g. sea-level rise or reduced sediment supply, is to quantify both accretion of the marsh surface and erosion of the marsh margin, evaluating the marsh system as a volumetric whole. This study demonstrates that a marsh system should be assessed in three dimensions rather than simply as a surface of accumulation. This is particularly important for open coastal marshes exposed to the erosive action of waves. |
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