CCRU Lunchtime Seminar: Linking sediment structure, hydrological functioning and biogeochemical cycling following de-embankment of restored coastal saltmarshes

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• Kate L Spencer [1], Simon J Carr [1], James A Tempest [2], Lucy Diggens [1], Gemma L Harvey [1], Michelle A Morris [1]
• Thursday 05 June 2014, 12:30-13:30
• Small Lecture Theatre, Department of Geography, Downing Site.

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Tollesbury MR site, Essex

Saltmarsh restoration (managed realignment) undoubtedly provides environmental enhancement, with vegetation quickly re-establishing following the breach of sea walls and subsequent tidal inundation of previously defended areas. However, these environments have been ‘disturbed’ by previous land use and there is little understanding of the impacts of this disturbance on wider ecosystem functions and the quality and quantity of the biogeochemical ecosystem services provided by these restored environments.

This study examines physical sediment characteristics, sediment structure (using X-ray microtomography), sub-surface hydrology (using pressure transducers), and sediment and porewater geochemistry (major and trace elements, major anions) in sediment cores collected from undisturbed saltmarshes and those restored by de-embankment.

Sub-surface sediments in restored saltmarshes have lower organic matter content, lower moisture content and higher bulk density than undisturbed sites. Using X-ray tomography a clear horizon can be observed which separates relict agricultural soils at depth with less dense and structureless sediments deposited since de-embankment. Sub-surface hydrological response to tidal flooding was subdued in the restored compared to the undisturbed site, suggesting that porewater flow may be impeded and/or flow pathways differ in restored saltmarsh sediments.

The undisturbed saltmarsh displayed typical vertical geochemical sediment profiles. However, in the restored sites total Fe and Mn are elevated at depth indicating an absence of diagenetic cycling, whilst porewater sulphate and nitrate increased at depth suggesting that vertical solute transport is impeded in restored sites. In surface sediments, though total Hg concentrations are similar, Hg methylation rates are significantly higher than in the undisturbed saltmarsh suggesting that surface anoxia and poor drainage may result in increased mobilization of Hg.

These findings have implications for the wider biogeochemical ecosystem services offered by saltmarsh restoration and highlight the need for integrated understanding of physical and biogeochemical processes.

Speakers:

Kate L Spencer [1], Simon J Carr [1], James A Tempest [2], Lucy Diggens [1], Gemma L Harvey [1], Michelle A Morris [1]

1 School of Geography, Queen Mary, University of London, Mile End Road, London, E1 4NS , UK. 2 Department of Geography, University of Cambridge

This talk is part of the Climate and Environmental Dynamics - Department of Geography series.

This talk is included in these lists:

• AUB_Cambridge Seminars
• Department of Geography
• Small Lecture Theatre, Department of Geography, Downing Site

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