The effects of crab bioturbation on Mid-Atlantic saltmarsh tidal creek extension: Geotechnical and geochemical changes

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Understanding saltmarsh response to sea-level rise is critical for management and mitigation of these valuable coastal areas. However, comprehensive field studies of sea-level driven changes to the marsh landscape that consider combined biological, geological, and hydrodynamic interactions are rare. This study analyzes ecophysical feedbacks from crab colonization and bioturbation on geotechnical and geochemical properties of the soil in a Mid-Atlantic Spartina alterniflora saltmarsh. The study area is within a marsh that is experiencing creek extension due to accelerated sea-level rise and increasing periods of marsh inundation. Measurements of redox potential, pH, belowground biomass, and soil strength reveal that intense crab bioturbation by Sesarma reticulatum significantly changes the biogeochemical properties of the soil. Oxidized conditions in the upper 10-15 cm of the marsh induced by burrowing causes enhanced degradation of S. alterniflora belowground biomass (roots and rhizomes, reduction from 1.9 ± 0.6 kg/m to 1.1 ± 0.4 kg/m ), which reduces the structural integrity of the soil. This process ultimately increases the erosion potential of the sediment in creek head areas (documented by a reduction in shear strength from 10 ± 7 kPa to 2 ± 1 kPa), facilitating creek extension in order to accommodate tidal flows. The pervasiveness of similar tidal creek morphology in southeast Atlantic saltmarshes suggests this process is occurring in other marshes with a moderate tidal range undergoing sea-level rise. © 2012 Elsevier Ltd. 2 2

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Estuarine, Coastal and Shelf Science

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