Publication Abstract

Changes in biota and sediment erodability following the placement of fine dredged material on upper intertidal shores of estuaries

Temporal changes in biota and sediment erodability following the placement of fine dredge material on the upper intertidal shores of estuaries in Essex, England

J. Widdows, M.D. Brinsley, N.D. Pope, F.J. Staff and S. Bolam 

Fine sediments derived from maintenance dredging in the estuarine and coastal zone may provide a potential resource for enhancing or creating intertidal habitats (i.e. ‘beneficial use’ schemes). This study investigates the temporal changes in biota and sediment erodability following the placement of fine dredge material on the upper shore at two trial ‘beneficial use schemes’ in Essex estuaries, England. There was a rapid process of sediment consolidation and dewatering within 7 days, reaching bulk densities and water contents typical of intertidal sediments within six weeks. This was accompanied by an increase in critical erosion velocity (Ū_crit) from 0.13 to 0.25 m s^-1 and a reduction in sediment erosion by two orders of magnitude. There was evidence of marked spatial (inter-site) and temporal (seasonal) variation in sediment stability which correlated with changes in the abundance of key species. The temporal changes in sediment erodability reflected the nature of benthic assemblages established during the recovery period (up to 19 months). There were statistically significant correlations between microphytobenthos chlorophyll a, extracellular polymeric substances (EPS) and Ū_crit, and between total abundance of tube building / dwelling polychaetes and oligochaetes (minus Hediste diversicolor) and mass of sediment eroded at 0.3 m s^-1.  The annual salt marsh plant, Salicornia europaea, was also found to reduce sediment erodability by reducing near-bed flows by up to 90%, as well as increasing Ū_crit. These biota represented ecosystem engineers with a functional role as bio-stabilisers. There were also significant correlations between Ū_crit and the abundance of Hediste diversicolor and Corophium volutator, and between sediment mass eroded at 0.3 m s^-1 and Hediste diversicolor and Hydrobia ulvae. These biota represented ecosystem engineers with a functional role as bio-destabilisers. Most of the recorded correlations were consistent with previous species-specific flume studies establishing density dependent effects on sediment erodability, thus indicating cause-effect relationships.

Reference:

J. Widdows, M.D. Brinsley, N.D. Pope, F.J. Staff and S. Bolam (2006) Changes in biota and sediment erodability following the placement of fine dredged material on upper intertidal shores of estuaries. Marine Ecology Progress Series, 319: 27-41

J. Widdows, M.D. Brinsley, N.D. Pope, F.J. Staff, S.G. Bolam* and P.J. Somerfield

Marine Ecology Progress Series, 319: 27-41