Sediment resuspension in a shallow Thalassia testudinum banks ex König bed

Abstract

Seagrass beds have been described as depositional environments due to their capacity to reduce current velocity and to attenuate wave energy. As sediment accretes in seagrass beds, they become shallower and may reach a depth where an equilibrium between deposition/erosion and plant mortality maintains the depth of the bed relatively constant. Although data on sediment deposition in seagrass beds is available, little is known about sediment resuspension in these plant communities. In the present study, suspended sediment concentrations in a Thalassia testudinum bed and an adjacent unvegetated area were compared over part of a neap tide and correlated with the prevailing hydrodynamic conditions. Sediment resuspension in the unvegetated area was induced mainly by waves while in the seagrass meadow it was caused by intensification of speed near the bottom during the flood tide. Under these conditions, suspended solid concentrations were higher within the meadow than in the adjacent unvegetated area. The sediment resuspension within the meadow during non-extreme conditions (neap tide and relatively calm winds) suggests that sediment resuspension is an integral part of sedimentary processes occurring in healthy seagrass beds which may be contrary to the commonly-held perception that seagrass beds are only sinks and not sources of suspended matter.