Effects of natural and artificial Thalassia on rates of sedimentation

Sediment traps were used to measure the rate of deposition in a Thalassia seagrass meadow and in an adjacent (sandy) grass-free area. The average depositional rate of mud in the Thalassia bed was 4.96 g trapˉ¹ weekˉ¹, and in the sandy area, it was 3.04 g trapˉ¹ weekˉ¹ in the summer. In winter, these rates were 1.60 and 1.50 g mud trapˉ¹ week ˉ¹, respectively.Electromagnetic current-meter measurements showed that the mean flow velocity in the grass-free area is higher than in the seagrass area. Therefore, the increased depositional rate of mud within the seagrass is due to slowing of water currents by the grass blades. Confirmation of the blade baffle effect was obtained by placing a 1-m² plot of artificial Thalassia in a grass-free area. Sediment traps in the artificial Thalassia contained 5.45 g mud trapˉ¹ weekˉ¹ as compared to 3.04 g mud trapˉ¹ weekˉ¹ in the adjacent grassfree area in summer. In winter, these rates were 1.82 and 1.50 g mud trapˉ¹ weekˉ¹, respectively.Epiphytes in the Indian River Lagoon had no detectable effect on the amount of mud deposited in Thalassia beds.