Currents and Sediment Transport in Mangrove Forests

A field study of the tidal currents, cohesive sediment dynamics and transport of organic carbon in a highly vegetated mangrove swamp was carried out at Middle Creek, Cairns, Australia. The interaction of tidal currents and the vegetation generated jets, eddies and zones of stagnant waters which were numerically modelled. A high value of the Manning friction coefficient ( n=0·1) was derived by the dense vegetation. About 80% of the suspended sediment brought in from coastal waters at spring flood tide was trapped in the mangroves, corresponding to about 10-12 kg of sediment m ^-1creek length/spring tide, resulting in a rise of the substrate by about 0·1 cm year ^-1. The selective trapping of clay was caused by flocculation of the finer particles in the mangroves. There was an indication of a slight inwelling of organic carbon. Creek water was readily differentiated from mangrove water by large differences in the molecular weight distribution of the dissolved organic carbon.