THE EFFECTS OF BIOTURBATION ON PARTICLE REDISTRIBUTION IN MEDITERRANEAN COASTAL SEDIMENT - PRELIMINARY-RESULTS

In order to quantify bioturbation processes in a coastal Mediterranean ecosystem, experiments were performed to determine sediment mixing rates resulting from macrobenthos activity. Particle flux was measured in situ for 22 days using luminophores, which are colored sediment particles with sizes ranging from 10 to 200-mu-m. In sediment depths from 0-5 cm, particle mixing was intensive due to high macrobenthos abundance. A small quantity of luminophores was transported down to a depth of 14 +/- 2 cm, where the macrofauna was represented principally by Polychetes. In a control experimental structure - without benthic fauna - no transfer of luminophores into the sediment was recorded. Sediment particle mixing measured in the ecosystem studied is intensive, and is the result of high macrobenthos activity. Different mixing modes occur with scales and rates depending on the organisms present. The luminophore profile resulting from bioturbation processes is explained by an intensive bioadvection sediment mixing added to a biodiffusive mixing with an order of magnitude of 10(-6) cm2 s-1. Tracer accumulations between 1 and 2 +/- 1 cm and between 4 and 5 +/- 1 cm are attributed to bioadvection activity of two or more distinct populations. Studies over a larger time scale have been undertaken to monitor developments in the observed subsurface maxima.