Influence of biota on spatial and temporal variation in sediment erodability and material flux on a tidal flat (Westerschelde, The Netherlands)

Annular flumes were used to quantify benthic-pelaqic exchanges in relation to changes in current velocity and sediment biota. Various physical, chemical and biological parameters were determined for 4 sites on the Molenplaat tidal flat in the Westerschelde (The Netherlands) during 2 field campaigns in May-June and August-September 1996. These Pcluded: the mass of sediment eroded, maximum and mean erosion rates, critical erosion velocity (U crit ), suspension feeding/biodeposition rate, oxygen and ammonium fluxes, density of macrofauna species, chlorophyll a (chl-a), colloidal carbohydrate, and physical properties of the sediment. The study showed marked and statistically significant spatial and temporal differences in the potential for sediment erosion. Sites in the centre of the tidal flat were less erodable than those on the edge. All sites on the tidal flat had a significantly (p crit and lower erosion rates) compared to September. The presence of a well-developed microphytobenthos community in June resulted in a statistically significant relationship between U crit and chl-a/colloidal carbohydrate (r = +0.85, p = 0.01). There was a significant relationship (r = +0.88, p = 0.005) between sediment erodability (mass of sediment eroded and erosion rate) and the density of the clam Macoma balthica , a major bioturbator of the surface sediments. Analysis of the data also demonstrated significant relationships between clearance rate and Cerastoderma edule biomass (r = +0.91, p C. edule biomass (r = +0.92; p