PHOSPHATE DYNAMICS TIED TO SEDIMENT DISTURBANCES IN ALFACS BAY (NW MEDITERRANEAN)

Field and laboratory experiments were performed on the sediments of an estuarine bay (Alfacs Bay, Spain, NW Mediterranean) to study the influence of sediment disturbances on phosphate dynamics. Massive release of soluble reactive phosphorus (SRP) from the sediment was found after 3 h of bell-jar incubations in resuspension conditions. Suspension of sediment particles in laboratory experiments showed fluctuating behaviour characterized by quick alternation between SRP retrieval from and release to the water under low SRP concentrations, and an exponential SRP decrease under high SRP concentrations. Besides raising SRP decay rates, resuspension of particles had the net effect of increasing SRP concentrations in the water column. The phosphate dynamics in resuspension conditions is explained on the basis of 2-step sorption and P-buffer exchange mechanisms. These are discussed in the scope of the processes involved (biotic and abiotic SRP uptake), nitrogen and phosphorus budgets in Alfacs Bay, phosphorus availability, and the survival of phytoplankton populations. Furthermore, the role of sediments in periodic storage of nutrients coupled to hydrodynamic conditions is addressed.