The estuary of the Palmones River is a small, shallow and eutrophic system, located in the South of Spain. Presently, it is dominated by the fast-growing macroalgae Ulva rotundata Bliding and Enteromorpha prol´ıfera J.G. Agardh, which respond efficiently to extreme nutrient input. The influence of macrophytes on phosphorus accumulation in sediment, over a long time-scale, was studied in this work. Different fractions of bound phosphorus were measured in four types of sediment: bare sediment (acting as control), sediment with Ulva, sediment with Enteromorpha, and sediment with Sarcocornia perennis perennis (L.) A.J. Scott, a chenopodiacean living on the border of the salt marsh. The results show that ulvaceans favour phosphorus storage in the sediment, throughout the settling of easily degradable organic matter and the subsequent retention of the phosphate being released from the sediment
