REACTIONS OF PHOSPHORUS WITH SEDIMENTS IN FRESH AND MARINE WATERS

The interactions of P with soils and sediments are examined in the con text of transport processes from land, through rivers to estuaries and coastal waters. In soil erosion, selective size: fractionation and pr eferential sorption to finer solids is crucial in the transport of P t o water courses. Problems in quantifying the sorption affinity and equ ilibrium phosphate concentration (EPC) of mixtures of different soils and sediments are identified. Riverine transport of P by suspended sol ids is usually very important and examples of the changes in the amoun t and composition of particulate P (PP) concentration during storm eve nts are discussed. Increased P content of solids during the first autu mn storms, probably reflect the resuspension of accumulated stream bed -deposits. The fate of P in estuaries and their importance as possible long-term sinks of P are discussed. The relatively high concentration s of dissolved P associated with riverine inputs are to some extent bu ffered by the relatively high concentrations of suspended sediments re sulting from tidal flows. Phosphorus may be released during transport to the sea due to decreases in the EPC, increases in salinity and rele ase from bottom sediments as a result of low oxygen conditions.