GEOCHEMISTRY OF DISSOLVED PHOSPHATE IN THE SEPIK RIVER AND ESTUARY, PAPUA, NEW-GUINEA

The natural regulation of phosphate in the Sepik River and Estuary, Papua, New Guinea, was investigated by fitting field measurements to a chemical model. Results indicate that ferric iron and phosphate in the river and salinity to 12 ppt in the estuary are primarily influenced by equilibration with a discrete amorphous solid phase. Dissolved ferric iron is saturated with respect to amorphous ferric hydroxide in the river and most of the estuary. Dissolved phosphorus is equilibrated with amorphous ferric hydroxide-phosphorus solid solution in river waters and the low salinity third of the plume. A modest input of phosphate, believed driven by disequilibrium, was observed at mid-estuary. Input is roughly equivalent to removal and is thought to be limited by a paucity of phosphorus in the solid phase. Oceanic fluxes of phosphorus from major Pacific Islands may not be large despite disproportionately large sediment fluxes, if other watersheds contain reservoirs of solid phosphorus as small as the Sepik River. © 1990.