PHOSPHORUS MOBILIZATION DURING WEATHERING: INSIGHTS FROM P-FRACTIONATION OF RIVER SEDIMENTS

Rivers provide an integrated weathering signal for drainage basins. Application of carefully calibrated chemical extraction techniques can reveal phosphorus-speciation of river suspended sediment. Relating P-speciation to physical-environmental characteristics of drainage basins provides insight into the weathering process. In particular, for a suite of rivers from the continental United States, such an analysis suggests that the weathering of sedimentary apatite is reaction controlled in colder, wetter catchments, whereas transport controlled dissolution appears to dominate in warmer, more arid catchments. Sedimentary apatite is vulnerable to dissolution in continental rocks and soils, but not in marine sediments. At the land-ocean transition zone, P-speciation of riverine and associated deltaic sediment suggests that ferric iron-bound phosphorus and organic phosphorus are vulnerable to dissolution, and provide biologically available phosphate to the coastal zone.