Mechanisms for release of sediment-bound phosphate to water and the effects of agricultural land management on fluvial transport of particulate and dissolved phosphate

Sediment-bound phosphate includes organic and inorganic forms, but the inorganic fraction contains most of the P that can be released into water. The non-apatite inorganic P (NAIP) fraction of sediment-bound phosphate varies considerably with geochemistry and anthropogenic additions (fertilizer, livestock wastes, P adsorbed from municipal wastewater discharges). A small fraction of the NAIP is sufficiently labile to desorb into water, and this release can be described by dissolution or adsorption/ desorption mechanisms. Agricultural practices, such as phosphate fertility management and conservation tillage, which affect the levels of phosphate and sediment leaving the land, will determine the partition of sediment-bound P and dissolved P in water draining into lakes, with implications for the availability of that phosphate to phytoplankton.