Phosphorus (P) is an essential element for all life and, under ambient conditions, is tightly cycled within the biosphere. However, human action has significantly altered the natural P cycle. Phosphate mining has depleted geological P reserves, while increased inputs of P to terrestrial ecosystems have enhanced fluxes of P to lakes and the oceans. On land, the soil system is a biogeochemical fulcrum, responding to the perturbed P cycle and ultimately determining the magnitude and timing of inorganic and organic P fluxes between terrestrial and aquatic ecosystems. Meanwhile in freshwater and marine aquatic environments, P inputs determine the trophic state of the ecosystem, while burial in sediments returns P to the geological sink. Throughout the P cycle, redox conditions play a key role in transformations and mobility of P.

This session investigates the P cycle in soil and aquatic systems across a range of scales. Contributions include:

• studies of soils and sediments on the pore and ped scales, including the application of novel techniques to study P
• investigations of the redox chemistry of P in natural systems
• meta-analyses of input-cycling-export of P from soils at multiple scales
• phosphorus cycling in coastal seas, including its role in coastal eutrophication and burial in marine sediments
• global P cycling on geological timescales

Keynote: Matt Pasek, University of South Florida