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State of the Global Phosphorus Cycle

30 September - 4 October 2009

Workshop Chair(s):
Tim Crews
Alan Townsend
Peter Vitousek




About the Workshop

Roughly a generation ago, environmental scientists began a concentrated effort to document the extent, pace and consequences of human alteration to EarthÝs major biogeochemical cycles. Early work stressed the links between carbon and climate, sulfur and acid rain, and nitrogen and a suite of environmental changes. For phosphorus, the concern was eutrophication of freshwater and marine ecosystems. Such work put biogeochemistry on the policy map, with some early positive outcomes, such as the reduction in sulfur emissions in the U.S., and the recovery of the Great Lakes. In the case of the carbon and nitrogen cycles, the problems are far from solved, but the last two decades have brought an explosion of scientific knowledge on how - and why - each cycle is changing, at every scale from local to global. As a result, substantive debates on how to mitigate the environmental threats are now happening in multiple sectors of society.

Yet, compared to the state of our knowledge on C and N cycles, phosphorus lags behind. We know humans have dramatically altered the global P cycle (and continue to do so), and we know that changes in P availability can substantially alter the structure and function of both terrestrial and aquatic ecosystems. We also know that interactions among the C, N and P cycles are pervasive, and often critical to understand if one wants to predict the behavior of any one of these elements. For example, soil P availability is likely to be a significant determinant of C storage (or loss) in both intact and converted tropical forests. Likewise, P availability can regulate inputs of reactive N to the biosphere, as well as their eventual fate. However, while we know humans are changing the P cycle, we lack a quantitative picture at regional scales of how much, how fast, and in what ways. Such information is essential not only for predicting well-recognized consequences of P enrichment, such as aquatic eutrophication, but also for understanding the ways in which the global C and N cycles will continue to evolve. Finally, useful reserves of reactive P are finite, and the long term sustainability of intensive agricultural systems depends on the careful management of P reserves.

A regionally-specific assessment of the global phosphorus cycle is needed. This activity was identified as a priority at the recent AGCI Workshop ýManaging the Global N and P Cycles.ţ Like nitrogen, the majority of human-driven changes to the P cycle are linked to modern agriculture, and thus prior assessments of the N cycle will be enormously helpful to the efforts for P. For example, the rise of globalized economies and the biofuel industry over the last two decades have caused massive shifts in agriculture, causing new regional hotspots for reactive N, and a steep rise in global trade of N-containing commodities. We expect to find similar dynamics for P, and can use much of the information assembled for the N assessments as a basis for our proposed work.

The goal of this workshop was to finalize a strategy to complete the assessment, to identify components of the work that individual participants would lead, and to galvanize the entire process.