3rd UF Water Institute Symposium Abstract

Submitter's Name Daniel Childers
Session Name Plenary Session 2 - Day 1
Category Plenary Session
Author(s) Daniel L. Childers,  School of Sustainability, Arizona State University (Presenting Author)
  Is Phosphorus the Rodney Dangerfield of Sustainability Challenges?
  Daniel L. Childers Professor, School of Sustainability Arizona State University Director, Central Arizona-Phoenix LTER Program Co-Director, Urban Sustainability Research Coordination Network The “Green Revolution” has led to a three-fold increase in food production in the last 50-75 years—and a more than doubling of the human population—but increases in crop production have required a concurrent increase in the use of inorganic phosphorus (P). A sustainable P supply is not assured, though: Food production depends on mineral P supplies that are non-renewable and are being depleted. Phosphorus is a non-substitutable necessity for all life. My presentation will address three objectives: 1) a brief review of the “human P cycle” and its implications for a sustainable future; 2) an overview of P-related urban research being conducted in Phoenix, and; 3) a short discussion of the “wicked problem” of P sustainability and, in particular, its comingling with many other more obvious sustainability challenges. Urban environments will increasingly dominate the landscape. Two recently published studies, co-authored largely with students, examine how P cycles in the Greater Phoenix Metropolitan Area. In one, we used a spatially explicit budget of the pools and fluxes of P to show that inputs are dominated by direct imports of food and fertilizer for local agriculture while most outputs were small, including water, crops, and material destined for recycling. Human density and associated infrastructure, especially asphalt, dominated the distribution of P pools across Phoenix. Phosphorus fluxes were dominated by agricultural production, with agricultural soils accumulating P. Phosphorus cycling was most affected by water management practices that conserve and recycle water, reducing water-borne losses from the urban ecosystem. Our budget explicitly linked processes that affect P cycling across space with the management of other resources (e.g., water). Our second study examined the food system in Phoenix as one of the most important contributors to the way P cycles through cities. In particular, we focused on the urban-agricultural interface between 1978 and 2008. We found that the proximity of urban populations and agricultural land uses, the co-location of dairies and feed production, the temporal switching of alfalfa and cotton production, and low runoff in this arid climate all facilitated serendipitous P recycling. Currently P is not strongly regulated or intentionally managed in most systems—urban, rural, or otherwise—but farmer behavior, market forces, and policies related to water and recycling unintentionally affected P cycling. Again, this study demonstrated the need to move towards more holistic resource management strategies to enhance urban sustainability. At a more global scale, the P sustainability challenge may not be receiving adequate respect for several reasons. First and foremost is the apparent lack of crisis. In fact, recent crises of food shortages and volatile fossil fuel costs have largely masked underlying P problems. Because mineral P deposits are not distributed evenly across the globe, future P scarcity will have national security implications. Phosphorus-induced food shortages are likely, particularly in developing countries where farmers are more vulnerable to volatile fertilizer prices. Sustainable solutions to such a future exist, and involve: 1) strategies that close the loop on the human P cycle, and; 2) approaches that embed the P issue in the complex and interconnected web of energy and resource sustainability challenges. Ultimately, only holistic strategies that deliberately couple P management with energy, water, and other resources are likely to achieve sustainability goals. And our very ability to feed ourselves may depend on the success of those goals.