Phosphorus Biogeochemistry and Wetland Function: The State of Our Understanding.

Worldwide phosphorus flows are estimated at 37 million tons per year, with 22 million tons annually being added from phosphate mining. However, economically recoverable supplies are estimated to be gone within the next 100 years (Vaccari 2009). Agricultural production as we know it depends on this essential element, but fertilizer runoff and wastewater discharge have led to massive eutrophication problems in water bodies worldwide and may in part be responsible for the offshore “dead zones”, like the 20,000 km2 found in the Gulf of Mexico. Is the “Gulf dead zone” due to the massive loss of wetland nutrient filtering capacity in the nation’s heartland or simply over fertilization? Wetlands often considered the key filtering or storage systems for nutrients on the landscape have been shown to treat nitrogen inputs effectively but have not proven to be an efficient ecosystem for the storage of P and in fact are often a source of P, even in constructed wetlands. While thousands of research studies have focused on P biogeochemistry in wetlands there have been few comprehensive analyses of what we understand and don’t about phosphorus cycling, P limitations and the role P has in wetland functioning on the landscape. In this paper I address a series of questions and current research that may help us better comprehend the complexity of P biogeochemistry in wetland systems. For example, for more than 50 years we have focused on measuring total phosphorus and SRP as our key measurements. Are these forms really the most important species of P we need to measure? What soil minerals control P availability and under what redox states, pH and C conditions? When does P control productivity, decomposition or C throughput in wetlands? Long-term phosphorus (P) storage is often related directly to the amount of P stored as organic P (OP) in peat based wetlands. However, what proportion of this if any is available to organisms within the ecosystem or what is the amount of OP that is exported as dissolved organic P (DOP) from wetlands? A comparative analysis of new studies from the literature as well as current research will be used to address these and other questions and provide a modern analysis of the importance of phosphorus to our wetland world.