Phosphorus Inventory for the Conterminous United States (2002-2012)

Area of Science:

• Environmental Science
• Water Quality Management
• Nutrient Cycling

Background:

• Efforts to reduce phosphorus (P) pollution for water quality improvement are not consistently effective.
• Lack of standardized P input/output data hinders evaluation of watershed management practices.

Purpose of the Study:

• To create a standardized inventory of phosphorus (P) trends across the conterminous United States.
• To assess P fluxes from agricultural, atmospheric, and human sources at the subbasin scale.

Main Methods:

• Compiled publicly available datasets for P fluxes (agricultural, atmospheric, human waste, point source) for 2002, 2007, and 2012.
• Developed estimates of agricultural legacy P surplus from 1945 to 2001.
• Analyzed P trends at the 8-digit Hydrologic Unit Code subbasin scale.

Main Results:

• Agricultural P inputs (fertilizer, manure) frequently exceed crop removal, leading to legacy P accumulation.
• Increased atmospheric P deposition in the Rockies may impact surface water P concentrations.
• Urban P fluxes declined in some areas due to P-reduction policies, despite population growth.

Conclusions:

• Standardized P accounting is essential for coordinating targeted interventions to reduce national water P concentrations.
• Understanding both contemporary and legacy P sources is key to effective water quality management.