Russell,M.J., Weller,D.E., Jordan,T.E., Sigwart,K.J. and Sullivan,K.J.(2008): Net anthropogenic phosphorus inputs: spatial and temporal variability in the Chesapeake Bay region. Biogeochemistry, 88, 285-304.


 We estimated net anthropogenic phosphorus inputs (NAPI) in the Chesapeake Bay region. NAPI is an index of phosphorus pollution potential. NAPI was estimated by quantifying all phosphorus inputs and outputs for each county. Inputs include fertilizer applications and non-food phosphorus uses, while trade of food and feed can be an input or an output. The average of 1987, 1992, 1997, and 2002 NAPI for individual counties ranged from 0.02 to 76.46 kg P ha-1 year-1. The overall area-weighted average NAPI for 266 counties in the region was 4.52 kg P ha-1 year-1, indicating a positive net phosphorus input that can accumulate in the landscape or can pollute the water. Large positive NAPI values were associated with agricultural and developed land cover. County area-weighted NAPI increased from 4.43 to 4.94 kg P ha-1 year-1 between 1987 and 1997 but decreased slightly to 4.86 kg P ha-1 year-1 by 2002. Human population density, livestock unit density, and percent row crop land combined to explain 83% of the variability in NAPI among counties. Around 10% of total NAPI entering the Chesapeake Bay watershed is discharged into Chesapeake Bay. The developed land component of NAPI had a strong direct correlation with measured phosphorus discharges from major rivers draining to the Bay (R2=0.81), however, the correlation with the simple percentage of developed land was equally strong. Our results help identify the sources of P in the landscape and evaluate the utility of NAPI as a predictor of water quality.

Keywords: Anthropogenic; Budgets; Nutrients; Phosphorus; Watershed』

 Study area
 Phosphorus budgets
 Phosphorus fertilizer application
 Net P import or export in human food and animal feed
 Food and feed consumption and non-food P
 Crop production
 Grazing livestock
 Pasture production consumed by grazers
 Livestock products for human consumption
 Geographic and temporal analysis
 Proxy variables for NAPI
 Discharge of NAPI
 County characteristics
 Net anthropogenic phosphorus inputs and geographic differences
 Temporal changes
 Phosphorus fluxes
 Proxy variables
 Percentage of NAPI discharged from Chesapeake Bay watershed
 Decoupled production and consumption
 Trade of feed and food
 Other possible fates of P
 NAPI's relationship to nutrient discharges
 Temporal trends

Fig. 1 Flow of phosphorus through agricultural and human reservoirs in the Mid-Atlantic region (including counties in NY state that overlap the Chesapeake Bay watershed). Numbers are average fluxes (kg P ha-1 year-1)

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