Phosphorus Fertilizer Pollution

Risksv03.00 credits/per_km2

Responsible:Niccolò Calandri

Phosphorus Fertilizer Pollution — Environmental P₂O₅ Loss from Agriculture

Overview

Phosphorus fertilizer pollution quantifies the fraction of phosphorus (as P₂O₅) applied to agricultural land that is lost to the environment through erosion and surface runoff. Phosphorus is a critical macronutrient for crop production, but when it enters aquatic ecosystems in excess, it becomes one of the most damaging pollutants for freshwater and coastal biodiversity.

Unlike nitrogen, phosphorus binds strongly to soil particles and moves primarily via surface runoff and sediment erosion rather than leaching. When phosphorus-laden sediments reach rivers, lakes, and estuaries, they fuel eutrophication — the excessive growth of algae and cyanobacteria. These algal blooms deplete dissolved oxygen upon decomposition, creating hypoxic dead zones where fish, invertebrates, and submerged vegetation cannot survive. Toxic cyanobacterial blooms further threaten aquatic organisms and drinking water supplies.

This layer uses the NPKGRIDS v1.08 dataset (Nature Scientific Data, University of Minnesota / Global Landscapes Initiative), which provides spatially explicit fertilizer application rates for 175 crop classes worldwide at ~10 km resolution (5 arc-minutes). A 15% loss fraction — representing the estimated share of applied P₂O₅ lost through erosion and runoff — is applied to derive the pollution map. The output is upscaled via bilinear interpolation to approximately 1.7 km resolution.

Calculation Methodology

Data access — NetCDF files containing per-crop P₂O₅ application rates (kg P₂O₅/ha/year) are read from AWS S3 via xarray
Aggregation across crop classes — Application rates are summed across all 175 crop classes, yielding the total P₂O₅ application rate per pixel
Pollution fraction application — A 15% loss fraction is applied to the total rate:
```
P_pollution = P2O5rate_total × 0.15
```
This fraction accounts for phosphorus losses predominantly through soil erosion and surface runoff
Bilinear interpolation — The native ~10 km raster is resampled to ~1.7 km output resolution (6× upscaling)
Visualization — The gnuplot2 colormap with PowerNorm (gamma = 0.4) is applied, mapping pollution values from 0 to 1,598 kg/ha

Data Sources

Code	Name	Provider	Resolution	Availability
`WRD_NPKGR_20`	NPKGRIDS v1.08	Nature Scientific Data / University of Minnesota	~10 km (5 arc-min)	2020-01-01 — 2020-12-31

Quality Range and Levels

Indicator	Unit	Range	Inverted
`fertilizer_pollution_p`	kg P₂O₅/ha/yr	[0, 20, 60, 150, 300, 1600]	Yes

Inverted = Yes: a higher value indicates greater phosphorus pollution and worse conditions for aquatic biodiversity.

Level	kg P₂O₅/ha/yr	Interpretation
A (Excellent)	0 – 20	Minimal phosphorus loss — negligible eutrophication risk
B (Good)	20 – 60	Low phosphorus loss — limited impact on water bodies
C (Moderate)	60 – 150	Moderate phosphorus loss — measurable eutrophication potential
D (Poor)	150 – 300	High phosphorus loss — significant algal bloom and hypoxia risk
E (Critical)	> 300	Very high phosphorus loss — severe eutrophication, dead zones likely

Technical Notes

Sum across all 175 crop classes yields the total P₂O₅ application rate per pixel
The 15% loss fraction for phosphorus reflects erosion-dominated pathways (compared to 50% for nitrogen and 30% for potassium)
Bilinear interpolation from ~10 km to ~1.7 km enhances spatial representation but does not add sub-pixel detail
Actual phosphorus loss rates vary with soil type, slope, rainfall intensity, tillage practices, and buffer strip presence
Data represent the year 2020

References

Lu, C. & Tian, H. (2017). "Global nitrogen and phosphorus fertilizer use for agriculture production in the past half century". ESSD, 9(1), 181–192. DOI: 10.5194/essd-9-181-2017
Lun, F. et al. (2024). "NPKGRIDS". Nature Scientific Data. https://www.nature.com/articles/s41597-024-04030-4
Carpenter, S.R. et al. (1998). "Nonpoint pollution of surface waters with phosphorus and nitrogen". Ecological Applications, 8(3), 559–568.
Schindler, D.W. (2006). "Recent advances in the understanding and management of eutrophication". Limnology and Oceanography, 51(1), 356–363.

Data Sources & References

Sources

WRD_NPKGR_20

Methodology

The Fertilizer Pollution P map shows phosphorus (P2O5) pollution using NPKGRIDS v1.08. P2O5 application rates are summed over 175 crop classes. A 15% loss fraction (erosion and surface runoff) is applied. Data is bilinearly interpolated from ~10 km to ~1.7 km and displayed with gnuplot2 colormap (PowerNorm gamma=0.4).