Phosphorus

Total phosphorus is an indicator of too much phosphorus in the water. Phosphorus attaches to sediment particles, so phosphorus and sediment pollution are linked. Phosphorus is an essential nutrient for all plants and animals. But too much phosphorus in the water causes algae to grow in large, dense algal blooms, which depletes oxygen for fish and other marine organisms.

When sediment runs off land, it can carry nutrients like phosphorus into the water.

How is it measured?

Chesapeake Bay

Total phosphorus was measured at approximately 159 stations up to 8 times during the periods of interest (April to October). Total phosphorus is the amount of dissolved phosphate and organophosphate in the water. The proportion of time that total phosphorus was above the threshold at each station was calculated.

Chesapeake Watershed

Total phosphorus was measured year round from 2012-2017. Total phosphorus is the amount of dissolved phosphate and organophosphate in the water. The proportion of time that total phosphorus was above the threshold at each station was calculated. Station scores were averaged to HUC12. HUC12 scores were area-weighted to the reporting region scores.

Threshold Levels

Chesapeake Bay

Thresholds were determined by salinity regime.

Salinity Regime Reference Community Thresholds (mg L-1)*
Tidal Fresh ≤0.06
Oligohaline ≤0.07
Mesohaline ≤0.04
Polyhaline ≤0.05

*EcoCheck (2011)

Chesapeake Watershed

Thresholds were determined by bioregion.*

Score Piedmont, Ridges, and Valleys Thresholds (mg L-1) Coastal Plain thresholds (mg L-1)
5 <0.01 <0.02
4 ≥0.01 - <0.03 ≥0.02 - <0.06
3 ≥0.03 - <0.05 ≥0.06 - <0.09
2 ≥0.05 - <0.06 ≥0.09 - <0.12
1 ≥0.06 - <0.09 ≥0.12 - <0.17
0 ≥0.09 ≥0.17

*EcoCheck (2013)