Orthophosphate 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. Orthophosphate is the form of phosphorus which is directly ready to be used by the plants, and therefore, immediately acts as fertilizer when discharged in water bodies.
How is it measured?
Guanabara Basin
Orthophosphate was measured at approximately 55 stations between 2013-2015. The proportion of time that orthophosphate was below the threshold at each station was calculated and then spatially averaged into reporting regions.
Data is provided by INEA.
Each sample is compared to a threshold to calculate a score from 0 to 100. All sample scores are averaged for each sampling location to reach a station score. All stations in each region are averaged to a region score. All regions are averaged to the overall indicator score.
Threshold levels
The orthophosphate threshold for the Basin is 0.1 mg/l.
The orthophosphate threshold was determined using the Class 2 Freshwater value from CONAMA for total phosphorus. The threshold for total phosphorus was used, because while INEA monitors orthophosphate, Brazilian CONAMA Resolution only has a threshold value for total phosphorus. The Class 2 Freshwater Total Phosphorus threshold for lotic habitat was used (0.1 mg/l) because rivers are moving waters.