Nitrogen is a nutrient of great environmental concern, because when in excess it is responsible for eutrophication. All living organisms need nutrients to grow and the nutrients need to be in the water to support the food chain. However, nutrients in excess disturb the natural food chain because some organisms proliferate at the expense of others. This is the case of algae, which grow faster in nutrient enriched environments requiring high demand of oxygen for decomposition when they die. Of all forms of nitrogen, DIN, Dissolved Inorganic Nitrogen (nitrates+nitrites+ammonium) is of great interest because it is the most bioavailable form of nitrogen used by algae.
How is it measured?
Guanabara Bay
The concentration of nitrates, nitrites and ammonium were measured at approximately 20 stations between 2013-2015 and then summed up to obtain the DIN. The proportion of time that dissolved inorganic nitrogen was below the threshold at each station was calculated and then spatially averaged into reporting regions.
Guanabara Basin
The concentration of nitrates, nitrites and ammonium were measured at approximately 55 stations between 2013-2015 and then summed up to obtain the DIN. The proportion of time that dissolved inorganic nitrogen 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
In the National Council of the Environment (CONAMA) Brazilian resolution there is no specific DIN threshold but there are individual thresholds for ammonium, nitrate, and nitrite. The thresholds for each considering a Class 2 saline water are:
- Nitrate = 0.7 mg/l
- Nitrite = 0.2 mg/l
- Ammonium = 0.7 mg/l
By summing these three values the threshold for DIN could be determined.
The dissolved inorganic nitrogen threshold for the Bay is 1.6 mg/l.
The dissolved inorganic nitrogen threshold for the Basin is 1.6 mg/l.
The Brazilian National Council of the Environment (CONAMA) Resolution has thresholds for Class 2 freshwater for nitrate, nitrite and ammonium. However, when we summed the values the threshold for DIN would be 11.5 mg/l. This is a very high value which is not protective of the ecosystem and would not support fish in the rivers. Thus, the Class 2 Saline waters threshold was used for the Bay and the Basin.