Introduction
The growth of living organisms is naturally limited by the supply of essential nutrients such as nitrogen and phosphorus. An excessive release of these substances into the environment reduces this limitation with a consequent reduction in oxygen concentration and therefore negative effects on the entire ecosystem. The use of agricultural fertilizers or industrial discharges rich in nitrogen and phosphorus are among the main causes of the eutrophication phenomenon. However, this effect must be distinguished between soils and waters as the behavior of fauna and flora is different for the two habitats. In this article, we will focus exclusively on analyzing eutrophication in surface waters. (for eutrophication in soil, refer to the private section). The most evident effect is the excessive growth of aquatic algae; whose overconsumption of oxygen is the cause of its reduction in waters.
The calculation model
The “oxygen demand” of a body of water is defined as the amount of oxygen it requires to reach a state of natural purity, representing the measure of its pollution by reducing substances. The units of measurement used are BOD (Biological Oxygen Demand) and COD (Chemical Oxygen Demand), both expressed in kg of O2. The standardization of eutrophication is done by reporting the quantities of the substances analyzed in kg of NO3 equivalents or kg of PO4- equivalents. The increase in nitrogen and phosphorus concentrations can be aggregated into a single potential contribution to biomass formation called eutrophication potential (NP - Nutrification Potential).
