Nutrient discharge from aquaculture operations in function of system design and production environment

In aquaculture, nutrient loading is defined as the difference between nutrients supplied with fertilizers and feed and nutrients harvested in the form of finfish, crustaceans, molluscs and seaweeds. On average, the production of finfish and crustaceans results in a net nutrient loading, while for the production of molluscs and seaweeds the nutrient loading is negative. In marine and brackish water aquaculture, on a global scale, more nutrients are extracted than added to the environment. However, in freshwater, more nutrients are loaded than extracted. In 2008, the global aquaculture production of finfish and crustaceans resulted in an environmental loading of 1.7 million metric tonnes of nitrogen ( N ) and 0.46 million metric tonnes of phosphorus ( P ). This nitrogen loading represents 0.9% of the human input to the N ‐cycle and 0.4% of the global N ‐cycle. For phosphorus, the loading from finfish and crustacean aquaculture represents 2.3% of the global annual fertilizer supply. With cage aquaculture, nutrients are directly discharged to the environment. Mitigation measures should be shared equally between all polluters involved. For land‐based aquaculture, the development of water re‐use systems is still in its infancy. Although still a minor contributor to global aquaculture production, recirculation technology shows that control and mitigation of pollution from aquaculture is possible. A 15–20 year goal should be to have all inland aquaculture operations applying water re‐use and purification technology and generating useful (waste) outputs in addition to standard aquaculture products.