Transformation and balance of nitrogen in Aquaculture Water

Nitrogen is one of the important elements of animals and plants in water. The content and distribution of nitrogen in water have a far-reaching influence on the yield and quality of fishery culture. Therefore, it is of great significance to study the transformation and balance of nitrogen in fishery water. It can help to improve the economic benefits of aquaculture, improve fishery water quality, and reduce the pollution degree of fishery wastewater.

Generally, in fishery water bodies

The main source of nitrogen is bait. Some of the nitrogen is converted into aquatic products. Improving the feed formula and feeding technology can not only increase the conversion rate of nitrogen, but also improve the water quality. Fish excrete molecular ammonia through their gills, and microorganisms in the water convert nitrogen oxides into molecular ammonia by decomposing residual bait and fish excreta. Molecular ammonia reacts with water to form ammonium ion (NH4+) and hydroxide ion (OH-). Therefore, there is a balance between molecular ammonia and ammonium ion in water. The sum of molecular ammonia and ammonium ions is called total ammonia nitrogen (TAN). The input of a large amount of bait can increase the concentration of total ammonia nitrogen in water, so that the concentration of molecular ammonia is too high, so as to damage the health of fish. The nitrogen content in fishery water is less than the difference between bait nitrogen and fish nitrogen, because molecular ammonia can be volatilized through the water surface, and it can also be transformed into nitrate (NO3-) by nitrifying bacteria, and nitrate (NO3-) can be partially converted into nitrogen and nitrogen oxides by denitrifying bacteria to volatilize into air. Nitrogen generally exists in water deposits in the form of nitrogen oxides and ammonium ions.

Studies have shown that about 90% of the nitrogen source in fishery water comes from bait, and the rest comes from air and other sources. About 1/3 of the nitrogen is converted into aquatic products, while about 30 percent of the nitrogen is volatilized into the atmosphere in the form of molecular ammonia or nitrogen or nitrogen oxides, and another 23 percent of the nitrogen goes into the sludge. The use of aerator and water circulation can accelerate the conversion of toxic ammonia to nitrate, thus reducing the formation and volatilization of molecular ammonia. In addition, the injection of water is beneficial to the suspension of organic matter in the sludge, thus reducing the formation of sludge. The addition of quicklime to the acidic water body can prevent the water quality from becoming acidic, which is beneficial to nitrification and denitrification of nitrogen. In addition, the addition of a small amount of bacteria or enzymes may contribute to the beneficial transformation of nitrogen.