What Is the Nitrogen Cycle?

Nitrogen Cycle is the material cycle of the ecosystem that describes the process of conversion between nitrogen and nitrogen-containing compounds in nature.

Nitrogen (N) is the most important component and an important ecological impact factor in natural wetland ecosystems. Its main sources are runoff input, atmospheric sedimentation, and biological nitrogen fixation. The migration and transformation of N in natural wetlands occur mainly in the wetland succession zone, which is a buffer zone with relatively strong biogeochemical activities. It is often regarded as the N source, N sink, and N converter of the wetland. The N attenuation in the succession zone is mainly carried out through denitrification, anaerobic ammonia oxidation, and wetland vegetation absorption. ^[2]

Artificial nitrogen fixation, that is, the production and application of chemical nitrogen fertilizers, large-scale cultivation of crops with biological nitrogen fixation capabilities such as legumes, and combustion of fossil fuels to produce NO and NO ₂ . man-made

Nitrogen is one of the three elements of plant nutrition, and is also a nutrient component of humans and animals. Three-quarters of the gas in the air is nitrogen, but nitrogen exists in various forms, and their conversion and utilization are very complicated. We commonly use chemical synthetic fertilizer nitrogen. After entering the farmland, some of them enter the soil with animal and plant residues and human and animal excrement nitrogen, and undergo various transformation processes driven by microorganisms to form a variety of Nitrogen gas. Some of them can directly migrate to the water body. Excessive nitrides cause nitrogen pollution in the water body, which not only endangers human health, but also becomes a factor of eutrophication of the water body. Nitrogen dioxide is also an important greenhouse gas, which enhances the greenhouse effect after entering the atmosphere. It can be seen only that nitrogen is not only an essential element of life, but also related to the human living environment. ^[3]

Causes of nitrogen imbalance in the nitrogen cycle

Nitrogen in the form of nitrogen in nature is called inert nitrogen, which has no negative impact on the ecological environment. Before the industrialization of production, the nitrogen balance was balanced in the nitrogen cycle system, that is, the nitrogen fixation and deamination effects were basically flat. When nitrogen is synthesized or burned by the chemical industry, it will be activated to form substances such as nitrogen oxides and nitrogen hydrides, which strengthens the role of nitrogen fixation. There are three ways to activate nitrogen: one is to artificially fix nitrogen to convert nitrogen in the air into ammonia; the other is to burn coal, oil, and natural gas in industrial production; and the third is the role of nitrogen-fixing plants. In the circulatory system, the balance of nitrogen balance will be related to the positive or negative effects of active nitrogen on human health and the living environment. Excessive "activation" of nitrogen will cause the original nitrogen fixation and deammonia to be out of balance, and the nitrogen cycle will be seriously disrupted. More and more activated nitrogen will begin to migrate to the atmosphere and water body in excess, and the cycle will begin to become ill, leading to global environmental problems. . Since the 1970s, humans have conducted extensive and in-depth research on the nitrogen cycle in ecosystems. SCOPE (International Commission on Science and Technology) raised global nitrogen overload as a potential environmental issue and chemical time bomb.

The dangers of nitrogen cycling

Nitrogen is one of the necessary nutrients for the normal growth and development of plants, so it is also the main limiting factor to improve productivity. In the agricultural ecology, if there is no active nitrogen, soil fertility, yield, protein content, soil organic matter depletion, soil erosion, and even desertification will be reduced. In the humid tropics, the soil will be strongly weathered and leached, and soil nutrients will be barren. Soil nitrogen and phosphorus have become restricted nutrients. Therefore, we must appropriately increase the nitrogen fertility in the soil, promote the sustainable development of agriculture, and ensure food security (enough calories) and nutritional security (provide all necessary nutrients, including protein).

Harm of nitrogen pollution in the nitrogen cycle

(1) Under the action of microorganisms, ammonia converted from nitrogen will form nitrates and acidic hydrogen ions, causing acidification of soil and water ecosystems and reducing biodiversity. In addition, ammonium is highly toxic to fish, so it is necessary to closely monitor the concentration of ammonium discharged from wastewater treatment and plants. In order to avoid the loss of fish death, the nitrification of ammonium in the water should be carried out before discharge, and it is an attractive solution to provide oxygen for nitrifying bacteria ventilation on land.

(2) Too much nitrogen in water leads to eutrophication. The consequences of eutrophication of water bodies are firstly the destruction of water resources, reducing the value of water use, directly affecting human health, and at the same time increasing the cost of water treatment; secondly, it causes a large number of deaths of fish and aquatic animals, destroys aquatic resources, and triggers " "Algal bloom" and "red tide" and other phenomena.

(3) Greenhouse effect and acid rain. Nitrous oxide, a nitrogen oxide, has a particularly strong ability to absorb infrared radiation, more than 200 times that of carbon dioxide, and is a terrible killer that causes the greenhouse effect. In addition to the greenhouse effect, nitrous oxide (commonly known as laughing gas) can also chemically react with ozone in the atmosphere, disturb the ozone layer, increase the intensity of ultraviolet light on the ground, and endanger human health. Nitric oxide and nitrogen dioxide are also one of the components of acid rain.

(4) NO ₂ ^- induces various diseases and even carcinogenesis. Once people get excessive amounts of nitrate from contaminated fruits and vegetables and drinking water, high blood pressure, congenital central nervous system disability, and non-Hodgkin's lymphoma can occur. As early as 1945, Comly reported that the high nitrate nitrogen content in drinking water affected the oxygen concentration in the blood of infants and caused methemoglobinemia or Blue-baby Syndrome; the burning of fossil fuels Nitrogen oxides form ground-level ozone and can trigger asthma. A large number of medical research reports have proved that the incidence of liver cancer, stomach cancer and other symptoms is also closely related to the amount of nitrate intake by the human body.

(5) Social issues. Municipalities must face social problems such as excessive NO _{3 in} groundwater and drinking water and increased medical costs. In rural areas near farmland, excessive levels of NO ₃ ^-in drinking water wells are also a problem.

Nitrogen cycle control measures

Nitrogen has affected the environment of China and the world in many ways. We should adopt scientific measures and policies to curb the damage to the environment and ecology by nitrogen. China is a large agricultural country. 70% of the activated nitrogen comes from agricultural production. The most fundamental method is to rationally fertilize and improve the efficiency of nitrogen fertilizer use. Therefore, reforming the existing farming system, promoting accurate fertilization, and strengthening the construction of agricultural technology extension systems are the key. In the industrial production process, to improve energy efficiency or reduce the amount of nitrogenous substances, fixed reduction sources can also be used for catalytic reduction, absorption, adsorption and other technologies to control, recycle or use nitrogen oxides in waste to achieve Harmless emissions. When wastewater is discharged, the concentration of ammonium must be closely monitored, and nitrification should be performed before discharge. In addition, large-scale breeding farms shall be monitored to prevent them from randomly discharging nitrogen pollutants into lakes and rivers.