Eutrophication of lake water bodies is the most important water pollution problem facing the world today. With the improvement of people’s quality of life, the rapid development of urbanization and industry, and the large-scale use of fertilizers and pesticides in agriculture, the eutrophication process of lake water bodies is accelerating, which has seriously affected the water quality and water environment of the lake, resulting in the lake’s own regulating function. Decrease, the water ecosystem is out of balance. The eutrophication of water bodies has received more and more attention, and the protection of water resources is an important topic for promoting social and economic development.
Water eutrophication is a phenomenon of water pollution caused by the excessive content of plant nutrients such as nitrogen and phosphorus. Under the influence of human activities, a large amount of industrial wastewater, domestic sewage and plant nutrients in farmland runoff are discharged into slow-flowing water bodies such as lakes, reservoirs, estuaries, bays, etc., causing rapid growth of algae and other plankton, and a decrease in dissolved oxygen in the water. The water quality has deteriorated and fish and other creatures have died in large numbers. Under natural conditions, as the rivers entrained alluvial deposits and aquatic debris continue to settle at the bottom of the lake, the water body will transition from oligotrophic to eutrophic, which is an extremely slow process. The eutrophication of water bodies caused by the artificial discharge of nutrient-containing industrial wastewater and domestic sewage can appear in a short time.
Eutrophication will affect the water quality of the water body and reduce the transparency of the water, making it difficult for sunlight to penetrate the water layer, thereby affecting the photosynthesis of plants in the water, which may cause the supersaturation of dissolved oxygen and cause a large number of fish deaths. At the same time, due to the eutrophication of the water body, a large number of algae with cyanobacteria and green algae as the dominant species grow on the surface of the water body, forming a layer of "green scum", causing the organic matter accumulated at the bottom to decompose and produce harmful gases and some under anaerobic conditions. Biological toxins produced by plankton can also harm fish. Because the eutrophic water contains nitrate and nitrite, people and animals who drink water whose content exceeds a certain standard for a long time can be poisoned and cause disease.
The algae contains chlorophyll a, the content is relatively stable, and easy to manually determine. Therefore, the concentration of chlorophyll a is an important parameter that reflects the degree of eutrophication of water bodies, and has important significance for the assessment of phytoplankton biomass and primary productivity. The chlorophyll a content of phytoplankton in the water can be measured to grasp the primary productivity and eutrophication level of the water body. In environmental monitoring, the chlorophyll a content is one of the indicators for evaluating the eutrophication of the water body.