Frequent outbreaks of lake eutrophication and harmful algal blooms have become major water environment problems facing the world. The reason is that nitrogen and phosphorus are over-injected into the water body due to the intensification of human activities, and it is increasingly difficult to control under the inducement of factors such as climate warming. Nitrogen and phosphorus, the two most important nutrients necessary for life, play different roles in the growth and outbreak of algae in lakes.
Recently, a study conducted by the Tong Yindong team of Tianjin University and a number of well-known research institutions at home and abroad shows that the large-scale construction of urban sewage treatment facilities is one of the important factors causing the "dietary imbalance" of algae nitrogen and phosphorus in lakes. The research result "The rapid improvement of sewage treatment facilities leads to the imbalance of nitrogen and phosphorus measurement in lakes in densely populated areas" was recently published in the proceedings of the National Academy of Sciences of the United States.
According to reports, mastering the long-term evolution of lake nitrogen and phosphorus balance is the premise of clarifying the changes in lake nutrient status and predicting the outbreak of harmful algal blooms, and it is also the basis for formulating future lake nutrient control goals. Tong Yindong's team investigated the historical changes in the nutritional status of 46 major lakes in China and found that from the perspective of the trend of change in the past decade, some lakes in the eastern region of China have begun to have the characteristics of poor eutrophication, which is manifested in the rapid decline of phosphorus concentration in lakes, the basic stability of nitrogen concentration, and the rapid increase in the measurement ratio of nitrogen and phosphorus elements, which may be an important factor leading to the competitive advantage of non-nitrogen-fixing cyanobacteria in lakes.
Tong Yindong introduced that in order to explain this phenomenon, the research team coupled the material flow analysis and the watershed transport model, estimated the variation characteristics of nitrogen and phosphorus fluxes into the lake, and found that since 2005, the nutrient input of lakes in China has achieved a transformation from "general increase" to "local decline", and the emissions of urban living sources have decreased significantly (especially in the eastern lake area).
The study also found that nitrogen relative to phosphorus in some anthropogenic discharge sources began to have excess, and the measurement ratio of nitrogen and phosphorus was seriously imbalanced: especially in urban domestic sewage discharge, due to the difference in the efficiency of nitrogen and phosphorus removal in sewage treatment, the ratio of nitrogen and phosphorus in the effluent increased by nearly 2 times compared with ten years ago.
This research result shows that the construction of urban sewage treatment facilities that meet the needs of water ecology should not only consider the functions of nitrogen and phosphorus removal, but also be vigilant about the impact of the imbalance of element proportions before and after sewage treatment on the water ecological environment. This study can provide an important reference for the formulation of municipal sewage treatment discharge standards that meet the needs of water ecology.