As the saying goes: auspicious snow bodes well for a good year. Because heavy snow can kill insect egg diseases and conserve water resources, so that everything in the coming year can be moistened and thrive. However, for plants in cities, heavy snow coverage is not necessarily a good thing, because snow melting agent is often used to ensure smooth road traffic.
The main components of traditional snow melting agents are a variety of chloride salts represented by sodium chloride, including calcium chloride, magnesium chloride and so on. After they are dissolved in water to form a salt solution, the freezing point will be greatly reduced. The thicker the salt solution, the lower the freezing point. The high concentration of sodium chloride will solidify at - 10 ℃, while when the concentration of calcium chloride solution is high enough, the freezing point will be about - 20 ℃. The salt solution is not only not easy to freeze, but also accelerates the melting of the surrounding ice and snow in contact with it, which is the basic principle of the snow melting effect of chlorine salt.
After heavy snow, when chlorine salt is sown on the road as snow melting agent, it will form a concentrated salt solution with the melted snow water rolled by motor vehicles, which is difficult to re freeze into ice, and promote the melting of surrounding snow at the same time. However, as the snow continues to melt, the salt solution is gradually diluted, and its ability to promote thawing and frost resistance is gradually reduced. When the salt solution is diluted to a certain extent by the melted snow water, it will no longer have the effect of snow melting. Therefore, in theory, the greater the snowfall, the more snow melting agents need to be put in. At the same time, the air temperature and ground temperature before and after snowfall will also affect the use effect of snow melting agent. Taking the snowfall in Beijing on November 1, 2009 as an example, 5500 tons of snow melting agent were sprayed in the urban area of Beijing. After they were completely melted, the concentration of sodium chloride in the snow water reached 458 mg / L.
The effect of snow melting has been achieved and the road traffic has been guaranteed. However, when so much salt is sprinkled on the road, the plants in the city will suffer. The salt solution after snow melting is mixed with the snow water and enters the urban drainage system or directly infiltrates into the urban underground water body. However, the salt that is not fully dissolved often accumulates on the green belts on both sides of the road with the snow cleared. In the era of no snow melting agent, piling snow on the roadside in this way not only saves time and effort, but also conserves the land. However, after spraying snow melting agent, the salt mixed in snow and snow water will pollute the water and soil at the same time. When the chloride ion concentration in the soil reaches more than 355 mg / L, most shrubs and trees will have obvious adverse reactions, let alone weak herbs.
When heavy snow comes, it is very important to ensure traffic. However, if the harm of snow melting agent to plants, water and soil is not fully considered, the ecological environment will be seriously affected.