The ocean is the cradle of life. Before the ocean appeared, the earth, like other planets in the solar system, was lifeless. The warm and humid air flow in the ocean is the main factor to form clouds and rain. Under the irradiation of sunlight, a large amount of water vapor rushed into the sky, drifted to the mainland with the airflow, and under the action of cold air, rainfall was formed, some of which returned to the poles and the ocean through rivers, and the other part infiltrated into the ground and became groundwater. However, in the cold regions of the North and South poles and the mainland, precipitation appears in the form of snow. Because the temperature is too low, it is difficult for a lot of snow to become hard ice, so glaciers are formed. Glaciers in Himalayas and Kunlun Mountains in China are the main water sources in Qinghai-Tibet Plateau and Xinjiang. Even our mother rivers, the Yellow River and the Yangtze River, all originate from the ice peaks and snow lines on the Qinghai-Tibet Plateau. Every summer, the sun shines on the ice peak, and the melted ice flows along the gully river to Yuan Ye and pasture, which becomes the main water source for local people and animals to drink water and irrigate agriculture and animal husbandry.
Abundant water resources bring vitality to everything and maintain ecological balance. Seen from space, the earth is a blue planet, and 7 1% of its area is covered with water. However, it is hard for people to imagine that the traditional concept of "inexhaustible" water has begun to become a scarce resource, and protecting water resources has become an important issue facing the whole world.
According to scientists' estimation, the total water storage capacity of the earth is 654.38+0.37 billion cubic kilometers, of which fresh water only accounts for 2.5%. 68.7% of fresh water is sealed in permanent snow in polar glaciers and mountains. Therefore, less than 65,438+0% of available fresh water exists in aquifers, rivers, lakes, soils, swamps, plants and the atmosphere, and a large part of it is difficult to obtain. According to the United Nations standard, a country is considered as a water-deficient country if its per capita annual water supply is less than 1000 cubic meters. China's population accounts for 22% of the world's total population, while its per capita freshwater possession accounts for only 8% of the world's total, and its per capita freshwater possession is only 1/3 of the world average. It is a well-known water-deficient country.
The most serious consequence of water shortage is the deterioration of people's health in some countries. According to the survey of the World Health Organization, 654.38+0 billion people in developing countries can't drink fresh water, and 654.38+0 million people worldwide die of diseases caused by drinking unclean or polluted water every year. What is even more disturbing is that in many parts of the world, there is a conflict crisis between countries for water resources. Another aspect that can't be ignored in the water crisis is the problem of urban water shortage. The list of cities most likely to face water shortage listed by the United Nations includes Beijing and Shanghai in China, as well as Cairo, Mumbai, Jakarta, Mexico and other megacities.
China is a mountainous and watery country, with more than 1500 rivers, and the basin area exceeds 1000 square kilometers. However, China has a large population and relatively poor water resources. As far as the whole world is concerned, the high development of industry not only uses more and more fresh water, but also pollutes rivers, lakes and oceans day by day, leading to marine red tides, the extinction of fish and shrimp in rivers, and some even become smelly rivers and dead rivers.
Protecting water resources and preventing water pollution have become the top priority of environmental protection.
■ The water of the whole earth is about 14× 10 17 cubic meters, of which more than 97% is seawater that human beings can't drink, and the rest is fresh water, but 77.2% of fresh water exists in glacier snow-capped mountains, 22.4% is soil water and groundwater, and the rest is surface water. In fact, the fresh water resources available for human development and utilization on the earth only account for 0.77% of the total water storage capacity of the earth.
■ China's total water resources are about 2.7× 10 12 cubic meters, ranking sixth in the world, but the per capita water consumption is very small, accounting for only14 of the world's per capita, ranking 88th in the world, and it is one of the 13 water-poor countries in the world. China is a big agricultural country. The annual water shortage in agriculture is about 300× 108 cubic meters, and the drought-affected farmland is 200-300 million mu. 80 million rural people have difficulty drinking water. Urban water supply is insufficient. There are more than 300 water shortages in 5 17 cities nationwide, with an annual water shortage of 58× 108 cubic meters.
Water environmental capacity refers to the amount of pollutants that a water body can contain or its ability to adjust and purify itself and maintain ecological balance without affecting the normal use of water. Water environmental capacity is one of the bases for formulating local and professional water discharge standards, and it is also used by environmental management departments to determine how many pollutants are allowed to be discharged in fixed waters.
There is about 1.36× 108 cubic kilometers of water on the earth, which is mainly distributed in the ocean, glaciers, ground, underground and atmosphere. The water used by human beings is basically fresh water, and the quality of fresh water only accounts for 0.63% of the total water quality of the earth. With the development of industrial and agricultural production, water consumption is increasing rapidly, and fresh water resources are becoming increasingly tense. At the same time, due to pollution, the available water is reduced, which further aggravates the contradiction of water shortage.
The situation of water resources in China is also quite severe. China's fresh water reserves rank sixth in the world, but due to its large population, its per capita possession is only 1/4 of the world average, ranking 88th in the world.
In the process of human metabolism, with drinking water and food, various elements in water enter various parts of the human body through the digestive tract. When water lacks some parts or some elements necessary for human life process, it will affect human health. For example, in some areas, water is short of iodine, and drinking this water for a long time will lead to "big neck disease", which is medically called "endemic goiter". When water contains harmful substances, it is more harmful to human body. Carcinogens can be brought into the human body by eating contaminated food (grains, vegetables, fish, etc.). ) and can also enter the human body through drinking water. According to the survey, the incidence of liver cancer, gastric cancer and other cancers in people who drink polluted water is about 6 1.5% higher than that in people who drink clean water. When mercury, cadmium and other elements in sewage are discharged into rivers and lakes, aquatic plants absorb and enrich them. After eating aquatic plants, fish are further enriched in the body. After eating poisonous fish, people are rich in mercury, cadmium and other elements, which makes people sick and die. In this way, from aquatic plants->; -> small aquatic animals; Fish->; Big fish-> The human body forms a food chain. The human body eventually becomes the "foothold" of elements such as mercury and cadmium.
Soil and water conservation refers to the comprehensive science and technology of preventing soil erosion, protecting, improving and rationally utilizing water and soil resources in mountainous, hilly and sandstorm areas, and maintaining and improving land productivity, so as to give full play to the economic and social benefits of water and soil resources and establish a good ecological environment. At present, soil and water conservation includes three measures: agricultural technical measures, forest and grass measures and engineering measures. Agricultural technical measures of soil and water conservation are mainly soil and water conservation tillage. Combined with farming, temporary small topography with certain water storage capacity is built on sloping farmland, such as district field, border field and furrow and ridge planting. The United States, the Soviet Union and other countries have also widely adopted the mulching cultivation method, the avoiding Great Leap Forward method and the less Great Leap Forward method. In addition, there are deep ploughing, close planting, intercropping and interplanting, fattening, grass-field rotation and so on. Are agricultural technical measures for soil and water conservation. Measures for forest and grass conservation, or plant or biological measures for water and soil conservation. Its main function is to improve the vegetation of the earth and increase the roughness of the surface, so as to reduce the impact of raindrops on the ground, increase soil infiltration, reduce surface runoff, slow down the flow rate and weaken the scouring force. The main function of soil and water conservation engineering measures is to reduce or stop soil erosion and develop and utilize water and soil resources by building various projects, changing small topography, intercepting surface runoff and increasing soil infiltration. According to the position and function, it can be divided into three categories: slope treatment engineering, river treatment engineering and bank protection engineering. Various measures, especially engineering measures and forest and grass measures, have always been interdependent and complementary.
Soil and water conservation is of great significance to the development of production and construction in mountainous, hilly and sandstorm areas, the improvement of land, the regulation of rivers and the mitigation of drought and sandstorm disasters.