Can you give me some information about water pollution?

Water is an indispensable natural resource for human development and the material basis for human beings and all living things to survive. In today's world, the water crisis caused by water shortage and pollution has become a complex problem in policy, economy and technology faced by any country and a major constraint to social and economic development. 1992 1 The United Nations held an international conference on water and environment in Iceland, calling for finding new ways to evaluate, develop and manage freshwater resources. In 1993, the World Bank put forward a new topic about water resources. FAO has recently established an international project on water and sustainable agricultural development (LAP-WASAD), which shows that water resources have attracted worldwide attention.

The development and utilization of water resources by human beings can be divided into two categories: one is to take the required amount of water from water resources to meet the needs of people's life and industrial and agricultural production, and then the consumption and quality change will occur, and then return to the water source in another place. The other is to take water (hydropower), develop water transport, aquatic products and water entertainment, and maintain ecological balance. This utilization does not need to take water from water sources, but it needs rivers, lakes and estuaries to maintain a certain water level, flow and water quality. The utilization of water resources discussed in this section is mainly the first type of water use.

3. The important role of water resources

1) Regulate the climate. Water is an important part of the atmosphere. Although the atmosphere contains only one millionth of the global water volume, the cyclic interaction between the atmosphere and water determines the water circulation movement of the earth and forms a climate that supports the survival of living things. The water in the atmosphere helps to adjust the global energy balance, and the water circulation movement plays the role of energy transfer in different regions.

2) Water mill shapes the surface of the earth. Running water created and promoted the formation of land landforms, rearranged the surface landscape and formed a delta. Water is the key factor of soil formation and the important factor of physical weathering of rocks.

3) Water has the function of material transportation. Water can transport all kinds of substances and nutrients. There are two forms of water transport substances: dissolved minerals and whole substances. All kinds of particles in the atmosphere can settle into water and then be transported by water. From this aspect, it can be seen that water can transport and spread environmental pollutants to farther and wider areas.

4) Water is an essential substance for all living things. Life cannot be formed without water. Water is the main body of organisms, and the water content in organisms accounts for 60-80% or even more than 90% of body weight. Water is an integral part of life protoplasm, participates in cell metabolism, and is also the medium of biochemical occurrence inside and outside organisms. Therefore, all life is inseparable from water. Water interacts with living things in various ways. In a region, water is one of the key factors to determine the vegetation community and productivity-it can also determine the types of animal communities, animal behavior and so on.

5) Water is the most basic material basis for human survival and production. Water is closely related to human beings. Life and production activities are inseparable from boiled water, a valuable natural resource. Water is not only an important part of human body, but also the medium of human metabolism. The water content of the human body accounts for 2/3 of the body weight, and to maintain the normal physiological metabolism of the human body, each person needs at least 2~3L of water every day. Industrial production, farmland irrigation and urban life all need to consume a lot of water. However, with the intensification of population and economic activities, the global water cycle has greatly deviated from its natural state, and the flow of water has changed significantly. The rapid growth of population has accelerated the consumption of water resources, the development of industrial and agricultural production has seriously polluted water bodies, and the destruction of forests has changed the direction of evaporation and runoff. These human activities have caused serious damage to water resources and made the world face a water crisis.

1, World Water Resources Survey

Natural conditions are different around the world, and precipitation and runoff are also very different. The island with the largest annual precipitation is Oceania (excluding Australia); Followed by South America, most of which is located in the equatorial climate zone, the water cycle is very active, and the precipitation and runoff are more than twice the global average. Europe, Asia and North America are close to the world average, while Africa is one of the driest regions in the world. Although the precipitation is close to the world average, the runoff is only 15 1mm due to the large desert area and strong evaporation. In contrast, Australia in Oceania is the driest, and its runoff is only 39mm compared with the precipitation of 76 1mm, because two thirds of Australia is desert and semi-desert.

2. Supply and utilization of world water resources

Usually, people regard the total amount of global land runoff into the sea as the theoretical total amount of water resources, that is, the total amount of global water resources is 47000km3, and this amount of water resources is unevenly distributed in the world, and the degree of water resources abundance and shortage varies greatly among countries. In the early days, human beings developed and utilized water resources, mainly in agriculture, shipping and aquaculture. , and industrial and urban domestic water consumption is very small. Until the beginning of this century, industrial and urban domestic water consumption still accounts for only about 12% of the total water consumption. With the rapid growth of the world population and the development of industrial and agricultural production, the consumption of water resources is increasing. World water consumption is increasing year by year. During the period of 1900~ 1975, it will increase by 3~5% every year, that is, it will double every 20 years or so. By the year 2000, the world's total water consumption will reach 600 billion m3, accounting for 15% of the world's total runoff.

With the progress of human civilization, the demand for water resources is increasing. The water consumption of 1985 is 3.5 times that of 1950. Among them, the proportion of agricultural water consumption in total water consumption decreased from 78.2% in 1950 to 610.5% in 1985; The proportion of industrial water and urban water in total water consumption increased from 22.7% in 1950 to 34.6% in 1985. But the water resources available for human use will not increase; Even because of man-made pollution and other factors, its quality will become worse and the available amount will be reduced. In addition, the distribution of fresh water resources in the world is extremely uneven, and the geographical location where people live is not commensurate with the distribution of water, which makes the contradiction between supply and demand of water resources great, especially in cities with concentrated industry and population. According to statistics, in the past 40 years, the world's agricultural water consumption has only increased by 2 times, industrial water consumption has increased by 7 times, and domestic water consumption has increased even more.

3. Causes of the water crisis

Judging from the total reserves and circulation of water, the water resources on the earth are abundant. If properly protected and utilized, it can be used by 20 billion people. However, due to the increasing consumption and pollution of available water, the shortage and crisis of available water resources are mainly due to the following reasons:

1) Impact of natural conditions: The distribution of fresh water resources on the earth is extremely uneven in time and space, and it is affected by climate change, resulting in the shortage of available water resources in many countries or regions. For example, the Yangtze River, Pearl River, Zhejiang, Fujian, Taiwan Province and Southwest rivers account for 8 1.0% of the total water, while the cultivated land in these areas only accounts for 35.9% of the whole country. However, North China and Northwest China are located in arid or semi-arid climate zones, with less rainfall and runoff and serious seasonal water shortage. North Africa and South Sahara, Arabian Peninsula, South Iran, Pakistan and West India are the areas with the largest annual average rainfall change, with the change range exceeding 40%. The same is true in the southwestern United States, northwestern Mexico, southwestern Africa, easternmost Brazil and parts of Chile. Therefore, there will be a regional water supply crisis in many parts of the world.

1. Overview: There are many rivers in China. There are more than 50,000 rivers with basin area above 1000km2, and about 1500 rivers with basin area above1000 km2. However, due to the influence of climate and topography, the distribution of rivers is very uneven. Most rivers are distributed in the humid and rainy monsoon region in the east of China, and the inland climate in the northwest is dry and rainy, with few rivers.

There are more than 2,300 lakes above 1 km2 in China, with a total area of 7 187 km2, accounting for about 0.8% of the national territory. The total reserve of lake water is about 708.8 billion m3, of which fresh water accounts for 32%.

China is also rich in glacier resources, with more than 43,000 glaciers in the western region. The total area is 58700km2, accounting for more than half of the total area of glaciers in Asia, with a total storage capacity of about 5.2 trillion m3.

The average annual precipitation in China is 6188.9 billion m3, the average precipitation depth is 648.4mm, the average annual river runoff is 271kloc-0/0.50 billion m3, and the comprehensive runoff depth is 2841mm. River runoff is mainly replenished by precipitation, and only about 50 billion m3 is replenished by glaciers. The average groundwater resources in China for many years is 828.76 billion m3.

According to analysis and calculation, the resources of surface water and groundwater in China are 2.7115 and 828.8 billion m3 respectively. After deducting the repeated amount of 727.9 billion m3, the national average total water resources for many years is 28124 billion m3.

2. Characteristics of water resources in China

The temporal and spatial distribution characteristics of water resources in China can be reflected by the distribution of water balance factors such as precipitation, evaporation and runoff:

1) the total amount of water resources is rich, and the per capita and per capita possession are small.

The average total water resources in China for many years is 28124 billion m3, of which river runoff accounts for 94%, which is lower than that of Brazil, the former Soviet Union, Canada, the United States and Indonesia, accounting for 5.8% of the total global runoff, ranking sixth in the world. The average runoff depth is 284mm, which is 90% of the world average and ranks seventh in the world. It can be seen that China is rich in water resources. However, China has a large population. Based on the population of 65.438+0.2 billion, the annual river runoff per capita is 2260m3, which is lower than the world average of 65.438+0/4, which is 65.438+0/6 in the United States, 65.438+0/8 in the former Soviet Union and 65.438+0/65.438 in Brazil. China has a vast territory, and the average river runoff per hectare of cultivated land is about 28320m3, which is 80% of the world average. Therefore, the contradiction between the quantity and demand of water resources in China is very prominent, with 7% of the world's cultivated land and 6% of the world's fresh water resources feeding 22% of the world's population.

With the growth of population, the demand for water for urbanization, industrialization and irrigation is increasing, and many water shortage problems will appear in 2 1 century. In the case of limited available fresh water, we should take active measures to protect precious resources. The following measures are generally taken.

1, improve water use efficiency and open up a second water source.

This is an important way to solve the current water shortage. The main methods are:

1) Reduce industrial water consumption and improve water reuse rate.

The main way to reduce industrial water consumption is to reform the production water technology, strive for less water and improve the recycling rate. For example, replacing the old open hearth furnace with an oxygen converter in a steel-making plant not only improves the steel quality, but also reduces the water consumption by 86-90%.

At present, many industrialized countries in the world regard improving industrial reuse rate as the main means to solve the problem of urban water use. Some countries have also set up special pipelines for industrial circulating water and achieved good results. In recent years, the reuse of reclaimed water in China has been gradually carried out. In some cities with particularly tight water resources, the water reuse rate has reached a high level, such as Dalian 79.5%, Qingdao 77.3% and Taiyuan 83.8%, but the overall level is still low, and the average industrial water reuse rate is only 20-30%.

If the average reuse rate of industrial water in China is increased from the current 20% to 40%. It can save water130,000 tons every day, and correspondingly save 2.6 billion yuan in water supply project investment. Water saving and economic benefits are considerable.

Improving the reuse rate of industrial water is not only an important measure for rational utilization of water resources, but also can reduce the output of industrial wastewater, wastewater treatment and water pollution.

2) Implement scientific irrigation to reduce the waste of agricultural water.

70% of the water in the world is used for agricultural irrigation, but the utilization rate is very low and the waste is serious. It is estimated that 37% of the world's irrigation water is used for crop growth, and the remaining 63% is wasted. Therefore, reforming irrigation methods is the greatest potential to improve water use efficiency.

Canal leakage is a common problem in irrigation development all over the world. According to the statistics of International Irrigation and Drainage Committee, the leakage loss of irrigation water is generally 15~30%, even as high as 50~60%. The leakage loss in China is generally 40-50%, even as high as 70-80%. Because most irrigation channels have no anti-seepage measures, the average water utilization coefficient of channels in the Yangtze River, Pearl River and southeast coastal areas in southern China is 0.6, while that in other areas is 0.5. It is estimated that the water loss caused by channel leakage in China can reach more than 654.38+0.7 billion m3. Therefore, the application of anti-seepage channels, underground pipes and other engineering technologies can achieve obvious water-saving effects.

Improvement of irrigation methods is an important way to save water in agriculture. The drip irrigation system developed by Israel in 1960s can send water directly to the place near the roots of plants, minimizing evaporation and water leakage. At present, the development trend of irrigation water-saving technology abroad is to adopt a complete drainage and irrigation pipeline system, which has the advantages of low energy consumption, fast water delivery, uniform water distribution, small water loss and no influence on mechanized farming. In addition, some countries have also studied new irrigation technologies, such as surge irrigation, horizontal border irrigation and the use of automatic vertical pipes. The Nebraska Institute of Agriculture and Natural Resources has designed an irrigation computer program, which uses the data collected by various small weather stations to calculate the evapotranspiration rate of different crops grown in various regions and guide farmers to adjust irrigation dates. Automatic irrigation technology uses computer to control flow, monitor leakage, adjust water consumption under different wind speeds and soil moisture, and optimize fertilizer consumption. The latest research in China shows that drip irrigation under film is a new irrigation technology suitable for arid and semi-arid areas with high water use efficiency.

3) Recycle urban sewage and open up a second water source.

Recycling and reusing wastewater to make it an available resource is another way to improve water use efficiency. In Tokyo, the urban water recycling center recycles waste water through slow sand filtration in a tertiary water treatment plant, and after chlorination and disinfection, it is used to flush toilets in high-rise buildings. Beijing has also established a similar "intermediate channel" system.

2. Adjust water flow to increase reliable water supply.

The first reason of water shortage is the influence of natural conditions, such as climate, geographical location and uneven distribution of fresh water. People try to solve this problem by regulating water flow and developing new water sources.

1) Reservoir construction: The reservoir is built to regulate the flow, and it can store excess water in the wet season to supplement the insufficient flow in the dry season. It can not only improve the water supply capacity of water sources, but also serve many purposes such as flood control, power generation and aquatic product development. At present, there are 1 0,350 reservoirs on rivers in various countries, with a storage capacity of more than 1 100 million m3 and a total storage capacity of 4 1 10,000 m3.

However, in many industrialized countries, with the increasingly difficult choice of reservoir construction sites, the cost of adding new water storage facilities has increased rapidly, and the development speed of reservoirs has obviously slowed down. Reservoir construction in developing countries is still in its heyday. When building a reservoir, we must also study the impact on the watershed and the ecosystem around the reservoir, otherwise it will cause adverse consequences.

2) Inter-basin water transfer: Inter-basin water transfer is an expensive project to increase water supply, which is to adjust from a water-rich basin to a water-deficient basin. Because of its high cost and serious environmental damage, many countries no longer carry out large-scale inter-basin water transfer. In recent years, Pakistan's West-to-East Gas Transmission Project, Australian Snow Mountain River Water Diversion Project, and China's Yellow River Diversion Project, Luanhe River Diversion Project and Luanhe River Diversion Project are all large-scale projects to supply water from abundant water basins to water-deficient basins, and China's South-to-North Water Diversion Project has also started.

3) Groundwater storage: At present, more than 20 countries are actively planning to replenish groundwater artificially. In the United States, local water conservancy institutions in California store about 2.5 billion cubic meters of water underground every year. By 1980, two water conservancy project demonstration areas in Quanzhou have stored 34.5 million m3 of water. Its average unit cost is at least 35~40% lower than that of the newly-built surface water reservoir. In the autumn of 1984, the US Congress passed legislation and approved the construction of aquifer recharge demonstration projects in the western states of 17. In the Netherlands, after artificial recharge of groundwater, the problem of water supply in dry season is solved, and the aquifer reserves are increased by 2-3 million m3 every year.

4) Seawater desalination: Seawater desalination can solve the problem of freshwater shortage in coastal cities. At present, the global seawater desalination capacity is 2.7km3/a, which is less than the global water consumption 1‰. Saudi Arabia, Iran and other countries account for 60% of the world's seawater desalination equipment capacity, and the world's largest seawater desalination pipeline water diversion project has been built in Saudi Arabia.

5) Towing an iceberg: The project cannot be realized in the near future and is still in the planning stage. It is estimated that a small piece of ice floe in Antarctica can obtain 654.38+0 billion m3 of fresh water, which can be used by 4 million people for one year.

6) Restore the water quality of rivers and lakes: Restore the water quality of rivers and lakes through comprehensive prevention and control of water pollution. That is to say, the relationship between water self-purification, sewage treatment scale, sewage treatment efficiency and water quality target and its cost is studied by using the method of system analysis, and the water quality simulation, prediction and evaluation technology are applied to seek the optimal treatment scheme and formulate the water pollution control plan. Rivers treated in this way, such as the Delaware River in the United States, the Thames River in Britain and the St. John River in Canada, have all recovered their water quality and increased their fresh water supply.

7) Rational utilization of groundwater: Groundwater is one of the most important water resources, and its reserves are second only to polar glaciers and exceed the sum of river water, lake water and atmospheric water. However, due to its slow replenishment speed, over-exploitation will cause many problems. In the development and utilization of groundwater resources, the following protective measures shall be taken:

(1) Strengthen the investigation of underground water sources, master hydrogeological data, make overall planning and rational layout, and consider the comprehensive utilization of surface water and groundwater in a unified way to avoid over-exploitation and abuse of water sources;

(2) Artificial recharge is adopted, but attention must be paid to prevent groundwater pollution;

(3) Establish a monitoring network to keep abreast of groundwater dynamics and water quality changes, so as to take timely preventive measures.