How to distinguish rivers, lakes and seas?

The original meaning of "Jiang" refers to the Yangtze River, just as "He" refers to the Yellow River. The difference between rivers can be seen from two angles:

(1) Geographical differences (South River and North River)

For example, the rivers in the south of China are often called "rivers", such as Yangtze River, Pearl River, Qiantang River, Minjiang River, Nujiang River, Jinsha River, Lancang River, Yarlung Zangbo River, Lijiang River and Jiulong River. It can be seen that southerners are generally used to calling rivers "rivers".

Rivers in the north are often called "rivers", such as Yellow River, Huaihe River, Weihe River, Jinghe River, Luohe River, Fenhe River, Qinghe River, Liaohe River, Yinma River, Qinhe River, Qaidam River and Tarim River. It can be seen that northerners are used to calling rivers "rivers".

People's division of river names is slightly different from the traditional north-south division.

Tibet, Sichuan, Chongqing, Hubei, Jiangxi and Zhejiang (inclusive) are often called "rivers" in the south and "rivers" in the north. This is the difference in naming habits between the north and the south.

② Scale difference (big "river" and small "river")

Although there is a general geographical division, nothing is absolute. When people name a river, they will also call it "Jiang" or "River" according to its size.

Let's look at the exceptions: Nenjiang, Yalu, Heilongjiang, Songhua and Wusuli rivers in the north (Liuyang River and other rivers in the south). These rivers are called "rivers" in the north, and their similarities are length, flow and basin, and they are all large in scale. So in addition to the habit of naming the rivers in the area, people usually refer to some small rivers.

What is the "sea"? In modern people's concept, it refers to "the part of the ocean near the land", but in ancient people's understanding, great lakes similar to the sea are also called "sea", and the names of Caspian Sea, Qinghai and Erhai Lake have been passed down to this day. "Sea" is vast, so it can refer to things with "big" or "many" meanings: it can refer to "big capacity and big breath", such as "sea bowl", "people" and "sea boasting". It is worth noting that "sea" can also refer to "foreign sea", such as "begonia" and "date palm". Accordingly, "Hainei" refers to China. To understand this problem, we have to browse the history of the ocean.

"Sea" used to be synonymous with direction, and there is a saying in ancient books that "it is universal". This shows that in the eyes of the ancients, the sea is the end of the world, so it can be used as the name of the direction. The reason why the ancients formed this concept of space can be found in the pronunciation training of the word "sea" by the ancients: "The beauty is gloomy." "People in the sea are dark and ignorant." Practice shows a historical fact: due to the lack of navigation ability, our ancestors had to look at the boundless sea without knowing its details, let alone knowing that there was a new continent beyond it, so they regarded it as the end of the world.

China's ancestors thought that the Central Plains of the Yellow River valley where they lived was the center of the world, so they called their country China. The aliens around China are considered to be around the earth, so they are also called "sea" because they are close to the sea. In ancient books, there is a saying that "Jiuyi, Buddy, Qirong and Liuman are called the four seas". In this way, "sea" naturally becomes a series of words such as "China", "inland" and "overseas", which are actually expressions of ancient people's understanding of the ocean through colored glasses.

What is a lake?

A water body with wide water area and slow direction change formed by accumulated water in land depression. Under the geological action of crustal movement, glaciation, river erosion and siltation, many depressions are formed on the surface, and lakes are formed by accumulated water. Reservoirs and dams formed by accumulated water in depressions of open-pit mining points are also among the lakes, which are called artificial lakes. Lakes are different from rivers because their flow is extremely slow, and they are different from the ocean because they are not in direct contact with the ocean. Under the influence of the natural geographical conditions of the basin, the substances in the lake basin, lake water and water interact and restrict each other, which makes the lake evolve continuously. Lakes have different names, usually using dialect names. China's customary names for vicious, flat, pond, sea, bubble, swing, lake, berth, Cuo, Noel, etc. are all nicknames for lakes.

There are many lakes in the world, such as the famous lake in the table 1 There are many lakes in China, about 2,300 of which are larger than 1 km2, with a total area of 7 1 1,000 km2. On the other hand, there are 2,848 lakes with an area of 83,400 square kilometers. With an area of more than 4,000 square kilometers, Qinghai Lake is the largest lake in China. Tibet is 47 18m above sea level, which is the highest lake in the world, with a lake area exceeding 1000 km2. Tianchi Lake is located in Baitou Mountain, with a water depth of 373 meters, which is the deepest lake in China. Chaeryi Salt Lake in Qaidam Basin is famous for its rich lake salt reserves. See Table 2 for the main lakes in China.

Lake basin refers to the surface depression that contains lake water. The original topography and plane shape of the bottom of the lake basin largely depend on the genesis of the lake basin. According to the dominant factors of lake basin formation, lake basins can be classified into the following categories: tectonic lake basins formed by crustal tectonic movements (such as faults and folds); Glacier lake basin formed by glacier advance and retreat or ice body fracture and uneven heating of ice surface; Crater lake basin formed by dormant crater after volcanic eruption; A dammed lake basin formed by landslides, landslides or volcanic eruptions that blocks valleys or valleys; Water lake basin formed by erosion and deposition of water or dissolution of water; Aeolian lake basin formed by wind erosion; In addition, there are meteorite lake basins formed by large meteorites hitting the ground.

Once a lake is formed, it evolves under the constant action of external natural factors and various internal processes. A large amount of sediment and biological debris carried by rivers entering the lake are deposited in the lake year after year, and the lake basin gradually becomes shallow and becomes land, or gradually becomes swamp with the development of aquatic plants along the coast. In arid climate, due to climate variation, the melting water of ice and snow in inland lakes decreases, and the groundwater level drops, which is not enough to compensate for evaporation loss, which often causes lakes to shrink and dry up, or salt substances accumulate and enrich in lake basins, and lakes become increasingly salinized, and finally become dry salt lakes. Some lakes are drying up because of export cuts and water outflow. In addition, the lake will shrink and expand due to factors such as crustal change and climate change.

Morphological parameters of a lake The shape of a lake depends on its origin and development process. Artificial lakes are generally deep and steep, but with the change of lakes, some characteristics of some artificial lakes can gradually disappear. Crater lake is usually small and deep. For example, Tianchi Lake in Baitou Mountain, China has an area of only 9.8 square kilometers and a depth of 373 meters. The morphological characteristics of lakes affect the physical and chemical properties of lakes and the distribution law of aquatic organisms. The morphological parameters of the lake are: area, which generally refers to the area and volume of the lake at the highest water level, and refers to the amount of water stored in the lake basin, which changes with the water level. Length, that is, the shortest distance between the farthest two points on the shore of a lake, can be a straight length or a folded length and width according to the shape of the lake. The former is the maximum distance and average width between two opposite banks that are roughly perpendicular to the length direction. Refers to the lake shore length at the highest water level, the development coefficient of the lake shore, the ratio of the lake shore length to the circumference equal to the lake area, the lake recharge coefficient, the ratio of the lake basin area to the lake area, the lake island rate, the ratio of the total area of the lake island to the lake area, the maximum depth, the vertical distance between the highest water level and the deepest point at the lake bottom, the average depth, and the quotient of the lake volume and the corresponding lake area.

Lake classification can be divided into tectonic lake, glacial lake, crater lake and dammed lake according to the origin of lake basin. According to the drainage conditions of lakes, they can be divided into outflow lakes that are discharged into the sea through rivers and inland lakes that cannot flow into the sea. Judging from the thermal state of the lake, the average temperature of the lake is above 4C all the year round, and it is a tropical lake with positive stratification except for the same temperature in autumn and winter. The average temperature of the lake is sometimes above 4 degrees Celsius and sometimes below 4 degrees Celsius. Stratification in summer and anti-stratification in winter. It is a temperate lake with the same temperature in spring and autumn, and a frigid lake with the average temperature below 4C all the year round. Except for the same temperature in spring and summer, it is in reverse stratification. According to the up-and-down circulation phenomenon of the lake, it can be divided into: the lake is frozen all the year round, and the lake is stable without circulation period; The water temperature is below 4C, and there is only one cycle in summer. Warm single-cycle lake with water temperature above 4C and only one cycle in winter; A double-cycle lake, experiencing two cycles in spring and autumn; The water temperature is above 4C, and there is an oligocycle lake with stable stratification and occasional circulation. The annual change of water temperature is small, the stratification is weak, enough heat is obtained during the day, and the heat dissipation at night produces a multi-cycle lake. According to the salinity of the lake, it can be divided into: freshwater lake with salinity < 1 g/L; Salt lake with salinity of 1 ~ 35g/L; Salt lakes with salinity > 35g/L can be divided into eutrophic lakes, eutrophic lakes and eutrophic lakes according to the nutrients in the lakes. Some lakes are classified according to other standards.

According to the characteristics of motion elements changing with time, lake motion can be divided into periodic motion, such as lake wave, lake ripple and lake flow with ripple; Non-periodic movements, such as drifting and huffing and puffing, can be divided into mixing, lake flow, increasing or decreasing water, waves and ripples according to the movement mode. According to their vertical position in the lake, they can be divided into surface movement and internal movement. Various forms of sports often interact and combine with each other. The movement mode of the lake depends on the layered structure, internal density distribution, force nature, duration, periodicity and spatial distribution of the lake.

Lake water level can be divided into periodic and non-periodic according to the law of change, and the periodic annual change mainly depends on the recharge of lake water. In plateau lakes, the highest water level is in summer and the lowest water level is in winter. Generally speaking, the water level of lakes with groundwater recharge has little change. Some lakes have periodic diurnal changes due to the influence of lake breeze, tide, freezing and melting of ice and snow. Affected by the land breeze, the average water level of Lake Victoria in Africa is 9.9 cm higher during the day than at night. This aperiodic change is usually caused by wind, air pressure, rainstorm, etc. During the same period, the change of Taihu Lake water body in China is caused by the northeast wind of stubble, which can make the water level in the windward bank increase by 1. 1 m, and the water level in the leeward bank decrease by 0.75 m. In addition, the water level can also change greatly due to human activities such as crustal changes, river bed undercutting at the estuary and irrigation power generation.

Thermal characteristics of lake water Lake water absorbs solar energy and gains heat, but it loses heat through evaporation, effective radiation and convection heat exchange between water surface and atmosphere. The transport and exchange of lake heat can be expressed and calculated by the lake heat balance equation (see lake heat condition). Because it is difficult to accurately determine some elements of lake heat balance (such as lake evaporation rate), water temperature is usually used to express the thermal dynamics in lakes. Solar radiation mainly increases the temperature of the lake surface, and the temperature change in the lower part of the lake is mainly caused by the convection and turbulent mixing of the lake. Different temperatures of lakes will also cause density differences, leading to convective circulation of unstable water layers. Above the depth of convective circulation, the water temperature tends to be consistent. Wind disturbance can make shallow lakes have the same temperature phenomenon in any season. However, wind disturbance can only affect the upper layer of deep-water lakes, so there will be different temperature distributions in the upper and lower layers vertically. The intermediate layer with drastic temperature change between the upper and lower layers is called thermocline. The temperature of the lake has a certain annual and daily variation, which is most obvious in the surface layer of the lake and decreases with the increase of depth. The freezing point of lake water depends on its salinity and hydrostatic pressure. In addition, the icing on the lake is also related to the wind. Under the same climatic conditions, different lakes are still the same lake.

Radiation and optical characteristics of lake water The radiation characteristics of lake water determine the temperature of lake water and affect the distribution of physical and chemical properties of lake water, and the reproduction, growth and development of various organisms in lake water are also related to the radiation characteristics of lake water. Some sunlight shining on the lake enters the water body, and some is reflected. Part of the sunlight entering the water body is absorbed and part is scattered. Even in shallow lakes, only a small part is absorbed by the lake bottom through the water layer. Most of the sunlight injected into the lake is absorbed by the top water body, and only 1 ~ 30% reaches the water layer with the depth of 1 meter, and only 0 ~ 5% penetrates into the depth of 5 meters. However, less than 65,438+0% of the water enters the depth of 65,438+00 meters. The ability of lakes to absorb and scatter sunlight is related to the quantity and particle size of various suspended substances in water. The more suspended matter, the larger the particles, the smaller the absorption and scattering ability of light, and the less the components scattered to the water surface. The depth of light penetrating into the water decreases with the increase of lake turbidity.

Chemical characteristics of lake water According to the types of main ions contained in lake water, lake water is usually divided into carbonate water, sulfate water and chloride water. The chemical types of lake water reflect the process of water quality changing with the change of salt content in lake water. The salt content of lake water in different areas varies greatly, and there are seasonal changes. Freshwater lakes in China are mainly concentrated in the middle and lower reaches of the Yangtze River. The salinity of lake water is generally150 ~ 500 mg/L. Saltwater lakes and salt lakes are mainly distributed in Qinghai-Tibet Plateau, Inner Mongolia and Xinjiang. The salinity of salt lakes is mostly 1 ~ 20g/L, and the concentration is increasing day by day. The salinity of salt lake is generally around 300g/L, and the chemical types are complete. Oxygen and free carbon dioxide in dissolved gas are dissolved in water.

Lake resources Lake water is an important part of global water resources. The total area of lakes (including freshwater lakes, saltwater lakes and salt lakes) on the earth is about 2,058,700 square kilometers, and the total water volume is about176,400 cubic kilometers, of which the fresh water reserves account for about 52%, accounting for about 0.26% of the global fresh water reserves. The lake can be continuously renewed, and the renewal cycle of different lakes is different. The replacement cycle of the lake depends on its volume and the annual runoff in and out of the lake. In China, Poyang Lake has only been updated for 9.6 days, while Taihu Lake has been updated for about 299 days. The regional distribution of fresh water reserves in lakes is very uneven. 40 great lakes in the world, such as Lake Baikal, Lake Tanganyika and Lake Superior, account for 4/5 of the total fresh water in the world. The total fresh water of Poyang Lake, Dongting Lake, Taihu Lake, Chaohu Lake and Hongze Lake in China is about 55.3 billion meters. Lakes are an important part of waterway transportation. They are rich in fish, shrimp, crabs and shellfish, and produce lotus, lotus root and water chestnut. Unreasonable exploitation of lake resources will lead to the decline of lake fishery resources, the reduction of lake area and the swamp of land around the lake.