Natural causes of swamp formation

Question 1: Natural causes of swamp formation 1. Precipitation is concentrated in summer, with heavy rainfall;

2. High latitude, low temperature and weak evaporation;

3. Low terrain and poor drainage;

4. The soil is thick and has permafrost, so the surface water is not easy to seep down.

Question 2: The causes of swamp formation have various reasons.

first

In humid areas, rivers bring sediment into lakes. Due to the sudden widening of the water surface, the water flow slows down, and the sediment is deposited by the lake, forming a shoal. A part of tiny substances drifted to the open part of the lake with the current and settled to the bottom of the lake. As the years passed, the lake became shallower and shallower. And with the different depths of the lake, various aquatic plants gradually multiply. In the shallow waters along the coast, reeds and cattails grow; In deeper places, water lilies, duckweeds and water lilies often grow; In the depths of the lake, there are various algae such as POTAMOGETON. These plants continue to grow and die, and a large number of rotting plant residues continue to accumulate at the bottom of the lake, gradually forming peat. With the gradual sedimentation at the bottom of the lake, new plants appear and develop from the periphery of the lake to the center of the lake, and the lake becomes smaller and shallower. When the sediment in the lake increases to a certain limit, the lake with wide water surface becomes a shallow swamp with weeds.

In addition to the evolution from lakes, swamps have the following situations:

Along the river in the low-lying plain, aquatic plants can grow and gradually form swamps under the condition of shallow water and slow flow. In coastal lowlands, being repeatedly submerged by seawater, weeds and reeds grow on the beach, and salt marshes can also be formed. In some plateaus and mountainous areas, due to the ground snow in winter, the snow melts in the spring and summer of the following year, and the ground water accumulates, and short grass and bryophytes are mixed, which can also form swamps.

In the forest area, the garbage under the forest keeps piling up, as if to cover the ground with a thick quilt. It can not only store a lot of rainwater, but also reduce soil evaporation and keep it in an excessively humid state. Due to the carbonization process, most of the mineral nutrients in the soil are leached, which leads to the death of vegetation and is replaced by lush bryophytes. Bryophytes can retain a lot of water, slow down the decomposition process of plant residues, and peat begins to accumulate, gradually forming a swamp. This phenomenon of forest swamping can be seen in the forests of Daxing 'anling Mountains in China.

In some too humid areas, weeds proliferate in large numbers, forming thick grass layers, which makes the soil aeration worse, the carbon content gradually decreases, the original plants gradually decline, and plants such as sedge and sphagnum grow. These moisture-loving plants have strong water storage capacity, so the water conditions are strengthened and the meadow swamp develops rapidly. This is how some grasslands in western Sichuan were formed.

Of course, due to geological evolution, lakes form swamps due to the accumulation of plants and sand. Due to the accumulation and storage of leaves or vegetation, forests form swamps.

The following are the distribution and classification of some swamps in China:

(1) swamp wetland. China's swamps are about 1 1.97 million hectares, mainly distributed in Sanjiang Plain, Daxing 'anling, Zoige Plateau, seashore, lakeside and river bank in the northeast. There are woody swamps in the mountains and herbaceous swamps in the plains. ? Sanjiang Plain, located in the northeast of Heilongjiang Province, is a low plain alluvial by Heilongjiang, Songhua River and Wusuli River. It is the largest freshwater swamp distribution area in China, and there are about11.3000 hectares of marshes left in 1.990. Sanjiang plain is mostly a latent swamp without peat accumulation, and there are few peat swamps. Marshes generally have obvious grass roots, which are spongy, with large porosity and strong water retention. The utilization of resources in this area is mainly agricultural reclamation and commodity grain export. Marshes in Daxing 'anling and Xiaoxing 'anling are widely distributed and concentrated, accounting for 9% in the north of Daxing 'anling and 6% in Xiaoxing 'anling. The types of swamps in this area are complex, and peat swamps are developed, mainly forest swamps and meadow swamps, which is one of the areas rich in peat resources in China. ? Zoige Plateau, located in the northeastern margin of Qinghai-Tibet Plateau, is the largest and most concentrated peat swamp area in China. Especially in the middle and lower reaches of Heihe River, there are closed undercurrents, wide valleys, swamps all over the bottom, and deep peat layers, and the swamp rate reaches 20%-30%. This area is dominated by herbaceous peat bogs with rich nutrition, and compound bogs are developed. Zoige Plateau is an important grassland in China. ? Seaside, lakeside and river bank are mainly reed swamp distribution areas. Reed marshes in coastal areas are mainly distributed in the muddy coast from the north of the Yangtze River to the mouth of the Yalu River, and concentrated in the alluvial delta where rivers enter the sea. Reed marshes with different widths are generally distributed around the larger lakes in China. In addition, reed marshes are often distributed in the middle and lower reaches, whether they flow out of the river or into the river.

(2) Lake wetlands. There are various types of lakes in China, showing different regional characteristics. According to statistics, there are 27 1 1 natural lakes in China, with a total area of about 90864 square kilometers. According to the differences in natural conditions, resource utilization and ecological management >>

Question 3: A brief analysis of the natural causes of swamp formation in Tongtianhe Basin, with low terrain and poor drainage.

Underground permafrost, water is not easy to seep down.

Melting water in mountainous snow and ice

High altitude, low temperature and weak evaporation.

Question 4: Analysis of the causes of floods? Analysis of the causes of swamp formation? Cause analysis of flood disaster in Wufen River

Cause analysis of river flood disaster: natural causes (mainly from three aspects: water system characteristics, hydrological characteristics and climate characteristics); Man-made reasons (mainly from the destruction of vegetation around the lake and land reclamation).

Analysis of river regulation measures

Upstream: the principle of regulation is flood regulation, which is to build reservoirs and plant trees; Mid-stream: the principle of flood control is to store flood separately, by building reservoirs and storing flood separately; Downstream: the principle of regulation is flood discharge and water control, and the practice is to reinforce dikes, dredge rivers and dig rivers.

The first situation: the northeast; Middle and lower reaches of Yellow River and Yangtze River; Huaihe river basin; Causes and countermeasures of floods in pearl river basin and other places.

(1) Reason:

A. Natural reasons: there are many tributaries of the water system (fan-shaped water system and dendritic water system); River bend (Jingjiang reach); Lack of natural rivers flowing into the sea (Huaihe River); Low-lying (Haihe River, Pearl River). Hydrological characteristics There are many rainstorms in summer, and the river surges. Climatic characteristics: the precipitation lasts for a long time and is concentrated (such as the rainy weather in the Yangtze River basin); The change of summer monsoon intensity (the second highest intensity: drought in the south and waterlogging in the north; Weak subtropical high: waterlogging in the south and drought in the north); The influence of typhoon; El Nino phenomenon, etc.

B. Man-made reasons: excessive logging leads to increased soil erosion and riverbed uplift; Reclamation around the lake weakens the regulation ability of the lake; Irrational construction of water conservancy projects (Weihe River Basin).

② Prevention measures: planting trees and building shelter forest system; Returning farmland to lakes; Building water conservancy projects; Bend and straighten, and reinforce the levee; Excavation of the river channel into the sea (Huaihe River); Construction of flood diversion area; Establish flood forecasting and early warning system.

The second case: try to analyze the causes of the Yangtze River flood.

① Natural reasons: a. Characteristics of water system: There are many broad tributaries in the basin; The middle and lower reaches are mostly plains, with curved rivers, slow water flow and poor drainage. B. Hydrological characteristics: it flows through humid areas, with abundant precipitation, long flood season and large amount of water in the main stream. C. Climatic characteristics: In some years, the climate is abnormal, and it rains heavily in the basin, resulting in flooding.

(2) Man-made factors: a. Excessive logging, serious vegetation destruction and intensified soil erosion, resulting in reduced water conservation, runoff regulation, peak shaving and drought compensation; Sediment enters the river, silting up and raising the river bed, which reduces the flood discharge capacity of the river. B. Reclamation and siltation around the lake cause the lake to shrink and the flood peak storage capacity to decrease.

The third situation: the natural causes of the Huaihe River flood: concentrated precipitation and heavy rain; There are many tributaries in the middle and upper reaches with large flow; There is no natural river flowing into the sea downstream, so the drainage is not smooth. Measures: Excavate a new river into the sea (or: dredge the river, reinforce the dam, and build a flood discharge area).

The fourth case: the causes of serious floods in Bangladesh: ① natural causes: strong southwest monsoon, heavy rain and abundant precipitation; Low-lying, poor drainage; Ganges and Yarlung Zangbo rivers meet here and enter the flood season at the same time. ② Human factors: high population density, much vegetation destruction in the upper reaches and serious soil erosion.

Formation conditions of ice flood

The formation of ice flood must meet two conditions: first, there is an ice age; The second is from low latitude to high latitude. In China, the most serious ice flood is the Yellow River, which mainly occurs in the upper and lower reaches (that is, the Shandong reach).

Cause analysis of swamp: high latitude (altitude), low gas explosion, weak evaporation; Flat terrain and poor drainage; Frozen soil development.

The first case: the natural reasons for the formation of swamps in Sanjiang Plain in China are: high latitude, low temperature and weak evaporation; Low-lying, poor drainage and wide distribution of frozen soil; The water system is developed and there is a phenomenon of ice flood.

The second case: the causes of the formation of the Siberian swamp in Russia.

Question 5: How did the swamp form? Marsh is formed by the interaction and restriction of many natural and geographical conditions. But the main conditions are the influence of climate, hydrology, geology and geomorphology and human activities.

1. Climatic conditions Frequent over-wetting of soil surface is the direct cause of swamp formation, and soil moisture status mainly depends on climate. In wet areas with abundant precipitation, there is too much water on the surface, high air humidity and weak evaporation. Except for areas with large surface cutting and developed river network, swamps almost occupy the whole ground, not only low-lying landforms, but also swamps on hillsides and even river basins. Swamp has become the main feature of natural landscape in this kind of area. In areas with insufficient and unstable humidity, the distribution area of marshes is reduced, and only distributed in closed-flow depressions, lakesides, floodplains and places where the groundwater level is close to the surface. In areas with little precipitation, dry climate and insufficient water, swamps are rarely encountered, and only in areas where rivers are flooded or groundwater is exposed will swamps develop.

The formation of peat bogs depends not only on water conditions, but also on thermal conditions. Peat can only be formed and accumulated when new organisms are added after the death of swamp plants every year, which is greater than the number of decaying substances every year. Atmospheric and soil temperatures, on the one hand, affect the growth rate of plants in the growing period, on the other hand, restrict the decomposition intensity of dead plant residues. In the cold climate, the temperature in the growing period is low, which is not conducive to the growth of plants. Plants grow slowly every year, but they decompose very little. Under the tropical and subtropical climate conditions, the temperature is high during the growing period, the growth of plants is accelerated, and the decomposition intensity of organic matter is also increased, even exceeding the growth. However, under the conditions of high temperature and high humidity, there are also some peat deposits.

In the northern hemisphere, with the regular change of climate latitude, the average cumulative intensity of swamp and peat is also distributed in a strip shape. In the Arctic tundra, the swamp coverage rate reaches 50%, and the thickness of peat is only 20 ~ 30 cm. With the increase of peat thickness in the south, the swamps in the north of Taijialin are the most widely distributed, with a coverage rate of 60-70% and a cumulative thickness of 3-4m. In the south-central part of the Taiga forest belt, the peat layer reaches the maximum thickness, about 8-9m, but the swamp coverage rate gradually decreases, only 25-35%. Further south, the peat layer becomes thinner, and peat bogs are rarely seen except in tropical rain forest areas.

Climatic conditions play an important role in the formation and development of swamps in Sanjiang Plain. This area belongs to temperate humid and semi-humid monsoon climate zone. Although the annual average precipitation is not much, the seasonal distribution is uneven, mostly concentrated in summer and autumn. By the end of 10 or the beginning of 1 10, the temperature dropped, and a large amount of water was frozen on the surface or soil layer, resulting in excessive water accumulation or humidity on the surface after thawing in the following spring. In addition, the freezing period is long, the frozen layer is thick (as deep as 1.5 ~ 2. 1 m), the soil is sticky, which is not conducive to water infiltration, the surface is often too wet, and swamps are widely developed.

2. Geological and geomorphological conditions The influence of neotectonic movement on the surface morphology is direct and obvious. The long-term subsidence of an area has caused a landform structure with high periphery and low middle, and accumulated deep loose materials. The flat surface, weak erosion capacity, winding rivers and low drainage capacity are beneficial to water collection and stagnant flow. It can be seen that the geological structure and landform conditions provide a good space for the formation of swamp.

Sanjiang plain is a long-term subsidence area of neotectonic movement, with low-lying and flat terrain and surrounded by mountains on three sides. There is much precipitation in the surrounding mountainous areas and abundant runoff in the plains. The plain area is extremely low and flat, slowly inclining from southwest to northeast, with a total slope of110000. Therefore, some small and medium-sized rivers in the area are developed, and most of them have no obvious rivers, which are typical swamp rivers with low discharge capacity. In the process of long-term subsidence, clay and sub-clay layers of lake facies and flood plain facies are accumulated on the surface, and the water permeability is weak, so that a large number of collected surface water can not seep and accumulate to form swamps.

After the Quaternary Ice Age, the famous Zoige swamp area in China sank for a long time, forming a complete mountain plain with an altitude of more than 3,400 meters, surrounded by high mountains. The interior of the mountain plain is relatively low and flat, bearing the runoff supply formed by mountain meltwater and precipitation, and carrying a lot of sediment here. On this basis, quite deep river and lake sediments were accumulated, which hindered water infiltration, promoted excess water on the surface and provided favorable conditions for swamp formation.

Iii. Hydrological conditions The hydrological characteristics of an area are restricted by climatic and geomorphological conditions. Hydrological characteristics also play an important role in the formation of swamps. Surface water and groundwater are the direct sources of marsh recharge, and recharge is directly related to runoff conditions.

The swamps in China are mostly developed in rivers with small slope, large curvature, many tributaries and wide floodplain ...