Swamp is that the surface and underlying soil are often excessively wet, and there are wet plants and marsh plants on the surfacepeatAccumulated or with no peat accumulationGley layerExisting land.[1]
The formation of marshes mainly depends on the geomorphic conditions and hydrothermal conditions.[2]
There are marshes in all parts of the earth except the Antarctic region, where no marshes have been found.Generally speaking, the Northern Hemisphere is more than the Southern Hemisphere, and it is mainly distributed in the Eurasian continent in the Northern Hemisphere and the subarctic, cold and temperate regions in North America.The marsh area in the southern hemisphere is small, mainly distributed in the tropics and some temperate regions.The largest peat swamp area in the world is located in the western lowlands of Siberia, which is 800 kilometers wide from north to south and 1800 kilometers long from east to west, accumulating 40% of the world's peat.China's marshes are mainly distributed in the Sanjiang Plain in the northeast and the Qinghai Tibet Plateau.[3]
The marsh is basically interpreted as a large area with low-lying ponding and overgrown weedsMire area。[5]
In a broad sense, swamp refers to everythingWetland。The narrow sense of swamp emphasizes the existence of a large amount of peat.[5]
The terms used in literature vary from country to country.The Russian word БОлОТО refers to the wetland whose peat layer reaches more than 30 cm (without sulfur dry state).In English, several nouns refer to different types of marshes, and the meanings given by different scholars are also different.But the word bog often means richpeatAs the peat and ponding are acidic, it is often translated as“Acid marsh”。Marsh and swamp usually refer to mineral soil wetlands. MarshherbMainly, swampWoody plantMainly.Japan is collectively called "Shihara", which is a special name for peat“Peatland”。[5]
Causes
Announce
edit
Long term over wetting of soil surface is the direct cause of marsh formation.
The reasons for long-term over wetting of soil are: (1)water meadowIn low-lying land, due to the gentle slope and heavy soil viscosity, the surface water drainage is not smooth or the infiltration is difficult;(2) The water balance of the soil layer in the forest cutting area or the burned area is destroyed due to the loss of the great water absorption of trees;(3) Groundwater overflow zone formed due to frequent exposure of spring water;（4）irrigated areaDue to excessive irrigation, etc.In addition, the seasonal thawing will also promote the process of swamping in places suitable for the growth of lower plants in the frozen soil zone.During the development of some marshes, because the accumulation rate of dead plant remains is greater than the decomposition rate, there is a muddy accumulation layer, calledPeat bog, most marshes in cold temperate zone belong to this category;The cumulative speed of some marsh plant residues is less than or equal to the decomposition speed, and only a certain thickness of grass root layer appearsGley swamp, Northeast ChinaSanjiang plain Most of the marshes belong to this category.[6]
mire type
Announce
edit
There is no uniform standard for the classification of marshes in the world, and there is no recognized classification standard and scheme in China.[7]At present, there are mainly the following classification methods and types:
Classification of development process
According to the development process of peat bogs, mainly the accumulation process of peat carbon can be divided into low, middle and high bogs, namely, eutrophic, mesotrophic and oligotrophic bogs.[8]
Eutrophic swamp, also known asLowland swampIs the initial stage of swamp development.The marsh surface is low-lying and often becomes surface runoff andgroundwaterA gathering place.The water supply is mainly groundwater. With the flow of water, a large amount of minerals are collected, which is rich in nutrients,ash contentHigh content.The pH values of water and peat are acidic to neutral, and some are alkaline due to the influence of bedrock at the bottom of the soil.For example, Northwest Sichuan, ChinaZoige swampOf peatAlkaline reactionBecause the bedrock in this area is mostly calcareousshaleWith limestone interlayer, the pH value is about 8.The plants in the eutrophic swamp are mainly sedge, reed, kobresia, equisetum, alder, willow, birchlarch、Falling feather pine、Chinese pinewait.[8]
Poverty-stricken swamp, also known asHigh swampIs often the last stage of marsh development.With the development of marsh,SphagnumGrowth,Peat layerThickened, the middle part of the marsh is uplifted, higher than the surrounding area, so it is called high level marsh or uplifted marsh.Water supply only depends onAtmospheric precipitationThe water and peat are strongly acidic, with a pH value of 3~4.5.ash contentIt is low in content and poor in nutrition, hence its name.Swamp plants are mainlybryophyteIt forms tall moss mounds with small shrubs such as jasmine, blueberry and herbaceous plants such as cotton sedge, especially with sphagnum as the advantage, so the poverty-stricken swamp is also called sphagnum swamp.Mainly distributed inNorthern coniferous forest belt, due to excessive water, cold and poor nutritionhabitatSphagnum has become the dominant plant, and a few herbs, short shrubs and trees can live in the Sphagnum marsh, such as Peucedanum chinense, blueberry, larch, etc. The dominant plants areSphagnum。[8]
Mesotrophic swamp, also known asMedian swamp, belonging to the transition type between the above twosurface waterMixed supply, medium nutrition.There are rich and poor marsh plants.There are many bryophytes, but no moss mounds have been formed,Surface morphologyFlat.[8]
Classification of peat accumulation
Since the soil of marsh land can be divided into peat soil and gley soil, marsh land can be divided intoPeat bogandGley swampTwo categories.[8]Peat bogIt is not widely distributed, and the peat layer is not thick, mostly tens of centimeters or about one meter.Gley swampIt is widely distributed. The surface of this kind of marsh is too wet for a long time or there is thin layer of ponding. The soil layer is seriously gleyed. There is a thick grass root layer, but no peat accumulation.[9]
Vegetation classification
According to the growth of vegetation, swamps can be divided intoHerbaceous swamp、Peat moss swampandWoody swamp。Herbaceous swampIt has many types and wide distribution. The perennial water or soil is permeable. Carex and gramineous plants are dominant. Almost all of them are perennial plants. Many plants have rhizomes and often interweave into thick grass root layer or mat layer, such as reeds and some carex marshes.Peat moss swampIt is mainly distributed in the northern coniferous forest belt. Due to the watery, cold and nutrient poor habitat, sphagnum becomes the dominant plant, and a few herbs, small shrubs and trees can live in sphagnum marshes, such asPeucedanum chinense, blueberry, larch, etc.Woody swampThe vegetation of the marsh is mainly woody nutrient plants. The marsh is a natural treasure house of fiber plants, medicinal plants and nectar plants. It is a good place for birds and fish to live, reproduce and fatten. It has the function of humid climate and purifying the environment.[10]
Classification of geomorphic conditions
According to the geomorphic conditions and the characteristics of Chinese marshes, it can be divided intoPlain swamp、Plateau swampandMountain swamp。The Three Rivers Plain in Northeast China is the largest and concentrated lowPlain swampThe area is dominated by herb gley marshes, and peat marshes are developed in some areas.There are typicalMountain swamp, which is rare in China-Ledum palustre -Peat moss marsh and larch blueberry peat moss marsh, mountain marsh contains rich biological resources and peat resources.Plateau swampIt is a special type of marsh in the world.In the early 1960s, researchers investigated the original marshes of Ruoergai Mountain and found that the grasslands that the Red Army passed during the 25000 li Long March were the most concentrated plateau marshes in China and the world.[7]
wetland ecology
Announce
edit
The plants in the marsh are luxuriant, generallyEmergent plantMore grass, the height of grass depends on different geographical and climatic conditions: marsh grass in lower latitudes is higher, and marsh grass in higher latitudes is shorter, even most of it is moss.Lotus、LotusIs also a swampWetlandThey belong to emergent plants.Some wet loving and waterlogging tolerant tree species will grow very large in marshes. One obvious feature is that their roots are often very thick.In addition, there are many animals living in the marsh, forming different types ofBiome。[8]
Swamp plant
Swamp plants grow on the surface that is too wet and the soil is anaerobichabitatUnder the condition, its basic life style isEpiphyteAnd aboveground budding plants.Dense clumps of Cyperaceae, such as Carex, Cotton Cyperus, Artemisia, etc., are dominant. The way of ground bud tillering is suitable for the environment with more water and less oxygen, and forms different shapes of grass hills: point, block, ridge, ridge, etc.The formation of the last three types of grass hills is not only related to the biological characteristics of the constituent plants, but also related tofrozen soilIs related to erosion.They are the main source of peat.In addition, swamp plants generally stemAerenchymaDeveloped, which is also the adaptation to less oxygen.[8]
Trees and shrubs with high position buds and above ground buds in forest swamps.The trees in the poverty-stricken swamp are poorly developed, isolated and scattered, low curved, withered and slow growing, forming small and old trees.For example, 150 year oldLarix gmeliniiThe tree is only 4.5 meters high;North American larch is 150 years old and only 30 cm tall.Shrubs include Betula and Salix.Small shrubs include Duxiang, Vaccinium, Cassia, cranberry, red berry moss, etc.They often form advantages in the poor marshLamellaThere are many kinds and large coverage.[8]
In mesotrophic and oligotrophic swamps, there are many species of ground bud bryophytes with large coverage, often forming dense ground cover and moss mounds.Among them, peat moss is the most developed.The height of peat moss mounds varies. The moss mounds in China and Japan are generally shorter, less than 0.5 meters, and those in Europe and North America are slightly higher.[8]
according toMarsh waterDifferent from the nutritional status of peat, swamp plantsEutrophic plantandOligotrophic plant。In theGroundwater rechargeThe plants growing under the conditions of rich nutrition and high ash content are called eutrophic plants.Such as reeds, carex, alder, larch, etc;In theAtmospheric precipitationNutritional poverty dominated by supplyash contentThe plants growing under the condition of less content are called oligotrophic plants.Poor plants have special adaptability to harsh environment: some plants have the ability to grow continuously at the top, such as peat moss andPolytrichum juniperinum Some plants have the ability to grow adventitious roots, such asPueraria rotundifoliaTherefore, they can absorb nutrients and water from the surface of the marsh.Some marsh plants haveXeric Structure, such as evergreen leavesLeathery, YesvillusThis can prevent excessive transpiration of water, and also adapt to strong acid substrate.There are also insect catching plants in the marsh that can nourish animals. They use the glands on the leaves to digest the protein of animals to make up for the lack of nutrition.There are many kinds of calophytes and pitcher plants in China, and Sarracea andDionaea muscipula, Tierra del Fuego in South AmericaDroseraandInsect trapping vegetable。[8]
Swamp animal
Different types of marshes inhabit different animals.Enriched marshes, especially those near the lakeside, are rich in animal species, including mammals, birds, reptiles, amphibians, fish, invertebrates and insects.MammalsOtter, water voles and water shrews as representatives.There are many birds, including many snipeswading birdCranes and herons, ducks and geese, birds of preySwamp swanEtc.Amphibians include toads and frogs.Reptiles have snakes.There are also many kinds of fish.Diptera larvae in the water.Herb marshes usually have many animals, such as voles and muskrats, and the soil contains oligochaetes, spiders and nematodes.Nematodes can obtain oxygen from the aerenchyma of plants under anaerobic conditions, and even can survive under anaerobic conditions.The animals in woody swamps are mainly birds and transit mammals, such as bears, muntjacs, wolves, etc.Forest swampOfsoil animal There are oligochaetes, diptera larvae and nematodes.The peat moss swamp has no shelter, the soil is strongly acidic, and the nutrition is poor, so there are few animals, but it can be seeninvertebrateCollembola, spiders and acari, etc.[8]
Swamp biome
The marsh biological community is stratified due to the different effects of light, heat, humidity, air, substrate, etc. on different parts, and has different structures and compositions from different heights on the ground to different depths of the soil layer.[8]
The structure of swamp formed by forest swamping is complex.EutrophicationForest swampThe aboveground part ofShrub layer, wet herbaceous layer.The grass mound is developed in the herb layer.The underground part is composed ofLitter layerAnd peat layer (with living roots).[8]
There are few species of plants in the poverty-stricken forest swamp, and its structure is simple. The sparse forest is formed by sparse trees above the ground, and the small shrub layer and peat moss layer are wet and acid resistant under the forest. The peat moss buries part or all of the grass hills, and sometimes there are no trees.The underground part has peat layer (containing a few living roots).[8]
The mesotrophic forest swamp belongs to the transitional type between the above two types of swamps.There are rich plant species, both poor and rich plants, so the structure is more complex.There are arbor layers on the groundShrub layer, shrub layer, vegetation layer, moss ground cover layer, no moss mound.There is a peat layer (containing living roots) underground.[8]
The marsh formed by the lake, at the initial stage, the plants, depending on the depth of water and light conditionsLakeshoreIt is distributed horizontally towards the center of the lake, including carex plant beltEmergent plantThe first two zones form a swamp.At mesotrophic stage, moss and peat moss layer appeared on the lake surface.Poor marsh stage,lake basinFull of peat, the lake surface is dominated by peat moss layer, and the surface is uplifted.[8]
Profile Map of Artemisia Carex Marsh on Qinghai Tibet Plateau, China[11]
The meadow marsh formed by meadow marsh can be divided into grass hill and wet depression between hills according to different hydrological conditions.The hills are humid and rich in plants. Carex is the dominant species (Kobresia is dominant in high mountains and plateaus).There are miscellaneous grasses in it. There is water in the depressions between hills, and wet plants grow.The underground part has grass root layer and peat layer (with a few living roots).[8]
Europe still has a variety of high (poor), low (rich) mosaic swamps.Peat hills can be as high as several meters, growing peat moss, lichen and small shrubs;Wet depressionCyperaceaeSuch as flowering plants and mosses.[8]
Material cycle
Announce
edit
Carbon cycle
Swampycarbon, is the decomposition of carbon dioxide from the atmosphere and dissolved in water, as well as organic matter in peat.Swampycarbon cycleFirst, plants carry out photosynthesis, fix carbon dioxide in the atmosphere, and synthesizecarbohydrate。Some carbohydrates arePlant respirationFunction consumption, produce carbon dioxide, return to soil and atmosphere, and complete the simplicity of carbonCyclic process。Secondly, plant residues pass throughPeatizationThe peat is formed in the process. Under the action of aerobic bacteria, the organic matter in the peat is decomposed, and the released carbon dioxide participates in the carbon cycle of the ecosystem.The organic matter of peat contains cellulose andhemicelluloseEtc.Polysaccharides are decomposed intomonosaccharide, such asglucoseEtc.glucoseThe decomposition products under different conditions and under the action of different microorganisms are very different.There are two situations of perennial ponding and seasonal ponding on the marsh surface, and the release process of carbon dioxide is different under these two situations.Seasonal ponding swampDry seasonWhen glucose is decomposed by aerobic bacteria and fungi, carbon dioxide, water andenergy, carbon dioxide returns to soil and atmosphere.In rainy season, the glucose in perennial ponding marsh or seasonal ponding marshAnaerobic bacteriaDecomposition, first formedOrganic acidandcarbon dioxide, finally releasedmethaneAnd hydrogen.Carbon dioxide is an intermediate product, part of which is returned to the atmosphere.[11]
Comparison of carbon content in peat[11]
The carbon content of peat is high, but the type of peat varies with the type of swamp;Accordingly, the carbon content of peat is also different.In addition, on thePeat organic matterUnder the condition that the content is basically the same, the carbon content is related to the degree of decomposition. The higher the degree of decomposition is, the higher the carbon content is, and vice versa.The carbon content of peatGeologic AgeAnd increase.It is estimated that it will take 5000 to 8000 years for the carbon content to increase by 2-3%.Because carbon accumulation depends on the slow secondary condensation process, dehydration process andDecarboxylation。[11]
Coal is a carbonaceous material, which may be peat formed by plant residues in ancient marshes through pressure diagenesis in a long geological period.Coal due toCrustal movementOnly after weathering or human burningcarbon dioxideThe form of carbon is released into the atmosphere and participates in the carbon cycle of the earth.This kind ofcarbon cycleThe cycle of is much longer than the atmospheric carbon cycle.[11]
Nitrogen cycle
Nitrogen cycleThe process is more complex than the carbon cycle.Swamp ecosystemThe sources of medium nitrogen include free nitrogen in the atmosphere, a small amount of nitrate nitrogen and ammonium nitrogen carried by precipitation, and nitrogenous organic substances in peat, such as proteinhumic acid, alkaloids, etc.[11]
Free nitrogen in the atmosphere cannot be directly absorbed by plants. It can only be absorbed by plants through the nitrogen fixation of nitrogen fixing bacteria.There are symbiotic actinomycetes living in the bundle shaped big root nodules at the roots of alder, a marsh plant. They can fix nitrogen in the atmosphere, so there is more nitrogen in the alder marsh.[11]
The nitrogen cycle in the marsh is mainly that the nitrogen containing organic matter in the peat releases nitrogen through complex biochemical processes under the action of microorganisms, but the decomposition process of nitrogen containing organic matter under aerobic conditions is different from that under anaerobic conditions.Aerobic bacterial decomposition occurs on the surface of peat in dry season, and nitrogen containing organic matter in peatmicroorganismUnder the action of, it is converted into ammonia.A part of ammonia is returned to the soil and used by plants;Another part can be found in Asianitrifying bacteriaAnd nitrifying bacteriaNitriteandNitrateClass, absorbed by plants.[11]
Nitrogen content in peat[11]
Under the condition of perennial ponding on the marsh surface, anaerobic bacteria activity is the main activity, and aerobic bacteria activity is also present.Nitrogen conversion toDenitrificationProcess oriented.Denitrifying bacteriawithNitriteandNitrateAs a source of oxygencompound formNitrogen is converted into free nitrogen and returned to the atmosphere, realizing the nitrogen cycle.[11]
More than 90% of nitrogen compounds in peat areOrganic nitrogen。The nitrogen content of peat varies with the type of peat. The nitrogen content of rich peat is high, while that of poor peat is low.[11]
Movement of marsh water: Except that some marshes have surface flow in some periods of time, most of the marsh runoff is the marsh surface flow with lateral infiltration in porous media.
Temperature, freezing and thawing of marsh: the surface temperature and daily variation amplitude of marsh with ponding or saturated surface water on the surface are smaller than that of general ground, while the surface has no ponding and is close to dry peat marsh and dry gley marsh on the contrary.The vertical depth of daily temperature change in marshes is generally small.The marshes in high latitudes are frozen. WhenPhreatic levelWhen reaching the swamp surface, the freezing process starts late, and the freezing is slow and the depth is small.When the surface organic matter is nearly dry, it cools quickly and freezes early, but the lower layer freezes slowly and the freezing depth is small.Similarly, spring thaws late and thaws through late.[12]
Utilize protection
Announce
edit
Swamp is bothland resourceIt also has valuable peat and rich biological resources. In addition, it has certain significance in maintaining regional ecological balance.The marsh cannot be regarded as "wasteland" and blindly reclaimed.Should be based onmire type And the characteristics of the distribution areas, combining rational development and utilization with protection.[13]
The large area of marsh distributed in the source area of the river is the reservoir of water, which has the function of water storage and water conservationRiver rechargeIt can reduce the supply of a rainfall to the river, weaken the peak value of the river and delay the occurrence time of the flood peak, and also make the water in the year not flow out completely, extending the catchment time.Therefore, it should be protected.[13]
Swamp is a large natural reservoir. It can increase atmospheric humidity and regulate rainfall through water surface evaporation and plant transpiration, which is conducive to the growth of forests and crops, promoting the development of agriculture, forestry and animal husbandry, and also has a good effect on human health.Therefore, great care must be taken to develop marshes to prevent the ecological balance of the area from being damaged due to development.[13]
There are many animal and plant resources in the marsh.Like reedsPapermaking raw materialsandman-made fiberAnd knitting materials, which have high economic value.The young leaves of Kobresia and Carex are good forage for livestock.Forest swampBerries, such as blueberriesLonicera caerulea It is edible and also the raw material for wine making.There are many medicinal plants in the marsh, such as golden lotusAlisma orientalis, arrowhead, peat moss, etc.These plant resources should be rationally used in a planned way and cultivated and protected.There are abundant plants and water resources in the marsh. They are some migratory birds, such as preciousRed-crowned crane、black necked Crane, swans and many water birds.For theseAnimal resourcesProtection and management should also be strengthened.[13]
SwampypeatIt contains a large number of plant spores and pollen, which is of scientific value for studying the formation and evolution of ancient climate, ancient vegetation, and the development law of ancient geography. Therefore, all marshes cannot be taken as development objects, and some of them should be absolutely protected.on the other hand,Eutrophic swampThe ground is relatively flat, of which the peat layer is thinMarshlandWith certain potential fertility, it can be improved into pasture or reclaimed into farmland after drainage and drainage.The marshland can be transformed by means of mixing sand and digging drainage ditches, and vegetables and rice can be planted, which has been successful in many countries.Abundance of forest areasCarex bogAfter trenching, drainage and platform building, the survival rate of afforestation is high, generally more than 90%.At the same time, the abundantPeat resourcesIt can be used as fuel.Peat can also be madeSoil conditioner、Nutrient soil, nutrition bowl, etc. are used for gardening flowers.In addition, in thePeat bogIn addition, it also contains a wide range of applications in agriculture, industry, energy and environmental protectionPeat resources。However, all large-scale reclamation, development and utilization must be fully demonstrated, and the possible ecological consequences must be fully considered.And the development should be limited, and supplementary measures should be taken to protect the ecological balance during the development.[13]
