Analysis of Land Degradation and Desertification
Types of land degradation and desertification
Desertification in our province can be divided into water erosion, wind erosion and salinization from the genetic types; Morphological types can be divided into rocky desertification, soil desertification, gravel desertification, desertification and salinization. Water erosion is soil erosion. It is the main cause of rocky desertification, soil desertification and sand desertification. Soil erosion mainly occurs in hilly areas and loess distribution areas. It involves a wide range and is harmful. Wind erosion is the main cause of desertification. Mainly distributed in the sandy soil area and loess distribution area of the alluvial plain of the Yellow River. The hazards of quicksand and sandstorm in this area are also quite serious. Salinization mainly occurs in the low-lying and waterlogging-prone areas of the alluvial plain of the Yellow River and the fan-edge areas of ancient crevasses, and its harm has been gradually reduced since the 1980s. According to vegetation coverage, soil erosion modulus and soil organic matter content, water erosion desertification is divided into 9 categories; According to the soil quality, micro-topography and vegetation of sandy land, wind erosion and desertification are divided into four categories; According to the degree of salinization, salinization can be divided into two categories. See table 10.5. 1 for details.
2. Land degradation and desertification in Henan Province
(1) soil erosion
In the early days of the People's Republic of China, the area of soil erosion in our province was 6 120000 hm2. According to 1985 remote sensing survey, soil erosion modulus is 6.58 million hm2, exceeding 500 t/a.km2, accounting for 40% of the whole province. Among them, the area with moderate erosion (≥ 3,000 t/a.km2)1400,000 hm2 accounts for 27% of the hilly area. The hilly area of the province loses 236 Mt of soil every year, which is equivalent to 97000 hm2 of cultivated land in 20 cm mature soil layer. According to "Provincial Ecological Environment Construction Plan" issued by 1999, our province has accumulated 2597000hm2 of soil erosion control area and 3463000hm2 of remaining soil erosion area. Due to deforestation and greening, the area of soil erosion increases 16000 hm2 every year, and the province loses soil 120 Mt every year, resulting in a considerable loss of cultivated land of 24000 hm2. N.P.K nutrient loss is equivalent to standard fertilizer 1 Mt According to this remote sensing survey, there are 3,634,000 hm2 (≥ 500t/(a km2)) of hilly areas where land degradation occurs due to soil erosion, accounting for 58.3% of the hilly areas above 25,000 hm2. Among them, the area with moderate erosion (≥ 3000 t/a km2) and desertification tendency is 3.323 million hm2, accounting for 53.3% of the hilly area above 2. The areas with serious soil erosion in the province are:
Table 10.5. 1 Analysis Table of Land Degradation and Desertification in Henan Province (Remote Sensing Survey)
A. Loess area
The total area of loess area in our province is 1656000 hm2. Among them, 962,000 hm2 of loess covers the mountains, hills, beams and headlands with strong soil erosion, accounting for 58% of the loess area. The loess area is the "area with the largest soil erosion" in our province, with soil erosion modulus exceeding 5000 t/a.km2
B. Bad areas
Inferior land refers to low mountains, hills or terraced fields with sparse vegetation, poor rock cementation and poor water holding capacity. From Mesozoic to Tertiary, the strata are usually composed of mudstone, shale and glutenite, which is an area prone to landslides. In case of rainstorm, it can be mixed with topsoil to form a very harmful debris flow. Typical areas include the Yuan Shao-Xiaolangdi reservoir area in the southwest of Jiyuan, Lushi basin, Lingbao Zhuyang basin and Hebi platform.
C. Bare rock mountain area
According to the degree of soil erosion from heavy to light, it can be roughly divided into Songji Mountain, Taihang Mountain-Wuwang Mountain, Xiaoshan, Xiong 'er Mountain, Waifangshan Mountain, Funiu Mountain, Dabie Mountain and Tongbai Mountain. Among them, the soil erosion in the mountainous areas of central and northern Henan is the most serious, followed by western and southern Henan. The valley destroyed by vegetation in the mountainous areas of northern and western Henan is often the source of debris flow. It is worth noting that the Dabie mountain area in southern Henan Province has also become a new source of serious soil erosion due to the development of economic forest land such as tea, chestnut and tung oil. In addition, mining development zones, especially bauxite, gold and coal development zones, also belong to vicious soil erosion areas.
D. sloping farmland
According to this remote sensing survey, there are 2,448,000 hectares of cultivated land with a slope above 2 in our province, accounting for 30.438+08% of the cultivated land area in our province. The distribution area of sloping farmland is 3.982 million hm2, accounting for 24.03% of the land area above Grade 2, which is the main source of soil erosion in our province and the direct victim of soil erosion and soil fertility decline. Among them, the cultivated land with 2 ~ 6 degrees slope is 990,000 hm2, accounting for 40.04%; 6 ~ 15 sloping farmland is 793,000 hm2, accounting for 32.4%; There are 539,000 hectares of sloping farmland with 15 ~ 25, accounting for 22.0%; Cultivated land with slope above 25 125000 hm2, accounting for 5. 1%. It should be pointed out that a large proportion of sloping farmland above 6 in our province is terraced fields, which reduces the intensity of land erosion to some extent. However, the terrace construction is not standardized, and it is still cultivated land with gentle slope, which slows down the natural slope. The task of transforming these terraces is still arduous.
See table 10.5.2 for the situation of returning farmland to forests and grasslands in Henan province.
(2) Land desertification and river siltation
A. Land desertification. Soil desertification, rocky desertification and sandy desertification are the direct consequences of soil erosion. Among them, soil desertification mainly occurs in low hills covered with loess and distribution areas of loess beams and headlands; Rocky desertification is mainly distributed in Taihang Mountain, Songji Mountain, northern Shandong Province and areas with poor landforms. Gravel desertification is dominated by flood alluvial fans and moraines at the eastern and southern foothills of Taihang Mountain. The degree of desertification is positively correlated with the intensity of soil erosion.
B. siltation of reservoirs and rivers. Another direct hazard of soil erosion is the siltation of reservoirs and rivers. The annual sediment discharge of the Yellow River is 1600 Mt, which is deposited in the Henan section of 120 Mt, and the annual deposition height of the reach below Jin Meng is 3 ~ 10cm, which makes the Yellow River form a secondary suspended river with high troughs and low beaches. The riverbed of the Yellow River in the main tributaries of the province, the Yiluo River and the Qinhe River, also has an average siltation height of 65,438+0.8m. The riverbed of the Liusha River, a tributary of the Huaihe River, has been silted up by 0.9 ~ 2.25m. In the large-scale water control project, the sediment in Sanmenxia Reservoir 1960 to 1983 of the Yellow River is 541mm3. Siltation of Luhun, Baisha, Baoshan and Zhaopingtai reservoirs 10 1 Mm3 (a large reservoir is quite lost); Large reservoirs such as Suya Lake, Yahekou and Danjiang also have serious siltation, which reduces the storage capacity and threatens the safe use of the reservoirs. The siltation height of 300,000 ponds in the whole province is generally greater than 1 m, and the annual siltation of 258,000 ponds in Huaihe River Basin is 22.76 million m3, of which 300 ponds in Lushan Mountain have silted up to 1 15, accounting for 38.3% of the total.
Table 10.5.2 Table of Returning Farmland to Forest and Grassland in Henan Province (Remote Sensing Survey)
3. Wind erosion and desertification
Wind erosion and desertification mainly occur in the alluvial plain of the Yellow River, especially in the old channel area of the Yellow River, the modern crevasse fan and the flood area of the Yellow River. Desertification types can be divided into three types: active dune sandy land (sandy wasteland), semi-fixed dune sandy land and flat sandy land. Medium-coarse sand undulating sand dunes are mostly distributed in the ruins of the old Yellow River and the tops of crevasse fans, such as crevasse fans of Han and Song Dynasties in hua county and Neihuang, crevasse fans of Ming and Qing Dynasties in Lankao and Shangqiu, crevasse fans of Zhongmou in Qing Dynasty and prehistoric crevasse fans of Xinzheng and Weishi. Flat sandy land dominated by fine sand and silty sand is mostly distributed in the outer edge or downstream area of the above belt. The people of Henan have made painstaking efforts to control sandstorms. By the early 1980s, forest farms and fruit bases such as Xinzheng Jujube, Neihuang Jujube and Quan Min Grape had been built in most sand dunes, and a relatively complete farmland forest network had been built in Pingsha farming area. Since 1980s, the farmland network of forest farms and plains in sandy areas has been seriously damaged, and the coverage rate of forest network has decreased by 2.75 percentage points compared with the peak in the mid-1970s, which is equivalent to deforestation of 456,000 hm2. Deforestation leads to the intensification of wind erosion and desertification. The area of active and semi-active sandy land is 67700 hm2, and the weather of desertification and sandstorm has increased sharply, which is a painful lesson in the history of greening in our province.
According to the remote sensing survey in 1985, the total area of sandy land in our province is 1742000 hm2, including flat sandy land 1550000 hm2, dune land 138000 hm2 and mobile and semi-fixed sandy wasteland of 52000 hm2. According to 1999 planning data of ecological environment construction, there are 668,000 hectares of desertified land in our province, including 40,900 hectares of mobile semi-mobile sand dunes. Deforestation and reclamation of sandy land is 26,800 hm2. According to this remote sensing survey, the total area of land threatened by desertification in our province is 1859000 hm2, of which 457000 hm2 is active and semi-active dune sandy land, accounting for 4.60% of the plain area. It is still an arduous task of ecological construction in our province in 2 1 century to strengthen greening, wind prevention and sand fixation in sand areas.
4. salinization
The salinization area of our province is also mainly in the alluvial plain of the Yellow River. Salinization mainly occurs in modern and ancient Yellow River back river depressions, gentle slopes and fan edges under crevasse fans, depressions between fans, and depressions with poor drainage along canals and rivers. Its soil quality is mainly clayey silt and loam, and it belongs to fluvo-aquic soil according to soil science classification. Salinized soil in micro-platform is generally distributed in the slope and depression of crevasse fan. The main salts in soil are chloride and sulfate, and the salt content in topsoil is 0.2% ~ 2% or higher. Alkaline soils are mostly distributed in shallow depressions and their marginal areas, commonly known as "old alkali bubbles". The main salts in the soil are carbonate and bicarbonate, and the salt content in the topsoil is 0. 1% ~ 0.5%. Its salt content is lower than saline soil, but its replaceable sodium content is high and alkaline, and its pH value can reach 8.5 ~ 9.5 or higher. High evaporation intensity and high groundwater level are the main factors for the formation of saline soil. The annual precipitation in the saline soil distribution area of our province is less than 700 mm, but the annual evaporation 1800 ~ 2200 mm is three times different. In the low-lying areas where the groundwater level is less than 3 m, continuous intense evaporation will cause salinization of the surface soil. The salinization degree of surface soil is generally light in rainy season and heavy in winter and spring.
The degree of soil salinization in our province is closely related to the area and irrigation situation. In the early days of the People's Republic of China, there were 240,000 hectares of saline-alkali land in our province,1.957,330,000 hectares. Due to the Great Leap Forward, 196 1 year increased to 870000 hm2. After adopting irrigation control measures, it was reduced to 270,000 hm2 by the time of investigation in 1974. In the early 1980s, the total area of salinized soil was 722,000 hm2, including 297,000 hm2 of severely salinized soil and 20,000 hm2 of saline-alkali land. Since 1980s, due to the continuous drought and the vigorous development of well irrigation, the groundwater level has dropped rapidly. A large-scale drop funnel with a depth of 8500 km2 has been formed in northern Henan, with the groundwater level generally deeper than 4 m and the central water level buried about 20 m. The groundwater level in Shangqiu area in eastern Henan has also dropped below 4 m, and the area of the funnel with a depth of more than 6 m is about 2500 km2, accounting for 1/4 of the whole area. Therefore, a basic factor of salinization is weakened. In addition, irrigation by diverting water from the Yellow River and silting up the land causes a large area of primary saline soil to be washed away by salt and covered by one or several layers of viscous silt, and the salt separation also reduces the degree of salinization. Therefore, by the end of 1990s, the area of saline soil in our province had been greatly reduced. In the early 1990s, there were 180000 hm2, and 1997 was 126000 hm2. However, it should be pointed out that reduction does not mean radical cure. There are still 405 thousand hectares of land in our province with slight salinization or salinization tendency. Once the groundwater level rises above 3 m under the condition of meteorological and hydrological irrigation, salinization may still occur again. Therefore, these areas are designated as "potential salinization areas". Some improper industrial and mining behaviors will also lead to salinization. For example, the secondary salinization area of Yantian Development Zone in Yexian County has reached13.5km2. ..
To sum up, the land degradation area of the whole province is 8.574 million hm2, accounting for 5 1.76% of the total land area. Among them, the cause of water erosion is 6310000 hm2; ; The causes of wind erosion and salinization are 1859000 hm2 and 405000 hm2 respectively. The land with desertification tendency in the whole province is 5.687 million hm2, accounting for 34.32% of the national territory. Among them, the cause of water erosion is 3,590,000 hm2, the wind erosion and desertification are1859,000 hm2, and the serious salinization tendency is 238000 hm2. The areas with serious desertification tendency in the whole province include hills with soil erosion of more than 5000 t/a km2, movable semi-fixed sand dunes and areas with serious salinization tendency, * * * with 1902500 hm2, accounting for1.48% of the national territory. Wetland degradation will be described in detail below and has not been included in the field of land degradation.
5. Wetland degradation
The International Convention on Wetlands stipulates: "Wetlands refer to swamps, peatlands or waters that are static or flowing for a long time or temporarily, or fresh water, brackish water or saline water bodies, including sea areas with a water depth of no more than 6 m at low tide". On land, wetlands have many important functions, such as flood storage and drought prevention, climate regulation, soil erosion control, land reclamation promotion, degradation of environmental pollutants and protection of biodiversity. , known as the "kidney of the earth". Our province is located at the intersection of subtropical zone and warm temperate zone, and the ecological regulation and biodiversity protection of wetlands are particularly important. Wetlands are the habitat of a large number of rare birds. However, since the founding of the People's Republic of China, especially since the 1990s, the natural wetlands in our province have been shrinking. At the end of the 20th century, the wetland area was only half of that in the middle of the 20th century. In the early days of the People's Republic of China, it was estimated that the wetland area was close to 1.50 million hm2. Remote sensing survey was 65,438+0,376,5438+300 hm2. During the period of 65,438+0,989 ~ 65,438+0,993, the wetland area (water plus swamp) was 65,438+0,654,338. Although there are differences in the criteria of these surveys (such as beach ownership), it is an indisputable fact that the wetland area continues to shrink. The main factors of wetland shrinkage are:
A. the river runoff decreases and the beach area dries up; Wetland vegetation withers or is reclaimed. The typical area is in the Yellow River beach.
B. Wetlands inside and outside the city have shrunk or disappeared due to drainage or landfill. Typical areas such as Zhengzhou, Kaifeng, Shangqiu and some counties in eastern Henan.
C. Marsh wetlands are shrinking due to drought, reduced inflow of surface water, drainage and reclamation, and groundwater exploitation. Typical areas such as the old Yellow River wetland, the Yellow River back river depression, Huaihe Lake plain wetland and so on.
D. The area of reservoirs in constructed wetlands increases, while the areas of pits and ponds decrease. Long-term construction of large and medium-sized reservoirs due to siltation area reduction (Sanmenxia, Luhun, Baiguishan, Suya Lake, etc. ).
Among the existing 665 197 hm2 wetlands, the wetland area that is still degraded due to human activities reaches 466803 hm2, accounting for 70% of the total wetland area. It can be seen that the wetland ecosystem in our province is seriously threatened, as shown in table 10.5.3.
Table 10.5.3 Statistics of Wetland Utilization Status and Threatened Situation in Henan Province
(Quoted from Lin et al. Henan Wetland)
Comprehensive investigation and evaluation of land resources in Henan Province by remote sensing
Comprehensive investigation and evaluation of land resources in Henan Province by remote sensing
Comprehensive investigation and evaluation of land resources in Henan Province by remote sensing
Comprehensive investigation and evaluation of land resources in Henan Province by remote sensing