Study on environmental geological indicators in typical areas
The grassland of Xilin Gol League (hereinafter referred to as Ximeng) belongs to the grassland area of Eurasia, located in the central part of Inner Mongolia Autonomous Region, one of the four grasslands in China, and located at 4 1 3 1'~ 46 45' north latitude. East longitude11151'~119 58'. The grassland in Xilin Gol League is one of the famous grasslands at home and abroad, which consists of five parts: forest grassland, meadow grassland, typical grassland, desert grassland and grassland sandy land. The grassland in Xilin Gol League is an important green barrier in northern China, which has long blocked the eastward invasion of sand and dust from grasslands in Central Asia and western China, and played a very important role in the ecological environment protection around Beijing and Tianjin and the whole North China. The overall environmental feature of Xilin Gol League grassland is that the natural landscape of grassland is basically well preserved at present, and it is one of the largest preserved natural grasslands in the world.
I. Overview of the study area
(1) Terrain
Xilin Gol League is located in the middle of Inner Mongolia Plateau, which is an area with the plateau as the main body and various geomorphic units coexisting. Due to Mesozoic and Cenozoic continental deposits, especially Cenozoic river and lake facies, aeolian sand and loess, the original folded mountain topography is not obvious. In addition, after long-term erosion, weathering and quasi-leveling, the relative height difference of the mountain is only tens of meters, but the maximum is hundreds of meters, lacking mountains and obvious gullies, forming the landform of the old times.
Xilin Gol League has a vast territory, flat terrain and small height difference, with an altitude of 900 ~ 1300m. There is little logging on the plateau, and wind erosion is the main factor. The whole terrain is high in the south and low in the north, slowly inclining from southwest to northeast, with an average elevation of 1000 meters or more. The highest peak is Gulu Gesulula, bordering Chifeng City, with an altitude of1967 m; The lowest is in the south of Baolage Sumu Nairi Mudele Gacha in Dongujimqin Banner, with an altitude of 839.7 meters. ..
② Climate
Xilin Gol League is located in the mid-latitude inland, which is controlled by westerly circulation all the year round, mainly influenced by mid-latitude weather system, and the influence of monsoon circulation depends on seasonal changes. The winter monsoon has a long influence time, but the summer monsoon is not easy to reach, and the influence time is short. The landform in the Union is relatively complete, with the plateau as the main body, and the yinshan mountains in the south and Daxinganling in the east extend in the northeast-south-southwest-southwest direction. Due to the barrier of topography and mountains, as well as the geographical location, Ximeng area has long been controlled by polar continental air mass, and the winter wind has a great influence, which has typical continental climate characteristics of drought, little rain and severe changes in cold and summer.
The grassland in Xilin Gol League belongs to the semi-arid continental climate in the middle temperate zone. The basic characteristics of the climate are: long and cold winter, warm and little rain in summer, windy spring and autumn, large temperature difference between day and night, little precipitation, and the same season of rain and heat. The average annual precipitation is 200 ~ 400 mm, mostly concentrated in June ~ August, accounting for about 70% of the annual precipitation. The precipitation variability is large, which is manifested in the uneven distribution of precipitation between years, the disparity between rainy years and rainy years, and the unstable, uneven and uneven variation of precipitation, resulting in spring drought, summer drought and continuous drought in spring and summer, which affects the growth and yield of pasture; The annual average temperature ranges from 0℃ to 4℃, and the distribution trend decreases from southwest to northeast. The extreme maximum temperature is 39.9℃ and the extreme minimum temperature is -42.4℃, which is an area with large daily temperature difference in China. The annual average frost-free period is 100 ~ 136d, with the final frost period mostly in the middle and early June and the first frost period in the early September. The annual average evaporation 1500 ~ 3000 mm, and the evaporation in most areas is 6 ~ 10 times of precipitation, which is an important reason for soil drought. The sunshine duration is 2900 ~ 3200 h, which is one of the regions with abundant solar radiation in China. The annual average wind speed is 4 ~ 5.5m/s, and the number of windy days is 60 ~100d (grade 6 ~ 8), with abundant winds in most areas.
(3) Hydrology
1. Surface water
Daxinganling in the east and Yinshan Mountain in the south of Xilin Gol League form a watershed, with the internal water system of the plateau in the north and the outflow water system in the south. The main leaders of the Alliance include Luanhe River System, Wulagai River System and Huerqiaganuoer River System, with a drainage area of 58,096 km2. Among them, Luanhe River is an outflow water system, and others are internal drainage.
Xilin Gol League is one of the areas where inland lakes gather. According to statistics, there are as many as 1363 lakes in China, with a total storage capacity of 355.4 billion m3. Among them, there are 672 freshwater lakes with a storage capacity of 2 billion cubic meters. Due to the dry climate and strong wind in Ximeng, there are the most weathered lakes, followed by tectonic lakes. Lake water supply mainly depends on rainfall, and groundwater recharge is less, so it changes regularly every year. When the rainy season comes, the water level rises and the lake surface expands. In other seasons, the lake surface drops and many small lakes dry up.
2. Groundwater
Ximeng is rich in groundwater resources, with an annual recharge of 5.4 billion m3 and an exploitable amount of 654.38+055.4 billion m3. It can be divided into four hydrogeological units: mountain hills, lava platforms, intermountain basins and sandy land.
In the hilly areas of China-Mongolia border, north of Dongwuzhumuqin Banner, east of Xilinhot and east of Erenhot, the buried depth of water level is generally less than 5m, the water volume is large, and the total amount of dissolved solids is less than1g/L; In the lava platform area of Abaga Banner in the southeast of Xilinhot, the water level is buried at a depth of 30 ~ 70m, or more than 70m, and the total dissolved solids are less than 1g/l, which is magnesium bicarbonate type water. The lava platform in Huitengxili, south of Xilinhot, is a water-deficient area with a buried depth of over 70m and low water abundance. The intermountain basins such as Wuzhumuqin Basin and Erlian Basin in China are rich in Quaternary pore water and confined water, and the buried depth of water level varies with topography, and the total dissolved solids are generally1~ 2g/L; The groundwater in Hunshandake sandy land is mainly replenished by precipitation, condensed water and fissure water in hills, with little water and poor water quality, and the total dissolved solids around saline-alkali lake can reach as high as 73g/L..
(4) Soil
1. Soil type
Chestnut soil is widely distributed under the grassland vegetation in the middle of Xilinguole grassland, which is the most important part of soil coverage in Ximeng. Generally speaking, it is located in the west of Mandu Baolige in Dongwuzhumuqin Banner to the east of Zhu Rihe Line in Sunite Right Banner, occupying vast low hills, mountain plains and high plains. In addition, there are other soil types in Ximeng, such as grey forest soil, grey cinnamon soil, chernozem soil, meadow soil, brownish calcium soil, aeolian sandy soil and swamp soil.
2. Physical and chemical properties and fertility
The soil texture of Ximeng can be divided into four categories: sandy soil, loam, clay loam and clay. Sandy soil is mainly composed of gravel, with low water retention capacity, low fertility and variable soil temperature, which is mainly distributed in Hunshandake and Gahai Ersu sandy land and its surrounding areas. Loam is homogeneous in texture, high in silt content, good in permeability, low in water and fertilizer conservation, and prone to drought, wind erosion or desertification. It is mainly distributed in Dongwuzhumuqin Banner, Xiwuzhumuqin Banner, Xianghuang Banner, Taibus Banner and Duolun County. Clay loam is mostly distributed in Wulagai basin, Ejinanao basin and lowlands along the river, with uniform texture, good water and fertilizer conservation and strong drought resistance. Mainly clay, with heavy texture, compact structure, strong water and fertilizer conservation ability and poor permeability, is mostly distributed in Daxing 'anling and other depressions between hills and lakes in Qixian County.
Most of Ximeng is slightly alkaline. In terms of regional distribution, the pH value is gradually increasing from east to west. The hills, terraces and sandy land in the middle are slightly alkaline soils with pH of 7 ~ 8.5, and some soils in the western plateau are more than: 8.5 alkaline. In addition, most low-lying areas are alkaline.
The content of soil organic matter in Ximeng ranges from 8.57% to 0.66%, and its distribution characteristics are: the content of soil organic matter in mountainous areas decreases from top to bottom, and the content of soil organic matter in zonal areas decreases from east to west, that is, chernozem → chestnut soil → brown calcium soil. The distribution characteristics of soil total nitrogen content in Ximeng are as follows: soil total nitrogen is positively correlated with organic matter content, and alkali-hydrolyzable nitrogen is also positively correlated with total nitrogen content. It is similar to organic matter in distribution, that is, it shows a decreasing trend from east to west. Soil available phosphorus in Ximeng is deficient, and the content of available phosphorus in most soil types is less than 5× 10-6. The content of available potassium is rich, and the content of most soils is higher than 150× 10-6.
(5) Vegetation
Ximeng belongs to semi-arid and arid continental climate in China belt. The basic type of zonal vegetation formed under this climatic condition is typical grassland. In addition to typical grasslands, there are meadow grasslands, forest grasslands, desert grasslands and sandy grasslands.
There are 8 representative formations in the typical grassland of Ximeng. Stipa grandis. Stipa grandis), Stipa krylovii, Leymus chinensis, Clerodendrum, Agropyron cristatum, Artemisia frigida (form. Artemisia frigida) and thyme grassland (form. Asiatic foxtail pea
2. Study on environmental geological indicators of grassland degradation in Xilinguole.
Xilingol Grassland is one of the four famous grasslands in China, which was once famous for its abundant aquatic plants. Grassland degradation, desertification and ecological environment deterioration in Ximeng are becoming more and more serious. According to the survey data, the area of wind erosion and desertification in the whole league is 1.2 1.6 million km2, accounting for 64% of the total grassland area in the whole league. Among them, light wind erosion desertification area is 5 1.27 million km2, moderate wind erosion desertification area is 41.30 million km2, and strong wind erosion desertification area is 1. 1.48 million km2. Vegetation coverage decreased from 35 15% in 1984 to 27 12% in 1997. The soil erosion is getting worse and worse. The area of light soil erosion is17120,000 km2, accounting for 8 1 12% of the total land area. The area of moderate soil erosion is121070,000 km2, accounting for 56 19%. From 1949 to 1995, the desertification area of Hunshandake sandy land increased from 21570,000 km2 to 31050,000 km2, with an average annual increase of more than 65438+3000 km2, while the mobile sand dunes increased from 1960 to 30,700 at present.
Looking at all kinds of related factors of grassland degradation in Xilin Gol League, the main reasons are: drought and water shortage, prominent contradiction between grass and water, increased load of grassland population and livestock, and enhanced contradiction between grass and livestock. Years of drought have caused the growth height, yield and grassland coverage of natural grassland to decrease geometrically. Among many factors causing grassland desertification and degradation in Ximeng, persistent drought and lack of water resources are the main contradictions.
The process of grassland degradation is inevitably accompanied by changes in soil properties, including changes in soil physical and chemical properties, loss of soil nutrients and decline of soil fertility. According to the research, the decrease of grassland vegetation coverage reduces the organic matter entering the soil and accelerates the decomposition speed. The development to humification leads to the decrease of water content, the single grain structure, the strengthening of mineralization process, the gradual accumulation of soluble salts, the strengthening of salinization trend, the strengthening of water evaporation, the drying of soil, the decline of fertility and the development of soil in the direction of degradation.
(1) Climatic precipitation
Xilin Gol League is the main pastoral area and forage base in the autonomous region, and the precipitation distribution decreases from southeast to northwest. The average precipitation in Siqi (county) in the south and Xiwuzhumuqin Banner is 300 ~ 390 mm, which decreases to the northwest, while that in Erenhot City is only 140 mm. Therefore, the frequency of drought also increases from southeast to northwest. According to the precipitation statistics in recent 50 years:
1953-In the 53 years from 2006, the regional light drought (the percentage of precipitation anomaly is 0 ~-25%) * * occurred in 14, and the moderate drought (the percentage of precipitation anomaly is -25% ~-75%) was/kloc-0. -75%) for two years, the frequency of mild drought was 26.4%, the frequency of moderate drought was 20.8%, the frequency of severe drought was 3.8%, and the cumulative percentage drought frequency was 5 1%.
During the period from1955 to May1year 2006, the regional light drought * * occurred 18 years, with a moderate drought frequency of 35.3%, a moderate drought frequency of 15.7% and a cumulative percentage drought frequency of 5 1%.
The results show that the probability of mild drought in Xilin Gol League region is higher, the probability of moderate drought is second, and the probability of severe drought is the smallest. According to the interannual analysis, the drought years in Xilinhot are from 1982 to 1986 and 1999 to 2002. Xiujimuqin Banner 1962 ~ 1968, 1970 ~ 1973, 1975 ~ 1977,1999 ~. Therefore, the grassland community is in a state of serious water shortage for a long time, the plant growth will be greatly inhibited, and the species will tend to be single. This is one of the important factors of grassland degradation.
(2) Surface hydrology
Precipitation is the main water source for grassland growth, and rivers and lakes on the surface are places for water storage. The change of basin area and lake area indicates the change of climate and precipitation to a great extent, and can also indicate the process of grassland degradation. Due to the continuous drought, the water surface of some lakes in Xilinguole grassland has shrunk or even dried up due to lack of water. For example, the water surface of Chagannaoer (lake name) in 1950s was 1270 km2, and the lake surface has shrunk by 20 km2 so far. Lake Dalinor is the core area of national nature reserve, with an area of 228.84 square kilometers and a storage capacity of about 654.38+600 million cubic meters. The water environment is characterized by high salt content and strong alkalinity. With the destruction of ecological environment and the increase of lake evaporation year by year, the water quality of lakes has an obvious deterioration trend. The changing trend is from fresh water to brackish water to salt water to salt lake. The research shows that the water level of Dalianoer Lake fluctuates stably, and the pH value of water quality is mainly affected by precipitation. In 20 years, the pH value is generally between 9.30 and 9.80, showing a slow upward trend. Comparing the research results of 1975 and 1996 ~ 1998, the main chemical factors such as water salinity, total alkalinity, secondary ions, sodium ions and permanganate index are all on the rise.
Figure 4-2 Percentage of Annual Precipitation Anomalies in Xilinhot and Xiwuzhumuqin Banner
Table 4- 12 Changes of hydrochemical factors concentration in Darinol Lake
After more than 20 years of changes, the main chemical factors in the main lake area range from 2.6% ~ 198. 1%, in which the salt content increased by 8.6%, the total alkalinity increased by 1.1%,and the sodium ion increased by/kloc-0.
Xilin River is a large inland river on Xilin Gol grassland in Inner Mongolia Autonomous Region. Originated in Baiyinchagan Noor Beach near Qianweng Lake in Huanggang Liangshan, Sukeshelu Mountain, it flows to Xilinhot and flows into Baiyin Noor in the northwest. The total length of Xilin River is 175km, which is above Xilinhot Reservoir 135km. According to the data of 1965, the annual average flow of Xilinhot River is 0.745s/m3, and the annual average water volume is 23.49 million m3. However, in recent years, due to the influence of climate fluctuation and human activities, nearly 40km of the lower reaches of Xilin River has almost dried up, and the water volume has dropped sharply.
(3) Groundwater
As a "warehouse" of groundwater for grassland growth, groundwater plays a more direct role in the growth and development of plants. The research shows that the depth of groundwater level largely determines the growth of surface vegetation.
The dynamic type of groundwater in Xilinhot area is precipitation-infiltration-evaporation type. The recharge sources of groundwater resources are mainly precipitation and surface water infiltration. The main influencing factor is precipitation, followed by evaporation and groundwater exploitation intensity. The data show that the groundwater in the rainy season in Xilinhot area shows an upward trend as a whole, but the rising range is not consistent with the starting time, the duration and the peak time in different sections. Along the Xilin River, the buried depth of groundwater is shallow, and the rising range is also large, but it lags behind due to the influence of river water and the regulation of upstream reservoirs. However, in other areas, the increase of groundwater depth reflects quickly, while in summer and autumn when evaporation is strong and agriculture and animal husbandry are irrigated, the groundwater level drops because of the relatively small effect of rainfall. It shows that the groundwater level is restricted by precipitation and evaporation. In recent years, the groundwater level in this area has been declining continuously, mainly due to less precipitation and insufficient recharge, while evaporation and various water consumption have increased.
(4) Topographic features
The above landforms have a certain control effect on the vegetation distribution, and the vegetation distribution of different landforms has certain regularity, so the ability to inhibit the deterioration of the ecological environment is not the same. The change of surface morphology, such as the change of bare soil area and quicksand area, can indicate the degradation process of grassland and land from the state
The undulating ground morphology makes the distribution of grassland different in type, height and coverage. According to the field investigation, on the relatively undulating terrain, the vegetation coverage tends to decrease with the elevation, and the average height tends to decrease. The vegetation coverage at the top of hilly terrain is the lowest, while in the gullies between hilly terrain, grassland is often rich. Because of the topography, these places are often the gathering places of surface water and groundwater flow, and the water conditions for plant growth are relatively sufficient. If the position is on the relatively dark side, the evaporation intensity will be greatly reduced.
Affected by sunshine and evaporation, the vegetation coverage on shady slopes is generally higher than that on sunny slopes. According to research, since 1990s, the desertification trend of Xilinhot grassland has intensified, and the area of mobile sand dunes has increased by 14.3 km2 every year. The vegetation coverage of sandy land decreased from 30% ~ 40% on sunny slopes and 60% ~ 70% on shady slopes in 1960s to 65,438+00% on sunny slopes and 30% ~ 40% on shady slopes now. In addition, due to wind erosion, the distribution height of grassland on the windward side is low, and the leeward side is higher than the windward side.
(5) Physical and chemical properties of soil
Physical and chemical properties of soil include physical and chemical properties of soil. Physical properties of soil mainly refer to soil temperature, water content, soil texture and structure, while chemical properties of soil mainly refer to soil chemical composition, synthesis and decomposition of organic matter, transformation and release of mineral elements, soil pH value and so on.
In order to verify the influence of soil physical and chemical properties on grassland degradation, a field investigation was conducted in the typical grassland area of Baiyinxile Ranch in Xilinhot City, Inner Mongolia (see Appendix "Field Investigation Methods" in this section for details), with an investigation area of about 240km2 and 59 investigation points. The topography, soil, hydrology and vegetation in the study area were investigated in detail.
Table 4- 13 List of Survey Points in Typical Grassland Area of Baiyinxile Ranch, Xilinhot City, Inner Mongolia
sequential
1. Physical properties of soil
(1) Texture and structure.
The soil texture of Ximeng grassland can be divided into sand, loam, clay loam and clay. Sandy soil has low water retention capacity, low fertility and variable soil temperature. The loam has uniform texture, high silt content, good permeability, poor water and fertilizer conservation, and is prone to drought, wind erosion or desertification; Clay loam has uniform texture, good water retention and fertility, and strong drought resistance; Clay is thick in texture, compact in structure, strong in water and fertilizer conservation and poor in permeability. Soil structures are granular, granular, clastic, columnar, massive and nucleated. Granular soil is most conducive to plant emergence and rooting, followed by granular, lumpy and columnar soil, and nucleated and nucleated soil is worse.
According to the field investigation results of typical grassland area in Baiyinxile Ranch, Xilinhot City, Inner Mongolia, the soil in this area is mainly sandy soil and clayey silt, and some parts are light loam with coarse particles, high sand content, poor soil cohesion and desertification.
(2) particle composition.
The soil covering the grassland surface is a kind of porous material with great changes in properties, and its solid component-the particle size of the soil constitutes the soil skeleton, which reflects the texture of the soil. With the aggravation of grassland degradation, soil particle composition changes, clay content tends to decrease and sand particles increase. Different particle sizes have different contributions to the formation of soil aggregate structure and water and fertilizer conservation, and the reduction of clay particles inhibits the physical properties of soil such as expansion, plasticity and ion exchange.
According to the field investigation results of typical grassland area in Baiyinxile Ranch, Xilinhot City, Inner Mongolia, the soil in most places is sandy soil or clayey silt with low clay content, mainly sandy soil, which is easy to desertification.
(3) Water content.
Soil moisture is one of the most important components in soil. Generally speaking, the movement of soil moisture corresponds to the soil temperature, and it is disturbed by Qualcomm liquid phase in the process of infiltration, drainage, evaporation and root water absorption. In the process of grassland degradation, soil water content decreased, especially in the upper layer (0 ~ 20 cm).
According to the field investigation results of typical grassland area in Baiyinxile Ranch, Xilinhot City, Inner Mongolia, there is no direct relationship between the surface soil water content and grassland degradation. However, according to previous research results, low-moisture soil (water content 5% ~ 7%) and high-moisture soil (water content 8% ~ 10%) have great influence on forage growth and grass yield. The results show that the grass yield of high moisture soil is about twice that of low moisture soil. However, the soil water content in Baiyinxile pasture is mostly between 0.5 and 5.5, which is relatively low, which can be regarded as the related factor of grassland degradation.
(4) Bulk density.
Soil bulk density reflects soil compactness and is inversely proportional to soil porosity, air permeability and permeability. With the aggravation of grassland degradation, soil bulk density showed an upward trend. The increase of soil bulk density will inevitably affect the movement of water and gas in soil and the development of plant roots. However, the bulk density of 0 ~ 5 cm soil layer is the smallest in severe degradation stage. It shows that the interference of microorganisms and animals in the underlying soil makes the soil loose and the bulk density is small. However, in severe desertification, the wind erosion of the soil surface is serious, the vegetation is less, and the particles are blown off and fall back, which makes the soil loose and dry and the bulk density is the smallest.
According to the field investigation results of Baiyinxile Ranch in Xilinhot, Inner Mongolia, the bulk density of the surface soil (0 ~ 5 cm) is generally between 1.2 ~ 1.5g/cm3, and the lowest is 0.8 1g/cm3(PC30 survey area, non-degraded grassland). However, with the increase of degradation degree, the soil bulk density showed an upward trend, and the maximum value was 2.07 g/cm3(PC36 survey site, lightly desertified grassland).
2. Chemical properties of soil
PH value. Soil pH value is a comprehensive reflection of soil base, and it is also related to soil water content. According to previous studies, crops and pastures need slightly alkaline soil with a pH value of 7.0 ~ 8.5. When the pH value is lower or higher, the growth of plants is inhibited.
According to the field investigation results in the typical grassland area of Baiyinxile Ranch in Xilinhot City, Inner Mongolia, the pH value of most soils is between 7.20 and 8.64, and only a few places are acidic or the pH value is higher than 9.0. It shows that the soil in this area is suitable for plant growth from the point of view of pH value.
(vi) Soil nutrients
Soil nutrients mainly depend on the quantity and composition of soil minerals and organic matter. Through the element correlation analysis of 17 1 soil samples collected from the typical grassland area of Baiyinxile Ranch in Xilinhot, Inner Mongolia, the results show that total nitrogen and available nitrogen are significantly positively correlated with total carbon content, and total nitrogen is also significantly positively correlated with available nitrogen, indicating that soil organic matter contains a certain proportion of nitrogen, and a certain proportion of nitrogen can be converted into available nitrogen needed by plants. Through the correlation analysis of soil elements at different depths, taking N element in 5 1 soil sample as an example, there is a certain positive correlation, which shows that the soil-forming environment is similar and the soil-forming process is the same, which leads to the similar process and degree of element migration and transformation in soil profile. In addition, the analysis data show that the content of total nitrogen, total phosphorus and other elements in the surface soil is relatively low, which is a soil with poor nutrient conditions and an important manifestation of soil degradation. Through the analysis of coefficient of variation, the contents of total nitrogen and total phosphorus in 17 1 sample vary greatly, and the coefficient of variation is 73. 1 1% and 43. 1 1% respectively, indicating that the soil has a tendency of degradation and has the characteristics of degraded grassland.
Table 4- 14 Correlation matrix of soil nutrient elements in typical grassland area of Baiyinxile pasture in Xilinhot, Inner Mongolia (sample number = 17 1)
Table 4- 15 Correlation analysis of soil nitrogen at different levels in Baiyinxile Ranch, Xilinhot City, Inner Mongolia (sample number =57)
1. Soil organic matter and nutrient elements
Soil organic matter is an important material basis of soil fertility, which directly affects soil physical and chemical properties and biological activity, and is a decisive factor reflecting soil fertility and fertilizer supply characteristics. At present, there are many indicators reflecting the status of soil organic matter, including the quantity and activity of organic matter and the quality of humus.
The total nitrogen content in the soil represents the greatest potential to provide the needed nitrogen for plants. With the increase of desertification gradient, the total nitrogen content in soil decreased. The ratio of carbon to nitrogen of soil organic matter is an important index. If the C/N ratio is large, it is impossible to supply N to plants at the initial stage of mineralization, because the assimilation amount of microorganisms will exceed the available N provided by mineralization, which may make the phenomenon of N deficiency in plants more serious. However, if the C/N ratio is very small, it can supply the effective N needed by plants in the early stage of mineralization. Therefore, the ratio of carbon to nitrogen plays a vital role in plant growth. In the process of grassland desertification, the soil C/N ratio showed an upward trend, indicating that with the significant decline of soil C and N, the texture became thicker and the shortage of plant N became more prominent.
According to the correlation of soil elements in the typical grassland area of Baiyinxile Ranch in Xilinhot, Mongolia, Corg (organic carbon) has a significant positive correlation with total N. The average C/N of 17 1 sample is 9.766, and the coefficient of variation is 60. 12%, which is inconsistent in space. The C/N value of most samples fluctuated in the range of 7 ~ 15, and a few samples reached 40 ~ 50, indicating that the grassland in some places in this area had begun to degrade and even had the effect of soil desertification.
Fig. 4-3 Corg-N correlation of soil in typical grassland area of Baiyinxile Ranch, Xilinhot, Inner Mongolia (sample number = 17 1)
2. Trace elements in soil
Organisms are composed of more than 60 elements, among which C, H, O, N, Ca, P, Mg, Na and other elements are called macro elements. Iron, zinc, copper, manganese, chromium, selenium, molybdenum, cobalt and fluorine, which account for less than 0.0 1% of the total biomass, are trace elements. Although the content of trace elements in organisms is not much, it is closely related to the survival and health of organisms. Excessive intake, insufficient intake or lack of them will cause different degrees of physiological abnormalities or diseases. The most prominent role of trace elements is closely related to vitality and can play a huge physiological role. These trace elements must be provided directly or indirectly by soil. Up to now, there are 18 kinds of essential trace elements related to human health and life, namely iron, zinc, copper, manganese, chromium, selenium, cobalt, iodine, nickel, fluorine, molybdenum, vanadium, tin, silicon, strontium, boron, ruthenium, arsenic and so on.
The available forms of six trace elements (B, Mo, Cu, Zn, Fe and Mn) in 0 ~ 20 cm topsoil from 57 sampling sites in Baiyinxile Ranch, Inner Mongolia were analyzed. The average content order of six trace elements is Mn > Mn；; Fe & gtZn & gtCu & gtB& gt； The contents of molybdenum, manganese and iron are much higher than the other four elements and the national average. The average values of the other four elements are lower than the national average.
Table 4- 16 Effective Contents of Six Trace Elements in Surface Soil of Baiyinxile Pasture in Xilinhot, Inner Mongolia: μ g/g
According to the Records of Ximeng, the available forms of six trace elements in soil of Ximeng are shown in Table 4- 17.
Table 4- 17 Available States of Six Trace Elements in Soil of Ximeng: × 10-6
It can be seen that the effective contents of elements B, Mo and Zn in this area are lower than the critical value of element deficiency. In addition, the contents of available iron and available manganese in this area far exceed the above range, and the reasons need to be further discussed.
From the analysis of trace elements in plants, it can be seen that the average contents of B, Mo and Cu are within the normal range, while the contents of Zn are slightly lower than the normal range. The average content of iron and manganese is much higher than the normal range, which should be related to the high content of iron and manganese in soil. In addition, it does not rule out the factors of plants themselves, which may make the element content of different plants vary greatly.
Table 4- 18 Contents of Available Forms of Six Trace Elements in Plants of Typical Grassland Area of Baiyinxile Ranch, Xilinhot City, Inner Mongolia Unit: μ g/g
The change of element content in plants is always related. From Table 4- 19, it can be seen that iron and manganese, iron and zinc, iron and copper, copper and zinc are significantly positively correlated, iron and molybdenum, copper and molybdenum are negatively correlated, but not obviously, and other elements are positively correlated.
Table 4- 19 Correlation Analysis of Six Trace Elements in Plants of Baiyinxile Ranch in Xilinhot City, Inner Mongolia (number of samples =57)
In view of the above research results, whether the excessive enrichment of iron and manganese elements in this area affects the evolution and degradation of vegetation in this area needs further investigation and monitoring.
Attachment: Working methods of field investigation
I. Overview of the work area
The experiment was carried out in the typical grassland area of Baiyinxile Ranch in Xilin Gol League, Inner Mongolia. The area is located at11630 ′ ~11645 ′, 4333 ′ ~ 4340 ′ north latitude, and 12 15m above sea level. It belongs to temperate semi-arid continental climate, with drought and little rain in spring, windy and sandy, and long cold winter; The annual average temperature is 0℃, the daily temperature difference is large, the annual average precipitation is 300~450 mm, and the precipitation variability is large. 70% of the precipitation is concentrated in July, August and September, with an annual average sunshine duration of 2600 h, frost-free period of about 170 d, annual average wind speed of 3.2 m/s and windy days of 7 1 d, with 4438+0 d. The main vegetation type in this area is "Stipa grandis+Leymus chinensis" typical grassland. The zonal soil is chestnut soil. Xilin River runs through this area from east to west.
Two. working methods
(1) general rules of work
The basic working scale of the calibration area is 1∶50000, and the basic sampling density is 1 point /4km2. Several transverse sections are arranged every 20 kilometers along the Xilin River, and 3-4 sampling points are set for each section.
(2) Sampling survey
1. Vegetation survey: set 1 quadrat (5m×5m) at each sampling point, and measure the vegetation coverage, the proportion of dominant grass species and the average plant height in each quadrat respectively. Collect samples of dominant grass species.
2. Soil investigation: 65,438+0 soil profile with a depth of 50cm was dug at each sampling point, samples were taken at 0 ~ 65,438+00 cm, 20 ~ 30 cm and 40 ~ 50 cm with Luoyang shovel, and undisturbed soil samples were taken at 0 ~ 65,438+00 cm with aluminum boxes.
3. Hydrological investigation: collect surface water and groundwater samples near the sampling point.
Third, data collection.
(a) vegetation survey and testing
1. Vegetation coverage: visual method.
2. Proportion of dominant grass species: 1 ~ 2 dominant grass species were selected visually, accounting for more than 70% of the total vegetation in the sample plot, and their proportions were estimated respectively.
3. Average plant height: randomly select 5 ~ 10 plants, measure their natural height and take the average.
4. Detection of dominant grass species: including 14 total element analysis: cadmium, lead, chromium, nickel, arsenic, mercury, copper, zinc, iron, manganese, boron, molybdenum, selenium and fluorine. The determination methods include atomic fluorescence spectrometry (AFS), plasma spectrometry (ICP-OES) and plasma mass spectrometry (ICP-OES).
(2) Soil investigation and testing
1. Investigation and description of soil profile: draw a histogram according to the excavated profile and describe it.
2. Determination of soil particle composition: Screening method is adopted.
3. Determination of water content: Geotechnical test method is adopted.
4. Soil element test
(1)24 total aNalySis items: pH, TOC, n, p, k, na, Ca, Mg, Fe, Mn, Cu, Zn, b, Mo, Ni, Pb, Cd, Cr, As, Hg, si, al, Se, f.
(2) Available state analysis 13: available nitrogen, available phosphorus, available potassium, available boron, available molybdenum, available copper, available zinc, available iron, available silicon, available manganese, available sulfur, exchangeable calcium and exchangeable magnesium;
(3) Analysis of ion exchange state (including water-soluble state and ion exchange state) 1 Item: cadmium, lead, chromium, nickel, arsenic, mercury and selenium.
(4) Atomic fluorescence spectrometry (AFS), emission spectrometry (ES), plasma mass spectrometry (ICP-MS), tabletting X-ray fluorescence spectrometry (XRF), ion-selective electrode method (ISE), oxidative cracking gas chromatography, plasma spectrometry (ICP-OES), oxidative cracking potential method, etc.
(3) Hydrological investigation and testing
Detection of surface water samples and groundwater samples: including arsenic, mercury, nickel, lead, chromium, cadmium, copper, fluorine, selenium, zinc, nitrogen, phosphorus, potassium, sodium, calcium, magnesium, chlorine and other 22 ions. Determination methods include plasma mass spectrometry (X series), atomic fluorescence spectrometry (AFS-230) and plasma spectrometry (IRIS).