Figure 3-3 Geographic Location Map of qingzhen city
The average elevation of Qingzhen is1350m, which is located in the north of Yuan Qiu and Miaoling Mountains in central Guizhou. The terrain is high in northeast and southwest, and low in central and south. Qingzhen city has a subtropical monsoon climate, which is cool and warm, with an annual average temperature of about 14℃, slightly higher in the valley area and an annual precipitation of 1200mm. Qingzhen city has a complex landform, mainly hills and mountains, with strong karst development and a vast artificial lake. The largest artificial lake in this province is located in the south of qingzhen city. Qingzhen has 10 townships with a total population of 434 125. There are Miao, Buyi, Dong, Yi, Shui, Hui, Gelao and Bai ethnic minorities in the county.
Qingzhen city, like other karst areas in the province, is a fragile ecological environment. In the past development, the basic food and clothing was obtained by destroying the ecology, which led to the common problems in karst areas: agricultural ecological environment degradation, poor agricultural foundation and low agricultural production level; The rural industrial structure is unreasonable; Uneven development among regions, etc. The strata and rocks exposed on the surface of qingzhen city include pre-Sinian residual sandstone, residual tuff and slate, Sinian, Cambrian, Carboniferous, Permian, Triassic, Jurassic limestone, dolomite and shale, Tertiary conglomerate, Quaternary sediments and Hercynian basalt. Among the exposed strata in this city, carbonate rocks are the most widely distributed, * * *10/4km2, accounting for 67.94% of the city's total area, so karst landforms have become the main features of this city's landforms. Especially the karst landforms in Liu Chang, Machang, Hualong, Wangzhuang, Xindian, Yachi, Hanjiaba, Undercurrent and Woodcarving in the northwest, and shae and Dagu in the west are the most typical. There are relatively few non-karst areas, mainly distributed in a few areas in the east, southwest and south of qingzhen city, namely along Xiaoba-Wenshui-Tiechang-Yungui, MaiQuan-Xiaodian Mountain-Luohan-Zhongzhai-Poyan, Woli-Hexi Cave-Xiguan-Zhoujiaqiao, Yinchang, Yangba and a few areas in the west of qingzhen city and the east of Hongfeng Lake, and the rest are karst areas. At the same time, due to repeated deforestation and steep slope reclamation, vegetation coverage is lost and soil erosion is serious, which eventually leads to rocky desertification.
1. remote sensing image interpretation of karst rocky desertification intensity grade
The interpretation of remote sensing images of karst rocky desertification in qingzhen city, like the whole province, follows the workflow and technical route of karst rocky desertification interpretation, and has certain independence and representativeness in the establishment of remote sensing interpretation indicators.
1. Interpretation characteristics of lithology and geological structure
Lithology in karst and non-karst areas is closely related to rocky desertification. The area of carbonate rock lithology is karst area, and the degree of rocky desertification is high, which varies according to the outcrop of rocks.
The strata and rocks exposed on the surface of qingzhen city include pre-Sinian metamorphic rocks, metamorphic tuffs and slates. Limestone, dolomite and shale of Sinian, Cambrian, Permian, Triassic and Jurassic; Tertiary conglomerate; Quaternary sediments; Hercynian basalt and so on. The strong Yanshan movement has caused the formation of nearly north-south folds in the eastern strata and northeast folds in the western strata. Strike faults are developed in the fold belt, which are interwoven into a network horizontally and obliquely, and the soluble rocks and insoluble rocks in the interbedded layers are staggered in a strip shape. Under the interaction of internal and external forces, various karst and normal landforms are gradually formed. Himalayan movement further activated this area, and Paleogene gravel also fractured, controlling several continental red sedimentary basins today.
Since Quaternary, the crust has risen obviously. After two large orogenic movements and a series of dissolution, erosion and denudation, rocks are exposed in a large area, forming a typical karst landform, while on the gentle terrain, it is a non-karst zone. Geological structure is the dominant factor to form the basic skeleton of landform, and it is also the main basis to divide landform types and divisions. Geomorphological landscape also reflects the geological characteristics of different tectonic systems. Judging from the distribution of mountains and rivers, the main mountain systems and rivers in qingzhen city are almost in the same direction as the tectonic line, and several major mountains in the northeast, such as Yungui Mountain, Baota shan Mountain and Jiulong Mountain, are all in the north-south direction. It is completely consistent with the axial and stratigraphic strike of Laoheishan fold anticline and Daweiling anticline. The same is true of the two major rivers. The undercurrent river, main river and Longtan River all run in the north-south direction, while maotiaohe runs in the northeast direction, which is almost consistent with the strike of rock strata and faults.
2. Interpretation characteristics of landform slope of rocky desertification grade
The degree of rocky desertification is also closely related to the slope. Generally, the higher the slope, the more serious the erosion, the more serious the soil erosion, the faster the rocky desertification process and the higher the degree of rocky desertification. On the contrary, the slope is slow, the erosion is slow, the soil and water conservation is good, and the degree of rocky desertification is low.
When other indicators such as local surface texture and vegetation status are fixed, the grade of rocky desertification mainly depends on the slope of the terrain. Geomorphological interpretation mainly uses graphics, tones and shadows. The figure of landform image includes the features of plane outline and surface fluctuation, while hue and shadow are helpful to observe and analyze various landform forms and obtain the information of landform and its components. In mountainous areas, under the sunlight, the sunny slope receives light intensity, with high brightness value and light color; Shady slope has small brightness value and dark tone.
Therefore, the hue of mountain images is very uneven, the shadow patches of high mountains are small, and the hue difference between low mountain and hilly images slows down. The shape of the top of the mountain and the steepness of the hillside are mainly interpreted according to the change of color. For example, the top of the mountain is generally triangular, protruding from the shadow to the south, and the apex of the triangle is the top of the mountain. If the tone changes slowly or obviously at the top of the mountain, it means that the light receiving surface is round or flat. The boundary between the shade of the two slopes is the ridge, and the shade of the shady slope of the ridge is also divided into shades. Light shadows and uniform distribution indicate gentle slopes, dark shadows or shadows indicate steep slopes, and the low-lying place between the two ridges is a valley. Canyon and wide valley can be clearly distinguished in the image. The slopes on both sides of the canyon are steep, and the bottom of the canyon is often covered with shadows. The image color is mostly dark, the bottom of the wide valley is flat, and farmland and residents are often distributed. The image feature of karst basin is that it is surrounded by mountains on all sides, with a low basin-like terrain in the middle, and the flat color is relatively uniform.
Karst landforms are characterized by alternating positive and negative landforms, and the landforms appear chaotic. In karst landform area, there are many unique landforms, such as solitary peaks and peak forests, dissolution funnels, sinkholes, dissolution depressions, dissolution basins, undercurrents, blind valleys and so on. There are many funnels on the gently inclined limestone layer, some of which are single or in groups, and most of them are round and oval. Some are filled with loose sediments, which are lighter in color. The butte and the peak forest are normal karst landforms with dark images. The subsidence is light-colored negative terrain; Form an alternating and messy atlas. According to the above image characteristics, we can roughly judge the basic landform. For the interpretation and acquisition of the slope, in addition to the depth of the shadow of the reference image, it is more important to obtain it from the superposition of1/200,000 qingzhen city slope vector map and1/50,000 topographic map.
3. Interpretation characteristics of soil layer and vegetation
Karst areas are different due to different soil thickness and vegetation coverage. Generally speaking, in areas with thick soil layer and high vegetation coverage, the degree of rocky desertification is light or no rocky desertification phenomenon. In areas with thin soil layer and low vegetation coverage, the degree of rocky desertification is higher.
In the TM4, TM3 and TM2 bands of remote sensing images, it is sensitive to the reflection of vegetation. When the indexes such as texture, lithology and slope are determined, the indexes for drawing polygon spots and judging the intensity level of rocky desertification are vegetation, vegetation coverage and vegetation structure information determined by the depth and tone of the image (Table 3-5).
4. Field operation verification
In the investigation of remote sensing images, field verification is an indispensable and important link. Through the supplementary investigation of the work in this work area, the remote sensing interpretation sign of rocky desertification intensity classification was established, and the corresponding field photos were taken for interpretation and analysis of rocky desertification intensity. In order to correctly interpret satellite images and ensure the accuracy of investigation, the location of route crossing is marked as a sign on Qingzhen remote sensing image map, and the pre-judgment results of images along the route are checked by combining topographic map and geological map. The actual position is located by GPS, and then combined with the coordinates on the image to judge. After the investigation, we began to interpret satellite images.
Observation point 1: Boluo village, qingzhen city, with satellite positioning: N26 38.005', e 106 25.65'. This point is a closed peak-cluster depression with typical karst landform. The image on the west side is red with white, which is mild or moderate rocky desertification. The vegetation type is low shrub, and the vegetation coverage rate is less than 45%. It is a rocky mountain area that is difficult to use, with undeveloped gullies and stone buds and low utilization degree (photo 3-2). In the southeast, the image features red, the vegetation coverage rate reaches 90%, and the slope is steep, which is a potential rocky desertification. Once the vegetation is destroyed, it is easy to form rocky desertification (photo 3-3).
Observation point 2: Guizhou Aluminum Mine Factory, with satellite positioning: N2638.005 ′, E10625.65 ′. This rock stratum is exposed in the Lower Cambrian, which is a non-karst area. Its image features a white block structure, not rocky desertification, mainly due to artificial mining, resulting in a large number of rocks exposed. The exposed rock stratum on the east side is limestone, with green-red image characteristics and sporadic white spots exposed, and the vegetation coverage rate is about 80%. The vegetation type is low shrub, which is mild or potential rocky desertification (photo 3-4).
Observation point 3: Yachi River Canyon, with satellite positioning: N26 5 1.345', E 106 10.454'. The image feature of this point changes from yellow to red with white. The soil layer on the platform is thick, and the steep slope is seriously reclaimed. It is a karst area, a stage of rocky desertification process, and a place where potential rocky desertification is difficult to use (photo 3-5).
Table 3-5 Standard Pseudo-color Image Feature Table
Second, the spatial data analysis of karst rocky desertification
1. Spatial distribution of intensity grades of rocky desertification in qingzhen city.
Through the interpretation of satellite remote sensing images, the spatial distribution map of rocky desertification intensity levels in qingzhen city karst area is finally generated (Figure 3-6), and the area, points and percentage of each level are counted by using the data analysis function of GIS (Table 3-6) for further analysis.
Table 3-6 Grade Table of Rocky Desertification Intensity in qingzhen city
Through statistical analysis and calculation, non-karst areas in qingzhen city are mainly distributed in the east and southwest of qingzhen city, accounting for 14.38% of the total area of qingzhen city, while karst areas account for 85.62%. Among them, the rocky desertification-free areas are mainly distributed around Hongfeng Lake in the south-central part of Qingzhen, the potential rocky desertification areas are mainly distributed in the northeast and north of qingzhen city, and the mild rocky desertification areas are mainly distributed in the west and southwest of qingzhen city. Moderate rocky desertification is mainly distributed in the northwest of qingzhen city and the west of Hongfeng Lake, with a small amount in the central region, while intensive rocky desertification is mainly distributed in the central region of qingzhen city, with a small amount in the east of Hongfeng Lake and the northwest of qingzhen city. The area of rocky desertification in qingzhen city accounts for 24.67% of the total area, of which light rocky desertification accounts for 17.3 1%, moderate rocky desertification accounts for 6.46% and severe rocky desertification accounts for 0.90% (Figure 3-4).
2. Analysis of the relationship between rocky desertification intensity grade and lithology.
Yachi area in Qingzhen belongs to Upper Permian in geology, interbedded with limestone and shale. Because flint rock is dense and hard, moderate rocky desertification is typical. To the east of Jiutoudapo, it belongs to Yelang Formation of Triassic. The upper part is shale, the middle part is limestone and the lower part is shale, which is soft and weak in weathering resistance. However, it is still strongly consolidated rock in clay rock, and even slightly rocky desertification develops. The surrounding area and its extension to the east of the Acropolis belong to the Lower Permian, dominated by limestone and limestone, with shale at the bottom, and then eastward to maotiaohe and the northeast of the Acropolis.
From the eastern part of Weicheng town to the southern part of Xinfa and other places, it belongs to the Lower Triassic Maocaopu Formation, with dolomite in the upper part, limestone in the middle part and limestone in the lower part. Because of the unstable position of this dolomite, it often transits to dolomitic limestone or limestone in the lateral direction, so most of this area is rocky desertification-free. The upper Triassic Songzikan Formation is located to the east and near Machang, with limestone dolomite and argillaceous dolomite mixed with shale, and moderate rocky desertification is typical. There are mainly Maocaopu Formation and Yelang Formation of Lower Triassic, and Upper and Lower Permian around Liu Chang, where potential rocky desertification and mild rocky desertification are mixed. Hongfeng Lake is surrounded by Hongfeng subgroup of Huaxi Formation in Anxike Stage of Middle Triassic, which is mainly dolomite with shale, and occasionally dissolved breccia and gypsum interlayer. Except in the west, all of them are dominated by potential rocky desertification and mild rocky desertification. Different lithology will lead to different intensity, grade, area and degree of rocky desertification (Table 3-7).
Figure 3-4 Scale Map of Rocky Desertification Intensity Grade in qingzhen city
Table 3-7 Distribution Area Table of Rocky Desertification Intensity Grades in Karst Areas of qingzhen city (unit: m2)
According to the comparative analysis, the distribution ratio (Figure 3-5) and specific gravity (Figure 3-6) of each lithology can be obtained. It can be seen that the distribution of lithology in qingzhen city plays a leading role in the distribution of rocky desertification, in which the rocky desertification is mainly distributed in limestone dolomite area, accounting for 42% of the total karst area in qingzhen city, followed by limestone shale area, accounting for 19% of the total karst area, and the dolomite distribution area with the least rocky desertification area accounts for 10% of the total karst area in qingzhen city. In limestone dolomite area, the potential rocky desertification is the most widely distributed, accounting for about 62% of its area, followed by the rocky desertification-free area, accounting for 16%, and the intensity rocky desertification is the least, accounting for 1% (Figure 3-7).
Potential rocky desertification is most widely distributed in calcareous shale area, followed by mild rocky desertification and non-intensity rocky desertification (Figure 3-8). There are many non-rocky desertification, potential rocky desertification and mild rocky desertification in dolomite area, while the intensity rocky desertification only accounts for 1% (Figure 3-9). Potential rocky desertification accounts for 58%, followed by mild rocky desertification accounts for 26%, potential rocky desertification accounts for 12%, moderate rocky desertification accounts for 1%, and severe rocky desertification accounts for 3% (Figure 3- 10). In the areas where dolomite and limestone are alternately distributed, the potential rocky desertification is dominant, the proportion of non-rocky desertification and mild rocky desertification is similar, and there are more moderate rocky desertification and severe rocky desertification (Figure 3- 1 1). Based on the above comparison, non-rocky desertification is mainly distributed in dolomite area, followed by limestone shale, dolomite and limestone mixed area, and limestone area is the least; Potential rocky desertification is mainly distributed in limestone dolomite area, and dolomite area is the least; Mild rocky desertification is mostly distributed in dolomite and limestone areas, and the least is calcareous dolomite areas. Moderate rocky desertification is mainly distributed in the mixed area of dolomite and limestone, and the limestone area only accounts for1%of the total area of this area; Intensity rocky desertification is the most widely distributed in limestone area, but hardly distributed in calcareous shale area.
Figure 3-5 Distribution Proportion of Rocky Desertification with Different Lithology
Figure 3-6 Specific gravity map of rocky desertification intensity grade of each lithology
Figure 3-7 Scale Map of Rocky Desertification Intensity of Lime Dolomite
Figure 3-8 Scale Diagram of Rocky Desertification Intensity of Lime Shale
Figure 3-9 Scale Diagram of Intensity Grade of Dolomite Rocky Desertification
Figure 3- 10 Proportion of Rocky Desertification Intensity Grades in Limestone
Fig. 3- Intensity grade ratio of rocky desertification in dolomite and limestone +0 1