Geography and natural environment overview

This section is written by Niu Pingshan. Niu Pingshan, Shijiazhuang University of Economics.

1. Overview of physical geography

(1) Geographical location and transportation

The Nihewan Formation strata are widely distributed in the Datong Basin in northern Shanxi and northwest Hebei. Yangyuan and Yuxian basins in China and Yanhuai basin in Beijing. Among them, the three basins of Datong, Yangyuan and Yuxian were once a unified large lake basin during the Quaternary period, which was called the "Nihewan Basin" in a broad sense. The generally known "Nihewan Basin" starts from the Xujiayao site at the junction of Shanxi and Hebei in the west, to Shixiali in Yangyuan in the east, and to Xiheying in Yu County in the south. The locations of mammal fossils discovered in Quaternary lacustrine sediments and the ancient Stone tool sites are mainly concentrated here. The "Nihewan Basin" or "Nihewan Rift Basin" referred to in this book is limited to this range. In order to have a more comprehensive understanding of the physical geography and environmental conditions of the "Nihewan Basin" and its surrounding areas, this section expands the scope of coverage to the broad "Nihewan Basin".

The broad "Nihewan Basin" is roughly within the range of 39°00'~40°20' north latitude and 112°15'~115°10' east longitude. The west and north are bounded by mountains such as Hongtao Mountain, Qifeng Mountain, Cailiang Mountain, and Xiong'er Mountain. The southern and eastern borders are surrounded by Mantou Mountain, Hengshan Mountain, Matou Mountain, Liuling Mountain, Baijiantuo Mountain, and Xiaowutai Mountain. The total area is about 9000km2 (see Figure 1-1).

The transportation in the basin is convenient, with the Daqin Railway running through the entire region, Tongpu Railway, Huai (Lai) Wei (County) Railway, Xuanda Expressway, National Highway 109, 207 and other national and local railways and highways Arterial lines and rural roads form a transportation network that extends in all directions, providing direct access to cities such as Beijing, Hohhot, Taiyuan, Shijiazhuang, Zhangjiakou, and Qinhuangdao.

(2) Meteorology and Hydrology

The Nihewan Basin belongs to the East Asian continental semi-arid monsoon climate zone. According to the statistics of many years of meteorological data in Yangyuan and Yu County, the annual average temperature is 6.0~7.3℃ . In winter, controlled by the powerful Mongolian high pressure, cold and dry winter winds blowing from the mainland to the ocean prevail, resulting in frequent cold wave weather. The coldest month is January, with an average monthly temperature of -11.5℃ and an extreme minimum temperature of -35.3℃. Summer is mostly controlled by the Pacific high pressure, but because it is located in a mountainous area with changeable terrain, it is easy to form unstable convection, so thunderstorms and hail are common. July is the hottest month, with an average monthly temperature of 22.7°C and an extreme high temperature of 38°C. Spring is dry and windy. Strong updrafts from the ground often roll up dry and loose soil, resulting in sandstorms, causing the loss of soil moisture, nutrients and fine particles. The average annual precipitation in the basin is 360 to 420mm, with the maximum precipitation being 616.3mm and the minimum precipitation being 224.0mm, mostly concentrated in July to August. The general climate characteristics of the region are drought in spring, mild summer, cool autumn, and cold winter; low precipitation, high dryness, and severe drought; annual precipitation variability is about 24%; and the crop growth period is moderate.

Sanggan River, the first-level tributary of Yongding River, is the largest river in the region. It forms the Sanggan River system with its main tributaries Hun River, Huangshui River, Yuanzi River, Yuhe River and Huliu River. . The Sangqian River originates from Guancun Mountain, one of the main peaks at the northern end of Luya Mountain in Shanxi Province. It flows through the Datong Basin in the northeast direction, enters the Yangyuan Basin to the east of Cetian Reservoir, and flows out of the basin through the eastern canyon of Shixiali. According to data from the Shixiali Hydrological Station, the multi-year average runoff of the Sanggan River is 16.78m3/s, with a maximum flow of 1160m3/s (1967.8.11) and a minimum flow of 0.024m3/s (1978.7.7).

The Huliu River flowing through the Yuxian Basin originates near Heilugouliang in Guangling County, Shanxi. It passes through the Yuxian Basin and enters the Yangyuan Basin from near Beishuiquan Town. It flows for more than ten kilometers and ends in Yangyuan small ferry flows into Sanggan River. The multi-year average flow rate is 4.92m3/s, the maximum flow rate is 347.0m3/s (1958.7.11), and the minimum flow rate is zero (1971.6.16).

Figure 1-1 Geographical and transportation location map of Nihewan Basin

The Sanggan River system has the unique characteristics of rivers in northern my country, that is, due to the rainy summer and concentrated precipitation, it often The formation of short-term torrents with high sediment content can easily lead to river flooding; droughts occur in winter and spring, and the flow rate is greatly reduced, and even dry periods occur. Therefore, the landforms of wide floodplains and narrow shallow riverbeds were created, and meandering riverbeds were developed.

(3) Overview of pre-Quaternary geology and landforms

Nihewan Basin is located in the northern part of the Fenwei fault depression structural basin, surrounded by undulating mountains. The northern part is the remnants of the Yinshan Mountains. Except for a few peaks, the altitude of the watershed is mostly below 2000m. To the south is the Hengshan Mountains (including Xiaowutai Mountain) at the northern end of the Taihang Mountains. Most of the peaks are over 2000m, among which the highest peak of Xiaowutai Mountain is 2882m (Dongtai). The altitude in the central valley area is mostly above 800m, with the lowest being 780m. The height difference between the river valley and the surrounding mountains is mostly between 500 and 1000m, with the extreme height difference being nearly 2100m. The distribution height of the Quaternary strata in the basin can reach an altitude of about 1200m in the northern piedmont, and most of the rest of the area is below 1100-1000m.

The Quaternary strata and rocks before the exposure of the bedrock mountains around the basin mainly include: ① Archaean black cloud plagioclase gneiss, plagioclase amphibolite gneiss, flower Gangneiss, amphibolite, amphibolite, migmatite and marble, etc.; ② Shale, glauconite shale, quartz sandstone, chert nodules (or strips) of the Proterozoic Changcheng System and Jixian System Dolomite, dolomitic limestone, siliceous limestone, fine-crystalline limestone, flint striped limestone, argillaceous dolostone, etc.; ③ The corners of the Cambrian, Ordovician, Carboniferous, and Permian of the Paleozoic Conglomerate, conglomerate, sandstone, shale, clay rock, coal-bearing rock series, bamboo-leaf limestone, oolitic limestone, dolomitic limestone, crystalline limestone, chert-containing dolomitic limestone, etc.; ④ Mesozoic Conglomerate, sandstone, breccia, claystone, coal-bearing rock series, andesite, tuff, andesitic agglomerate, rhyolite, trachyte, etc. from the Jurassic and Cretaceous periods; ⑤ Sporadic distribution of different periods Intrusive rock bodies such as granite, diorite, syenite, diabase, gabbro, syenite porphyry, quartz porphyry and Cenozoic Paleogene basalt, etc.

II. Overview of the modern ecological environment

(1) Water resources and hydrochemical environmental characteristics

Because it is located in a semi-arid climate zone, the overall water resources in the basin are There is a shortage and uneven distribution. The Sanggan River and its main trunk and tributaries are the main rivers that collect surface water in the convergence area. Surface water resources in these valley areas are relatively abundant, while other areas are relatively poor. Calculations show that the average annual amount of atmospheric precipitation water resources received by the basin ranges from 3.24×109 to 3.78×109m3/a. Among them, the multi-year average precipitation water resources in the Yangyuan Basin are 7.54×108m3/a, the self-produced runoff is 0.655×108m3/a, the external inbound water is 1.07×109m3/a, the outbound water resources are 1.09×109m3/a, and the exploitable amount of groundwater About 0.32×108m3/a.

The water chemical characteristics of the area from the eastern Yangyuan Basin to the north of Dongyaozitou in the Yuxian Basin basically represent the modern water environment characteristics in the eastern Nihewan Basin. According to the author's investigation of this area from 2005 to 2006, the multi-year monitoring data of Qianjiashawa and Shixiali hydrological stations reflect that the chemical types of surface water are HCO3-Ca and HCO3-Na. According to data from 18 sampling points, the chemical types of groundwater in the area are relatively complex. According to Shukarev classification, the chemical types of groundwater in the eastern part of the basin are mainly HCO3-Na+Mg type, followed by HCO3+SO4-Na+Mg type and HCO3-Na type water. According to the Kurlov expression, the anion combination types of groundwater water chemistry are mainly HCO3-SO4-Cl type and HCO3-Cl-SO4 type; the cation combination types are mainly Na-Mg-Ca type, followed by Mg- Na-Ca type. The average contents of various chemical components of groundwater in the eastern basin measured in 2005 are shown in Table 1-1 and Table 1-2.

Table 1-1 Statistical table of the average content of chemical components in groundwater in the eastern Nihewan Basin (2005. 7)

Table 1-2 Chemical groups in the groundwater in the eastern Nihewan Basin Statistical table of average content (2005. 10)

(2) Soil

The soil in Nihewan Basin has parent materials of multiple origins, among which the soil is mainly distributed in the bedrock exposed areas. Residual slope deposits, slope alluvial deposits and flood alluvial deposits at the foot of slopes and piedmont areas, alluvial deposits in river valleys, loess on loess platforms and basin edges, and lakes exposed on the bank slopes on both sides of the Sanggan River and Huliu River. River sediments, etc.

Based on the theory of pedogenesis, comprehensive soil formation conditions, soil formation characteristics and soil properties, and referring to the "Second National Soil Census" classification method, through field investigation and statistics, the soil in the eastern Nihewan Basin has There are 7 soil categories: leaching soil, semi-leaching soil, calcareous soil, semi-liquid soil, primary soil, saline-alkali soil and anthropogenic soil. Humid warm leach soil, semi-humid warm semi-leaching soil, semi-arid thermocalcic soil, light semi-hydrogen soil, dark semi-hydrogen soil, soil primary soil, stony primary soil, saline soil, irrigation soil , rice soil and other 10 subclasses, 12 soil categories, 23 subcategories, 41 soil genera, and 61 soil species (see Table 1-3). After measurement, the average nutrient content and trace element content of some major soil species and soil genera are shown in Table 1-4 and Table 1-5.

Table 1-3 Statistical table of soil types in the Nihewan Basin and its surrounding mountains

Continued table

Table 1-4 Some major soil types in the eastern Nihewan Basin Statistical table of average nutrient content in various layers of soil types

(According to Niu Pingshan et al., 2007)

Table 1-5 Average content of trace elements in different soil types in the eastern Nihewan Basin Statistical table

(3) Vegetation and plant resources

1. Vegetation distribution

The vegetation in the Nihewan Basin ranges from warm temperate deciduous broad-leaved forest to temperate semi-arid zone , characteristics of transition from arid grassland. The surrounding mountainous areas are dominated by forest vegetation. At an altitude of 1200-1800 m, there are deciduous broad-leaved forests dominated by oak, mountain birch, poplar, and miscellaneous wood forests (with temperate coniferous pine forests in between). 1600 ~ 2300 m is dominated by coniferous and broad-leaved mixed forests such as white barley, green barley, stink fir, North China larch, white birch, and birch. 2100 ~ 2500 m is the distribution zone of North China larch, white barbarian, green barbarian, smelly fir and other coniferous forests. Subalpine meadows are distributed above 2400 m (sometimes above 2000 m).

Semi-arid and arid shrub grasslands are widely distributed in low mountains, loess hills, ridge plateaus, and foothills. Their vegetation composition characteristics are: ① The warm-loving central Asian grassland components are in the vegetation composition Play a leading role, such as Stipa macrophylla, Miscanthus longus, Gobi Stipa, etc. ② Some drought-tolerant components in the East Asian flora account for a larger proportion, such as Leyte chinensis, Potentilla sinensis, Lespedeza dauri, Lespedeza multiflora, Artemisia vulgaris, etc. ③ Contains shrub species on low hills and hills: such as jujube, meadowfoam, caragana, etc. ④ There are many common herbaceous plants, such as fescue, Cryptosporum adenospermum, Leymus chinensis, thyme, alfalfa, skullcap, spurge spurge, water chestnut, thread-leaf chrysanthemum and farmland weeds, etc. The piedmont and river valleys are vast agricultural farming areas with less natural vegetation.

2. Plant resources

There are many plant species in Nihewan Basin. According to the preliminary survey data of plant resources in Xiaowutai Mountain Nature Reserve, Yu County and Yangyuan County, *** 106 families, 486 genera, and 1,350 species of wild higher plants were discovered. Among them, wild higher plants are mainly herbaceous plants (1109 herbaceous species; 241 woody species, accounting for 17. 9%), and are mostly distributed in nearly 20 families (accounting for 71. 8% to 74. 4% of the total). Among them, five families, chrysanthemum, grass, rose, bean, and ranunculus, have a dominant position, accounting for 40. 3% to 45. 6% of the total species (Table 1-6).

Table 1-6 Statistical table of 20 major plant families in the Nihewan Basin and its southern mountains

3. Socioeconomic overview

Nihewan Basin in a broad sense It is under the jurisdiction of three cities: Datong and Shuozhou in Shanxi Province and Zhangjiakou in Hebei Province, which mainly includes the urban areas of Datong and Shuozhou, all of Shanyin, Huairen, Datong, and Yangyuan counties, and Yingxian, Hunyuan, Zuoyun, and Yangyuan counties. Most or part of Gao and Yu counties.

(1) Overview of mineral resources

The basin and its surrounding mountains contain rich mineral resources (only incomplete statistics of Yangyuan indicate that there are 55 proven mineral species. above). Among the proven mineral resources, coal resources are the most abundant. Among them, Datong coal is world-famous and Yuxian coal is nationally famous. In addition, iron, manganese, copper, zinc, molybdenum, phosphorus, graphite, kaolin, bentonite, limestone, marble and other minerals are relatively abundant.

(2) Overview of industrial and agricultural production

The coal industry is the pillar industry in the area, and industrial enterprises such as transportation, chemical industry, and electric power around the coal industry all account for

Has an important position. In addition, industrial industries and craft processing industries such as building materials, machinery manufacturing, construction, food processing, medicine, brewing, papermaking, ceramics, carpets, and fur processing are also relatively developed, and relevant townships, village offices, and individual enterprises are developing rapidly.

Except for the urban areas of Datong and Shuozhou, all counties are rich in land resources and are mainly agricultural, with a large per capita arable land area. For example, in the Yangyuan Basin, the agricultural population density is small (average less than 140 people/km2), and the per capita cultivated land area is about 0. 26 hm2 (3. 9 acres).

The main food crops in the area include corn, millet, millet, sorghum, beans, potatoes, and a small amount of wheat, rice, etc. The main cash crops are oil crops, sunflowers, vegetables, melons, etc. With the development of agricultural modernization technology, vegetable bases in urban suburbs and river valleys are constantly expanding, and production bases for improved varieties and local specialties are being formed. For example, in recent years, a vegetable production base has been formed in the section from Huashoying to Shixiali in the Sanggan River Valley. Some high-quality vegetables, mainly celery, are becoming famous and high-quality specialties in the region and are sold all over the country. In the Huliu River Valley, cultivating improved corn varieties is the specialty of local farmers, making the area a designated breeding base for improved corn varieties. In the loess platform and loess gully area in the eastern part of the basin, apricot forest land cultivated through introduction and local cultivation is forming an apricot flat base. In addition, in forestry, fresh fruit economic forests such as apples, peaches, plums, and pears have developed rapidly, and protective forests, water conservation shrubs, and animal husbandry have all developed to a certain extent.

(3) Culture and Tourism

The Nihewan Basin not only contains long and rich prehistoric human culture, but also preserves rich and colorful ancient and modern civilizations, making nature and The cultural landscape is integrated, and the tourism resources that have been formed and potential are immeasurable. Among them, the world-famous Yungang Grottoes are located on the northwest side of the basin. Among the "Five Mountains" in my country, Beiyue Hengshan Scenic Area is located in Hunyuan County on the south side of the basin. In addition, the famous cultural and natural tourist attractions and attractions in the area include Huayan Temple, Puhua Temple, Nine Dragon Wall and Guanyin Hall in Datong City, Xuankong Temple, Yongan Temple and Qianfoling in Hunyuan, and the Quaternary Temple in Datong County. Volcanic geological relics, the Brahma Temple Tombs, Pure Land Temple, and Pingshuo Han Tombs in Shuocheng District, Shuozhou City, the old Guangwu Ancient City and Guangwu Han Tombs in Shanyin, the Jinshatan Tombs in Huairen, and the Huayan Temple Brick Pagoda , Tomb of King Danyang, wooden pagoda, Wenshu Temple, Yongzhen Temple in Yingxian County, Yuxian Sky Grassland, Xiaowutai Mountain, Feihu Valley, Yuzhou Ancient City, Xigubao, Huayan Temple, Daiwang City, Chongtai Temple, folk society Fire and paper-cut art, numerous prehistoric human cultural relics in the basin, etc. These scenic spots and attractions are important tourism resources in and around the Nihewan Basin.