An overview of the resources and environment conditions and major geological problems in the Yangtze River economic zone, China

Yu-u Jn, Ln-un Ln, L- Cn, Hu-yon N, W-y G, Hn-xn Cn, Gn-y Z,Gu-ln Wn, Y-zon Bn, Yun L, Mn-tn L, Cn-xun Tn, Jn-wn Su, Qun-pn Zou,T-l Zn, Yun L, Hon-yn Lu, K Pn, Hn-m Wn

a Nanjing Geological Survey Center, China Geological Survey, Nanjing 210016, China

b China Geological Survey Water Ring Department, Beijing 100037, China

c Wuhan Geological Survey Center of China Geological Survey, Wuhan 430205, China

d Chengdu Geological Survey Center, China Geological Survey, Chengdu 610081, China

e Geophysical and Geochemical Exploration, Chinese Academy of Geological Sciences, Langfang 065000, China

f Oil and Gas Survey, China Geological Survey, Beijing 100029, China

g Institute of Hhydrogeology and Hnvironmental Geology, Chinese Academy of Geological Sciences, Shijiazhuang 050061, China

h China Institute of Geo-environmental Monitoring, Beijing 100081, China

i Institute of Karst Geology, Chinese Academy of Geological Sciences, Guilin 541004, China

j Institute of Geomechanics, Chinese Academy of Geological Sciences, Beijing 100081, China

k Shanghai Geological Survey Research Institute, Shanghai 200072, China

ABSTRACT

Focusing on the Yangtze River economic zone, the previous geological researches are systematically summarized, resources and environment conditions and major geological problems which are needing to be concerned in land planning and construction are studied. The results show that the resource conditions of cultivated land, shale gas, geotherm, lithium and so on are superior in the Yangtze River economic zone, and the resources and environment conditions are conducive to develop the modern agriculture,clean energy industry and strategic emerging industries. 3×1013 m2 farmlands without heavy metal pollution are concentrated; there are three national level shale gas exploration and development bases with explored reserves of 5.441×1011 m3; geothermal availability is 2.4×109 t of standard coal each year,equivalent to 19% of the amount of coal in 2014; Asia's largest energy lithium metal ore deposit is found.In some parts of Yangtze River economic zone, there are some major geological problems such as active faults, karst collapse, ground subsidence, landslide-collapse-debris flow, affecting the river-crossing channels, high-speed railway, urban agglomeration and green ecological corridor planning and construction. Those problems should be concerned, and the relevant suggestions and countermeasures are put forward. Meanwhile, the ideas to further support the development of the Yangtze River economic zone are put forward.

Keywords:

The Yangtze River economic zone

Resources and environment conditions

Major geological problems

Environmental geology

Hydrogeology

Disaster geology

1. Introduction

Yangtze River economic zone covers Shanghai, Jiangsu,Zhejiang, Anhui, Jiangxi, Hubei, Hunan, Sichuan, Chongqing,Yunnan, Guizhou and other 11 provinces (municipalities),which has an area of about 205.3 km2, total land area of 21.4%, population of 580 million, total population of 42.7%,gross domestic product 26 trillion that is 45.6% of the country's total (2013), is one of the regions that have the most powerful overall strength and strategic supporting in China.

The concept of Yangtze River economic zone was first put forward in September 1985 when China implemented the“seventh five-year plan”, which pointed out that we should vigorously develop horizontal economic ties with eastern and western regions. On September 12, 2014, the state council issued the guiding opinions on promoting the development of the Yangtze River economic zone by relying on the golden waterway, marking that the construction of the Yangtze River economic zone has become a national strategy.

According to the data, in the 1920s, some famous geological experts conducted researches on the geomorphology and geology of the Yangtze River economic zone, and published works and papers such as the geology of the lower Yangtze River, the progress of Yunnan geology research, and the early Hercynian orogeny in the northern Yunnan (Yin ZX, 1936; Guo WK, 1942; Pan YT, 1988).After 1949, with the needs of the development of economic construction, especially after the 60’s, geological and mining departments of 11 provinces and cities, including Jiangsu,Shanghai, Sichuan and so on, carried out a large number of geological investigations in the Yangtze River economic zone and accumulated abundant data (Bureau of Geology and Mineral resources of Guizhou province, 1987; Bureau of Geology and Mineral resources of Jiangsu province, 1989;Bureau of Geology and Mineral resources of Zhejiang province, 1996; Huang HZ et al., 1996). In recent years,although there is a large amount of literature on the Yangtze River economic zone, no research results of regional resources and environmental conditions relating to economy and geography (Chen XY, 2007; Yang GS et al., 2015) in the Yangtze River economic zone. In view of this, this paper studies resource and environment conditions and the major geological problems which are needing to be concerned in land planning and construction in the Yangtze River economic zone, in order to provide geological support for the economic construction and land planning.

2. Geological setting

The topography of Yangtze River economic zone is high in the west and low in the east. The geomorphology and geological conditions are complex, and the resources and environmental conditions and major geological problems are closely related to geomorphology and geological background.

The Yangtze River economic zone can be divided into four landforms, which are low mountain plain in the east,low-middle mountain in the southeast, middle-high mountain in the southwest, and the Qinghai-Tibetan Plateau. From the perspective of spatial distribution, taking shiyan-shaoyang line as the boundary, the west is mainly mountainous terrain,and the east is mainly plain platform landscape. In the west,taking guangyuan-lijiang line as the boundary, and the west is extremely high mountainous, and the east is mainly middle mountainous. In the eastern region, taking shaoyang-nanjing line as the boundary, the south is dominated by the lowmountain landform, and the north is mainly the landform of the plateau.

In the Yangtze River economic zone, the strata from Archean group to Quaternary system of Cenozoic group are well developed. On the tectonic, its main body is the craton-Yangtze block with the distribution of the North-East direction, make a series of strong activity orogenic system around the limit, the western margin of Qiangtang-Sanjiang orogenic system, the north rim of north China block(southern), Qinling-Qilianshan-Kunlun mountain orogenic system (eastern), southern margin of Jiangshao-Pingxiang-Chenzhou collision zone and Cathaysian orogenic system.The sedimentary environment, magmatism, metamorphism and tectonism of each continental block and orogenic system are different.

The Yangtze River economic zone has complex geological tectonic evolution history (Shu LS, 2012; Zhang GW et al., 2013). It is the period of continental block basement formation during the Archean to early proterozoic era, and in the middle proterozoic-neoproterozoic for supercontinent pyrolysis to form three oceans development to more continental margin arc basin system form, into the orogenic system, in the late neoproterozoic to the middle Triassic in north China and Yangtze continental marginal hyperplasia and its polymerization period between each other,since the late Triassic mainly influenced by the dual effects from southwest India plate and Eurasian plate continental and continental collision orogeny caused by material extrusion of the qinghai-tibet plateau toward to the east, and the westward subduction of the Pacific plate (Wu ZH et al., 2016; Sun YJ et al., 2016).

The hydrogeology and engineering geological conditions of Yangtze River economic zone are complex. Groundwater types are more complete, including pore water, karst water,fissure water and pore fissure water. Clastic rock type fracture-pore water is mainly distributed in Sichuan basin,bedrock fissure water throughout the hilly, karst fissure cavern water, mainly distributed in the Yunnan-Guizhou plateau in the west, unconsolidated rock pore water and confined water mainly in Yangtze delta plain, the Boyanghu lake plain and Jianghan and Dongtinghu lake plain in the Quaternary system aquifer. The rock and soil mass are divided by medium and structural features, and it is mainly composed of whole hard bedrock, semi-cemented rock, loose soil, special soil and so on.

Geomorphology, geological structure, hydrogeology and engineering geology condition is complicated in the Yangtze River economic zone, and a significant difference was found in the middle and lower reaches, therefore, regional active faults, karst collapse, landslide, collapse, debris flow disasters, land subsidence and other major geological problems also present different distribution characteristics.

3. Methods

On the basis of systematically combing geological survey data and results before in the Yangtze River economic zone,according to comprehensive research and analysis evaluation surrounding resource and environmental conditions and major geological problems focusing on land planning and construction in the Yangtze River economic zone, this article formed four advantageous resources and environment conditions and four river-crossing channels, high-speed railway, urban agglomeration and the construction of green ecological corridor planning major geological problems judgment and understanding. In the process of comprehensive research and analysis and evaluation, has held six integrated achievements communication workshop, and has set up a farmland, shale gas, geothermal, mineral resources, active faults, karst collapse, landslides, debris flows geological hazards such as project team, studied in detail resource and environment conditions and the major geological problems that should be paid attention to in the land planning and construction in the Yangtze River economic zone, and compiled a series of regional geology, mining and environment datum. Comprehensive research and analysis and evaluation over a year, to participate in the research unit has the China geological survey, the China land survey and planning institute, as well as Jiangsu, Zhejiang, Shanghai,Anhui, Jiangxi, Hubei, Hunan, Sichuan, Chongqing, Yunnan,Guizhou 11 provinces (cities) of land and resources (bureau),bureau of geology and mineral resources exploration,geological survey institute, geological environment monitoring station, etc., to participate in research personnel nearly 200 people.

4. Results

4.1. Favorable resource environmental conditions in the Yangtze River economic zone

The Yangtze River economic zone has abundant heavy metal-free arable land resources, good potential for exploiting shale gas, geothermal energy and other clean energy, and large reserves of strategic mineral resources such as lithium,rare earth, vanadium-titanium, tungsten-stannum, and so on,which is good for supporting the development of the Yangtze River economic zone.

4.1.1. The 0.3×1013 m2 of heavy metal-free arable land and 122.4×109 m2 of green Se-rich arable land provide good conditionsfordevelopingmodernagricultureand characteristic agriculture in the Yangtze River economic zone

The Yangtze River economic zone owns 0.453×1013m2arable land, accounting for 33.4% of China’s total arable land area. According to a geochemical survey on the quality of the 0.36×1013m2arable land, the environmental quality of the arable land is generally good, with heavy metal-free arable land totaling 0.3×1013m2(Table 1), accounting for 83.3% of the surveyed area and mainly distribute in the Sichuan Basin,Jianghan Plain, Poyanghu Plain, Caohu Plain, Dongtinghu Plain and Taihu Plain (Xie XJ et al., 2002; Wang QH et al.,2011; Liu YP et al., 2012; Cheng HX et al., 2015). The heavy metal-free arable land is to be first included as permanent basic farmland where food production core areas and main farm produce preponderant areas will be created.

The survey discovered 122.4×109m2green Se-rich arable land (Table 1 and Fig. 1) mainly located in the Chengdu Plain,Jianghan Plain, Poyanghu Plain, Taihu Plain and Jinqu Basin,with Hunan, Hubei, Jiangxi, Anhui and Zhejiang each possessing more than 13.3×109m2Se-rich arable land in theYangtze River economic zone. It is recommendable to promote the experience of Jiangxi’s Fengcheng and Hubei’s Enshi in developing Se-rich arable land (Zhang YA, 1994; Fu BY, 2009; Wu WL et al, 2010; Zhang X et al., 2015; Ren YH,2017), properly plan and utilize the Se-rich arable land resources, and create a number of Se-rich industry parks or famous, characteristic, high-quality farm produce industry bases.

Fig. 1.The distribution of cultivated land without heavy metal pollution and rich selenium cultivated land in the Yangtze River economic zone.

Table 1.The distribution of cultivated land without heavy metal pollution and green rich selenium cultivated land in the Yangtze River economic zone.

4.1.2. The 15.5×1013 m3 of recoverable shale gas, accounting for 62% of the nation’s total shale gas in the Yangtze River economic zone, provides good conditions for building a clean,low-carbon energy industry zone

The Yangtze River economic zone has tremendous potential for shale gas resources (Chen XJ et al., 2010; Liang C et al., 2012; Li YJ et al., 2013; Guo TL et al., 2013, 2014;Bao SJ et al., 2016), boasting 15.5×1013m3of recoverable resource which is 62% of the nation’s total recoverable resource. So far, China has a proved geological reserve of 5441×109m3of shale gas, concentrated in Chongqing ’s Fuling, Sichuan ’s Changning-Weiyuan and Yunnan ’s Zhaotong of the Yangtze River economic zone (Guo XS et al.,2014; Wu KY et al., 2016; Zhai GY et al., 2017), among which Funing has a proved geological reserve of 3806×109m3of shale gas and the first shale gas development base built in China (Wang SY, 2014) with annual capacity of 35×109m3.

With the support of the Ministry of Finance, China Geological Survey of the ministry of land and resources has made a succession of great discoveries and progresses in shale gas survey during 2015–2017 year. In Sichuan basin peripheral, Wuling mountain, Yunnan-Guizhou-Guangxi, the middle and lower Yangtze areas, 6 square kilometers to the exploration of new area were opened, and 9 sets of new strata series in the complex tectonic zone outside of the basin were expanded, 10 shale gas prospect areas, such as Zhengan-Qiuyang, were selected, with 14 favorable exploration blocks,including Zhengan, Zigui and so on. A breakthrough was made in Anye 1 well in Zunyi, Guizhou, and Eyiye 1 well Yi Chang, Hubei (Zhai GY et al., 2016, 2017).

Four geological strata have found shale gas and oil and gas in Permian qixia group, Silurian Shiniulan group, the upper ordovician Wufeng group-lower Silurian Longmaxi group and Ordovician Baota group of Anye 1 well, among them, the Shiniulan group of gas-bearing strata thickness 68 m, gas testing, daily production of more than 100000 m3, is a high yield gas well. 6.02×105m3/d, unimpeded flow of 12.38×105m3/d of high-yielding shale gas flow is obtained from the Cambrian Shuijingtuo group (formation formed in about 500 Ma ago) of Eyiye 1 well, and the great discovery of the world's oldest shale gas reservoir has been achieved in the Sinian Doushantuo group (formation formed in about 600 Ma ago) from the well. Western Hubei Zigui, Western Hunan Cili, middle Hunan Shaoyang, Sichuan Huayingshan, Anhui Xuancheng and so on, China geological survey deployment of shale gas survey also made important progress.

More efforts are to be employed in shale gas resource survey and exploration by organizing the third round of public bidding for shale gas exploration blocks to involve more qualified and financially and technically strong market players into shale gas E&D, expediting the construction of the three national integrated shale gas development pilot zones including Chongqing’s Funing, accelerating technical innovation and boosting shale gas-related industries.

4.1.3. The abundant shallow geothermal energy and hotwater geothermal resources with annual available heat equivalent to 2.4×109t standard coal that are equivalent to 19% of the coal consumption in 2014, are good for boosting urban energy conservation and emissions reduction, and geothermal-related industries

The survey and assessment indicate that the planned areas in the 11 provincial capitals of the Yangtze River economic zone have tremendous potential for shallow geothermal energy (Lin WJ et al., 2013; Zhou ZY et al., 2015; Xu W,2008; Wang GL et al., 2012), with annual available heat equivalent to 2.0×109t standard coal. If this energy is substantially exploited and utilized by using geothermal pump systems, the annual cooling area in summer will be 24.6×109m2and the annual heating area in winter will be 44.2×109m2,reducing 1.66×109t of CO2emission every year. Geothermal energy utilization projects are present in all the 11 provincial capitals. In fact, there are 720 such projects all together,covering more than 900×105m2. The economic and social benefits are remarkable. Hot-water geothermal resources are chiefly distributed in the Sichuan Basin, Jianghan Basin,Subei Basin, Huaibei Plain and the mountainous areas of western Sichuan and western Yunnan (Fig.2) (Chen MX et al., 1994; Hu SB et al., 2001; Xu M et al., 2011), with 69.3×109m3of recoverable geothermal water every year,equivalent to 0.40×109t standard coal, of which only 1.2% is utilized every year. The Yangtze River economic zone of geothermal industry is in its infancy, the low degree of resources utilization, but they are rich in geothermal resources, wide distribution, development prospect and market potential is tremendous, it will play an important role in energy conservation and emissions reduction (Geological environment bureau of ministry of land and resources, 2007;Fang GA, 2011; Yang RH et al., 2011; Wang Q et al., 2016).

Fig. 2.The distribution of geothermal resources in the Yangtze River economic zone.

It would be necessary to pay more effort in nonprofit geological exploration on shallow geothermal energy and hotwater geothermal resources, reduce the risks of commercial exploration, and encourage exploitation and utilization through price subsidies, tax reliefs or other policies to support geothermal heating and cooling, greenhouse breeding and hot spring tourism.

4.1.4. The large reserves of strategic mineral resources such as lithium, rare earth and rock salt etc. in the Yangtze River economic zone are good for pushing forward emerging industries that include new material, high-end manufacturing and new energy automobiles, etc.

The Yangtze River economic zone possess more than 80% of the country’s rare earth and titanium reserves, and lithium,tungsten, stannum and vanadium reserves take up more than 50% of the country ’s total. The world ’s largest tungsten copper deposit was found in zhuxi, jiangxi, with a proven tungsten resource of 344×105t. The largest energy metallithium deposit in Asia has been discovered in Sichuan’s Jiajika, with a proved resource reserve of 281×105t. A super molybdenum deposit has been discovered in Anhui’s Jinzhai,with a resource reserve of 246×105t, ranking the first in Asia and the second in the world. It has the world-leading large reserve of heavy rare earth, mainly distributed in Ganzhou,Jiangxi and Yueyang, Hunan, etc. (Yuan ZX et al., 2012;Wang DH et al., 2013, 2013a, 2016; Wang RJ et al., 2015).The proved vanadium-titanium reserve is 6.6×109t, mainly distributed in Sichuan, Yunnan, etc. The proved tungstenstannum reserve 650×105t, mainly distributed in Jiangxi,Hunan, Yunnan. The Yangtze River economic zone is rich in rock salt resources, with 23 underground large and mediumsized rock salt mines (Fig. 3). Among them, the proven reserves of Jiangsu Huaian salt mine are more than 2500×109t(Xu YT, 1993), ranking the top in the world. The buried depth of salt layer is between 700–2500 m underground, the accumulated thickness of salt layer is 240–1050 m, and the maximum thickness of single layer is 130 m. The salt cavern space formed by rock salt mining is huge, which is beneficial to the safe storage of imported oil and gas and “west-east gas transmission”. Compared with the surface oil and gas storage facilities, the salt cavern is called “a storage with high strategic safety” (Song GH et al., 2004; Ding GS et al., 2006).At present, more than 2000 salt caves have been developed and utilized in the world. The United States has hundreds of them, while Germany has nearly 100 and the number is still increasing (U.S. Energy information administration, 2013;Gas infrastructure Europe, 2013; Yin JP, 2014; Pan N, 2016).

Fig. 3.The distribution of large and medium-size rock salts in the Yangtze River economic zone.

It is recommendable to make the best use of strategic mineral resources such as lithium, molybdenum, rare earth,vanadium- titanium and tungsten-stannum, to boost strategic emerging industries that include lithium battery, rocket and thermonuclear reaction fuel, special alloy, superconducting material and aerospace industry, etc. It is suggested to strengthen the exploration and suitability evaluation of fine geological structure of underground rock salt strata such as Huaian and so on, accelerate the construction of underground oil and gas storage reservoirs, and build the first batch of demonstration bases of underground oil and gas reserve of national oil and gas strategy.

4.2. Major geological problems and suggestions affecting land planning and construction

The Yangtze River economic zone, which spans the eastern, central and western terrain ladders, features diverse geomorphic units, complex geological conditions and high exposure to geological disasters such as active faults, karst collapse, landslide, rock fall, debris flow and surface subsidence. The survey reveals 94 main active faults (Wu ZH et al., 2016) (Fig. 4), 235000 km2of high karst collapse-prone regions (Fig. 5), 107000 landslide, rock fall and debris flow disaster hazardous points (Li Y et al., 2013; Qu XY et al.,2016) (Fig. 6) and approximately 20000 km2of serious surface subsidence regions (Jiang YH et al., 2015), to which high attention will have to be paid when planning and implementing the river-crossing channels, high-speed railways and important city agglomerations.

4.2.1. Geological suitability of 95 planned river-crossing channels

83 of the 95 planned river-crossing channels have good geological suitability while 12 have poor geological suitability. Further geological investigation would be necessary in respect of the active faults and karst collapse problems to determine the proper location and cross-river method for the channels.

According to the effects of active faults and karst collapse on the safety of the river-crossing channels, the geological suitability of the locations for the channels was preliminarily assessed. The result indicates that the locations for 83 of the 95 planned river-crossing channels have good geological suitability while 12 have poor geological suitability (Table 2 and Fig. 7): the locations for nine channels, including Jiangsu’s Changtai, Hubei’s Wuxie and Sichuan’s Baitashan,are subject to active faults, while Hubei’s Wuhan Line 11,Jiayu and Chibi are exposed to karst collapse. In planning and implementing the river-crossing channels, it would be important to conduct further geological investigation and determine proper locations for the channels.

Table 2.Major geological problems affecting the construction of the river-crossing channels in the Yangtze River economic zone.

Fig. 4.The distribution of activity fracture and earthquake in the Yangtze River economic zone.

Fig. 5. The susceptibility evaluation map of karst collapse in the Yangtze River economic zone.

Fig. 6.The distribution and susceptibility evaluation map of landslide, collapse and debris flow in the Yangtze River economic zone.

Fig. 7.The distribution of the high-speed railway, the river-crossing channels and major geological problems in the Yangtze River economic zone.

The cross-river options for the 95 channels were preliminary compared according to engineering geological suitability. As the 48 river-crossing channels in the upper reaches of the Yangtze River are located in the river sections where the watercourses are deeply cut, and riverbed is thickly covered with pebble gravel, which is not good for building tunnels, plus the bedrock is shallowly buried and the bank is steady, which are good for building bridges. So, building a bridge across the river would be a suitable choice. In view of the cut depth of the watercourses, the thickness and homogeneity of the riverbed deposits, the deep-water horizon of the rivers and the bank stability, 27 of the river-crossing channels in the middle and lower reaches of the Yangtze River should be built in the form of a bridge, 12 in the form of a tunnel and 8 in the form of either a bridge or a tunnel (Table 3).Further investigation of the underwater topographical and hydrological conditions of the watercourses, the engineering geology of the riverbed deposits, and shoreline stability,combining with construction technology and traffic conditions, would be necessary to determine the proper crossriver method.

Table 3.Recommended methods for the under-river channels in the Yangtze River economic zone.

Table 4.Surface subsidence in the Yangtze River Delta Agglomeration and the affected cities.

4.2.2. 434 km of the Hukun high-speed railway line are exposed to geological hazard, for which strengthen monitoring, early warning and control would be necessary;high attention of the problems such as karst collapse and soft soil subsidence should be paid to the planned route for Nanjing-Anqing and Wuhan-Wanzhou sections of Huhanrong High-speed Railway

The 2264 km long Hukun High-speed Railway runs through the middle and lower Yangtze plains, Hunan-Jiangxi hilly-mountains and Yunnan-Guizhou Plateau. 434 km of this railway line is exposed to geological hazards, and 24 km of the Jiaxing section runs through surface subsidence regions.Recent years’ measurements indicate that, while the overall subsidence tends to slow down, local areas’ annual subsidence rate is still greater than 10 mm. Hence more effort should be made in monitoring groundwater level variation and surface subsidence. Along the Zhangshu-Pingxiang section in Jiangxi,Xiangtan-Loudi section in Hunan and Pu’an-Panxian section in Guizhou, karsts are developed, and coals are concentrated.The huge volumes of groundwater drained during coal mining could induce surface subsidence anytime, thereby affect the operating safety of 392 km of the high-speed railway line. It is recommendable to strengthen monitoring groundwater level and surface collapse, or deformation caused by groundwater drainage in the coal mine areas along the line. Along the Songming section in Yunnan, active faults are developed. 18 km of the section runs through IX-X seismic intensity zones.Many earthquakes have taken place in history, with that in 1833 being M8. It is recommendable to take seismic mitigation measures against earthquake and perform micromotion monitoring during operation.

When selecting the route for the Nanjing-Anqing and Wuhan-Wanzhou sections of the planned Huhanrong riverside high-speed railway, high attention should be paid to geological problems such as karst collapse and soft soil subsidence. Along the Nanjing-Anqing section, the karst covers 1780 km2in and around south bank’s Tongling-Chizhou area, where more than 100 karst collapses have already taken place. In the meantime, soft soil extends in large, continuous patches along the south bank of the Yangtze River, covering 4900 km2. In the north bank’s Hexian-Wuwei-Anqing area, on the contrary, the geological conditions are good. Hence preference should be given to the Nanjing-Wuewi-Anqing route. As to the Wuhan-Wanzhou section, the Qianjiang-Jingzhou-Zhijiang area is exposed to serious soft soil problems: the lines with soft soil thickness larger than 5 m total 190 km; the Tianmen-Jingmen area contains mass karst and mining subsidence regions covering 2400 km2; while in the Tianmen-Dangyang area, the bedrock is shallowly buried, and the subgrade is highly stable. Hence preference should be given to the Wuhan-Tianmen-Dangyang-Wanzhou route.

4.2.3. The main geological problems for the Yangtze River Delta, Middle Reaches of the Yangtze River and Chengyu Urban Agglomeration are respectively surface subsidence,karst collapse, landslide, rock fall and debris flow hazards,for which urban geological risk assessment would be necessary to ensure proper planning of the urban layout

The Yangtze River Delta Urban Agglomeration has experienced an urban sprawl leading to serious over exploitation of groundwater and heavy regional surface subsidence, especially Shanghai, Suzhou-Wuxi-Changzhou and Hangzhou-Jiaxing -Huzhou, where the subsidence areas with accumulated subsidence greater than 200 mm total nearly 10000 km2, though subsidence has been effectively controlled after years of efforts and the subsidence rate has slowed down: the subsidence was commonly lower than 7 mm in 2014. Despite this, however, new signs of surface subsidence have been discovered in Jiangsu’s Yancheng and Dafeng and tend to expand. The subsidence areas with accumulated subsidence greater than 200 mm total more than 10000 km2(Table 4), the maximum being more than 25 mm in 2014. It would be necessary to regulate the groundwater exploit in Shanghai, Suzhou-Wuxi-Changzhou and Hangzhou-Jiaxing-Huzhou where surface subsidence tends to slow down, strictly control the groundwater exploit in the coastal areas of Jiangsu where surface subsidence is intensifying, and further strengthen the monitoring, early warning and risk control of surface subsidence.

Urbanization of the Middle reaches of Yangtze River Agglomeration is typically challenged by karst collapse risks.Survey reveals that the highly karst collapse-prone regions are chiefly in Wuhan, Huangshi-Ezhou riverside region,Ruichang-Jiujiang- Pengze riverside region, Leping-Feng cheng-Pingxiang region and Hunan’s Ningxiang, where 19 urban planning zones are exposed to karst collapse, covering 4700 km2(Table 5). Wuhan, which is the most exposed to karst collapse, has suffered 23 karst collapses over the past 10 years, of which 17 was induced by pile foundation implementation or groundwater drainage. It is therefore important to assess the karst collapse risk zones of the urban construction land, strengthen the prevention, monitoring and early warning of karst collapse, and regulate the project implementation and construction.

Urbanization of the Chengyu Agglomeration is chiefly challenged by earthquake, landslide, rock fall and debris flow risks. A number of important towns in 24 counties/cities,including Dujiangyan, Shimian and Baoxing, are situated along the Longmenshan fault belt or Yingjing-Yanjin fault belt, where they are heavily subject to earthquake. 26 cities at or above county level, including Hanyuan, Pingshan,Yunyang and Wangzhou, are situated on the periphery of the Sichuan Basin, where they are exposed to landslide, rock fall and debris flow hazard (Table 6). It would be necessary to limit the urban population of the areas subject to active faults,properly plan the construction of towns in these areas, and make more effort in the risk assessment, monitoring, early warning and comprehensive management of geological disasters in mountainous towns in western Sichuan and northeastern Chongqing.

Table 5.Karst collapse in the Middle reaches of Yangtze River Agglomeration and the affected cities.

Table 6.Main geological concerns in the Chengyu agglomeration and the affected cities.

4.2.4. Construction of the ecological corridor should be paid high attention to arable land acidification, groundwater pollution and mine geological environmental destruction, for which measures should be taken to limit arable land acidification, strengthen groundwater management and protection, boost the transformation and upgrading of mineral industry, and the construction of green mines

The survey reveals 0.15×1013m2acidic arable land in the Yangtze River economic zone, accounting for 43% of the surveyed area. The acidic arable land is mainly located in Jiangxi, Hunan, Ningbo-Taizhou coastal area and Jinhua Quzhou Basin. Compared with the result of the second national soil survey, some areas display remarkable arable land acidification trend. As acidification can activate heavy metals in the arable land, result in the leach of nutrient elements and impair the workability of the arable land, it would be necessary to control the pollutant emission of acidic substances and the application of acidic fertilizers, limit the acidification trend of arable land, implement crop rotation and cause the arable land to turn towards better quality.

The survey reveals serious nitrogen and heavy metal pollution in the groundwater, and prominent organic pollution in the Yangtze River economic zone, with 17% of the pollution samples exceeding the limit. Nitrogen pollutants in groundwater are primarily nitrate and ammonia-nitrogen, with 14.1% of the groundwater exceeding the permitted nitrogen limit. The main victims are the agricultural areas. The overlimit ratio of heavy metals such as mercury, cadmium and chromium are 3.5%, sporadically found on the outskirts ofcities and in the vicinity of industrial or mining facilities. The over-limit ratio of toxic or hazardous organic pollutants such as CTC is 0.6%, mostly dotted in or around industrial zones.It is therefore important to control groundwater pollution in and around source regions and towns, focus on prevention and natural restoration, combine monitoring and early warning with engineering treatment, and inhibit groundwater deterioration.

Many earthquakes took place in history, with a magnitude of 8 in 1833. There are more than 54000 mines along the Yangtze river economic zone, and most of the metal mines,such as iron, manganese, lead and zinc, are mainly smallsized dispersive mining. Large and medium-sized mines make up only 7%, which is lower than the country’s average of 10%. Traditional exploitation and utilization methods have resulted in heavy destruction to mine geological environment.As of 2014, the destructed land amounted up to approximately 5000 km2; the stock of solid waste was 84 ×109t; and the annual wastewater emission was more than 27×109m3. It is recommendable to expedite mining intensification and updating, strengthen the construction of the 14 large mineral resource bases (Table 7 and Fig. 8); complete the construction of the 227 national-level green mine pilot zones within theshortest time, carry out green mines construction vigorously,improve the mine geological environment and maintain a balance between mines and the local areas.

Table 7.Large mineral resource bases in the Yangtze River economic zone.

Fig. 8.Distribution of large-scale mineral resources in Yangtze River economic zone.

5. Geological work scenarios of the 13th Five-Year Plan period in support of the Yangtze River economic zone

During the 13thFive-Year Plan period, China Geological Survey, MLR will carry through the spirit of the Fifth Plenary Session of the 18thCentral Party Committee and the Recommendations of the Central Party Committee for the 13th Five-Year Plan for Economic and Social Development regarding the promotion of the development strategy of the Yangtze River economic zone, target the major tasks of supporting the functional upgrading of gold waterways,building three-dimensional transport corridors, updating industries, building new urbanization and creating green ecological corridors, orient at studying and solving the major geological problems that affect and restrict the development of the Yangtze River economic zone, and carry out geological survey in the Yangtze River economic zone, deployed in the"four economic zones" (the Yangtze River Delta, Wanjiang,Middle Reaches Yangtze River and Chengyu), “three development lines” (riverside, seaside and high-speed lines)and “four key regions” (major engineering regions, important metallogenic regions, major problem regions and important ecological regions), and involving seven tasks:

First, environmental geological survey on the Yangtze River Delta, Middle Yangtze River and Chengyu Agglomerations around the new urbanization strategy;second, mineral resource survey on the Middle and Lower Yangtze River, Three-River Region in Southwest China,western Hunan and western Hubei, and shale gas resource survey on Sichuan-Chongqing, western Hubei and Yunnan-Guizhou around industry upgrading; third, engineering geological survey on riverside, seaside and along high-speed railway development zones around the construction of major project and major infrastructures; fourth, karst collapse survey and active fault survey in main fault belts along the Upper and Middle Yangtze River around momentous geological problems; fifth, 1:250000 geochemical survey of arable land quality in Central West China and 1:50000 survey in East China around modern agriculture; sixth, environmental geological survey on ecologic fragile regions including Danjiangkou reservoir region, Poyanghu region and Three Gorges reservoir region around the construction of ecological corridors; and Seventh, researches on the Yangtze River and lake evolution since late pleistocene and coupling relationship of geological disasters, major water conservancy engineering and geological environment multivariate response, critical zone of the earth, the resource environmental bearing capacity evaluation, basins of earth system science theory method and so on in the Yangtze River economic belt around basins of geological environmental characteristics.

In order to step up the geological survey of the Yangtze River economic zone, China Geological Survey, MLR will convene a “Symposium on the Geological Survey of the Yangtze River economic zone” together with the land and resources departments of the 11 provinces (municipalities) of the Yangtze River economic zone, establish an innovative interlocked central-local coordination mechanism for geological work under which, with the support of the Ministry of Finance and following the principle of administrative and financial power division between the central and local governments, a RMB 1.2 billion central government fund,plus local financial funds, would be arranged to advance geological survey, and set up a land and resources environmental carrying capacity assessment, monitoring and early warning system to provide greater support for the development strategy of the Yangtze River economic zone.

6. Conclusions

(i) The Yangtze River economic zone has superior arable land, shale gas, geothermal and lithium resources, including 0.3×1313m2concentrated heavy metal-free arable land, three national-level shale gas E&D bases with proved reserve of 5441×109m3, annual available geothermal heat equivalent to 2.4×109t standard coal or 19% of the coal consumption of 2014, and the largest energy metal lithium deposit in Asia. Its resource environmental conditions are good for modern agriculture, clean energy and strategic new industries.

(ii) The Yangtze River economic zone has diverse geomorphic units, complex geological conditions and high exposure to geological disasters such as active faults, karst collapse, landslide, rock fall, debris flow and surface subsidence. The survey reveals 94 main active faults, 235000 km2of high karst collapse-prone regions, 107000 landslide, rock fall and debris flow disaster hazardous points and approximately 20000 km2of serious surface subsidence regions, to which high attention will have to be paid when planning and implementing the river-crossing channels, highspeed railways and important city agglomerations, and relevant suggestions and countermeasures are put forward.

(iii) Based on the demand-problem-goal oriented, the paper puts forward the idea of geological work to support the development of geological work of the Yangtze River economic belt during the 13th five-year plan. Seven survey and research work of the environmental geology, energy minerals and so on mainly deployed in the “four economic zones” (the Yangtze River Delta, Wanjiang, Middle Reaches Yangtze River and Chengyu), “three development lines ”(riverside, seaside and high-speed lines) and “four key regions” (major engineering regions, important metallogenic regions, major problem regions and important ecological regions).

Acknowledgment

Jointly supported by geological environment comprehensive survey project of the Yangtze economic zone of China geological survey (gp2015-03-02) and Nanjing-Shanghai-Wenzhou town planning area 1:50000 environmental geology survey project of China geological survey (DD20160246). The authors would like to express heartfelt thanks to the meticulous care, guidance and support from leaders of China Geological Survey at all levels on the Yangtze River economic belt and the researchers including Bao Shujing, Zhou Guohua, Xu Mingcheng, Yin ping, Sun Jichao, Zhang Jinde, Li Ruimin, Wu Zhonghai, Huang Bolin,Zhang Senqi, Yang Qiqing, Jing Jihong, Li Minghui, Qi Fan,Lu Hua, Li Xiao, Ling Qinglong, Li Yunhuai, Li Zhigang,Xiao Shangde, Li Shuotao, Fan Yi, Wang Fan, Yang Man,Wei Changli, Liu Xi, Luowei, Meng Wei, Zhu Guangyi, Zhu Yuezhang, Shao Changsheng, He Jun, Qi Xin, Zeng Chunfang, Dai Jianling, Meng Hui, Qu Xueyan, Zhao Jiankang, Yu Jun, Sun jianping, Fu Yongpeng, Xie Zhongsheng, Tan Jianming, Ma Teng, Zhou Xun, Huang Jingyu, Tian Fujin, Xing huaixue, Jia Junyuan, Yang hui,Shun Qiang, Liu Lin, Yang Guoqiang, Jing Yang etc. The revision form anonymous reviewers and the Executive Editorin-Chief Dr. Yan Yang have greatly approved this manuscript,the author would like to express sincerely thanks to them.