Responses of Vegetation and Soil to Artificial Restoration Measures in Abandoned Gold Mining Areas in Altai Mountain, Northwest China

Abstract

Gold mining plays an essential role on the social and economic development. However, mining activities leads to destructive changes in ground structure and biodiversity, triggering considerable environmental problems. This study proposed a field observation to evaluate the short-term efforts of the artificial restoration measures taken by the Two-River Source Nature Reserve Administration from 2010 to 2015 in an abandoned gold mining area in Altai Mountain, Northwest China. The effects of different ecological restoration measures on soil and vegetation recovery were examined by calculating the richness index, dominance index, diversity index, evenness index, aboveground biomass, vegetation coverage, species number and soil-rock ratio index of the recovered area. Further, a principal component analysis (PCA) was used to compare the efficiency of each artificial measure. The results showed that gold mining activities cause serious environmental degradation in natural landscapes. The soil-rock ratio of the abandoned mining area was reduced by 98% compared with the original grassland. The surface vegetation was destructively destroyed, and the surface soil was stripped. Restoration measures considerably improved ecological conditions, which were reflected by surface biomass, diversity index and the soil-rock ratio, as well as accelerated ecological rebuilding processes in abandoned mining areas. The ecological efficiency of the single restoration measures assessed, such as soil measures, water replenishment measures and biological measures, was not significant. The average values of various indexes of these measures showed lower values of 0.12–0.45. The combination of various measures can not only improve the soil environment but can also lead to changes in plant community diversity and significant ecological efficiency. This was reflected by the values of various indexes, which reached higher values of 0.4–1.21. As far as the same kind of restoration measure is considered, the longer the restoration period, the better the recovery effect.

1. Introduction

Gold mining activities leads to considerable environmental pollution and ecological degradation [1,2,3]. The original landscape of mining areas has changed greatly, and new geomorphologic forms, such as land slide, fractures and slopes destroyed the ground surface [4]. Furthermore, mining activities has greatly changed the landscape pattern and increased fragmentation due to its inevitable consequences including deforestation, surface damage and tailing piles [5,6]. This processes adversely affect to both the spatial pattern of the ecological system and the ecological process [7]. Therefore, the seriousness of ecological problem caused by mining on the surrounding environment determines why the mining area needs to be repaired repeatedly. For this reasons, on the basis of regional, landscape and engineering scale, a series of technological planning and methods are combined with ecological restoration technologies to form a planning scheme which will be helpful in applying restoration planning at the regional or landscape scale [8].

Ecological restoration in mining areas should focus on nature restoration, combined with the project measure. The restoration of fragile environment in mining area needs a variety of ecological engineering technologies and corresponding measures [9,10]. Research shows that applications of ecological engineering could also enhance bio diversity and the ecosystem function [11]. Comparing with traditional technologies, this approach takes longer time, but the long-term restoration efficiency would be more reliable [12]. Degradation of soil is the greatest challenges to ecological restoration, hence, preference should be given to the restoration of soil quality. Revegetation is the most studied and used method. One of the major barriers to mine restoration and revegetation is the low fertility of mine soils. Therefore, the planting of hyperaccumulators is very useful in stabilizing the bare area and in minimizing the pollution problem [13]. Stabilize the soil and control the pollution by revegetation is probably the most realistic approach to the reclamation of mine land [14].

To make an effective restoration planning that can maximize the overall success of restoration efforts and minimize the costs, it is necessary to comprehensive understand the environmental problems and the complexity of ecological processes in mining areas. Josa et al. analyzed the failure of some common practices of opencast mine restoration in a Mediterranean semi-arid environment in northeast Spain and indicated that the erosion of embankments during rainfall were controlled by fast-growing herbaceous species in opencast mining area. Such species needs adequate of water for survival. If water is scare, these species can rapidly disappear and leads to more serious land degradation in mining area [14]. The key for the sustainable development of the mining industry is rehabilitation and ecological reconstruction of mine lands [15]. However, the lower reclamation rate and incompleteness of restoration is a common problem in most areas of China. The environmental management of mining areas in China first began in the 1950s. Rapid ecological reclamation has been carried out in China since the 1980s [16], but the reclamation rates are still very low, below 20% [16,17]. The restoration efficiency is still not ideal, and instability of the ecosystem in mining areas has still not been improved.

The Altai Mountain area, with its rich vegetation landscapes and mining resources, has always been considered an essential tourist site and mining base of Xinjiang [17]. However, due to the predatory exploitation of mineral resources in the Two-River (the Ertish river and Ulungur river) Source Nature Reserve in the Altai Mountains over the past few decades, the natural landscape seems to be ruined. During the mining activities, the forest, grassland and surface soils along the riverbed were removed [18]. After the gold was mined, the Environmental Protection Bureau of Xinjiang was obligated to restore the landscape in order to avoid land degradation in a process called soil reconstruction. This process includes the reallocation of the original soil layers over the craters, followed by the stabilization of the soil’s chemical properties and then the re-establishment of vegetation. For the restoration and improvement of the ecological environment of abandoned mining areas in Altai Mountain, the state and local governments have launched a series of ecological restoration projects [19]. In 2010, the Altai Two-River Source Reserve Administration began to recover the abandoned gold mining area. As a consequence of five years of unremitting efforts, they initially completed the ecological restoration progress in more than 3000 acres of damaged areas. Moreover, systematic disposal measures, including the smoothening of surfaces, the casing of soil, mud spraying, making of temporary sheepfolds, sowing of grass and tree seeds and fencing of afforestation, were also completed in the most seriously damaged area of Altai Mountain, named the Kuermutu region, in 2015. This study evaluates the effectiveness of these measures by examining the vegetation and soil index in the selected study site. The proposed framework is expected to be of high relevance in the general monitoring of the successfulness of ecological restoration projects.

2. Data and Methods

2.1. Overall Characteristics of Study Area

An abandoned gold mining area (geographical coordinates 46°31′31.63″ N–48°33′27.85″ N, 88°57′56.61″ E–91°04′05.90″ E) in Two-River Source Nature Reserve in the Altai Mountains, Xinjiang was selected as the study area (Figure 1). The climate condition of this area belongs to the cold continental climate of the temperate zone, with an annual mean temperature of −2 °C. The annual precipitation ranges from 300 mm to 350 mm, while the annual evaporation rate ranges from 838.3 mm to 1469.6 mm [20].

2.2. Sample Plot Selection

In the Kurmutu ore block, an area with flat terrain was selected as the sample plot. Firstly, the sample plot was mechanically leveled by large machinery. A total of five plots with the size of 500 m × 500 m were arranged. The distance between each sample plot was more than 1–3 km. Sample plots were surrounded by fences to prevent animals from trampling and eating.

2.3. Artificial Measures Taken by TRNRA

An experiment was designed and implemented by the Two River Nature Reserve Administration (TRNRA) in an abandoned gold mining field named Kuermutu gold mining field starting in 2010 with the following steps: (1) mechanically leveling the surface (L). Undulating uneven areas were smoothed by using a bulldozer, and deep grooves or slope areas were smoothed by using flat handling equipment. (2) Planting black currant in smoothed areas (L + P). Black currants were planted in the smoothed area. Seedlings over 50 cm in height and with developed roots were planted on the smoothed areas with a spacing of 1 m × 2 m. (3) Earthing and planting were conducted on leveled areas (L + E + P). Mountain chernozem soil from the area surrounding the experimentation area was artificially covered on the leveled surface by using a shovel. The thickness of the soil was 4 cm, and the black currant seedlings were planted with a spacing of 1 m × 2 m. (4) Earthing, planting and scattering seeds was conducted on leveled areas (L + E + P + S). On the basis of measure 3, mixtures of seeds of three types of grass, Volga fescue (Festuca valesiaca), blue oat grass (Helictorichon) and hairgrass (Deschampsia caespitosa), were planted. (6) Irrigation measures were enacted. Spring floods were artificially led to the experimentation area once a month with an amount of 400 m³/mu.

2.4. Examination of Restoration Efficiency

In view of the particularity of gold mining activities, this study compares the ecological environment of original grassland and abandoned mining areas and analyzes the impact of gold mining activities on the ecological environment of mining areas from three aspects: landform, soil content and surface vegetation.

2.4.1. Vegetation and Aboveground Biomass

Field surveys can generate accurate information related to vegetation dynamics and their drivers. In this study, a simple, rapid and flexible quadrat method was proposed to examine the restoration and surface biomass of vegetation. Five quadrats with the size of 1 m × 1 m were randomly selected from each experimentation area, and the flora species (N), number of species (n), height (h) and vegetation coverage were recorded. Then, the upper part of the grass on the ground was cut off and weighed on an electronic balance with an accuracy of 0.5 g, resulting in the fresh weight of aboveground biomass (m).

2.4.2. Determination of Soil-Rock Ratio

The most serious damage to abandoned gold mining areas is due to the loss of fine soil particles. Therefore, the soil-rock ratio of each selected quadrat was measured. Soil samples with a size of 40 cm × 40 cm and at a depth of 20 cm were selected. All the soil and stones were dug out, plant roots and other sundries were picked out, and soil blocks were ground out with a long stick. Afterward, the soil samples were passed through a 5 mm sieve mesh. The soil sample that could pass through a 5 mm sieve was recorded as soil M₁, and the soil sample that could not pass a 5 mm sieve was recorded as M₂. Their weight was weighed on an electronic balance with an accuracy of 0.5 g. The soil-rock ratio (w) was calculated by using the following equation:

w (%) = M₁/M₂ × 100%

(1)

2.4.3. Similarity Coefficient

The similarity between the number of surface species in the original grassland and the number of surface species after artificial restoration was calculated with the following equation:

S_s = 2X/(a + b)

(2)

where a is the number of surface species in the original grassland, b is the number of surface species after artificial restoration, and S_s is the total number of surface species in the original grassland and artificial restored area.

2.4.4. Diversity Index

In this study, the Gleason richness index, Simpson dominance index, Shannon–Wiener species diversity index and Pielou evenness index [21,22] were calculated to examine the community diversity in the artificial restored areas.

The Gleason richness index (D) is calculated as follows:

D = S/ln

(3)

where S is the total number of species in the community, and A is the quadrat area.

The Simpson dominance index (D₁) is calculated as follows:

$$D_1=1-{\displaystyle \sum P_i^2}$$

(4)

where P_i is the relative importance of a species, P_i = W_i/W, W_i is the number of individuals of species i, and W is the total number of individuals of all species in the quadrat.

The Shannon–Wiener species diversity index (H’) is calculated as follows:

$$H^{\prime }=-{\displaystyle \sum P_i\ln P_i}$$

(5)

where P_i is the proportion of individuals belonging to species i in all individuals.

The Pielou evenness index (J) is calculated as follows:

J = H′/ln S

(6)

where H is the Shannon index, and S is the number of species in the quadrat.

3. Results

3.1. Surface Damage after Gold Mining

In this study, the terrain, soil, vegetation coverage and vegetation diversity index were analyzed to evaluate the surface damage to the gold mining area. Gold mining takes up a large area of land resources, disturbs the surface and changes the topographic relief, which is manifested in the process of large-scale mechanized gold mining. Furthermore, the raw soil at the bottom is overturned, resulting in the disintegration of the structure of the soil profile (Figure 2).

Among the 20 mining sites randomly surveyed in the Kurmutu section, 90% of the gold mine wasteland has increased topographic relief. After gold mining, the surface is excavated manually or mechanically, the surface vegetation in the Kurmutu section is destructively destroyed, the surface soil is stripped, and the deep soil is lost. As a result, the topographic relief of the grassland has increased. It can be seen from Figure 2a that the surface of the original grassland is relatively flat. The average topographic height difference is low, with a value of 0.5 (Figure 3). However, in the abandoned gold mine areas (Figure 2b), the average height difference between the top of the mound and the bottom of the pit (4.5 m) was significantly higher than the original grassland. Figure 3 presents the topographic height difference (a) and soil-rock ratio (b) of the original grassland and abandoned mining area (Figure 3).

It can be seen from Figure 3b that the soil-rock ratio of the original grassland is 2.45%, and this ratio of the abandoned mining area is reduced by 98% compared with the original grassland to only about 0.05%, which indicates that the soil structure is destroyed and the soil parent material is lost after mining. However, gold mining activities lead to changes in the slope and aspect of the surface. Further research needs to be carried out by evaluating the surface movement and deformation, panel width, panel length, mining height, face advance rate and damage of overburden strata to reveal the changes in the terrain that occur due to mining activities in this area. In the original grassland, there were plenty of forest and grassland vegetation species in the Kurmutu section. After gold mining, a large number of surface vegetation species were lost. Compared with the original grassland, the Simpson index and Shannon–Wiener index in the abandoned mining area show a significant downward trend and demonstrate significant differences from the original grassland. The plant diversity in the abandoned mining area is reduced by 86.67%, indicating that the grassland is damaged after mining, the plant species are seriously affected, and the plant species are greatly reduced (Figure 4).

It can be seen from Figure 4 that the diversity index (0.18 and 0.2), surface biomass (12 g) and vegetation coverage (3%) of the abandoned mining area were much lower than that of the original grassland. The Simpson dominance index of the original grassland was 0.8, and this index in the damaged area is only 0.18. A significant difference can be found in the Shannon–Wiener index between the original grassland and damaged areas. The fresh weight of the surface biomass of the original grassland was 1307 g/m^2, while in the damaged area, this value was only 2 g/m². After mechanical leveling of the damaged land, the vegetation coverage recovered a little; for example, after being leveled for one year, the vegetation coverage was 2%, and after being leveled for 5 years, the vegetation coverage was increased to 12%. However, compared with the 92% vegetation coverage of the original grassland, there is still a big gap (Figure 4).

Overall, the stripping of surface soil and the hollowing out and washing of underground soil caused by gold mining are the internal reasons for the decline of surface vegetation.

3.2. Restoration Effect of Artificial Measures on Surface Vegetation and Soil

3.2.1. Restoration Effect of Soil Measures on Surface Species

To examine the effects of the soil measures on the surface species, we selected two experimental plots to analyze the recovery of surface species under the coverage of soil and coverage of sheep manure. After soil measures, whether annual or perennial herbs or shrubs, the number of species increased significantly. The percentage of annual herbs decreased by 17%, and the percentages of perennial herbs and shrubs increased. Soil properties also improved significantly (Figure 5).

The soil-rock ratio of the abandoned mining area was only 0.2%. After using the measure of covering with soil, the ratio increased to 1.8%, and after using the measure of covering with sheep manure, this ratio increased to 0.7.

3.2.2. Effect of Water Replenishment Measures on Surface Vegetation Diversity Index and Soil Restoration

To evaluate the effects of water replenishment measures, including flood irrigation, drip irrigation and mud spray, on the vegetation diversity and soil restoration, we analyzed the vegetation diversity index, surface biomass and soil-rock ratio of the experimental plots (Figure 6).

It can be seen from Figure 6a that the Simpson index, Shannon Wiener index and Pielou index under flood irrigation are the highest, followed by mud spraying, and the diversity index under drip irrigation is low. The soil-rock ratio shows the same trend as diversity indexes; that is, under the condition of flood irrigation, the soil rock ratio is the largest, followed by mud spraying. The soil-rock ratio under flood irrigation is significantly higher than that under slurry spraying and drip irrigation. For example, the soil-rock ratio under flood irrigation is 22.1 times and 20.3 times higher than under drip irrigation and mud spraying, respectively. Alternatively, there was little difference in biomass under different water replenishment measures.

3.2.3. Effects of Biological Measures on Surface Vegetation Diversity Index and Soil Restoration

Two types of biological measures, including the stationing of sheep and the planting of blackcurrant, were used to restore the abandoned mining area. In the same way, we examined the restoration effects of these biological measures by calculating the diversity index, surface biomass and soil-rock ratio (Figure 7).

It can be seen from Figure 7 that, after using biological measures, the diversity index is increased. For example, before using biological measures (abandoned areas), the Simpson index, Shannon–Wiener index and Pielou index were 0.18, 0.11 and 0.24, respectively. After using the measure of stationing sheep, these indexes increased to 0.58, 0.18 and 0.66, respectively. Similarly, after using the measure of planting blackcurrant, these indexes increased to 0.31, 0.63 and 0.48. The surface biomass and soil-rock ratio also show an increasing trend.

3.2.4. Effects of Combination of Various Measures on Vegetation and Soil

Comparing the restoration effects of various measures, it is known that among the single measures, the measures of flood irrigation and covering of soil have a good effect on soil restoration, and the measures of flood irrigation, covering of soil, stationing of sheep and mud spraying have a good effect on the restoration of vegetation diversity and biomass in the abandoned mining area. To improve the recovery efficiency, the TRNRA adopted a combination of two single measures. To examine the restoration effects of these measures, we analyzed the diversity index, surface biomass and soil-rock ratio of the restored area (Figure 8).

It can be seen from Figure 8 that, in the double-measure restoration of the mining area, the impact of each measure on vegetation diversity indexes is not significant. However, from the numerical point of view, the Shannon–Wiener index under the measure of flood irrigation + covering of soil is generally high. The combinations of flood irrigation + covering of soil and covering of soil + stationing of sheep have a good effect on the restoration of surface biomass. The combination of flood irrigation + covering of sheep manure has a good effect on the improvement of soil properties; in other words, under this measure, the soil-rock ratio showed its highest value compared with other measures.

3.2.5. Comparison of Restoration Efficiency of Different Measures

Principal component analysis (PCA) was used to compare the restoration efficiency of different measures. A total of 13 types of restoration measures were analyzed with 6 indexes, as presented in

Table 1. Recovery efficiency of different measures.

Measures	Vegetation Coverage (%)	Simpson Index	Shannon-Wiener Index	Pielou Index	Surface Biomass (g)	Soil-Rock Ratio(%)
Leveled for one year	2	0.1	0.15	0.16	11	0.12
Leveled for five years	16	0.21	0.25	0.31	31	0.66
Covering with soil	34	0.22	0.39	0.42	44	1.8
Covering with sheep manure	35	0.24	0.41	0.38	41	0.7
Flood irrigation	42	0.57	0.78	0.53	175	2.3
Drip irrigation	35	0.24	0.37	0.3	198	0.12
Mud spray	32	0.27	0.46	0.34	251	0.13
Stationing of sheep	39	0.58	0.18	0.68	82	0.42
Planting blackcurrant	67	0.33	0.61	0.48	54	0.58
Flood irrigation + covering with soil	55	0.54	1.16	0.61	310	2.1
Flood irrigation + covering with sheep manure	53	0.41	0.81	0.46	135	3.2
Covering with soil + stationing of sheep	42	0.45	0.74	0.47	340	1.4
Stationing of sheep + mud spray	41	0.41	0.64	0.48	250	0.6

.

In this study, on the basis of Mathematical and Statistical Properties of Sample Principal Components, written by Jolliffe, 2002 [23], the correlation score matrix, initial eigenvalue, cumulative contribution rate, eigenvector matrix and comprehensive principal component scores and rankings for various recovery measures were obtained. The specific statistical methods are explained in detail in references [23,24,25]. The comprehensive scores and rankings of various recovery measures are presented in

Table 2. Comprehensive score and ranking of various recovery measures.

Measures	Comprehensive Scores	Ranking
Flood irrigation + covering with soil	0.4288	1
Flood irrigation + covering with sheep manure	0.3839	2
Covering of soil + stationing of sheep	0.2323	3
Stationing of sheep + mud spray	0.1979	4
Planting blackcurrant	0.0982	5
Flood irrigation	0.1124	6
Mud spray	−0.0735	7
Drip irrigation	−0.1713	8
Covering with sheep manure	−0.2765	9
Stationing of sheep	−0.3221	10
Covering with soil	−0.4769	11
Leveled for five years	−0.5243	12
Leveled for one year	−0.6752	13

.

The negative value of the evaluation result is the result of data standardization, which cannot be intuitively understood as the worst benefit of these measures. Because the data are standardized, 0 is taken as the average level of each evaluation index. According to the comprehensive score, the ranking of different restoration measures can be determined. This method is persuasive and consistent with other evaluation methods.

It can be seen from Table 2 that the comprehensive scores of different recovery measures are very different. In general, single restoration measures, such as leveling, mud spraying and covering with sheep manure, can only supply soil parent material or soil moisture in the damaged mining area. Because a single measure is basically considered from one aspect, there are certain defects. The ecological environment problem in the mining area is the result of the interaction of various factors. Therefore, the restoration efficiency ranking of a single restoration measure in this study is relatively low. However, the combination of various measures can achieve ecological restoration regarding the water, soil, topography and other aspects. The combination of various measures can not only improve the soil environment and change the competition intensity of plants above and below the ground but also cause changes in the diversity pattern of plant communities. For example, the recovery efficiency of flood irrigation + covering with soil and flood irrigation + covering with sheep manure is very good, and the total score ranks first and second because sufficient water can promote the exertion of the effects of nutrients. From the principal component ranking of different recovery measures, it can be seen that the longer the implementation period of the same recovery measure, the better the recovery effect.

Overall, both single measures, including soil measures, biological measures and water replenishment measures and a combination of various measures, have greatly improved soil and vegetation conditions in the abandoned gold mining areas. Before taking artificial recovery measures, since both the soil and vegetation were seriously damaged, the soil-rock ratio, vegetation coverage, surface biomass and various vegetation indexes showed low values (close to 0). After taking restoration measures, these indexes significantly increased, indicating that the artificial measures effectively recovered the soil and vegetation.

4. Discussions

The gold deposits in the study area were extracted by open-pit mining, which is controlled by metallogenic conditions and distributed on riverbeds, floodplains and riverbed terraces with good natural conditions [26]. Before gold mining in these areas, both the vegetation coverage and the thickness of the soil layer was generally high. Gold mining activities have brought destructive damage to the surface environment via the process of mining. The fertile soil layer has been lost, and the forest and grassland have become barren land with vertical and horizontal gullies, exposed sand and gravel, no vegetation and serious soil erosion. Soil is the material basis of vegetation growth. Especially in mining areas, soil not only provides the basic environment for vegetation implantation but also provides nutrients for its growth and development. Under the specific environmental conditions in the study area, the amount of soil content may have a certain impact on the growth of vegetation.

During the field survey, we found that the key to the ecological damage caused by gold mining activities is land degradation, and soil degradation is the inevitable result of vegetation degradation. On the contrary, soil degradation also leads to the decline of the water- and nutrient-carrying capacity of the soil. Therefore, the improvement of soil properties should be the most important link in the ecological restoration of abandoned mining areas. Soil content is an important environmental factor restricting the aboveground biomass of vegetation, which proves that the grassland vegetation in abandoned mining areas can be restored by improving the soil-rock ratio structure so as to restore the whole ecological environment. Generally, vegetation restoration is directional, which can be reflected by the changes in vegetation community composition and plant diversity [27]. The changes in plant species richness, diversity index, evenness index and dominance index in the process of vegetation restoration all indicate the restoration of the ecological functions of the vegetation community [28]. In this study, the Shannon–Wiener index, Simpson index and Pielou index for the measure of flood irrigation + covering of soil was much higher than for other measures, indicating that covering of soil and river overflow are conducive to accelerating the restoration process of species diversity in the abandoned mining area. This result also proves that for the restoration of any type of abandoned mining area, the simplest way is to cover the soil and provide flood irrigation, which can solve the common ecological problems of abandoned mining areas. Single measures are basically considered from one aspect, and combinations of various measures have a good effect on the restoration of abandoned mining areas. Our results are consistent with the views of Bai Weike et al. in the discussion of ecological reconstruction in mining areas [16,29,30,31]; that is, the ecological environment problem in the mining area is the result of the interaction of various factors [32,33]. Yang et al. analyzed the acidification, heavy metal mobility and nutrient accumulation in the soil-plant system of a revegetated acid mine wasteland in Guangdong province, China, and found that heavy metal extractability in the soils increased with time despite an increase in soil pH, which might be attributed to soil disturbance and rhizospheric plant processes, as well as being a consequence of the enhanced metal accumulation in plants over time [33]. The comprehensive treatment of the ecological environment in the mining area should take realizing the comprehensive restoration of the ecology in the mining area as the ultimate goal, which cannot be achieved by a single treatment. The goal of mine ecological restoration is to sustain a healthy ecosystem and to create a harmonious relationship between nature and humans. The ecological restoration should emphasize the process of assisting the recovery of the ecosystem that has been damaged or destroyed in the mining area. Making an ecological restoration plan is the key to the success of mine restoration.

5. Conclusions

(1)

Gold mining in Two-River Source Nature Reserve in Altai Mountains not only completely destroyed the original surface vegetation but also destroyed the growth conditions of vegetation. The soil-rock ratio in the abandoned mining area is 98% less than in the original grassland. The fresh biomass weight of the original grassland decreased by 99.8% after destruction. The plant diversity in the abandoned mining area was reduced by 86.67%, indicating that the grassland was damaged after mining, the plant species were seriously affected, and the plant species were greatly reduced;

(2)

The whole process of gold mining led to a series of serious damage to the terrain. After mechanical leveling of the damaged land, the vegetation coverage recovered, e.g., after being leveled for one year, the vegetation coverage was 2%, and after being leveled for five years, the vegetation coverage was increased to 12%, indicating that the leveling of the surface is a basic restoration measure for damaged mining areas;

(3)

Soil measures, water replenishment measures and biological measures have certain restoration effects on abandoned mining areas. Species increase after covering soil and providing sheep manure. The Simpson index, Shannon–Wiener index and Pielou index of surface vegetation and the soil-rock ratio under the measure of flood irrigation were higher than under the measures of drip irrigation and mud spraying;

(4)

The ecological environment problem in the mining area is the result of the interaction of various factors. The ecological restoration of gold mining areas occurs mainly by natural restoration, supplemented by manual measures to accelerate the restoration speed. The results of our principal component analysis show that although a single restoration measure has some effects on the restoration of abandoned mining areas, the restoration cycle is long, and the combination of various measures can more effectively restore abandoned mining areas.