INTRODUCTION
Vietnam possesses significant bauxite reserves, estimated at 5.5 billion tons, with the majority located in the southern central highlands The development of bauxite mining and aluminum projects, particularly in Lam Dong, is crucial for the country's economic growth and industrialization, reducing reliance on aluminum imports However, these mining activities have detrimental effects on the environment, including altered topography, loss of vegetation, erosion, and dust pollution in nearby residential areas To mitigate these impacts, mining projects must adhere to environmental restoration commitments, including reforestation efforts with species like acacia, coffee, tea, and rubber trees, which help improve soil quality and prevent erosion Currently, most post-mining areas have been replanted with acacia trees, which are now over a year old.
The importance of environmental rehabilitation following mining activities is underscored by the proposed research project titled "The Initial Assessment of Soil Improvement of Acacia Trees Planted in the Mining Areas of Tan Rai - Lam Dong Province." This project aims to evaluate the effectiveness of acacia trees in enhancing soil quality in regions affected by mining, highlighting the necessity of sustainable practices in post-mining land management.
STUDY SITE
Natural conditions
The Tan Rai bauxite mining area is situated within three communes: Loc Thang, Phu Loc, and Ngai Loc, in the Bao Lam
Geographical coordinates of mining area: 11038'08 '' to 11041'56 'degree north latitude.107049'54 '' to 107053'12 'east longitude
The mine is located in the eastern section of the BaoLoc - Di Linh plateau, characterized by a relatively flat terrain that slopes from northeast to southwest This area features elevations ranging from 30 to 80 meters, with regions that branch out or narrow between 100 to 400 meters The peneplain terrain is highly conducive to the development and formation of bauxite laterite, with the majority of bauxite deposits found on the peaks.
According to the document meteorological observation recent years ago (since 1990-
BaoLoc experiences an average annual temperature of 21.7°C and receives approximately 2,356.5 mm of rainfall each year The climate is divided into two distinct seasons: a dry season from November to April, with an average temperature of 20.5°C and total rainfall of 436 mm, and a rainy season from May to October, characterized by a higher average temperature of 22.1°C and significant rainfall of 2,248 mm This region is classified as a tropical monsoon climate, showcasing both wet and dry periods throughout the year.
The region is predominantly characterized by pine (Pinus latteri) forests and mixed plantations of coffee and tea However, many of these pine forests are diminishing as extensive areas are being cleared to create industrial tree gardens, particularly in the hilly zones adjacent to water resources, riparian areas, and lowlands.
Socio-Economic Conditions
The area is surrounded Bao Lam Tan Rai bauxite mine has a population of about 100,000 people, mainly ethnic Kinh, Koho, Chauma, Tay, Nung Population density is about
66 people / km2, distributed unevenly The majority of people living in hamlets formed residing along the provincial road, the population is mainly concentrated in LocThang town
Migrant populations engage in both cultivation and deforestation, with their economy primarily reliant on agriculture and forestry They predominantly grow coffee and tea in agriculture, while in forestry, they focus on logging and turpentine production, alongside the development of agroforestry models.
Economic growth is concentrated in a few small areas, primarily driven by pulp processing plants, fertilizer manufacturing, tea processing factories, weaving, building materials enterprises, and minor mechanical repairs The region enjoys stable political security and social order, which are continually being strengthened and developed.
The Tan Rai bauxite mines benefit from excellent traffic conditions, situated close to Highway 20, which connects Ho Chi Minh City to Da Lat Additionally, the newly established Loc Thang town is located adjacent to the mines, and the surrounding infrastructure has been fully developed to support mining operations.
- Regarding air traffic: mines located about 100km from Lien Khuong Airport Lien Khuong airport in existing routes: Hanoi - Da Lat and Ho Chi Minh City - Da Lat
Heavy trucks traveling from Ho Chi Minh City can efficiently navigate Highway 20, passing through Bao Loc and Loc Thang town before reaching Tan Rai Additionally, trucks coming from Phan Thiet can utilize Highway 8B, which provides a convenient route through Di Linh to Tan Rai.
-Regarding communication: mobile relay station of all providers formobile communication services have been installing in the region.
OBJECTIVES AND SCOPE STUDY
Goals
- Assess the current state of the environmental characteristics of the land in the areas after mining bauxite
- Analyze growth characteristic of acacia planted forenvironmental rehabilitation after mining bauxite in Tan Rai
- Assess soilcharacteristics under planted acacia after mining bauxite
- Assess impacts of the acacia plantation on soil improvementafter mining bauxite
- Propose recommendations to enhance the resilience of the land after mining bauxite.
Scope of the study
This study was conducted in the bauxite mining areas ofTan Rai - Lam Dong province Object of study is newly acacia plantation after mining
Acacia auriculiformis is a pioneering legume species selected for post-mining reforestation due to its ability to restore soil health and promote the regeneration of native broadleaf tree species First identified by Thai Van Trung, this resilient tree thrives in poor soils, effectively combats erosion, and can quickly establish a closed canopy when planted densely, making it a crucial choice for ecological restoration efforts.
Acacia auriculiformis have roots which have nitrogen-fixing nodules was renovated and restored under forest land
The study area is the Tan Rai bauxite mining areas, focusing on the area planted Acacia auriculiformisplantation forests
Scope of the study:-Focusing on the impacts of the- acacia plantationmodel on the environment and compare with thatof the other crops in the study areas.
METHODS
+ Collect secondary data from mining project in Tan Rai bauxite
Conduct field research to gather primary data on acacia growth from surveyed plots and analyze soil characteristics through soil samples This data collection focuses on acacia plantations at varying ages, specifically those that are one year and five years old.
Sixty typical sample plots, each covering an area of 100 m² (10m x 10m), have been established Three sample plots were set up for one-year-old Acacia trees, where the number of trees, trunk diameter, and tree height were measured The height of the trunk is represented as H, measured in meters, while the tree height is denoted as Hvn (m) Trunk diameter, indicated as D, is measured in centimeters and taken at various positions along the trunk.
Establishing 3 similar sample plots in Acacia 5 years old, which determine the number of trees, trunk diameter, tree height
To accurately measure diameter, calipers or a tape measure can be utilized Calipers provide a 2-dimensional measurement for calculating the average diameter, while a tape measure is used to determine the trunk's circumference Special rulers can then convert this circumference measurement into the corresponding diameter.
Tape measure diameter usually calculated by dividing perimeter divided by 3.1416 Placements to measure the diameter usually include original diameter D0, diameter at breast height D1,3
Height is an important factor to reflect the size of the tree With less than 5 meter trees often medication bamboo has incised dm
With 5 meter high trees, high measurement using geometric principles, or trigonometry Some commonly used rulercurrently Blume - leiss, Suunto
Collect six soil samples from each sample plot, resulting in a total of 36 samples from six typical plots The samples should be taken from two distinct soil layers: the first layer at a depth of 0-20 cm and the second layer at a depth of 21-40 cm.
Soil samples were analyzed in laboratory to identify some Physical, chemical characteristics:
Table 4.1 Name of factor andmethod
14 Porosity Calculated according to the formula P (%) (1-D / d) x 100
The general concept of the physical and mechanical properties of soil:
Soil possesses various physical and mechanical properties, including density, bulk density, porosity, adhesive qualities, ductility, hardness, and resistance These characteristics are primarily influenced by the mineral composition—both primary and secondary—as well as the particle composition of sand, silt, and clay, along with the organic matter present in the soil The interaction and coherence among these components ultimately determine the soil's texture.
Soil density refers to the mass of a unit volume of solid residential land, indicating how tightly soil particles are packed compared to an equal volume of water at 4°C.
To calculate the density of soil is followsthe formula: d = P / P1
Which in: d - Density of soil
P- Volume soil particles (dried, ranked Nazis together and no space air gap) in a determined volume (usually measured in g / cm 3 )
P1 - The volume of water stored in the same volume in terms T0: 4 0 C (g / cm 3 )
Soil density is primarily influenced by its mineral content, including primary and secondary minerals, as well as organic matter Since organic matter typically constitutes a small percentage of soil composition, the overall density largely depends on the minerals present Katrinski has developed a joint assessment to evaluate the proportion of cultivated land based on these mineral compositions.
Table 4.2.Classification of land follow density
> 2.70 Soil large quantities of Fe2O3
Bulk density of soil refers to the weight of a unit volume of soil in its natural state, measured in grams per cubic centimeter (g/cm³) after drying This measurement is obtained by inserting a cylindrical metal tube into the soil, ensuring it maintains a volume of 100 cm³, and then drying the sample to calculate its density using a specific formula.
P - Volume of natural land in cylindrical shut after being dried out (calculated according grams)
V - Volume of the tube shut (calculated according cm 3 )
Bulk density of soil particles depends on the density and texture of the soil Porous soils, rich in organic matter and humus usually have small bulk density
Soil porosity is the ratio% occupied gaps in the soil than the general volume of earth
The formula for calculating the porosity of the soil:
Calculating the volume of soil slits is challenging due to their complex shapes and varying sizes Therefore, to determine soil porosity, it is essential to indirectly calculate it using the density of the soil through a specific formula.
D - Bulk density of soil d - Density of soil
Soil porosity can range from 30% to 70%, influenced by various land types such as sand, barren soil, and mountainous terrain Key factors affecting porosity include soil texture and density.
Table 4.3.Classification soil with porosity
The general concept of thechemical properties of soil:
The chemical properties of soil are crucial for evaluating environmental health and the interaction between land and plants During growth, plants utilize elements from water and air, such as carbon (C), hydrogen (H), and oxygen (O), while also relying on essential nutrients from the soil, including nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), sulfur (S), and trace elements like iron (Fe), manganese (Mn), boron (B), zinc (Zn), and molybdenum (Mo) Understanding these elements is vital for assessing soil quality and fertility.
Soil acidity significantly impacts plant health by influencing the availability of essential nutrients, which are primarily inorganic compounds that dissolve best within specific pH ranges Each soil type has an optimal pH level for nutrient absorption, and the acidity also plays a crucial role in regulating microbial activity within the soil The pH value serves as a key indicator of soil acidity, affecting both nutrient exchange and overall soil health.
Humus in the soil serves as a sustainable nutrient source for plants, primarily formed through the activities of microorganisms, plants, and organic fertilizers The content, composition, and morphology of humus significantly influence the physical and chemical properties of soil, enhancing its porosity, aeration, and water retention capacity.
In soil N - P - K are the three most important factors for the growth and development of plants and are important indicators to evaluate soil fertility These elements are not fixed
It is variable in quantity in the soil due to the influence of environmental factors such as rainfall, temperature, humidity and in every stage of growth - growth of crops [4]
RESULT AND DISCUSSIONS
Environmental characteristics of the land after mining bauxite
With the entire extraction process vegetation and architecture ore zone changes Geological phenomenon primarily motivated phenomenon mining pits shore erosion
Aluminum ore mining and processing require significant water usage and generate substantial liquid and solid waste, with red sludge being the most concerning byproduct This hazardous waste has a high pH level and poses serious environmental risks due to its inability to decompose naturally.
Mining location have high rainfall (over 2000 mm / year), high risk of erosion, soil runoff large, unlikely to complete its land, the vegetation development after the exploitation of bauxite
Bauxite mining significantly reduces vegetation cover and leads to a decline in biodiversity The extraction process involves removing extensive areas of natural forests and cultivated plantations, including rubber, tea, coffee, cashew, and pepper, due to the thin layer of bauxite ore that is widely dispersed over large surface areas.
Air pollution is significantly impacted by the extraction and transportation of bauxite ore from mines to processing plants, resulting in dust emissions The level of air pollutants released from construction vehicles and machinery is largely influenced by the quantity of construction vehicles in operation, the condition of the machinery, and prevailing wind directions.
Figure5.1.Mining areaFigure 5.2 :The factory area
Characteristic of acacia growing on the site after bauxite exploiting inTanRai
Acacia plantations in Tan Rai bauxite mines are rapidly developing and enhancing the environment due to the tree's multiple uses As a perennial legume, Acacia not only provides valuable wood products but also offers protective benefits by limiting soil erosion and improving ecological conditions in midland and mountainous areas Its symbiotic nitrogen-fixing ability enriches soil nutrients, while its dense evergreen foliage contributes to a closed canopy within 2-3 years of planting Furthermore, Acacia plays a crucial role in improving microclimates and soil quality, making it an essential choice for timber production.
Figure 5.3.Soil surface after mining prepared for reforestation
This study evaluates the impact of acacia plantation forests on soil enhancement by measuring the growth characteristics of acacia trees at one year and five years old, specifically in areas previously exploited for bauxite mining.
Figure5.4.Acacia 1 year old Figure 5.5 Acacia 5 years old
The growth factors are shown in the following 2 table
Table 5.1.Data of Acacia 1 years old
The average tree height,H vn(m)
Areas 1-year-old tree: because small trees should not proceed measured diameter at breast height D1,3.In the 3 sample plots,average diameter from 1.09 to 1.3 ( cm) ,height from 0.9 - 1.1(m) Trees were underdeveloped
Table 5.2.Data of acacia 5 years old
The average tree height ,H vn (m)
In the 3 sample plots, average diameter from 10.5 to 11.2 (cm) ,height from 7.9 – 8.5(m) Plants grow well and survival rate is high
The chart 5.1.Comparison of survival rates between the 2 areas
Survival rate in- Acacia 5 years old higher than- Acacia 1 year old because in areas
Acacia 5-year-old- are well cared and were replantedthe dead trees In general, the development of the Acacia is quite fast
Acacia trees are rapidly growing and have a high survival rate, making them an effective choice for improving soil quality in various regions Their efficiency in soil enhancement surpasses that of traditional plantations such as coffee, tea, and rubber Additionally, large-scale Acacia planting helps to significantly reduce soil erosion.
Figure 5.6.Rubber trees Figure 5.7.Coffee treesFigure 5.8 Tea trees
Comparing soil characteristics ofAcacia plantation at different ages
Comparison of the physical elements in 2 areas
• Results of soil sample analysis are shown in table 6 and table 7
Table 5.3 Data of physical elements in acacia 1years old
Table 5.4 Data of physical elements in acacia 5years old
Layer 1 (0-20cm) Number of samples 9 9 9
Layer 2 (21-40cm) Number of samples 9 9 9
Chart 5.2.Comparison of soil physical elements in layer 1
The Acacia planting areas demonstrate favorable conditions for plant growth, characterized by high humus volume and porosity A comparison of the physical properties between the two regions reveals that the 5-year-old Acacia areas exhibit lower density and proportion compared to the 1-year-old Acacia areas.
Besides Acacia areas 5 years old has high porosity Prove the surface soil at 5 years old Acacia is better
Chart 5.3.Comparison of soil physical elements in layer 2
At layer 2, generally factors are still showing good quality soil Density of soil was identified as soil with humus average Because volume of humus decreases with depth, it
Bulk density (g/cm3) Density Porosity (%)
Acacia 1 year old Acacia 5 years old
Bulk density (g/cm3) Density Porosity (%)
Acacia 1 year oldAcacia 5 years old increases bulk density and porosity reduced.The data shows lower soil layer of─Acacia areas 5 years old─better
Type of soil Sand (%) Silt (%) Clay (%)
In general, soil in the study area has average soil texture is quite suitable for a variety of crops, ease of fertilizer and soil improvement.[3]
Compare the chemical properties of the soil in the study area
Chemical properties of soil are shown in table 9 and 10
Table 5.6.The chemical elements of the soil in acacia areas 1 year old
Fertilizer easy to digest (mg/100g soil) cations exchange (me/100g soil)
Table 5.7.The chemical elements of the soil in acacia areas 1 year old
Fertilizer easy to digest mg/100g soil) cations exchange (me/100g soil)
Chart 5.4.Compares the- layer 1 between the two areas
25 pH OM(%) N(%) P2O5(%) K2O(%) P2O5 (mg/100g soil) K2O((mg/100g soil)
Acacia areas 1 year oldAcacia areas 5 years old
Chart 5.5.Compares the - layer 2 between the two areas
14 pHKCL OM (%) N(%) P2O5(%) K2O(%) P2O5(mg/100gsoil) K2O(mg/100g soil)
Acacia areas 1 year oldAcacia areas 5 years old
Through figures and graphs we can make comparisons and comment on two areas
In the area of Acacia 1 year old
Soil acidity, measured by pHKCl, is crucial for understanding the soil environment Data analysis revealed that the exchange acidity in one-year-old Acacia areas in Tan Rai-Lam Dong bauxite shows pHKCl values of 4.66 for the first layer and 4.69 for the second layer These values are comparable to forested land, indicating no significant differences (Nguyen Van Toan et al., 2005) Overall, this acidity level is suitable for Acacia growth.
In the Acacia areas 5 years old
The pH KCl values show a gradual increase with depth, measuring 4.34 in the top layer (0-20 cm) and 4.41 in the second layer (21-40 cm) This upward trend in pH is attributed to the leaching of alkaline substances and cations from the surface layer to the deeper levels, resulting in a higher pH in the second layer compared to the first.
Organic matter in the soil:
In the Acacia- areas 1 year old
The analysis results showed that the organic matter content of the surface layer is relatively high at OM = 3.76% However, total organic content in the layer 2 quickly reduce
In the Acacia areas 5 years old higher than humus areas acacia 1 year old
The humus content decreases with depth This may explain by Acacia leaves’ fall and decompose quickly create a significant amount of soil humus
Compare the total nitrogen content:
Total nitrogen content in the acacia areas 5 years old higher than- acacia areas 1 year old
The total nitrogen content in the soil of two areas is classified as moderate to rich, while layer 1 shows a significant reduction in total nitrogen levels in layer 2 due to a rapid decline in organic content.
Compare total phosphorus and easy digest phosphorus:
The analysis reveals that the total phosphorus content in whole soil is notably high, exceeding 0.13% P2O5, with a significant decrease observed at greater depths In acacia areas that are 5 years old, there is a marked improvement in the levels of easily digestible phosphorus This increase can be attributed to targeted investments aimed at enhancing soil quality, ensuring that the phosphorus available meets the nutritional needs of Acacia trees.
Compare total Potassium and easy digest potassium:
Analysis of total soil potassium revealed significantly low levels, attributed to various factors The degradation of potassium in the soil is primarily due to its high mobility in tropical conditions and the substantial potassium demand of Acacia species.
The analysis revealed that the soil in certain mountainous regions of our country has a low exchange capacity for essential cations such as calcium (Ca++) and magnesium (Mg++) This deficiency is not limited to basalt-derived soils but is prevalent in various mountainous areas Erosion significantly contributes to the loss of strong cation exchanges, leading to the accumulation of iron and aluminum over time.
The level of dissolved aluminum depends on the pH value Al +++ concentrations rapidly decreased when pHKCl increase.[4]
Recommendations to strengthen the resilience of the land after bauxite mining
Due to the extended duration of the mining process, which typically covers an annual area of 50 to 70 hectares, it is essential to implement regreening measures and mitigate soil erosion post-mining Consequently, investors involved in environmental rehabilitation projects recommend that relevant authorities prioritize environmental considerations in their regulations.
Rehabilitation and restoration of mining environments occur every three years, focusing on the planting and care of trees After this period, the completion of the workload is confirmed in collaboration with the relevant authorities.
To mitigate environmental pollution in Vietnam, it is essential to implement advanced technology for sludge processing The country's tropical climate, characterized by heavy rainfall, allows water to overflow dams, which can lead to the runoff of toxic waste into soils, rivers, and streams downstream, resulting in widespread ecological damage.
- Adding potassium needed for the areas crops because of potassiumvery poordue to the nature of soil
Planting pine trees interspersed with fast-growing acacia is beneficial, as the development of acacia helps protect the pine and enriches the soil beneath its canopy This symbiotic relationship not only supports the growth of pine but also enhances soil quality, leading to improved overall efficiency in forest management.
- Quickly planted in the areas ended harnessing to greening barren land, land improvement, dustproof, prevent rainwater runoff phenomena on the surface erosion and improve ecological environment.
CONCLUSIONS
Bauxite mining in Tan Rai, Lam Dong, has significant negative environmental impacts, including altered terrain, loss of vegetation, and soil erosion Urgent remedial measures are necessary, particularly for the restoration of vegetation.
The land rehabilitation efforts in Tan Rai bauxite - Lam Dong have primarily centered on cultivating acacia species known for their rapid growth and high survival rates This approach aims to effectively restore and green the barren soil, addressing the urgent need for environmental recovery in the region.
The promotion of acacia planting in mining areas is beneficial for soil improvement, as it enhances both chemical and physical properties of the soil The pH levels in one-year-old acacia areas range from 4.66 to 4.69, while five-year-old acacia areas show pH values between 4.34 and 4.41, remaining within acceptable limits High humus content is observed, with values between 2.49 and 4.22, despite low potassium levels, which peak at only 0.108% in the surface soil and decrease to 0.09% at depths of 20-40 cm Nitrogen content is relatively high, ranging from 0.18% to 0.31%, and phosphorus levels are also elevated, between 0.22% and 0.39% The nitrogen-fixing ability of acacia contributes essential nutrients to the soil, compensating for nutrient loss due to leaching, and establishing acacia forests is crucial for the future development of diverse forest ecosystems.
The ongoing greening of the area involves mining practices that align with the planting of trees, particularly under the canopy of pines This approach not only enhances soil quality and prevents erosion but also significantly boosts the region's biodiversity.