Impacts of natural and anthropogenic factors on soil erosion

: Soil erosion is a serious issue that is caused by both natural and anthropogenic factors. Natural processes, including water and wind erosion, as well as higher temperatures, have been identified as leading causes of soil erosion. Additionally, anthropogenic factors, such as urbanization, road construction, agriculture, industry, mining, and others significantly contribute to this problem. These factors have resulted in the loss of biological productivity of the land and have inflicted damage on the entire ecosystem. Since 2000, soil erosion and desertification have become even more severe, exacerbating the problem. The soil of Mongolia, characterized by an arid and semi-arid climate with low precipitation and high temperature fluctuations, is highly susceptible to erosion with approximately 55% of it being classified as high or very easy to erode. This review provides a comprehensive overview of the natural processes and anthropogenic factors that contribute to soil erosion, as well as the current status of soil in various regions of Mongolia.


INTRODUCTION
Soil erosion has emerged as a pressing concern due to a combination of natural processes and anthropogenic factors [1].It refers to the detachment and transport of soil particles, which are eventually deposited in valleys, oceans, rivers, streams and distant areas [2].This phenomenon results in the loss of topsoil, reducing the productivity of agricultural, forest and grassland ecosystems, and negatively impacts the biodiversity of plants, animals, and soil microorganisms [3].Additionally, vehicular movement over soil disrupts its natural structural elements, causing displacement of particles [4].Factors such as rainfall, surface roughness, crop condition and vegetation cover play a crucial role in determining the severity of soil erosion, which is classified as slight, moderate, or severe [5].____________________________________________________________________________________________________________ Proceedings of the Mongolian Academy of Sciences PMAS Therefore, it is criticially important to implement effective soil conservation measures to minimize the detrimental effects of erosion on soil health and productivity [6].
Soil erosion is a global problem that affects numerous countries, including Brazil, Mexico, China and Malaysia, as highlighted earlier.Mongolia is also grappling with significant soil erosion concerns, with ongoing erosion observed from the southeast to the northwest in certain regions (Figure 1).The geographical and climatic characteristics of Mongolia play a significant role in triggering natural factors that compound soil erosion.Intense wind patterns and sporadic rainfall in some areas contribute to soil vulnerability, resulting in an increased degree of erosion.These natural factors, combined with anthropogenic influences, further intensify the severity of the problem.Anthropogenic factors, particularly overgrazing of pasturelands, improper land management practices, and deforestation disrupt the delicate balance of ecosystem.
Soil erosion is closely interconnected with desertification, which involves the transformation of vegetated land into barren areas [7][8].It is evident that both natural and anthropogenic factors contribute to desertification, just as they do to soil erosion.Natural factors include wind, water, and climate change, such as temperature fluctuations, dust storms, and precipitation [9].Anthropogenic factors include the construction of multi-branch highways, illegal mineral extraction, urbanization, road construction, agriculture, industry, mining, and the use of saxaul (a genus of shrubs or small trees belonging to the plant family Amaranthaceaa) as fuel, among others [10].
In Mongolia, the average annual temperature has increased by 2.1°C, while annual precipitation has decreased by 7% over the past 75 years [11].The primary driver of vegetation degradation in Mongolia is the decrease in precipitation and the rise in temperature [12].Indirect factors such as livestock grazing, land cultivation, and wildfires amplify the impact of climatic factors, increasing desertification in arid and semi-arid regions.In certain areas, fires destroy vegetation coverage which further increases desertification [13][14].Presently, 76.9% of Mongolian land is degraded and has been desertified, with 56% attributed to natural phenomena and 44% to anthropogenic factors (Figure 2).In greater detail, certain provinces in Mongolia (Dundgovi, Uvurkhangai, Govisumber, Dornogovi, Bayankhongor, Tuv, Gobi-Altai, and Umnugovi) exhibit higher levels of desertification, as shown in Figure 2. As of 2020, approximately 76.9% of land area in Mongolia had been affected by desertification to varying degrees, with 31.5%, 22.1%, 18.6%, and 4.7%, and classified as weak, moderate, strong and very strong respectively.
Over the past two decades spanning from 2000 to 2020, the process of desertification has continued to spread across Mongolia, extending from the northeast to the southwest of the country.During this period, geographical and climatic factors, along with anthropogenic factors, have collectively like conditions.

Natural factors
Two primary natural factors contribute significantly to soil erosion: water and wind intensity, as mentioned in reference [15].Both wind and water play a crucial role in influencing the density of soil particles, leading to a decrease in soil productivity through the reduction of topsoil thickness, rooting depth, organic matters, microbial activity, and the presence of higher subsoil clay content.Protecting plant cover is critical in preventing soil erosion [16][17].The productivity of plants, growth status and development of vegetation cover are largely dependent on climatic conditions, such as temperature, precipitation, and evaporation [18].

Wind erosion
Wind erosion occurs when loose, dry and bare soils are transported by strong winds.Sparse vegetation increases the vulnerability of soil to drying and erosion [19][20].Adequate plant cover on land can mitigate wind erosion by reducing the direct impact of wind on the soil surface, thereby slowing down wind speed and force [21].Conversely, direct sunlight reduces soil moisture, resulting in dry and loose soil conditions.Climate, topography and soil characteristics are the three main categories that influence wind erosion [22][23].Climate factors: Increasing wind speeds cause small soil particles on the surface to be blown and carried away by the wind.

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Sparse vegetation cover is a significant factor that accelerates soil erosion [17,24].Topography: Landscape position and shape act as barriers to reduce the wind force [25].Therefore, forests and pastures are less susceptible to wind erosion, while agricultural areas are at a higher risk.Soil characteristics: Sandy soils and mediumto-fine sandy soils with specific mechanical compositions are particularly vulnerable to wind erosion.The stability of soil particles plays a key role in reducing the risk of erosion [26][27].Soil particles smaller than 0.1 mm are blown into the air, medium-sized particles ranging from 0.1 to 0.5 mm are deflected and drummed, and large particles between 0.5 and 2 mm are carried by rolling on the surface [28].Large particles close to the soil surface and low moisture content also increase the susceptibility to wind erosion.Soil type and moisture, with higher humus content stabilizing the mineral part of the soil [29][30].

Water erosion
Water erosion is a significant contributor to soil erosion resulting from the accumulation of rainwater intensity and the force of running water [31].Heavy rainfall causes the movement of fertile soil particles and exacerbates soil and water erosion [32].The impact of raindrops on soil surface disrupts soil aggregates and dislodges small particles that are carried away, creating depressions in the soil [33].When water infiltrates the soil pores and creates pressure, it breaks apart soil aggregates, which leads to the dispersion of small soil particles on the surface [34].The compaction of these small soil aggregates hinders the penetration of rainwater, resulting in surface water accumulation that carries away small soil particles along the slope.
Precipitation intensity, topography and soil texture all play a role in water erosion [35][36].The rate of soil erosion tends to increase with higher rainfall intensity and steeper slopes [37].Sloping surfaces have a significantly impact on soil movement, with areas having slopes greater than 2° being susceptible to damage, while areas with a slope of greater than 8-10° are highly vulnerable to water-induced erosion [38].The water absorption capacity of soil depends on the particle size and humus content, with smaller soil particles increasing the risk of soil erosion.Rocky and sparsely vegetated soils are less affected by water erosion due to their low clay content and good water permeability.Conversely, soils with high clay content are more prone to waterlogging and rapid transport of small soil particles [39][40][41].
Wind erosion is a significant issue in the area of the Great Lake Depression and southern Mongolia, with annual soil erosion rate exceeding 100 t/ha.Southwestern region experiences severe wind erosion particularly in areas with sparse vegetation and strong winds (Figure 3a,c).
Additionally, wind erosion in Mongolia has increased from 2000 to 2020.In contrast, water erosion is most prevalent in specific areas such as the Great Lake Depression, the Mongolian Altai Mountains, and the Gurvansaikhan mountain, with erosion rates of 0.09 t/ha per year or higher.In most other regions of Mongolia, erosion rates range from 0 to 1 t/ha per year (Figure 3b,d).Figure 3e and 3f provide a visualization of the amount of soil eroded by wind and water between 2000 and 2020, with wind erosion occurring predominantly from southeast to southwest, while water erosion is observed from south to northwest.The southern region of Mongolia, characterized by sparse vegetation, is particularly vulnerable to rapid soil erosion.

Anthropogenic factors
As mentioned earlier, there are several anthropogenic factors that contribute to soil erosion.In this review, we focus on key concepts related to anthropogenic factors, including urbanization, road construction, pasturelands, agriculture, industry and mining.

Urbanization
Urbanization refers to the process of population concentration in urban areas, often characterized by the development of residential and industrial infrastructure.This process involves the replacement of natural vegetation and landscapes with impervious surfaces such as buildings, roads, parking lots, and sidewalks [42][43].These surfaces increase surface runoff during rainfall, leading to soil erosion and other negative environmental impacts [44].Urbanization also contributes to soil compaction through the use of heavy construction equipment, vehicles and foot traffic, which reduce the soil's ability to absorb water and increase its susceptibility to erosion.The removal of vegetation during urbanization further exacerbates soil erosion.Trees, shrubs and other plants play a crucial role in stabilizing the soil and absorbing rainfall, thereby reducing runoff and erosion [45][46][47].However, the removal of vegetation during urban development increases the vulnerability of soil to erosion.
Despite the material benefits that urbanization brings to human society, it also has significant negative environmental impacts, including soil erosion.The effects of soil erosion resulting from urbanization have direct impact on the economy, environment, and public health [48].Dust particles containing pollutants have the potential to degrade air quality, and among these particles, fine particles known as PM2.5 pose particular human health

(a,b) Wind and water erosion, 2000, (c,d) wind and water erosion, 2020, and (e,f) changes in wind and water erosion between 2000 and 2020 in Mongolia. Source: Desertification Atlas, Ministry of Environment and Tourism, Mongolia 2020
Proceedings of the Mongolian Academy of Sciences PMAS concern.These tiny particles are small enough to be suspended in the air and can be easily inhaled into the respiratory system, leading to various health issues [49].
According to data from 1990, global population was 5.28 billion, with 3.01 billion individuals residing in urban areas and 2.27 billion in rural areas.As of 2020, the world population had grown to 7.76 billion, with 4.36 billion living in urban areas and 3.40 billion in rural areas Indicating a doubling of the global urban population (Figure 4a).In Mongolia, the population increased to 3.28 million in 2020, with 2.25 million living in urban areas, also doubling compared to 1990 (Figure 4b).Over the past three decades, there has been a significant growth in urban population globally and in Mongolia as well, while the number of individuals in rural areas has remained relatively constant.

Road construction
Road construction has seen significant growth worldwide in recent decades, aiming to improve human mobility, goods transportation, and urban development.However, roads are known to concentrate runoff, leading to increased soil loss and sediment yield on hill slopes, ultimately degrading the water quality of nearby water bodies [50].Studies have shown that roadstream crossings serve as significant sediment sources, primarily due to erosion occurring on the road verges and fill slopes.This erosion reduces the capacity of pastureland and gives rise to gullies, leading to severe soil erosion [51].The bare and steep gradients of roadcuts and fill embankments generate runoff and sediment yield, while the absence of vegetation cover intensifies soil detachment and susceptibility to erosion by reducing soil cohesion and shear strength.Steep gradients also contribute to slope erosion by reducing water infiltration and increasing runoff accumulation [52][53].
Inadequate implementation of erosion control measures during road construction results in negative impacts, such as increased sedimentation in nearby waterways, reduced soil fertility and an elevated risk of landslides and other slope failures, particularly in areas with steep terrain or unstable soils [54].Soil roads play a significant role in soil erosion as the movement of vehicles and the passage of air dislodge lead to the loss of topsoil and nutrients, cause damage to aquatic ecosystems, reduced water quality and an increased risk of flooding [55].
In summary, road construction and dirt roads have a substantial impact on soil erosion.(Figure 5). Figure 5 shows the dirt roads in Khentii and Tuv provinces of Mongolia.In these rural areas, vegetation cover remains sparse due to irresponsible vehicle use, which poses risks such as dust pollution and river dry-ups.The lack of vegetation cover exacerbates soil erosion and increases the vulnerability of the surrounding environment to negative impacts.Pasturelands Livestock grazing has a significant impact on soil erosion, primarily influenced by factors such as vegetation cover, soil composition and topography [56][57].Vegetation cover: The removal of vegetation through grazing exposes the soil, particularly when grazing intensity and frequency are high.
Soil compaction: Livestock trampling and grazing also compact the soil, reducing its permeability and increasing surface runoff, which contributes to erosion.Topography: The effects of grazing on soil erosion vary depending on the topography of the land, with grazing on steep slopes causing more soil disturbance and runoff compared to flatter terrain [57][58][59].

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In Mongolia, a vast majority of agricultural land consists of pastures, accounting for 97% of the total land area.The grazing area has decreased over the years, while the number of livestock has increased significantly.This trend has led to intensified erosion rates due to overgrazing.Figure 6 illustrates the degradation of pasture capacity in all Mongolian provinces except Dornod.In 2020, approximately 67.1 million animals utilized pasturelands, indicating the direct impact of pasture degradation on livestock sector's capacity.This degradation has severe consequences, including increased vulnerability to drought and other risks.

Agriculture
Agriculture has been an integral part of human civilization for over 10,000 years.However, agriculture has indeed faced significant challenges in pest management, with pests causing substantial crop losses, particularly in fruits, vegetables and cereals.Losses of up to 78% in fruits, 54% in vegetables, and 32% in cereals have been reported.[60].To address this issue and to maintain agricultural productivity, pesticides are widely used in many countries.The application of pesticides has proven effective in reducing crop losses caused by pests by almost 35 to 42%.[61][62].To address this issue and maintain agricultural productivity, pesticides are widely used in many countries.The application of pesticides has proven effective in reducing crop losses caused by pests by almost 35 to 42%.[63].They are categorized into different types, such as herbicides, insecticides, nematicides, molluscicides and fungicides.Among these, herbicides are the most commonly used, accounting for approximately 80% of all pesticide used worldwide.[60].
While pesticides are important in pest management, their excessive and inappropriate use poses significant threats to soil health and biodiversity.Uncontrolled and excessive pesticide use can lead to a decline in soil fertility, regeneration and overall soil health.[64][65].This, in turn, can contribute to soil pollution and erosion, as well as negatively impact the diversity and abundance of beneficial organisms in the soil.
It is important to emphasize the need for responsible and judicious pesticide use in agricultural practices to minimize adverse impacts on soil and ecosystem health.Integrated pest management strategies, which combine various pest control methods and prioritize ecological balance, can help reduce reliance on pesticides and promote sustainable agriculture, while at the same time minimizing soil erosion and pollution.

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Asia accounts for the highest pesticide usage globally, with China being the largest consumer of pesticides.Other significant consumers in the region include India, Indonesia, and Vietnam.North America and Europe also have high rates of pesticide consumption, with the United States and certain European countries being major users.Although pesticide usage in Africa is relatively low, it has been increasing in recent years due to the industrialization and commercialization of agriculture.Table 1 presents the top 10 pesticide-consuming countries worldwide.China ranks the highest with usage at 55.5%, followed by the United States at 12.8% and Brazil at 11.9% (Figure 7).It is noteworthy that China and the United States have been consistently leading pesticide users since 1990.

Industry and mining
Industry and mining activities contribute significantly to soil contamination through the direct discharge of industrial and mining wastewater, which releases heavy metals into the environment.These heavy metals, including chromium, zinc, lead, cadmium, manganese, iron, and nickel, are nonbiodegradable and have a negative impact on soil quality throughout the year [66][67].Lead contamination is often associated with mining activities, while industrialization and urbanization have led to a widespread dispersion of cadmium, lead and chromium in the environment [68].Although copper, zinc and chromium are required in small amounts by living organisms, arsenic and lead can adversely affect the physiological processes of plants and animals [69].Even small amounts of these elements can have severe consequences for soil erosion, leading to a reduction in soil microorganisms, a decline in biodiversity and ultimately, soil infertility.Mercury, in particular, is a heavy metal used in gold extraction, which has a most negative impact on the ecosystems and public health [70].It exists in various forms in the environment and is released from both natural and human-made sources, such as volcanic eruptions, rock weathering, forest fires, mining activites, burning of fossil fuels and waste incineration [71].Once released, mercury can travel long distances through the atmosphere and can be deposited onto land or water surfaces through precipitation [72].In aquatic ecosystems, micro-organisms convert mercury into methylmercury, a highly toxic agent that accumulates in the food chain.Methylmercury is primarily produced in sediments and is taken up by small aquatic organisms like plankton and small fish, which are then consumed by larger fish, birds, and mammals.As mercury moves up the food chain, its concentration increases through biomagnification [73][74][75]

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and mammals, accumulate high levels of mercury in their bodies, resulting in toxic effects on their health and reproduction.Mercury enters terrestrial ecosystems through atmospheric deposition or runoff from contaminated water bodies.The mercury cycle in ecosystems is influenced by various factors, including the type and amount of mercury sources, the chemistry of the environment, the structure of the food web and the biological and physical processes that regulate mercury transformations and transport [76][77][78][79].Overall, the mercury cycle in ecosystems is a complex procedure and mercury pollution has equally harmful effects on human health and the environment.It is crucial to manage and reduce mercury emissions, as well as monitor and control its levels in food and water sources in order to potect public health and the ecosystem (Figure 8a).Proper rehabilitation efforts are essential once mining activities cease in order to prevent ongoing soil erosion and address other environmental issues.Additionally, land degradation near mining areas and adjacent road networks used for transportation can lead to soil erosion, dust, pasture degradation and water shortage [84][85].Furthermore, underground coal mining causes significant movement in surrounding rocks, resulting in surface subsidence and irreversible changes to surface morphology.These changes can give rise to geological disasters and environmental problems (Figure 8b).By implementing sustainable mining practices, including effective planning, management and monitoring of mining activities, it is possible to mitigate these impacts on soil erosion and promotes responsible resource extraction [86][87].

CONCLUSIONS
In summary, soil erosion is influenced by both natural and anthropogenic factors.Natural processes such as weathering and geological activities can initiate erosion, however anthropogenic factors intensify and accelerate the process, leading to more severe erosion.Moreover, anthropogenic factors like soil compaction, reduced soil Proceedings of the Mongolian Academy of Sciences PMAS fertility and increased runoff during rainfall events contribute to soil erosion.To address these issues, it is vitally important to implement effective erosion control techniques and adopt sustainable land use practices that prioritize the protection and enhancement of soil quality and productivity.These efforts are essential for preserving soil resources for future generations and ensuring the uninterrupted provision of vital ecosystem services.

Figure 3 .
Figure 3. (a,b) Wind and water erosion, 2000, (c,d) wind and water erosion, 2020, and (e,f) changes in wind and water erosion between 2000 and 2020 in Mongolia.Source: Desertification Atlas, Ministry of Environment and Tourism, Mongolia 2020

Figure 7 .
Figure 7. Pesticide usage, 2019.Source: Food and Agriculture Organization of the United Nations

Figure 8 .
Figure 8.(a) Mercury cycle in the ecosystem and (b) post-gold mining process.Source: La Pampa, an illegal gold mining hub in the Peruvian Amazon, in 2014.(AP Photo / Rodrigo Abd, File)