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Effects of climate and land use/cover changes on soil loss in the Three Gorges Reservoir area, China
Abstract and Figures
Climate and land use/cover changes are among the primary driving forces for soil loss, but their impacts are complex because of their interactions. Decoupling their effects could help to understand the magnitude and direction of soil loss change in response to human activities. Meanwhile, the overall and relative roles of land use/cover changes on soil loss could provide some scientific suggestions to regional ecosystem management. Here, the RUSLE model was applied to estimate the spatial-temporal variations of the soil loss rate in the Three Gorges Reservoir (TGR) area during 2001∼2015, then we decoupled the effects of climate and land use/cover changes on soil loss through scenario design. The results revealed that increasing rainfall could significantly exacerbate the soil loss caused by water erosion with annual 2.90 × 10⁷ t soil, but annual soil loss and rainfall of the TGR area presented opposite changing trends. The overall effect of all land use/cover changes could retain about annual 1.10 × 10⁷ t soil. However, only afforestation could potentially improve the soil retention service. Negative human activities would potentially aggravate soil loss with the annual amount of 1.40 × 106 t. Among them, storing water and urbanization contributed to 50% and 43% for the potential soil loss of the whole TGR area, respectively. Moreover, land use/cover changes and their effects on soil loss change exhibited distinct spatial variances. Afforestation accounted for 15.5% and scattered throughout the TGR area. Storing water of the Three Gorges Dam exacerbated soil loss in some counties which located downstream of the TGR area and were close to the dam, while urbanization exacerbated soil loss in other counties because of development policies and incentives. Our findings suggested that ecological restoration is difficult to offset the impact of climate change on soil loss, but could offset the negative environmental effects caused by urbanization and economic construction.
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... It is, therefore, vital to explore land use change and its driving factors in the LP at different stages of economic development to realize sustainable land use development. Although a large number of studies have been conducted on land-use change and its driving factors in the LP 11,[35][36][37][38][39] , most of them are based on the assumption that the relationship between explanatory and dependent variables is homogeneous in space and time, ignoring the spatial and temporal heterogeneity of key factors at any time. Empirical statistical analysis models cannot quantitatively describe the impact of different factors on land-use types, and it remains unclear how key factors affect land-use changes in space and time. ...
Exploring land use/cover (LULC) change is essential for the sustainable development of ecologically fragile areas. The main objective of this study was to clarify the characteristics and differences in the spatiotemporal changes of LULC on the Loess Plateau (LP) based on the transfer matrix and land use dynamics and to quantitatively describe the impact of natural factors on LULC using a geodetector. The results indicated that the overall LULC change in the LP was characterized by a decrease in the area of cropland, grassland, and bare land, and an increase in the area of woodland and built-up land. This trend shows a clear phase-change characteristic around 2000. LULC changes were primarily affected by human activities in the southeastern agricultural region. The project of returning farmland to forest and grassland had a great impact on LULC change in the central region. Vegetation was sensitive to temperature and precipitation, and the impact of LULC change was significantly higher than that in the humid region in the northwest arid region. NDVI, PRE, and TEM were determined to be the main contributors to LULC changes in the LP. These results provide a scientific basis for the sustainable development of LP.
... This observation aligns with results from Zhang et al. [90] in central Oklahoma and Jobin Thomas et al. [91] in the Pamba River Basin (PRB), India. While many studies have pointed out that precipitation is positively correlated with SEM [92,93], the relationship between rainfall and soil erosion exhibited complexity. Appropriate rainfall helps to form the surface structural sealing effect of the soil and reduces the SEM [94]. ...
The source region of the Yellow River (SRYR), known as the “Chinese Water Tower”, is currently grappling with severe soil erosion, which jeopardizes the sustainability of its alpine grasslands. Large-scale soil erosion monitoring poses a significant challenge, complicating global efforts to study soil erosion and land cover changes. Moreover, conventional methods for assessing soil erosion do not adequately address the variety of erosion types present in the SRYR. Given these challenges, the objectives of this study were to develop a suitable assessment and prediction model for soil erosion tailored to the SRYR’s needs. By leveraging soil erosion data measured by 137Cs from 521 locations and employing the random forest (RF) algorithm, a new soil erosion model was formulated. Key findings include that: (1) The RF soil erosion model significantly outperformed the revised universal soil loss equation (RUSLE) model and revised wind erosion equation (RWEQ) model, achieving an R2 of 0.52 and an RMSE of 5.88. (2) The RF model indicated that from 2001 to 2020, the SRYR experienced an average annual soil erosion modulus (SEM) of 19.32 t·ha−1·y−1 with an annual total erosion in the SRYR of 225.18 × 106 t·y−1. Spatial analysis revealed that 78.64% of the region suffered low erosion, with erosion intensity declining from northwest to southeast. (3) The annual SEM in the SRYR demonstrated a downward trend from 2001 to 2020, with 83.43% of the study area showing improvement. Based on these findings, measures for soil erosion prevention and control in the SRYR were proposed. Future studies should refine the temporal analysis to better understand the influence of extreme climate events on soil erosion, while leveraging high-resolution data to enhance model accuracy. Insights into the drivers of soil erosion in the SRYR will support more effective policy development.
... The first peak in the sedimentation velocity was observed in the 1980s and could be explained by the afforestation of the area surrounding the reservoir. Afforestation is a major source of disturbance and soil loss, resulting in the significant replacement of natural land cover (Huber et al. 2010;Huang et al. 2020) and consequent changes in watershed processes and ecosystem functioning. A subsequent peak in 2000 might be linked to an extreme forest fire in the watershed, potentially leading to an increased influx of soil into the reservoir. ...
Environmental reference conditions (RC) and historical trends are crucial for assessing the degree of freshwater impact and formulating restoration measures. This is particularly relevant for freshwater systems used as potable water sources. Using sediments from the Carlos Maggiolo reservoir (Minas, Uruguay), located in a watershed with a mining history, this study aimed to (1) establish metal (As, Cr, Cu, Ni, Pb, and Zn) RC using a predicted interval (PI) chemometric technique; (2) evaluate metal enrichment and toxicity over time and space; and (3) assess environmental changes examining geochemical proxies. Surface sediments from 29 stations were used to establish RC and a core from the dam area was sampled to infer past conditions. The sediments were submitted to partial digestion and analyzed by inductively coupled plasma optical emission spectrometry- ICP-OES. Enrichment factor (EF) calculated using both PI and bottom core values did not show significant differences over time. Over space and time, most metals primarily originated from natural sources (EF < 2). The PI in mg/kg was Cr: 23.74–37.32; Cu: 25.75–48.99; Ni: 16.29–25.55; Pb: 7.63–13.75; and Zn: 94.34–174.80. A stratigraphically constrained cluster analysis corroborated by a permutational multivariate analysis of variance categorized the reservoir into two zones: Zone I, before reservoir operation to ~ 1996, and Zone II from ~ 1997 to 2017. The average concentrations of the main metals of toxicological interest in zones I and II, respectively, were as follows: Cr 37.60 ± 1.59, 34.54 ± 1.49 mg/kg; Cu 49.76 ± 2.84, 44.55 ± 2.70 mg/kg; Ni 24.11 ± 0.67, 22.53 ± 1.22 mg/kg; Pb 12.40 ± 0.63, 13.52 ± 0.82 mg/kg; Zn 99.25 ± 3.12, 93.86 ± 4.42 mg/kg; Mn 1160.56 ± 68.88, 1441.61 ± 83.55 mg/kg; and P 1243.21 ± 271.56, 1128.42 ± 183.10 mg/kg. According to a principal component analysis, the period preceding reservoir operation until ~ 1985 was linked to mining activities and application of Cu2SO4, and the period from 1985s to 2000 was influenced by C and P concentrations due to increasing agricultural and afforestation activities in the watershed that consume P fertilizers. The most recent period, from 2000 to ~ 2017, was characterized by an increase in sedimentation rates mainly associated with erosion, particularly in the agricultural areas. This subsequent soil loss in the watershed could compromise the reservoir's useful life. This study contributes to a better understanding of metal geochemistry in subtropical reservoirs and aids in formulating effective recovery and restoration measures.
... However, the SOC SQI values of grassland and restored degraded land showed significant differences from the other LUMMs. This suggests that the high SQI values of grassland and restored degraded land were characterized by soils resulting from the accumulation of organic matter input from aboveground litter fall and root turnover, which increased both SOC and soil nutrients (Huang et al., 2020). Ma et al. (2022) demonstrated that variations in plant canopy coverage can affect soil structure by redistributing precipitation, and that plant roots can improve soil structure and reduce soil erodibility (Jiang et al., 2020). ...
Land degradation often results in poor soil quality in many parts of Ethiopia, including the study area. To address this issue and promote sustainable land management practices, various land use and management methods (LUMMs) have been implemented. However, little information is available regarding how these management practices influence overall soil quality dynamics of the study area. This study aimed at evaluating soil quality dynamics in the Urago micro-watershed, central highlands of Ethiopia, under major LUMMs: barren land (BL), grassland (GL), established farm boundary (EFB), restored degraded land (RDL), and stone-supported soil bund (SSB). Forty-five disturbed and fifteen undisturbed soil samples were collected from the ploughed soil layer (0–20 cm) of each LUMM and analysed for selected physicochemical properties to be used as indicators of soil quality. Principal component analysis and multiple correlation were used to select the minimum data set (MDS) to evaluate the overall soil quality index (SQI). The MDS included SOC, clay content, exchangeable Mg²⁺, and available P, which could replace other indicators for assessing the overall soil quality dynamics of the study watershed. The result showed notable variations in particle-size fractions, soil organic carbon (SOC), total nitrogen (TN), available P (av. P), and exchangeable Na⁺, K⁺, and Mg²⁺ levels among the LUMMs. RDL had higher sand and silt contents than SSB, whereas SSB had higher clay content compared to RDL, GL, and BL. GL, RDL, and EFB showed significantly higher levels of SOC, TN, and av. P, respectively, compared to other LUMMs. The obtained SQI showed that GL had the highest score (0.847), followed by SSB (0.703), RDL (0.701), EFB (0.644), and BL (0.628). This underscores the significance of stone-supported soil bund and restored degraded land as an efficient management method to enhance soil quality and agro-ecosystem through conserving soil and encouraging sustainable farming practices.
... Climate change and land use and cover change (LUCC) are the prime factors that impact hydrological processes of the TGRR Cheng et al. 2019;Wang et al. 2019aHuang et al. 2020). Climate alters the temporal and spatial distribution of precipitation patterns, directly modifying flood regimes (Donat et al. 2016;Gründemann et al. 2022). ...
Three Gorges Dam is the largest hydraulic infrastructure in the world, playing a pivotal role in flood mitigation. The hydrological responses of the Three Gorges Reservoir Region (TGRR) to climate change and human activities are unclear, yet critical for the Three Gorges Dam’s flood control and security. We simulated streamflow and water depth by coupling the Variable Infiltration Capacity model and the CaMa-Flood model. Daily discharge at the outlet of TGRR was well modeled with a relative error within 2% and a Nash-Sutcliffe efficiency coefficient of approximately 0.81. However, the flood peak was overestimated by 2.5–40.0% with a peak timing bias ranging from 5 days earlier to 2 days later. Runoff and water depth in the TGRR increased from 2015 to 2018 but decreased during flood seasons. Land use and land cover changes in 2015 (LUCC2015) and 2020 (LUCC2020) were analyzed to quantify their hydrological impacts. During the 2015–2018 period, land use conversion increased in built-up areas (+ 0.6%) and water bodies (+ 0.1%), but decreased in woodland grassland (-0.7%) and cropland (-0.1%). This led to a slight increase in runoff and inflow of less than 4‰ across the TGRR, a 7.70% decrease in average water depth, and a 15.4‰ increase in maximum water depth. Water depths in the TGRR decreased during flood seasons, and increased during non-flood seasons. Increasing water depth was identified in northern TGRR. This study clarifies the historical TGRR’s hydrological features under LUCC and climate changes, aiding regional flood mitigation in the TGRR.
Ecosystem service quality is closely linked to human well‐being, and sustainable provision of ecosystem service is essential for ensuring regional ecological security and achieving sustainability goals. An innovative valuation framework is introduced that combines land use/cover change (LUCC) analysis, supply and demand matrices and Gini coefficient calculations to assess the supply and demand of ecosystem services (ES‐S and ES‐D). Unlike traditional static methods, this approach captures intricate spatial and temporal mismatches, offering new insights into the impacts of LUCC on ES balance within the framework of sustainable development goals (SDGs). Taking the Three Gorges Reservoir Area (TGRA) as a case study, the findings indicate a significant decrease in cultivated land, accompanied by expansion of forest and built‐up area, driven by farmland‐to‐forest policies and urbanization. These shifts have improved the balance of provisioning and supporting services but have also intensified regional disparities, particularly in Chongqing, where demand outpaces supply. Furthermore, LUCC have altered the capacity of ecosystems in the TGRA to provide essential services, such as soil retention and water regulation, thereby supporting progress toward SDGs related to ecosystem sustainability. However, imbalances in cultural services persist, highlighting the need for targeted management strategies to optimize ES provision and support regional sustainability. This study underscores the importance of ongoing ES‐S and ES‐D assessments to inform sustainable land management policies in ecologically sensitive areas like the TGRA.
Background and Objectives The process of urban and rural population increase, and the impact of household competition in providing the basic needs of life, has caused the consumption of various resources to grow rapidly and unevenly in the 5 continents of the world. In such a competitive environment, the world's agricultural soil systems, by receiving the products of agricultural revolutions, have made the climate out of the global order. So, the purpose of this strategic research is to discover the missing links in the low cognitive of the Decision-making managers, in the biochemical and physicochemical historical process of the soil in the use of the products of the agricultural revolutions. Materials and Methods In this way, the conventional structure of culture and different environmental civilizations of the 5 continents of the world with the system of agricultural soils and climate has led to the use of the model (SMM) for the purposes of our research. For the meantime, two related and interconnected statistical methods have been used to achieve the desired global results. Also, in this section, the main components of process evaluation (10 main components of soil and 730 manuscripts of scientists from the world's most prestigious journals) has been used. For the process analysis of this research, strategic thinking, Excel and SPSS have been used. Results and Discussion According to the trend of anthropogenic effect on 10 components of the world's agricultural soils and the revelation of two effectiveness (CPEP=47.8% and CPAR=54.2%), global climate changes have appeared. In the meantime, the low cognitive effect of the components involved in the 5 continents of the world has been able to attribute 58.5% of climate changes to agricultural soils. Conclusion and Suggestions The results of this strategic multidisciplinary research, which was associated with the identification of driving factors (strengths and opportunities) and inhibiting factors (weaknesses and threats) in the world, showed that climate change is dependent on anthropogenesis. At the end of this exhausting effort, 10 strategic suggestions along with the pragmatism paradigm were communicated to the world.
Severe soil erosion challenges exist in China as a result of long-term human related activities and its erosion-prone land forms and climate. Anthropogenic forces that alter the physical landscape cause substantial soil erosion which have adverse impact on surface water bodies and therefore necessitating sediment control as important aspects of catchment management planning. In this review we focused principally on the erosion factors and how to prevent and/or mitigate them. The application of soil erosion models such as the universal soil loss equation, its modification and others were also studied. The results established by various researchers showed a relationship between impact of soil erosion and degradation on water quality indicating the source of pollutant as anthropogenic and industrial activities. These are the sources of particles and deleterious material that contribute to the surface water deterioration including the East Lake. The review revealed that erosion causes both on-site and off-site effects on land and also on water bodies thereby affecting its quality.
Development and protection are both vital human demands in ecologically vulnerable areas. An estimation of the land use/cover changes and their ecological responses could help to understand the regional ecosystem dynamics under various human demands and provide the scientific basis for managing and regulating ecosystems. In this paper, we analysed the spatial-temporal variations in land use/cover types and systematically quantified the relationships between these changes and environmental variables in the Three Gorges Reservoir area. Our results revealed that forestland coverage increased linearly to 53.48%, and that of construction land increased exponentially from 0.25% to 2.75% during 1990-2015. The land use/cover changes exhibited two distinct transformation phases: before and after impoundment. The mutual transformations among vegetation types were significant before 2000, while the forest, water and construction land coverages increased continuously by occupying cropland after 2000. The land use/cover changes were significantly correlated with environmental variables and were sensitive to three topographic variables namely, elevation, surface-height-fluctuation and slope. The vegetation dynamics were easily affected by the complex and rugged topography. Moreover, the responses of land use/cover changes varied among topographic variables. The two parameters estimated in the multiple linear regression, elevation and slope, were −0.164 and −0.268 for forestland change, −0.391 and 0.378 for water area change, and −0.068 and −0.061 for construction land change. Forest cover was so larger in the regions of higher elevation and steeper slope that afforestation occurred in the regions of moderate elevation and slope. Urbanization and impoundment mainly occurred in the regions of lower elevation , and the regions of steeper slope were more easily submerged, while urbanization mainly occurred in the regions of gentler slope. Therefore, the land use/cover changes due to ecological protection and economic development responded to the interactions among environmental variables and was targeted to different regions to reconcile the land use conflicts, providing a reference for ecosystem management in ecologically vulnerable areas.
Studies of land use/cover change (LUCC) and its impact on ecosystem service (ES) in monetary units can provide information that governments can use to identify where protection and restoration is economically most important. Translating ES in monetary units into decision making strongly depends on the availability of spatially explicit information on LUCC and ES. Yet such datasets are unavailable for the Three Gorges Reservoir Area (TGRA) despite its perceived soil conservation service value (SCSV). The availability of remote sensing-based datasets and advanced GIS techniques has enhanced the potential of spatially explicit ES mapping exercises. Here, we first explored LUCC in the TGRA for four time periods (1995–2000, 2000–2005, 2005–2010, and 2010–2015). Then, applying a value transfer method with an equivalent value factor spatialized using the normalized difference vegetation index (NDVI), we estimated the changes of monetary SCSV in response to LUCC in a spatially explicit way. Finally, the sensitivity of SCSV changes in response to LUCC was determined. Major findings: (i) Expansion of construction land and water bodies and contraction of cropland characterized the LUCC in all periods. Their driving factors include the relocation of residents, construction of the Three Gorges Dam, urbanization, and the Grain for Green Program; (ii) The SCSV for TGRA was generally stable for 1995–2015, declining slightly (<1%), suggesting a sustainable human–environment relationship in the TGRA. The SCSV prevails in regions with elevations (slopes) of 400–1600 m (0°–10°); for Chongqing and its surrounding regions it decreased significantly during 1995–2015; (iii) SCSV’s sensitivity index was 1.04, 0.53, 0.92, and 1.25 in the four periods, respectively, which is generally low. Chongqing and its surrounding regions, with their pervasive urbanization and dense populations, had the highest sensitivity. For 1995–2015, 70.63% of the study area underwent increases in this sensitivity index. Our results provide crucial information for policymaking concerning ecological conservation and compensation.
Soil erosion occurs extensively across China, leading to severe degradation of the land and ecosystem services. However, the spatial and temporal variations in soil erodibility (k) and the distribution of soil erosion across land use types and slopes remain unclear. We synthesized the results from 325 sites published in 152 literatures to analyze the factors affecting the k, such as land use type, climate, topography, soil, and vegetation restoration age. The results showed that areas with slopes >25° had a larger k factor (k = 0.1047) than did those with slope <6° (k = 0.0637) or 6–25° (k = 0.0832). The k from 2006 to 2011 (k = 0.0725) was higher than that from 1999 to 2005 (k = 0.058) and that from 2012 to 2016 (k = 0.0631). The k value initially increased with vegetation restoration age and then gradually decreased. Land use also had an impact on the k factor, with the k factor of cropland (k = 0.0697) being higher than that of grassland (k = 0.0663) but lower than that of forest (k = 0.0967). Across China, North Shaanxi, Heilongjiang, and South Guizhou, which are located in the Loess Plateau in Northwest China, the Black Soil region of Northeast China, and the Karst areas in Southwest China, respectively, were the three most severely eroded regions due to hydraulic erosion, frost‐thaw erosion, and high‐intensity erosion, respectively. Overall, the most important factors affecting the k were soil characteristics, followed by topography and climate. Among them, soil nitrogen and precipitation were the two most critical factors influencing the k.
The world is experiencing serious soil losses. Soil erosion has become an important environmental problem in certain regions and is strongly affected by climate and land use changes. By selecting and reviewing 13 extensively used soil water erosion models (SWEMs) from the published literature, we summarize the current model-based knowledge on how climate factors (e.g., rainfall, freeze-thaw cycles, rainstorms, temperature and atmospheric CO 2 concentrations) and land use change impact soil erosion worldwide. This study also provides a critical review of the application of these 13 SWEMs. By comparing model structures, features, prediction accuracies , and erosion processes, we recommend the most suitable SWEMs for different regions of the globe (Asia, Europe, Africa and the America) based on the evaluations of 13 SWEMs. Future soil erosion could be simulated using the RUSLE, LISEM, WEPP v2010.1, SWAT, EPIC, KINEROS and AGNPS models in Asia; the RUSLE, WEPP v2010.1, SWAT, EPIC, WATEM-SEDEM, MEFIDIS, AGNPS and AnnAGNPS models in Europe; the RUSLE, LISEM, SWAT, and AGNPS models in Africa; and the WEPP v2010.1, SWAT, EPIC, KINEROS, AGNPS and AnnAGNPS models in America. Finally, the limitations and challenges of the 13 SWEMs are highlighted.
Recent deforestation rates in Cambodia are among the world’s largest, while hydropower development has accelerated in the Mekong region. Deforestation accelerates erosion, increasing river sediments heading to reservoirs and decreasing hydropower production. Forest protection could be seen as a service to hydropower, which the FOR-POWER model quantifies. Using recent deforestation estimates, annual sediment accumulation is
calculated, followed by associated power generation loss, and annualized and present monetary value associated with benefits of forest conservation to hydropower. We evaluated four proposed medium-size hydropower dams (20–24 MW; 6–145m3/s design discharge), and found that extensive deforestation could result in annual sediment
accumulation of 360–930 million tons (reservoir dependent), but only 140–750 million tons in a forest conservation scenario. Overall, these reservoirs could lose 60–100% of storage capacity over 120 years at current deforestation rates, resulting in power loss net present values for Pursat-I, Battambang I and II dams of US 2.58, 44.8 and $28.8 million, respectively. A global sensitivity analysis showed that FOR-POWER was particularly sensitive to discount rates and electricity prices. The modeling tool developed for this study is transferable to other dams globally where hydropower development is accelerating and in need for better quantifying ecosystem services from surrounding watersheds.
Vegetation recovery is a promising strategy to mitigate soil loss risk across different landscapes and human disturbance levels. Uncertainties still exist in the impacts of forest restoration on soil erosion with respect to complicated terrain condition and land-use/cover pattern, especially in mountainous reservoir areas undergoing intensive human activities. Here, we assess the effects of forest restoration on controlling soil erosion in the Three Gorges Reservoir area (TGRA), China. The Revised Universal Soil Loss Equation and time-series data were used to estimate soil erosion and its changes in 2001-2015. The slope of soil erosion at a pixel level was estimated to determine the responses of soil erosion to forest restoration. The results indicate that the conversion of cropland to forest was the dominated land use/cover transformation process in the TGRA from 2001 to 2015. The mean annual soil erosion rate in the TGRA decreased, with an annual drop rate of 1.28%. Changes in the soil erosion rate presented significant spatial variations, with a significant decrease (1.09 t∙ha-1∙yr-1) in the terrain slope zones between 25° and 35°, where intensive forest restoration occurred. Within various land transformation processes, the slope of the mean soil loss rate was the highest (slope =0.71, p<0.01) in afforestation areas. Our findings reveal that forest restoration can effectively reduce soil erosion in mountainous reservoir areas, but there are significant variations in the various vegetation recovery processes with the time-lag effect and across elevational gradient. Although most forest restorations occurred in steep slope areas, slope steepness is still the dominated factor in the spatial variation of soil erosion in the TGRA. We suggest forest landscape restoration to fill the scale gap between soil erosion and forest restoration in hilly reservoir areas such as the TGRA.
Vegetation restoration on degraded lands has been encouraged worldwide due to its ecological services and function of controlling soil erosion and improving carbon (C) stocks in terrestrial ecosystems. Although the processes of runoff and sediment detachment and transport are well recognized, the effects of vegetation restoration on organic C loss through soil erosion are not fully understood within a given landscape. This study conducted a synthesis from 66 sites to evaluate the effects of vegetation restoration on annual C loss induced by soil erosion across the key areas of the 'Grain for Green' Program (GGP) in the Loess Plateau, China. The results showed that vegetation restoration has significantly reduced the annual C loss in sediment and from runoff. Since 2000, a total of 8.6 × 10 6 ha degraded land has been converted to forests, shrubs and grasslands under the GGP, which has reduced runoff by 1.5 × 10 9 m 3 and is associated with 7.3 × 10 3 Mg C; furthermore, lost sediment has reduced by 348.7 Tg, which is associated with 1.8 Tg C per year, across the Loess Plateau. In the zone with a mean annual precipitation (MAP) < 550 mm, the degraded lands that have been converted to grasslands and shrubs have reduced more soil and water losses than have the lands that have been converted to forests; additionally , in the zone with a MAP >550 mm, the degraded lands that have been converted to forests have less soil erosion than do the lands that have been converted to grasslands and shrubs. Moreover, C loss induced by soil erosion was mainly affected by plant cover, soil porosity, slope, land-use change, and rainfall intensity on the Loess Plateau. This study suggests that optimal vegetation restoration measures should be adopted based on local conditions to reduce C loss induced by soil erosion.
Soil erosion is a widespread environmental problem, which threatens the environmental sustainability. The Loess Plateau is one of the most severely eroded areas in the world. In this study, based on the Revised Universal Soil Loss Equation and Revised Wind Erosion Equation, the water erosion and wind erosion status from 2000 to 2015 were assessed. In addition, the underlying drivers of erosion process were investigated, and eventually the implications of constraint effect in soil erosion control were discussed. The results showed that both the wind erosion and water erosion were substantially lessened, and vegetation restoration due mainly to government-aided ecological restoration programs, as well as increasing precipitation and decreasing wind speed might have contributed to these trends. The constraint line analyses indicated that the vegetation cover had nonlinear and threshold effects on soil erosion through constraining the water condition (precipitation). Specifically, for the water erosion, before the rainfall is below the threshold (approximately 450-500mm), which means the rainfall (water condition) is not sufficient to maintain a good vegetation cover (about 30−40%), therefore the vegetation cannot efficiently prevent soil erosion. However, once the rainfall exceeds the threshold, the vegetations soil retention function will enhance and thereby reducing soil loss substantially. In terms of the wind erosion, vegetation cover has a lower (10%) and an upper (40%) threshold for controlling wind erosion. Plant cover lower than 10% does little to reduce wind velocity, while the effect of vegetation on reducing wind erosion basically reaches the maximum when plant cover is 40% or above. In the arid and semi-arid areas, the limited precipitation cannot support large areas of trees in a long-term if human disturbances are removed, thus the constraint effects of water condition (precipitation) on vegetation cover should be considered to improve the efficiency of afforestation and reforestation efforts aiming at mitigating and preventing soil loss.
It is widely recognized that vegetation restoration plays a key role in controlling soil erosion in China's Loess Plateau. However, the effects of vegetation types on soil erosion on steep slopes of the Loess Plateau are not yet fully understood. In this study, we carried out our experiments on surface runoff and soil loss monitoring at nine runoff plots with different vegetation types over a nine-year period from 2008 to 2016 to evaluate the effects of vegetation and rainfall on soil erosion. We classified forty-three rainfall events into three rainfall types based on a rainfall concentration index and further analyzed the sensitivities of the runoff and soil loss to these rainfall types. The results indicated that the grassland (Bothriochloa ischaemum L.) and shrubland (Sea-buckthorn) with high ground cover had a lower runoff depth and soil loss compared to the forestlands with poor ground cover with an average reduction of 50% in annual runoff depth and 92% in annual soil loss. Comparison of the mean runoff coefficient and soil loss in the three rainfall types demonstrated that rainfall events with high intensity and short duration caused more surface runoff and soil loss under all vegetation types. A power function fitted well in the runoff-soil loss relationship and the result showed that the grassland and shrubland had a smaller magnitude term which reflects less soil susceptibility to erosion. The research implies that the ground cover is an important factor in controlling soil and water loss and vegetation measures with high ground cover should be strongly recommended for soil erosion control on the Loess Plateau. It is helpful for vegetation restoration strategy and conserving soil and water on steep slopes of this area.