Although numerous studies have acknowledged that vegetation can reduce erosion, few process‐based studies have examined how vegetation cover affect runoff hydraulics and erosion processes. We present ...field observations of overland flow hydraulics using rainfall simulations in a typical semiarid area in China. Field plots (5 × 2 m2) were constructed on a loess hillslope (25°), including bare soil plot as control and three plots with planted forage species as treatments—Astragalus adsurgens, Medicago sativa and Cosmos bipinnatus. Both simulated rainfall and simulated rainfall + inflow were applied. Forages reduced soil loss by 55–85% and decreased overland flow rate by 12–37%. Forages significantly increased flow hydraulic resistance expressed by Darcy–Weisbach friction factor by 188–202% and expressed by Manning's friction factor by 66–75%; and decreased overland flow velocity by 28–30%. The upslope inflow significantly increased overland flow velocity by 67% and stream power by 449%, resulting in increased sediment yield rate by 108%. Erosion rate exhibited a significant linear relationship with stream power. M. sativa exhibited the best in reducing soil loss which probably resulted from its role in reducing stream power. Forages on the downslope performed better at reducing sediment yield than upslope due to decreased rill formation and stream power. The findings contribute to an improved understanding of using vegetation to control water and soil loss and land degradation in semiarid environments.
Forages reduced overland flow by 12–37%, and reduced erosion by 55–85%. Forages significantly increased Manning's friction factor by 66–75%. Medicago sativa reduces stream power more downslope than upslope. Forages reduced more sediment yield downslope than upslope.
•Water erosion decreased after the GFGP was implemented.•R contributed more than C in northern China, whereas the opposite occurred in the southern part.•Vegetation greening partially offsets the ...increasing rainfall pressure.
Soil erosion by water is a major threat to land degradation. The United Nations Decade on Ecosystem Restoration 2021–2030 calls for massive ecosystem restoration to address land degradation impacts. Due to the implementation of large-scale soil and water conservation programs in China (i.e., the Grain for Green Program), the area covered by vegetation has increased. Climate change may exacerbate soil erosion risk, while vegetation greening may alleviate this risk. This work aims to assess China's water erosion risk over the past two decades since the implementation of the Grain for Green Program (1999–2018) and explore the relative importance of precipitation and vegetation on erosion risk dynamics. An integrated method was developed using the Revised Universal Soil Loss Equation and the Pressure-State-Response model. An indicator contribution index was applied to detect the impacts of soil cover and management (C) and rainfall erosivity (R) on risk changes. The results showed that China's water erosion risk had a decreasing trend (23% between 1999 and 2018), especially in areas with middle and high state indicator values. R contributed more than C in northern China, whereas the opposite occurred in southern China. The contribution of R decreased while that of C increased. Vegetation greening partly offset the pressure from climate change. Overall, this work highlights the importance of vegetation recovery in reducing water erosion.
Climate change and human activities have caused a wide range of ecological risks in the Qinghai–Tibet Plateau (QTP) over the past two decades, such as land degradation and biodiversity loss. ...Therefore, it is imperative to assess the ecological security and drivers for its sustainable development. However, there still lacks a spatial understanding of ecological security in the QTP, as well as the geographic driving forces. In this study, a pressure–state–response (PSR) framework and the coupled fuzzy and obstacle degree models were used to evaluate the spatial pattern and factors that modulate ecological security of the QTP. The southeast of the plateau exhibited high pressure and state levels, indicating that population and economic development activities were concentrated in these regions owing to the good natural conditions. The ecological security evaluation value of the QTP is moderately low, with a median value of 47.4 (the full mark is 100). Seven regions with low ecological security were identified where targeted planning and governance measures should be implemented based on the local natural and economic conditions. Population density, net primary productivity index (NPP) of vegetation, and GDP per unit area were the main factors that modulated ecological security in the QTP, with obstacles accounting for 17.52%, 13.20%, and 12.97%, respectively. These results improve our understanding of the major vulnerable areas and main driving forces of ecological security, providing key information for optimization of ecological security pattern in the QTP.
•A combination method to determine ephemeral gully erosion is proposed.•A greater inflow strengthens ephemeral gully erosion, but decreases sheet erosion.•The deep incising of gully groove plays ...important role for steep hillslope of 15°.•A critical sediment concentration is proposed for ephemeral gully erosion or deposition.
Ephemeral gullies (EGs) are important erosion features that could account for as much as 70% of total erosion on the Loess Plateau of China. However, few quantitative studies have been conducted in the field on the impact and mechanism of upslope sediment runoff in EG erosion processes. A series of field rainfall simulation experiments were conducted on an artificial EG to investigate the impacts of upslope inflow with two flow rates (15 and 30 L min−1) and five sediment concentrations (20, 40, 80, 120, and 160 g L−1) on runoff and erosion processes within the EG. The results showed that the lower flow rate of 15 L min−1 increased soil loss by 26% compared with the higher inflow rate (30 L min−1). The lower inflow rate triggered greater sheet or rill erosion, whereas the higher rate mainly strengthened the incision of the main EG channel and led to increasing gully erosion. The channel shoulders expanded laterally very little, especially under the higher flow rate. Inflow sediment concentration had a major influence on EG erosion processes. With increasing sediment concentration, EG erosion and total slope erosion first increased, and then decreased. When sediment concentration exceeded 120 g L−1, the inflow sediment began to be deposited, and 120 g L−1 can be regarded as a critical value of EG erosion. These results are beneficial to establish a soil erosion model and to control ephemeral gully erosion in loess areas.
Abstract
Satellite observations since the early 1980s have revealed a trend of ‘Earth greening’ across global terrestrial ecosystems. Dryland vegetation is more sensitive to climate change and human ...activities. China’s drylands are among the largest in extent worldwide, and large-scale ecological restoration of these areas has been implemented since the late 1970s, which has resulted in more complicated but still poorly quantified vegetation dynamics. To figure out the vegetation dynamics and associated driving forces, we provide an assessment of the vegetation dynamics from 1982 to 2015 using the CO
2
fertilization effect function, principal component regression, Residual Trend analysis, and Breaks For Additive Seasonal and Trend methods based on the ERA5 climate factors and GIMMS 3.1 normalized difference vegetation index datasets. This study shows that anthropogenic impacts and CO
2
fertilization have jointly led to vegetation greening in China’s drylands since the 1980s, and ecological restoration has accelerated this greening since the 2000s. The results show that the vegetation greening in China’s drylands (41.51% of the study area, +0.60 × 10
−3
yr
−1
) is mainly driven by CO
2
fertilization (+0.55 × 10
−3
yr
−1
) and anthropogenic activities (+0.12 × 10
−3
yr
−1
). The anthropogenic effects are especially higher on the Loess Plateau (+1.01 × 10
−3
yr
−1
) and the Three-North region (+0.23 × 10
−3
yr
−1
). The vegetation dynamics shifts in 6.73% (31.64 Mha) of China’s drylands were directly attributed to anthropogenic impacts around the 2000s. When the anthropogenic effect was intensified, the vegetation dynamics shifted from no change to greening and vice versa, which significantly intensified the vegetation greening since the 1980s. These results capture the processes of ecological programs and provide an assessment of the effects of ecological restoration. This work provides a credible attribution of the vegetation greenness dynamics and trend shifts in China’s drylands, thus facilitating a better understanding of regional environmental change and management.
Assessing soil erosion in China’s severely eroded Loess Plateau is urgently needed but is usually limited by suitable erosion models and long-term field measurements. In this study, we coupled the ...Thorens and Soil Conservation Service (SCS) models to evaluate runoff and sediment yield during the 1980s and 2010s in the Xiaolihe watershed on the Loess Plateau. Results showed the proposed model framework had a satisfactory performance in modelling spatially distributed runoff and sediment yield. The Nash–Sutcliffe efficiency (NSE), percent bias (PBIAS) and the root mean square error-measured standard deviation ratio (RSR) were 0.93, 4.42% and 0.27 for monthly runoff; and 0.31, 62.31% and 0.82 for monthly sediment yield. The effects of land use changes on runoff and sediment yield were well captured by the SCS and Thorens models. The proposed modelling framework is distributed with a simple structure, requires relatively little data that can be obtained from public datasets, and can be used to predict runoff and sediment yield in other similar ungagged or poorly monitored watersheds. This work has important implications for runoff and erosion assessment in other arid and semi-arid regions, to derive runoff and erosion rates across large areas with scarce field measurements.
Land degradation threatens ecosystems and socio-economic development of Southern Africa. Evaluation of land degradation is widely conducted using a remote-sensed indicator to provide key information ...for alleviating degradation. However, the commonly used single indicator cannot reveal complex degradation processes. In this study, we conducted an integrated evaluation by utilizing linear regression, residual trend analysis, and sequential regression methods to detect visible, potential human-induced, and functional land degradation in Southern Africa. The results showed that visible, potential, and functional land degradation accounted for 8%, 9.6%, and 21.9% of the entire study area, respectively. In total, 34% (171.96 × 104 km2) of the region exhibited one or more forms of land degradation; 28.9% (146.01 × 104 km2) of the land experienced a single land degradation type, whereas 5.1% (25.95 × 104 km2) exhibited intensified degradation by two or three forms. Land degradation was more severe in South Africa, Angola, Botswana, and Mozambique. Potential degradation (11.76%) and functional degradation (56.88%) may co-exist with vegetation greening. This study suggests that a single indicator assessment underestimates the overall land degradation, and thus integrated indicators and methods are better for a comprehensive assessment. Spatial pattern and degradation process analyses are useful for the formulation of land restoration policies in Southern Africa.
Objective
A meta-analysis of the relevant literature evaluated the feasibility, safety, and potential benefits of single-incision laparoscopic appendectomy (SILA) relative to those of conventional ...laparoscopic appendectomy (CLA).
Methods
The major biomedical databases, including ClinicalTrials.gov, were searched up to January 2022 for relevant randomized controlled trials (RCTs). SILA and CLA were compared regarding patient body mass index, operative time, and perioperative complications. The Cochrane Handbook and RevMan 5.3 were used to judge trial quality and perform the meta-analysis, respectively.
Results
The 17 included RCTs comprised 2068 patients, of whom 1039 and 1029 patients underwent SILA and CLA, respectively. The operative time for SILA was longer than that for CLA (
MD
= 8.35 min, 95%
CI
= 6.58 to 10.11,
P
< 0.00001), but the cosmetic results from SILA were superior (
SMD
= 0.81, 95%
CI
= 0.58 to 1.03,
P
< 0.00001). However, the incidence rates were similar in terms of patient body mass index; postoperative pain scores; and rates of abdominal abscess, conversion to open surgery, ileus, surgical site infection, and overall perioperative complications between the two groups.
Conclusion
SILA is a safe technique for acute appendicitis, and its cosmetic outcomes are superior to those of CLA.
•Grass effects on overland flow and erosion reduction differ with grass species.•Above-ground grass parts retard flow and strengthen soil infiltration.•Roots played a predominant role in controlling ...soil erosion.•Slope position affected the effectiveness of grass in reducing sediment yield.
The effects of vegetation cover on overland flow and erosion processes on hillslopes vary with vegetation type and spatial distribution and the different vegetation components, including the above- and below-ground biomass. However, few attempts have been made to quantify how these factors affect erosion processes. Field experimental plots (5 m × 2 m) with a slope of approximately 25° were constructed and simulated rainfall (60 mm hr−1) (Rainfall) and simulated rainfall combined with upslope overland flow (20 L min−1) (Rainfall + Flow) were applied. Three grass species were planted, specifically Astragalus adsurgens (A. adsurgens), Medicago sativa (M. sativa) and Cosmos bipinnatus (C. bipinnatus). To isolate and quantify the relative contributions of the above-ground grass parts (stems, litter cover and leaves) and the roots to reducing surface runoff and erosion, each of the three grass species was subjected to three treatments: intact grass control (IG), no litter or leaves (only the grass stems and roots were reserved) (NLL), and only roots remaining (OR). The results showed that planting grass significantly reduced overland flow rate and velocity and sediment yield, and the mean reductions were 21.8%, 29.1% and 67.1%, respectively. M. sativa performed the best in controlling water and soil losses due to its thick canopy and dense, fine roots. Grasses reduced soil erosion mainly during the early stage of overland flow generation. The above-ground grass parts primarily contributed to reducing overland flow rate and velocity, with mean relative contributions of 64% and 86%, respectively. The roots played a predominant role in reducing soil erosion, with mean contribution of 84%. Due to the impact of upslope inflow, overland flow rate and velocity and sediment yield increased under the Rainfall + Flow conditions. The results suggest that grass species on downslope parts of semi-arid hillslopes performed better in reducing water and soil losses. This study is beneficial for forage selection, allocation and management practices, such as forage harvesting, when implementing restoration strategies to control soil and water losses.
Abstract
Grassland ecosystem functions are affected by global climate change and increasing aridity. Belowground components of soil and vegetation, such as specific root length, belowground biomass ...and soil organic carbon are important for maintaining these functions. However, aridity affects these components in different ways. This research evaluates changes in soil properties and plant attributes with aridity along a 2600 km aridity gradient in the arid and semiarid grasslands of Inner Mongolia. The aridity index was used considering the ratio of precipitation to potential evapotranspiration, where a higher value indicates greater aridity. Results showed an overall aridity threshold for grassland ecosystems of 0.67, where abrupt changes in belowground components were observed. The effect of aridity on specific root length changed from negative (−0.18) below the threshold to positive (0.24) above the threshold, with the emergence of coordination between aboveground and belowground plant characteristics. Aridity exhibited a negative effect on belowground biomass, increasing from −0.24 below the threshold to −0.55 above the threshold as the positive effect of relative grass abundance disappeared. The total effect of aridity on soil organic carbon showed a subtle change, but the driving pathways through which aridity affects changed from soil loss to aridity itself and vegetation cover at plot scale. These findings highlight how aridity affects belowground components in grassland ecosystems above and below the aridity threshold. They provide a basis for better understanding aridity-driven interactions in grassland ecosystems, and can be used to inform actions to protect grasslands under future climate change.
