Wind-water Erosion Crisscross Region Research Articles

Effects of Wind-Water Erosion and Topographic Factor on Soil Properties in the Loess Hilly Region of China.

Wind and water erosion processes can lead to soil degradation. Topographic factors also affect the variation of soil properties. The effect of topographic factors on soil properties in regions where wind and water erosion simultaneously occur remains complicated. To address this effect, we conducted this study to determine the relationships between the changes in wind-water erosion and soil properties in different topographic contexts. We collected soil samples from conical landforms with different slope characteristics and positions in the wind-water erosion crisscross region of China. We examined the soil 137Cs inventory, soil organic carbon (SOC), total nitrogen (TN), soil particles, soil water content (SWC), and biomass. 137Cs was applied to estimate soil erosion. The results show that the soil erosion rate followed the order of northwest slope > southwest slope > northeast slope > southeast slope. The soil erosion rate on the northwest slope was about 12.06-58.47% higher than on the other. Along the slopes, the soil erosion rate decreased from the upper to the lower regions, and was 65.65% higher at the upper slope than at the lower one. The change in soil erosion rate was closely related to soil properties. The contents of SOC, TN, clay, silt, SWC, and biomass on the northern slopes (northwest and northeast slopes) were lower than those on the southern slopes (southeast and southwest slopes), and they were lower at the upper slope than at the lower one. Redundancy analysis showed that the variation in soil properties was primarily affected by the slope aspect, and less affected by soil erosion, accounting for 56.1% and 30.9%, respectively. The results demonstrate that wind-water erosion accelerates the impact of topographic factors on soil properties under slope conditions. Our research improves our understanding of the mechanisms of soil degradation in gully regions where wind and water erosion simultaneously occur.

Land use effects on the dynamics of soil C, N and microbes in the water-wind erosion crisscross region of the northern Loess Plateau, China

The water-wind erosion crisscross region of the northern Loess Plateau in China is under constant pressure from severe erosion due to its windy and dry climate and intensive human activities. Identifying sustainable land use patterns is key to maintaining ecosystem sustainability in the area. Our aim was to appraise the impacts of different land use regimes on the dynamics of soil total organic C (TOC), total N (TN), and microbes in a typical watershed in the northern Loess Plateau to identify suitable land use types that can maintain soil fertility and sustainability. A field experiment was performed in Liudaogou watershed in Shenmu City, Shaanxi Province, China, where the dynamics of soil TOC and TN, microbial biomass C and N, microbial respiration, and net N mineralization in six typical land use types, dam land, rainfed slope land, deciduous broadleaf forest, evergreen coniferous forest, shrubland, and grassland, were measured in three different growing seasons. Land use type and season significantly affected TOC, TN, and the dynamics of microbial biomass and activity. As the most anthropogenically disturbed land use pattern, dam land was an optimal land use pattern for TOC sequestration due to its higher TOC and TN, but lower microbial activity. Soil TOC, TN, and microbial properties demonstrated a decreasing trend after natural grassland was converted to shrubland, forest, and rainfed slope land. Shrubland with exotic N-fixing Korshinsk peashrub (Caragana korshinskii Kom.) can maintain TOC, TN, and microbial properties similar to those in grassland. Soil TOC, NH4+-N, TN, moisture, and extractable C were the principal indexes for soil microbial biomass and activity and explained 88.90% of the total variance. Thus, grassland was the optimal land use pattern in the water-wind erosion crisscross region of the northern Loess Plateau to maintain ecosystem stability and sustainability.

The Interaction of Aeolian Sand and Slope on Runoff and Soil Loss on a Loess Slope via Simulated Rainfall under Laboratory Conditions

The wind–water erosion crisscross region, where the topography is complicated, is the most severe area of soil erosion on the Loess Plateau. The wind and terrain both have an impact on the soil water erosion process. In order to evaluate the effects of sand cover on runoff and soil loss characteristics, a series of experiments was conducted in two contrasting treatments. One treatment was a bare loess soil slope serving as the control, and the others were sand-covered loess slopes with five different slopes. The results showed that the runoff time, total runoff yield, and total soil loss were different between the sand-covered slope and the loess slope on the slope of 15°. The sediment concentration of the sand-covered slope was significantly higher than that of the loess slope during the entire rainfall process (p < 0.05). The increase in the slope gradient shortened the surface runoff initiation times and enhanced the total runoff volume and soil loss. The total runoff volume and the total soil loss were 39.7 L and 44.3 kg, respectively, on the sand-covered slope of 10°. When the slope gradient increased from 10° to 30°, the total runoff volume and the total soil loss increased by 22.8 L and 42.8 kg, respectively, while the surface runoff initiation times shortened by 300 s. For the sand-covered slopes, the erosion processes appeared to be mainly dominated by sediment transport. The correlation between soil loss rates and slope gradients demonstrated the secondary polynomial function. In addition, the critical slope of sand-covered slopes was from approximately 23° to 28°. The proportion of sand cover and slope responsible for soil erosion was 3:1, which means the wind effect was more important than the terrace factor in terms of soil water erosion in the wind–water erosion crisscross region. The results provide a theoretical basis for soil erosion control in this area.

Distribution characteristics of soil microbial communities and their responses to environmental factors in the sea buckthorn forest in the water-wind erosion crisscross region.

Soil microorganisms are an important part of forest ecosystems, and their community structure and ecological adaptations are important for explaining soil material cycles in the fragile ecological areas. We used high-throughput sequencing technology to examine the species composition and diversity of soil bacterial and fungal communities in sea buckthorn forests at five sites in the water-wind erosion crisscross in northern Shaanxi (about 400 km long). The results are described as follows: (1) The soil bacterial community of the sea buckthorn forest in the study region was mainly dominated by Actinobacteria, Proteobacteria, and Acidobacteria, and the fungi community was mainly dominated by Ascomycota. (2) The coefficient of variation of alpha diversity of microbial communities was higher in the 0-10 cm soil layer than in the 10-20 cm soil layer. (3) Soil electrical conductivity (36.1%), available phosphorous (AP) (21.0%), available potassium (16.2%), total nitrogen (12.7%), and the meteorological factors average annual maximum temperature (33.3%) and average annual temperature (27.1%) were identified as the main drivers of structural changes in the bacterial community. Available potassium (39.4%), soil organic carbon (21.4%), available nitrogen (AN) (13.8%), and the meteorological factors average annual maximum wind speed (38.0%) and average annual temperature (26.8%) were identified as the main drivers of structural changes in the fungal community. The explanation rate of soil factors on changes in bacterial and fungal communities was 26.6 and 12.0%, respectively, whereas that of meteorological factors on changes in bacterial and fungal communities was 1.22 and 1.17%, respectively. The combined explanation rate of environmental factors (soil and meteorological factors) on bacterial and fungal communities was 72.2 and 86.6%, respectively. The results of the study offer valuable insights into the diversity of soil microbial communities in the water-wind erosion crisscross region and the mechanisms underlying their interaction with environmental factors.

Monitoring Surface Deformation Associated With Soil Erosion in Loess Plateau With an Improved Small Baseline Subset Interferometric Synthetic Aperture Radar Algorithm

As a geomorphic process persistently occurring over the earth’s surface, soil erosion is one of the most serious environmental problems in the world nowadays, seriously threatening agriculture, natural resources, and ecosystem environments. Monitoring surface deformation associated with soil erosion will help to understand the dynamics of erosion process and the erosion mechanism. In this article, an improved small baseline subset interferometric synthetic aperture radar (SBAS-InSAR) technique is proposed to monitor the surface deformation over the wind-water erosion crisscross region in the Loess Plateau, China. In particular, a new deformation model considering both of the internal factors and external factors of soil erosion is introduced into the SBAS-InASR algorithm. The results show that the cumulative deformation is close to −200 mm during the investigated period. The deformation rate caused by precipitation is between −0.03 and 0.02 mm/mm. When the wind erosion factor changes by 1 unit, the deformation range is approximately −0.3–0.2 mm. Also, researchers found that the surface deformation is highly correlated to precipitation and wind. The root mean square errors (RMSEs) of the residual deformations estimated from the proposed model are smaller than those estimated from the conventional linear and period models, demonstrating that the proposed method is more suitable to model and analyze the surface deformation in wind-water erosion crisscross region.

Bryophyte diversity and microhabitat characteristics of bryophyte-dominated biological soil crusts development in water-wind erosion crisscross region of the northern Loess Plateau, China

Microhabitat factors play an important role in regulating bryophyte species distribution and the development of bryophyte-dominated biological soil crusts (hereafter bryophyte crusts). We investigated the distribution and development of bryophytes in eight microhabitats in the water-wind erosion crisscross region of the Loess Pla-teau. We used the line intercept transects to explore and quantify the influencing pathways of microhabitat factors on bryophyte diversity and analyzed the influencing pathways of plant cover, slope aspect, and slope gradient by using structural equation model to quantify influencing coefficients. Our results showed that: 1) The Patrick, Shannon, Pielou, and Simpson indcies of bryophytes under plant canopy were 63.4%, 66.6%, 91.0%, and 68.3% lower than that without plant canopy, respectively, while the thickness, biomass, and chlorophyll content of bryophyte crusts were 0.5, 0.2, and 1.3 times higher than that without plant canopy, respectively. 2) The Patrick, Shannon, Pielou, and Simpson indexes of bryophytes on the north slope were 0.6, 0.9, 5.6, and 0.9 times higher than those on the south slope, while the thickness, biomass, and chlorophyll content of bryophyte crusts were 0.3, 0.3, and 0.6 times higher than those on the south slope, respectively. 3) As the slope increasing from 14° to 34°, the Patrick, Shannon, Pielou, and Simpson indexes of bryophyte were decreased by 59.8%, 84.1%, 57.3% and 68.0%, and the thickness, biomass, and chlorophyll content of bryophyte crusts were decreased by 15.2%, 25.0%, and 16.5%, respectively. 4) The importance of the three microhabitat factors on bryophyte diversity and the development of bryophyte crusts followed an order of plant canopy cover > slope aspect > slope gradient. The primary influencing pathway varied among the microhabitat factors. In conclusion, plant cover, slope aspect, and slope gradient significantly affected the distribution of bryophytes species and developmental level of bryophyte crusts through direct and indirect pathways. Therefore, full consideration should be given to microhabitat conditions when using bryophyte crusts to control desertification.

Effects of grazing on soil organic carbon stocks in the revegetated grasslands on the Loess Plateau, China

Grazing is an important driving factor for soil carbon sequestration in grasslands. The objective of this study was to clarify the effects of grazing and its intensity on soil organic carbon stocks (SOCS) in the revegetated grasslands in the Loess Plateau region. With the grasslands excluded from grazing ＞20 years as the control, we investigated the SOCS in the 0-20 cm soil layer in three grazing intensities in the west, middle, and east of wind-water erosion crisscross region and the water erosion region. The intensity of grazing in the study was represented by the number of goat dung in the sampling sites, which included 0-10, 10-20, and more than 20 goat dung·m-2, respectively. Results showed that grazing significantly affected SOCS in the 0-20 cm soil layer in the west of crisscross region, 0-10 cm soil layer in the east of crisscross region, and 0-5 cm soil layer in the water erosion region. There was no significant effect in each soil layer in the middle of crisscross region. Only in the west of crisscross region, the SOCS in the grazing intensity of 0-10 and ＞20 goat dung·m-2 significantly decreased by 34.8%-50.9%, whereas the SOCS in each grazing intensity was not different from that in the enclosure in the other three regions. The SOCS was mainly affected by grazing intensity in the east of crisscross region and by soil physical and chemical properties and (or) litter biomass in the other three regions. In conclusion, grazing intensity of 10-20 goat dung·m-2 did not affect SOCS in the 0-20 cm soil layer in the revegetated grassland on the Loess Plateau, China.

Catchment properties controlling suspended sediment transport in wind-water erosion crisscross region

Study regionWuding River catchment, the wind-water erosion crisscross region on the Chinese Loess Plateau. Study focusThe wind-water erosion crisscross region suffers severe soil erosion in the world, and various catchment properties control fluvial processes. This study investigated suspended sediment (SS) transport characteristics in a typical catchment with two geomorphological types (aeolian sand and loess hilly). Lorenz curves and partial least-squares regression were used to quantify the SS transport characteristics and attributions. New hydrological insights for the regionThere were significant differences in the SS transport characteristics between the two geomorphological regions. In the aeolian sand region, the mean annual SS loads were much lower than that in the loess hilly region (P < 0.01) under similar precipitation and runoff conditions. Rivers in this region transported SS all year round. The relatively lower concentration indicated that extreme events did not dominate total SS load. Conversely, SS transport in the loess hilly region was highly concentrated during a few events in rainy season, with the largest 10% of the events transporting exceed 80% of the total SS load. Statistical analysis showed that drainage density, catchment slope, and soil texture were the dominant factors controlling SS load, while the concentration of SS transport events was more related to the perimeter-area fractal. These findings have important implications for fluvial sediment transport in arid and semi-arid environments.

Sand cover enhances rill formation under laboratory rainfall simulation

Soil erosion was severe in the wind-water erosion crisscross region of the northern Loess Plateau of China, where aeolian sand cover may enhance water erosion. In order to evaluate the effects of sand cover on runoff, soil loss and rill information, a series of rainfall simulation experiments was conducted in two contrasting treatments. One is a bare loess soil slope serving as a control, and another is a sand-covered loess slope (namely sand cover treatment). Nine simulated rains, 60 min each, were applied to each treatment in duplicates. The results showed that the runoff generation mechanism changed from infiltration-excess runoff in the control to subsurface saturation-excess runoff in the sand cover treatment. The runoff initiation was delayed about three folds in the sand cover treatment as compared to the control. Total runoff volumes and total soil loss in the sand cover treatment in each event were 1.1–1.2 times and 1.9–9.3 times those in the control treatment. A paired t-test showed that the runoff rates were greater in sand cover than in control in all events except for the last run at P < 0.05. The soil loss rates were greater in sand cover than in control for all events except the first rain at P < 0.05. Measured total rill length, width, and degree of rill dissection in the sand cover treatment were much greater than those in the control. The rill erosion of sand cover slope was dominated by the shallow and wider rills, while loess slope was dominated by the narrow and deeper rills. The results clearly indicated that a sand layer overlying a less pervious loess soil facilitated return flow and thus accelerated rill formation and development. This finding is in line with the common understanding that return flow in layered soil can promote rill formation and cause severe rill erosion, which is also important to understand the effect of wind-blown sand cover on water erosion in the wind-water erosion crisscross region.

Characteristics and controls of solute transport under different conditions of soil texture and vegetation type in the water–wind erosion crisscross region of China’s Loess Plateau

The analysis of solute transport characteristics in soil is of great significance in understanding nutrient cycling and pollutant migration in the Earth’s Critical Zone. The objective of this study was to investigate the transport characteristics and the influencing factors of Cl− in soils with different textures (sandy-S and loamy-L), and covered by different vegetation types (arbor-AR, shrub-SH and grass-GR) in the water–wind erosion crisscross region of the northern Loess Plateau of China. Results showed that the initial penetration time (TS: 12–80 min), entire penetration time (TE: 75–480 min), average flow velocity in the pore (V: 0.52–1.98 cm h−1) and the hydrodynamic diffusion coefficient (D: 0.75–2.55 cm2 h−1) of Cl− varied with different soil textures and vegetation types, and at different soil depths. The V and D associated with Cl− transport were highest in the 0–20 cm soil layer and decreased with increasing depth, while the opposite trend was observed for TS and TE. For the 0–1 m soil profile of the same texture but covered by different vegetation types, the average V and D followed the order of S-AR > S-GR > S-SH and L-AR > L-SH > L-GR, while the average TS and TE exhibited the exact opposite order. This behavior is caused by the varying distributions of root biomass under different vegetation types that affect the number of macropores, the connectivity density and the preferential flow paths in the soil. For the 0–1 m soil profiles of different textures covered by the same vegetation type, the average V and D followed the order of S-AR > L-AR; S-SH > L-SH; and S-GR > L-GR, while the average TS and TE showed the opposite trend. This is because the pore size and distribution in soil are significantly affected by soil mechanical composition. There are significant correlations between soil properties (e.g., bulk density, number of macropores, pore connectivity density, saturated hydraulic conductivity, soil organic carbon content and particle composition) and the transport parameters (e.g., V, TS, and TE). The pedotransfer functions using readily available soil properties can adequately predict V of Cl− transport under different conditions of soil texture and vegetation type. These results provide guidance for the rational configuration of artificial vegetation in different textural soils with respect to reduce nutrient loss and improve ecosystem functions in the northern Loess Plateau of China.

Revealing soil erosion characteristics using deposited sediment sources in a complex small catchment in the wind-water erosion crisscross region of the Chinese Loess Plateau

Sediment sources in catchments under the control of check dams in the wind-water erosion crisscross region are more complicated compared to other regions on the Chinese Loess Plateau. This is due to their general complexity, which mainly results from variation in soil, landform, vegetation, and erosion agents. Accordingly, we used the composite fingerprinting approach to trace sediment sources in a typical small catchment in this region. The aim was to reveal the erosion characteristics of the catchment throughout the trapping history of the check dam. Sediment sources were classified into three-source (paleosol, loess and sand) and four-source (paleosol-gully, loess-gully, slope bare of sand and slope covered by sand) groups on the basis of soil and landform types, respectively. Sediment sources throughout the whole trapping history of the check dam (1978–2010) could be classified into three stages according to variation in sedimentation rate. Results showed that depositional sediment in the check dam was primarily from gullies (averaging 80.1%), especially the paleosol-gully (>54.1%). The large contribution of gullies indicated that the main erosion agents were streamflow from rainstorm events and gravity. Coal mining also had a significant impact on contribution of sediment sources, especially for slopes. Since 1987, mining began to change the structure of hills in this region, leading to slope fissures, collapse, and landslides at junctions where gullies meet slopes, which increased the risk of slope erosion. This has caused an increase in sediment from slopes bare of sand distributed under condition of continues implementation of soil conservation measures, which converted sloping cropland into grassland or forest. Further studies are necessary to gain better insight into sediment transport and deposition within such complex environments, as well as to distinguish between the effects of multiple erosion agents.

Spatiotemporal variations in deep soil moisture and its response to land-use shifts in the Wind–Water Erosion Crisscross Region in the Critical Zone of the Loess Plateau (2011–2015), China

Soil water content (SWC) with a deep profile is crucial to land use management, soil and water conservation, and ecological restoration worldwide, including the wind–water erosion crisscross region in the Critical Zone of the Chinese Loess Plateau. To ascertain the spatiotemporal variation of deep SWC and its response to land-use shifts in the region, the SWC was monitored at four representative land uses (farmland, shrubland, natural grassland, and planted grassland) to a depth of 21 m. Monitoring occurred between 2011 and 2015 in the Liudaogou watershed of the Chinese Loess Plateau. The Hydrus-1D model was then applied to simulate the SWC dynamics for the different land-use types and scenarios of land-use shifts. The SWC exhibited a high spatial variability in the vertical direction both within a given soil profile and among the different land uses. In the 0–2 m layer, the soil texture and root biomass controlled the spatial-temporal variability of the SWC. The temporal variability was also controlled by meteorological factors. In the 2–21 m layer, spatial variability was controlled by the soil texture, while soil texture and root biomass influenced the temporal variability of the SWC. The Hydrus-1D model accurately simulated spatiotemporal variations of SWC in the 0–21 m layer and was more effective on layers minimally influenced by weather. Land-use shifts from farmland with shallow-rooted plants to those with deep-rooted plants intensified soil water consumption in the 3.5–5 m layer. For best-management practices, appropriate plant species should be considered based on climatic conditions and SWC regimes. A better understanding of this information is useful for plant species selection, soil water resource utilization, and land use policymaking in the wind–water erosion crisscross region of the Critical Zone and other similar regions around the world.

Response Relationship between Microtopographic Variation and Slope Erosion under Sand-Cover

Slope microtopography is an important factor that affects the process of slope erosion. We quantified the responses between microtopography and the amount of erosion on overland sand slope and loess slopes through an indoor artificial simulated rainfall experiment. Three continuous rainfall tests under 1.5 mm/min rain intensity were used to analyze the spatial variation of slope microtopography and soil erosion with three-dimensional laser scanning technology. Our results show that under 0.5, 1.0, and 1.5 cm sand-covered slopes, the runoff time of the first rainfall is delayed by 18, 19, and 23 min, respectively, compared with the loess slope. Furthermore, the average sediment concentration on the slope decreased with subsequent rainfall events. The total erosion of the slope under 0.5, 1.0, and 1.5 cm sand was 4.24, 3.57, and 5.40 times that of the loess slope, respectively. The erosion of the sand-covered slopes was much larger than that of the loess slope. The length of the main sand production area was about 2.4 times that of the loess slope and the peaks of the erosion amount of the slope were mostly distributed in the lower part of the slope. As the rainfall progressed, the microtopographic factors of the loess slopes increased significantly (p &lt; 0.05), and the microtopographic factors of the sand slopes increased, but not significantly (p &gt; 0.05). We found that the microtopographic factors with the strongest erosion responses to the loess slope and the sand-covered slope were surface incision and surface roughness. The response relationship between microtopographic variation and erosion of the loess slope was stronger than the sand-covered slope, and suggests that other, unaccounted-for factors may be affecting the erosion of sand-covered slopes. This study provides a reference for erosion mechanisms of the wind–water erosion crisscross region.

Soil nutrients of different land-use types and topographic positions in the water-wind erosion crisscross region of China's Loess Plateau

The Grain-for-Green program was implemented in China in 1999 to reduce soil erosion, increase biodiversity, conserve natural resources and improve the natural environment by modifying patterns of land use. The located field experiment about the influence of different land-use types (LUTs) on nutrient contents and changes in the soil profile or the degree of influence over time was conducted for many years in Liudaogou watershed. The contents of soil organic matter (SOM), total nitrogen (TN), total phosphorus (TP), available P (AP) and two inorganic N forms, ammonium-N (AN) and nitrate-N (NN), were determined in 0–200 cm soil profiles in five terraced and three sloped LUTs. The terraced LUTs were bare land (BAT), farmland (FAT), abandoned land (ABT), forage land (FOT, with alfalfa) and shrubland (SHT, with the peashrub Caragana korshinskii), and the sloped LUTs were farmland (FAS), abandoned land (ABS) and forage land (FOS). All of these LUTs were converted from traditional farmland except for FAT and FAS and they are carefully maintained for the last 50 years. SOM and TN contents were significantly higher after conversion from farmland to shrubland or grassland (15.6–34.9%) and decreased (51.5–77.1% for SOM in 0–40 cm, 49.7–72.1% for TN in 0–60 cm) with depth for all LUTs. TP and AN contents throughout the profiles were not significantly affected by land use, but NN was leached and accumulated in farmland only. AP content was highest throughout the profile in ABS when TP and AP contents were higher in sloped land than terraced land. SOM, TN and AN contents did not differ significantly for the same land-use patterns in the two topographies. SOM and TN contents in the surface soil increased with the length of recovery. Our observations demonstrated that the Grain-for-Green program has improved the nutrient contents and fertility of the soil and has increased SOM and TN stocks over time and that these effects were not limited to the topsoil. Abandoned land may be the optimal choice for nutrient sequestration in terraced and sloped land. Shrubland and artificial grassland are also recommended for increasing soil nutrient content in the area.

Spatial variability of plant community characteristics and its influencing factors in a small watershed of wind-water erosion crisscross region on the Loess Plateau, China

The small watershed is the basic unit of soil erosion control on the Loess Plateau. Consequently, the study of the spatial distribution and influencing factors of vegetation is the basis of vege-tation restoration and reconstruction in this region. A small watershed in the wind-water erosion crisscross region with the most serious soil erosion in the Loess Plateau was selected to investigate the changes of vegetation distribution and soil properties. The spatial variability of plant community characteristics and its main driving factors were studied by geo-statistical method and redundancy analysis (RDA). The results showed that there were 27 plant species in the small watershed, belonging to 12 families and 25 genera. Leguminous, Gramineous and Compositae plants were dominant families, contributing 59.3% of the total species. In general, the community structure was simple and the organization level was low. The aboveground biomass (AGB) and coverage (C) of the community reached 205.7 g·m-2 and 57.7%, which was higher than the mean value of grassland in northern China, but the level of species diversity was lower. There were medium spatial correlation in AGB, but stronger spatial correlation for C, Patrick richness index (R), Shannon diversity index (H), Simpson dominance index (D) and Pielou evenness index (J). The spatial distribution of AGB was mainly patchy and striped, which was highest at the semi-shady slope and near the outlet of watershed. Other community characteristics were relatively fragmented, and R, H and J were higher at the top of the semi-shady slope. AGB and C were mainly affected by soil organic carbon, mineral nitrogen, total nitrogen, soil water content, and altitude, while R, H, D and J were mainly affected by soil saturated hydraulic conductivity, bulk density, sand content, and silt content. The results are helpful for vegetation restoration and evaluation of ecosystem structure and function in the wind-water erosion crisscross region.

The characteristics of soil water and gas transport under different land use patterns in the water-wind erosion crisscross region

Understanding the effects of land use patterns on soil water and gas transport in the water-wind erosion crisscross region can provide guidance for high-efficiency use of limited soil and water resource in the ecological rehabilitation process on the Loess Plateau. To investigate the cha-racteristics of soil water and gas transport under different land use patterns and to study the relationships between soil saturated hydraulic conductivity (Ks), air permeability (Ka) and relative gas diffusivity (DP/D0), we collected soil samples (0-5 cm depth) from Caragana korshinskii land, abandoned land, alfalfa land, cropland, and bare land. Ks was measured by constant-head method. DP/D0 was measured by gas chamber method. Ka under field capacity (FC) was measured using the soil gas permeability meter. Results showed that soil bulk density (ρb) ranked as alfalfa land>bare land>abandoned land>C. korshinskii land >cropland, with that of abandoned land, bare land and alfalfa land being significantly different from that of cropland. Total soil porosity (Φ) ranked as cropland>C. korshinskii land>abandoned land>bare land>alfalfa land. Compared with cropland, Φ of alfalfa land, bare land and abandoned land was lower by 7.5%, 4.7% and 3.1%, respectively. Air filled porosity (ε100) ranked as cropland>abandoned land>C. korshinskii land>bare land>alfalfa land. ε100 of alfalfa land, bare land, C. korshinskii land and abandoned land was lower by 38.3%, 33.6%, 12.8% and 10.1%, respectively, as compared with cropland. Soil Ks ranked as abandoned land>C. korshinskii land>alfalfa land>bare land>cropland, with that of the abandoned land being significantly higher than the other four land use patterns. Soil Ka ranked as abandoned land>alfalfa land>C. korshinskii land>bare land>cropland, with that of abandoned land being significantly diffe-rent with cropland. Soil DP/D0 ranked as abandoned land> C. korshinskii land> alfalfa land>cropland>bare land, in which DP/D0 of C. korshinskii land and abandoned land was significantly higher than cropland by 36.8% and 61.6%, respectively. There were significant correlations between Ks and Ka, DP/D0 under FC conditions. Land use patterns significantly changed soil permeability. Farmland, abandonment, C. korshinskii, and alfalfa plantation improved hydraulic and gas transport parameters of the surface soil. In contrast, farmland and bare land had poor capability of soil water and gas transport.

The effects of tillage on sheet erosion on sloping fields in the wind-water erosion crisscross region of the Chinese Loess Plateau

Tillage complicates erosion on sloping fields, especially in regions of combined wind and water erosion. The wind-water erosion crisscross region of the Chinese Loess Plateau is an example of such a region wherein erosion is caused by the stimulating effects of tillage, rainfall, and wind. Sheet erosion is an important form of cropland soil erosion and is closely correlated to the productive capacity of land. It is important to better understand the influence of tillage on soil sheet erosion in order to estimate the loss of fertile surface soil and to provide suitable tillage recommendations for the cultivation of sloping cropland in this region, which is susceptible to multiple erosion factors. This study aims to clarify spatial distribution and variation of sheet erosion rates as affected by different tillage patterns on sloping cropland under different slope conditions. We applied beryllium-7 measurements and sediment collection methods to estimate sheet erosion rates to reveal the distribution of sheet erosion on bare sloping fields, to determine correlations between sheet erosion rates and slopes (0°, 5°, 10°, 15°, 20°, and 25°), and to analyze variation in sheet erosion affected by tillage patterns on a plot scale. Results show that sheet erosion increased in a top-down direction and achieved maximum values at the mid- or lower-mid section of slopes, then erosion rates decreased or sediment deposition occurred at the base of slopes. Sheet erosion intensified with an increase in slope gradient fitting to linear or exponential functions regardless of the tillage pattern used (i.e., whether solely applying autumn plowing or a combination of autumn and spring plowing). However, tillage patterns had an obvious effect on sheet erosion. Differences in sheet erosion caused by tillage patterns increased from 5° to between 15° and 20° before decreasing at 25°. This demonstrates that steep slope gradients will weaken tillage pattern effects on sheet erosion, thus becoming a significant impacting factor on sheet erosion. Based on sheet erosion rates, we recommend that cropland be converted to grassland or shrubland when slope gradients are greater than 20° in the study region. Notably, a decrease in tillage intensity (frequency) helped in the reduction of sheet erosion on sloping croplands, and further tillage practices associated with conservation tillage should be applied on sloping cropland to obtain better soil erosion control results.

Effect of vegetation utilization on runoff and sediment production on grain-for-green slopes in the wind-water erosion crisscross region.

To effectively utilize the vegetation on grain-for-green slopes in the wind-water erosion crisscross region, it is necessary to determine the reasonable vegetation utilization intensity. We set up runoff plots on slopes which were not cultivated and were closed for many years in the Liudaogou catchment, a typical catchment in wind-water erosion crisscross region of the Loess Plateau. With artificial simulated rainfall experiments, the characteristics of runoff and sediment yield on slopes (10&deg;, 20&deg; and 30&deg;) under different utilization intensity of vegetation were studied to select the reasonable utilization intensity. The results showed that the runoff rate in the process of rainfall simulation could be divided into two periods: rapidly increasing in the initial period and slow increasing or quasi-steady state in the middle and late periods. The variation of erosion rate during the rainfall was dependent on the slope. The utilization intensity had a significant effect on the runoff yield, which increased with the increasing utilization intensities. The slope gradient had a significant effect on the sediment yield, with the variation of sediment yield with slope gradient being: 20&deg;>30&deg;>10&deg;. Compared with the unused (natural) plots, the relative runoff and sediment increased with increasing utilization intensities. Predicted based on the rainfall data, annual soil erosion amount on the slope would be basically lower than the tolerance level of soil loss when the vegetation cover on the slope surface reached 25% in 15 years after abandoning reclamation. More attention should be paid to the restoration and management of vegetation on the slope of 20&deg; in this area.

Effects of mosaic-pattern shrub patches on runoff and sediment yield in a wind-water erosion crisscross region

Shrub patch fragmentation makes a substantial contribution to soil erosion in sandy regions. This study aimed to analyze the effects of mosaic-pattern shrub patch size on runoff and sedimentation in a wind-water erosion crisscross region. The influence of shrub patch size on runoff and sedimentation, and on several soil physical and vegetation factors was evaluated in a sandy Chinese landscape. Based upon the canopy diameter of Artemisia ordosica, a xerophytic shrub, three different patch sizes were set as the treatments, such as small (Ø < 60 cm), medium (60 < Ø < 160 cm) and large (Ø > 160 cm) shrub patches. Bare land served as control conditions. Three runoff plots were established for each shrub size, and runoff (Q) and sediment (SY) yields were monitored under natural rainfall conditions. The results indicated that rainfall distribution was uneven in the study area. Low-intensity (0–5 mm/h) and short-duration (0–5 h) rainfall events accounted for 82.6% and 71.7% of all events, respectively, during the 6-month test period, from May to October 2016. Linear regression indicated that Q and SY increased with increasing rainfall depth at the slope scale. The impact of rainfall erosion on bare land was the greatest. Compared with control plots, Q and SY reduction owing to the small, medium, and large shrub patches was 19.7% and 49.3%, 31.4% and 62.4%, and 35.9% and 94.9%, respectively. These results confirmed the different effects of shrub patches of different sizes on soil quality, runoff and sediment reduction. Besides, this study suggested that shrub patches could modify soil microhabitats on sandy soils, reducing the soil erosion rates and as well as favoring vegetation regeneration.

Fingerprinting sediment sources in the water-wind erosion crisscross region on the Chinese Loess Plateau

Sand sheet sources in the wind-water erosion crisscross region of the Chinese Loess Plateau have not been specifically identified. Spatially, we selected a transect that cuts across the eastern edge of the Mu Us Sandy Land, sand sheets distributed loess hills (sand-loess hills), loess hills, and adjacent rocky mountains to collect surface sediment samples. Temporally, we selected a site on a sampling sand-loess hill to collected depth incremental samples in a 320 cm depth soil profile to analyze sediment sources using the multiple composite fingerprinting approach. We screened out a group of optimal composite fingerprints that correctly classified sediment sources at 100%. Greater than half of all sediment on sand-loess hills originated from the sandy land area on the sampling transect, and roughly half from the sandy land in the soil profile, while the remaining sediment all originated from the loess hills, and rocky mountains had no contributing effect. Coarse particles (>100 μm) on sand-loess hills were mainly transported from the Mu Us Sandy Land, while fine particles were mainly from loess hills, indicating the importance of aeolian activity in the transport of sand from the Mu Us Sandy Land to loess hills. Environmental changes chronicled by sediment deposition at approximately 12.85 ka BP in the soil profile were primarily attributed to climate change. This study confirms that the composite fingerprinting approach is a feasible method for future studies on sediment sources in areas influenced by complex erosion agencies, landforms and soil types.