Institute of Soil and Water Conservation,Chinese Academy of Sciences and Ministry of Water Resources
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A simulation of rill bed incision processes in upland concentrated flows
No full textQuantifying rill bed incision provides fundamental information for process-based erosion modeling; while the morphodynamic and hydrodynamic mechanism in bed incision processes are still unclear. Thus, experiments were conducted to examine rill bed incision processes in upland concentrated flows. DEMs (2 mm x 2 mm resolution) obtained by photogrammetry were used for sill bed morphology analysis. Rill channel (2.0 m-long, 0.08 m-wide and 0.15 m-deep) with two slope gradients (15 degrees and 20 degrees) were subjected to four overland flow rates (1.0, 2.0, 3.0 and 4.0 L min(-1)). The results showed that sediment delivery, rill bed incision rate and average rill depth increased with inflow rate and bed slope. Sediment delivery increased from 0.060 to 0.226 kg min(-1) per 1 L min(-1) inflow increment and from 0.043 to 0.207 kg min(-1) when bed slope increased from 15 degrees to 20 degrees. In a well-developed rill channel, rill bed incision could be divided into three phases: pre-headcut formation (dominated by rill flow shear stress), headcut incision (dominated by headcut advancing) and post-headcut incision (dominated by rill flow shear stress). Headcut incision phase, which only accounted for 65% of rill bed sediment. In the pre-headcut formation phase, rill flow velocity, shear stress and stream power increased with increases of inflow rate and slope gradient. Conversely, flow velocity showed no evident trend with increased inflow rate and bed slope during headcut incision phase. Initial headcut advancing rate could be predicted by a non-linear function based upon soil characteristics, rill flow shear stress and headcut height. Sediment delivery showed a power function with the product of inflow rate and squared bed slope. Because rill bed incision is dominated by headcut advancement and incision, practices for controlling headcut initiation should be implemented to decrease hillslope soil loss
Factors that Influence the Vertical Distribution of Soil Water Content in the Critical Zone on the Loess Plateau, China
No full textIn arid and semiarid regions, determining the vertical distribution of the soil water content (SWC) in the Earth's Critical Zone is important for understanding hydrological processes and for evaluating soil water storage (SWS) levels. However, the vertical distribution of SWC and its storage in deeper layers are unclear due to the difficulties associated with soil sampling. In this study, we investigated the vertical distribution of the SWC and SWS, and analyzed the relationship between SWC and related soil properties, including bulk density (BD), sand, silt, clay, and soil organic C (SOC), from the top of the soil profile to the bedrock at five sampling sites on the Loess Plateau in China (Yangling, Changwu, Fuxian, An'sai, and Shenmu) by soil core drilling. The results showed that the SWC variations at the five sampling sites tended to become weak as the depth increased. The mean SWC of all sampling sites exhibited a decreasing trend from south to north, with a significant difference (P < 0.01). Stepwise multiple regression analysis and state-space modeling showed that the BD was an important factor that affected the variations in the SWC in the deep soil layer. The trend of vertical distribution of the SWS was similar to that of the SWC. The results of this study deepen our understanding of the water conditions in deep soil layers, as well as the evaluation of SWS on the Loess Plateau in China
Telling a different story: plant recolonization after landslides under a semi-arid climate
No full textAims We aimed to know how plant species colonize landslides under a semi-arid climate. Methods We selected 30 landslides triggered by the continuous rainstorms in the hilly-gullied region of the Chinese Loess Plateau in July 2013. We quantified post-landslide changes in a core list of soil properties, vegetation properties and plant functional traits and also analyzed their relationships. Results After landslides, there were no large changes in the soil properties except slope angle. Correspondingly, there were no large changes in plant species richness, species composition and the functional traits. The vegetation cover of scars (the newly exposed soil surfaces because of landslides) was significantly lower than those of deposits (the deposition zones of landslides) and undisturbed vegetated areas surrounding the landslides (control areas), but the vegetation recovery of scars should be only a matter of time. Conclusions Under the semi-arid climate of the area, landslides do not have profound effects on soil properties and plant species richness and composition, telling a different story from those landslides under other climate regimes and implying great potential for the restoration of landslides
Impacts of mollic epipedon thickness and overloaded sediment deposition on corn yield in the Chinese Mollisol region
No full textTopsoil loss and overloaded sediment deposition profoundly influence soil productivity. Understanding the changes in crop yield with the decrease of topsoil thickness and the increase of sediment deposition depth is crucial to elucidate the effects of soil erosion and deposition on soil productivity. However, little information is available concerning how mollic epipedon thickness and overloaded sediment deposition affect crop yield in the Mollisol region of Northeast China. The objectives of this study were to quantify the effects of mollic epipedon thickness and sediment deposition depth on corn (Zea mays L.) yield in the Mollisol region of Northeast China. Simulated field experiments, including seven mollic epipedon thicknesses (0, 5, 10, 15, 20, 40 and 60 cm) and five sediment deposition depths (0, 7.5, 15, 22.5 and 30 cm) were conducted in two independent experiments, respectively. The results showed that corn yield reduced as mollic epipedon thickness decreased, and corn yield reduced more sharply when mollic epipedon thickness was less than 20 cm. Compared with the control treatment with 60 cm mollic epipedon, the corn yield reductions were 8.2%, 15.8%, 21.3% and 24.2%, respectively, for the treatments with 15, 10, 5 and 0 cm mollic epipedon. Moreover, the negative impacts of overloaded sediment deposition at the corn seeding stage on corn yield were also analysed in this study. The corn yield significantly decreased as sediment deposition depth increased. Compared with the control treatment without sediment deposition, the corn yield was decreased by 31.7% for the treatment with 30 cm sediment deposition depth. Additionally, a logistic function between corn yield and mollic epipedon thickness and a linear function between corn yield and sediment deposition depth were fitted. Cross-validation implied that the two equations had acceptable accuracy. Therefore, prevention of soil erosion and reduction of adverse influences of overloaded sediment deposition are cornerstones of sustainable agriculture in the Chinese Mollisol region
Estimation of wind and water erosion based on slope aspects in the crisscross region of the Chinese Loess Plateau
No full textThe crisscross region of the Chinese Loess Plateau is affected from both wind and water erosion, and their relative contributions remain unclear. A combination analysis of Cs-137 inventories, surface soil sample properties, and the local wind condition allows the measurements of total soil erosion, as well as the rates of wind and water erosion that are independently affected by slope aspect at a experimental site in the study area. This study selected eight straight slope for investigation. Although the slopes had similar gradients, lengths, elevations, shapes, vegetation conditions, soil types, and land-use types, they faced different aspects. This study tested the soil organic matter content, particle size, specific surface area, and Cs-137 inventory, including the mean Cs-137 reference inventory from a region of flat grassland near a century-old temple located on the top of a hillslope. Water erosion were assumed to be similar for slope aspects on condition that rainfall and environmental conditions were similar, and differences in erosion on slope aspects were mainly attributable to wind erosion. This assumption was confirmed by stepwise linear regression analysis, and wind erosion was estimated from total erosion and water erosion. The east-facing slope experienced almost no wind erosion, and erosion (91.4 t ha(-1) year(-1)) it experienced was primarily caused by water according to estimation of total erosion and analysis to wind conditions. Based on the assumption that water erosion was similar on all slopes, the west-facing slope exhibited a similar rate of water erosion to the east slope, while the rate of wind erosion was 16.9 t ha(-1) year(-1). The northwest slope had the highest wind erosion rate (42.3 t ha(-1) year(-1)), while the slope opposite to it (the southeast slope) had the highest wind deposition rate. Wind erosion on average contributed 27.4% to total erosion on windward slopes (northwest and north), while deposition occurred on the opposite leeward slopes (southeast and south). Although water erosion was found to be the primary driver of soil loss in this watershed, the effect of wind erosion cannot be neglected. It was mainly response for the erosion difference on slope aspects
Soil fertility increases rapidly during the 6-10 yr following conversion of cropland to grassland in China's Loess Plateau region
No full textChange in land use causes changes in soil properties and soil fertility, with long-term effects on ecosystem and crop productivity. This study determined soil fertility along sequential conversion of cropland to grassland in China's Loess Plateau. Soil samples were collected in 2015 at two sites in the semiarid region, following the conversion of cropland to grassland. Soil particle-size distribution, bulk density, pH, organic carbon (OC), total nitrogen (TN), total phosphorus (TP), available potassium, and available phosphorus were measured in this study. In addition, we analysed the changes of soil OC, TN, and TP, and evaluated soil fertility after the conversion from cropland to grassland. The establishment of grassland significantly increased soil OC, N, and P content, especially in the 0-10 cm soil layer. The highest change in soil OC, N, and P content occurred 6-10 yr after land conversion. The measured soil variables did not change significantly after 10 yr of land conversion. The overall increase in soil fertility after the land conversion was 13% at one site and 26% at the other site. The results suggested that establishing grassland could enhance soil fertility in the semiarid Loess Plateau region of China, and this enhancement is optimal 6-10 yr after the establishment of grassland
Influence of soil and water conservation measures on soil fertility in the Beijing mountain area
No full textSoil and water conservation (SWC) measures can be adopted to conserve soil and water and improve soil fertility. The degree to which SWC measures improve soil fertility is affected by the type of SWC measure, soil type, climate, etc. The purpose of this study was to study the effect of the main SWC measures implemented in the Beijing mountain area on soil fertility. Six runoff plots, including a fish pit (fallow) (FPF), fish pit (Platycladus orientalis L. Franco) (FPP), narrow terrace (fallow) (NTF), narrow terrace (Juglans regia L.) (NTJ), tree pan (Juglans regia L.) (TPJ), and fallow land (FL), were established to analyze the differences in soil fertility in the Beijing mountain area. Soil samples were collected in 2005 and 2015 from the six runoff plots. Soil particle size; soil total nitrogen (TN), total phosphorous (TP), total potassium (TK), alkali-hydrolysable nitrogen (Ah-N), available P (Av-P), and available K (Av-K); and soil organic matter (SOM) were measured. The soil integrated fertility index (IFI) was calculated. The results showed that the soil nutrient content and IFI significantly decreased from 2005 to 2015 in the FL plot and significantly increased in the five runoff plots with SWC measures. Compared to the other runoff plots with SWC measures, the FPP plot more significantly improved the soil nutrient content and IFI. The TN, Ah-N, Av-K, SOM, and IFI in the FPP plots increased by 98%, 113%, 61%, 69 and 47%, respectively, from 2005 to 2015. The IFI for the FPP, NTJ, and TPJ exceeded the average IFI of the farmland soil in the study region. The results indicated that the combination of engineering practices and vegetative measures effectively improved soil fertility. These results may be helpful for selecting SWC measures, land-use planning and monitoring and assessing soil fertility
Spectral Characteristics of Biological Soil Crusts under the Different Types in the Water-Wind Erosion Crisscross Region on the Loess Plateau
No full textThe study on spectral characteristics of biological soil crust in the water-wind erosion crisscross region in the Loess Plateau has important scientific value for the identification of biological soil crust based on remote sensing technology at regional scale, also provides important technical support for estimating the effect of biological soil crust on regional soil erosion control. The spectra of higher vegetation as well as the biological soil crust of algae with different coverage and different types of mosses were measured and quantified by Surface Species Spectrometry. The results are as follows, the algal bio-soil crust has similar spectral characteristics with soil in the water-wind erosion crisscross region in the Loess Plateau, and there is no obvious "peak valley" characteristic in the spectral curve. The reflectivity was reduced by the increasing coverage of the biological soil crust. Compared with the bare area, the spectral reflectance normalized mean of algae biological soil crust deceased 8. 64%, 15. 80% and 23. 09% respectively in the coverage of 10% to 20%, 30% to 40% and 50% to 60% in the visible area. The absorption characteristic at 680 nm (Chlorophyll) became increasingly obvious and the absorption valley at 2 200 nm (secondary mineral) became smaller as the coverage of algae biological soil crust increased. The spectral curve of moss biological soil crust showed the reflection peak of the green band, the absorption valley of the red light band and the high reflection of the near infrared band, which is similar with the vegetation. In the range of 760 similar to 930 nm, the slope of moss biological soil crust was 2. 5 to 4. 5 timed higher than that of vegetation. The study can provide some theoretical basis and technical support for the identification of biological soil crust
Loess Thickness Variations Across the Loess Plateau of China
No full textThe soil thickness is very important for investigating and modeling soil-water processes, especially on the Loess Plateau of China with its deep loess deposit and limited water resources. A digital elevation map (DEM) of the Loess Plateau and neighborhood analysis in ArcGIS software were used to generate a map of loess thickness, which was then validated by 162 observations across the plateau. The generated loess thickness map has a high resolution of 100 m x 100 m. The map indicates that loess is thick in the central part of the plateau and becomes gradually shallower in the southeast and northwest directions. The areas near mountains and river basins have the shallowest loess deposit. The mean loess thickness is the deepest in the zones with 400-600-mm precipitation and decreases gradually as precipitation varies beyond this range. Our validation indicates that the map just slightly overestimates loess thickness and is reliable. The loess thickness is mostly between 0 and 350 m in the Loess Plateau region. The calculated mean loess thickness is 105.7 m, with the calibrated value being 92.2 m over the plateau exclusive of the mountain areas. Our findings provide very basic data of loess thickness and demonstrate great progress in mapping the loess thickness distribution for the plateau, which are valuable for a better study of soil-water processes and for more accurate estimations of soil water, carbon, and solute reservoirs in the Loess Plateau of China
Identifying a suitable revegetation technique for soil restoration on water-limited and degraded land: Considering both deep soil moisture deficit and soil organic carbon sequestration
No full textRevegetation is an important means to improve the ecosystem services delivered by degraded land; however, inappropriate revegetation can result in severe soil desiccation and ecosystem degradation in water-limited regions. Here we evaluated seven common revegetation techniques by considering both deep soil moisture deficit and soil organic carbon (SOC) sequestration on the Loess Plateau of China, attempting to identify a suitable method for soil restoration of severely degraded ecosystems. The seven revegetation techniques considered were: two single-species shrub plantations (Caragana korshinskii and Hippophae rhamnoides), two single species tree plantations (Platycladus orientalis with terracing and Robinia pseudoacacia), and three mixed plantations (P. orientalis/H. rhamnoides with terracing, R. pseudoacacia/H. rhamnoides, R. pseudoacacia/P. orientalis). A 12-year-old abandoned cropland served as the control. The results showed that the single-species plantation of P. orientalis with terracing had the lowest soil moisture deficit in deep layers (200-800 cm) but also had the lowest SOC sequestration. In contrast, the mixed plantation of R. pseudoacacia/H. rhamnoides had the highest SOC sequestration but also had significant deep soil moisture deficit. In contrast, the mixed plantation of P. orientalis/H. rhamnoides with terracing showed near-zero deep soil moisture deficit and significant, positive SOC sequestration. Therefore, this mixed plantation was identified as representing a suitable revegetation technique for this region. The results here suggest that appropriate mixed tree/shrub plantations with appropriate land engineering measures could deliver effective soil restoration in such environments. Our results provide an insight into revegetation in areas with degraded land