Search

Abstract The adjustment of land use can alter the near soil surface characteristics and thus likely affects soil erodibility. However, few studies have been carried out to assess the variations in soil erodibility under different land uses on the Loess Plateau after many slope farmlands have been converted to green lands in the past several decades. This study was conducted to quantify comprehensively the effects of five typical land uses (cropland, orchard, grassland, shrubland and woodland) on soil erodibility based on soil cohesion (Coh), saturated conductivity (K s), the number of drop impact (NDI), the mean weight diameter of soil aggregates (MWD), soil penetration resistance (PR) and soil erodibility K factor from different aspects, as well as a comprehensive soil erodibility index (CSEI) produced by a weighted summation method. The results showed that Coh of grassland, K s of woodland, and MWD and NDI of shrubland were the maximum, while PR of woodland and K of shrubland were the minimum among five tested land uses. Soil erodibility (reflected by CSEI) of shrubland was the minimum, while cropland had the maximum CSEI. Compared to cropland, soil erodibility decreased by 15.5%, 53.0%, 77.2% and 59.6% for orchard, grassland, shrubland and woodland, respectively. The variation in soil erodibility under different land uses was closely related to near soil surface characteristics. Soil erodibility increased with soil bulk density, and decreased with biological soil crust thickness, organic matter content, plant litter density, and root density. The results are helpful for optimizing spatial planning and improving eco-environment on the Loess Plateau. Highlights • The adjustment of land use altered near soil surface characteristics greatly. • Soil erodibility decreased significantly with vegetation restoration. • Near soil surface characteristics affected soil erodibility significantly. [ABSTRACT FROM AUTHOR]

Abstract Terraces and check-dam construction are widely used to control soil and water on the Loess Plateau, China. However, it is not known whether dam fields behave as soil phosphorus sources or sinks. This study quantitatively assessed the effects of check-dam and terrace construction on soil total phosphorus (STP). It also investigated the factors that influenced STP. A total of 1010 soil samples (five land uses and five soil depths) were collected in a small watershed on the Loess Plateau. The probability density function of the Weibull distribution was used to analyze the STP sources on the dam field land. The results showed that the highest STP concentration was recorded in the dam field land. Furthermore, the STP concentration mean values for the five land-use types decreased in the following order: dam field > terraced land > grassland > forestland > sloping cropland. The highest clay content value was also recorded in the dam field land. Soil total phosphorus was significantly and positively correlated to soil organic carbon (SOC), but negatively correlated to sand content (P < 0.01) in all areas. Across the entire soil profile down to 60 cm depth, the STP levels for the five land-uses were dam field, 2.78 kg/m2; terrace, 2.86 kg/m2; grassland, 2.98 kg/m2; forestland, 2.84 kg/m2; and sloping cropland, 2.83 kg/m2. The percentage contributions made by the four land use types to the soil total phosphorus deposited in the dam field were 50% (sloping cropland), 33% (grassland) and 17% (forestland). Therefore, check dam constructions behave as a sink for soil phosphorus on the Loess Plateau, China. Highlights • Relatively high sampling density and sampling depth study on the Loess Plateau, China • Dam field and terraced land showed significantly higher STP than the other three land uses. • The STP deposited in dam field land across the watershed mainly came from sloping cropland. [ABSTRACT FROM AUTHOR]

Soil moisture plays a fundamental role in eco-hydrological processes in the semi-arid Loess Plateau. Catchments on the Loess Plateau can be generally divided into the hillslope domain and gully domain. However, the soil moisture variations linked to topographic domains and land use types remain poorly understood. Therefore, in this study, differences in soil moisture among three typical land use types (forestland, native grassland, and farmland) were investigated and compared between the spatial domains of hillslope and gully in the Jiegou catchment on the semi-arid Loess Plateau of China. Additionally, the spatial variations in the soil moisture of the 0–100 cm layers were explored in both wet and dry periods to evaluate the seasonal effects of different spatial domains and land use types. The results showed that including gully soil moisture weakly increased the spatially averaged soil moisture in the catchment but obviously increased the variability during wet periods. In contrast, the spatial means decreased weakly while the variability obviously decreased during dry periods. Soil moisture in forestland was lower than that in native grassland and farmland at all spatial domains during both wet and dry periods. The results also indicated that surface soil moisture (0–10 cm) differs between spatial domains but not land use types, which mainly due to the differences of evapotranspiration on the two topographic domains. In contrast, deep soil moisture (80–100 cm) differs among land use types but not spatial domains, which because of the differences of root water uptake among land use types. In addition, slope aspect played a more important role than slope gradient and elevation in the distribution of soil moisture at the hillslope domain. This was because the slope aspect affected the ground temperature by receiving different solar radiation, and further affected the soil evaporation and vegetation transpiration. Therefore, the results of this study indicates that both topographic domains and land use types should be considered when attempting to characterize soil moisture variability or modelling surface hydrological processes at catchment scale in heavily gullied regions. [ABSTRACT FROM AUTHOR]

Reduced streamflow is a major concern in the Haihe river basin, which supplies water for agriculture, industry and the growing population along the river. The upper Sang-kan (USK) river basin is the headwater of the Haihe river. To understand the drivers of streamflow change in this basin, effects of land use change and climate variability on temporal flow variability were studied using the Soil and Water Assessment Tool (SWAT). The calibration and validation results of the Scenario 0 ( S 0) model (with land use of 1986 and climate derived from 1979 to 1990) indicated that SWAT simulated monthly streamflow well. This was indicated by the Nash–Sutcliffe model efficiency ( NS ) and the Coefficient of Correlation ( r 2 ) for monthly flow, which were 0.89 and 0.91 for the calibration period (1981–1985) and 0.79 and 0.82 for the validation period (1986–1990), respectively. After calibration and validation of the SWAT model ( S 0), three different scenarios were simulated and compared in order to study the effects: Scenario 1 (land use of 2000 and climate during the 1979–1990 period, abbreviated as S 1), Scenario 2 (land use of 2012 and climate during the 1979–1990 period, abbreviated as S 2), and Scenario 3 (land use of 2012 and climate during the 2001–2012 period, abbreviated as S 3). By comparing the simulated hydrological results of S 0 vs. S 1 and S 2, and S 2 vs. S 3, and the annual changes in water use, it can be concluded that the recent perennial drought in the USK river has mainly been caused by human activities; warmer temperatures and less rainfall resulted in streamflow declining by 39.1%, while land use changes and the accompanied water use change for irrigation resulted in surface runoff increasing by 37.6% and streamflow increase between 2.2% and 3.9%, during the period of 1986–2012; increasing ground water and surface water usage for urbanization, industrialization, and reservoir constructions can be attributed from 63.1% to 64.8% of the perennial drought in USK river in recent years. The hydrological simulations provided a better understanding of streamflow changes in the USK basin. The study results can be helpful to maintain ecosystem services and sustainable water use in this region and in the Haihe River basin. [ABSTRACT FROM AUTHOR]

Soil water content (SWC) is a critical variable in studies of hydrological processes and the soil–plant–atmosphere continuum, especially in arid and semi-arid regions such as the Loess Plateau. Knowledge of the effects of vegetation types on soil water dynamics would aid in understanding the mechanisms responsible for water shortages and addressing the problem of poor long-term vegetation recovery. To evaluate the response of soil water storage (SWS) to different land use types during long-term natural vegetation succession, we examined soil moisture under different land use types (grassland, shrubland and forestland) at different times (2005 and 2014) in the Ziwuling forest region, located in the central part of the Loess Plateau, China. Our results showed that vegetation type had a significant effect on SWS in the 0–500 cm soil layer. The SWS in grassland and shrubland was significantly higher in August 2014 than in August 2005, but the pattern was reversed for forestland. In the same year, the SWS was highest in grassland, intermediate in shrubland, and lowest in forestland. SWS and SWC showed a highly significant and positive relationship in the 0–60 cm soil layers ( P < 0.01), and both soil bulk density (BD) and soil total nitrogen (TN) showed a significant relationship with SWS. In addition, the SWC and soil total porosity (TP) showed a significant positive relationship in the 0–20 cm soil layer ( P < 0.05). These results are expected to provide insights into land water management and inform efforts to estimate the productivity and sustainability of semiarid ecosystems. [ABSTRACT FROM AUTHOR]

Prehistoric land use at the Guobei site and its relationship with the local environment are examined by applying OSL dating, micromorphological examination and geo-physical analysis. The majority of the OSL dates are of early to middle Holocene ages and are thus comparable to many OSL dates derived from other studies in the same region. According to the particle size analysis, silt-sized particles (2–60 μm) were predominant throughout the profiles examined. However, there are spatial and temporal variations of different size groups of particles throughout the profiles, which provide complementary information for the micromorphological interpretation. The total organic component of the samples examined through LOI is relatively high (all > 2%), with those of the overlying Holocene deposits higher than those of the underlying Malan loess by about 0.2%. Moreover, in all three profiles, the highest organic contents appear in the palaeosols, confirming that there was greater organic accumulation during soil formation periods. The groundmass of most slides collected from the early to middle Holocene horizons displays a very homogeneous pattern, while the abundance and distribution of different kinds of pedo-features, mainly including clay textural, calcitic, iron/Mn and crustal features, vary greatly temporally and spatially. These different lines of information demonstrate diversified pedo/sedimentary processes due to variations in micro-environmental conditions and cultural activities. We discuss the importance of a palaeo-ecological perspective, allowed by the geoarchaeological study, to an improved understanding of the relationship between loess, changing hydrology, prehistoric farming practice and land use, and long-term landscape change in the Chinese Loess area. This will thus contribute to a comparison on the dynamic relationship between loess and prehistoric farming in other regions of the world such as Europe and North America. [ABSTRACT FROM AUTHOR]

In the last 30 years, a number of large-scale multi-ecological projects have been implemented on the Chinese Loess Plateau, where there has been a significant trend toward ecological restoration, which will certainly affect the spatial distribution of soil cabon sequestration. We investigated 180 topsoil sites (to 20 cm depth) to enhance the understanding of the spatial patterns of soil organic carbon (SOC) and its dominant influencing factors in the Luoyugou watershed (72 km 2 ), which is a typical watershed in the gully-hill area of the Loess Plateau, China. The results indicate that the SOC in the Luoyugou watershed follows a distinct spatial pattern, whereby the SOC increases as altitude increases. The SOC of the mountain ridge area (high elevation area) is measurably higher than that of the sides of the valley. Four spatially interpolated methods (IDW, Ordinary Kriging, land use types and multiple linear regression) were used to express the SOC spatial patterns, but all of them have low estimate accuracy because the SOC in the hilly loess area is highly heterogeneous given the complex topography and land use/cover. The estimate accuracy should improve with the Normalized Difference Vegetation Index (NDVI), given auxiliary information. SOC in the Luoyugou watershed is influenced by altitude, land use, and NDVI. Altitude has a significant relationship with SOC in the Luoyugou watershed. Annual precipitation significantly increases with increased altitude, and land use/vegetation cover changes between terraced cropland, orchard to grassland, and woodland. The SOC of Luoyugou has no significantly correlated relationship to topographic indices (slope, upslope area, and TWI), which have been profoundly disturbed by human activity, particularly by the conversion from sloped land to terraced cropland. The study results show that afforestation can significantly increase SOC. The SOC in immature forests (10 years old) is 17.91% higher than that in terraced cropland, but 32.25% lower than that in 30-year-old forests. The SOC concentration of 30-year-old forest is significant higher than that in other land cover. On a 10-year time scale, orchard is not a good ecological restoration type for increasing SOC; the contribution to enhancing SOC is not obvious and even shows a weak decreasing trend. In general, the SOC sink role of the Loess Plateau is being enhanced by ecological restoration. [ABSTRACT FROM AUTHOR]

Land use and its adjustment may greatly affect soil detachment process by overland flow via altering soil properties, root systems, and tillage operations, but few studies were performed to quantify their effects on soil detachment in the Loess Plateau. This study was conducted to investigate the potential effects of land use on soil detachment capacity by overland flow ( D c , kg m − 2 s − 1 ) using natural undisturbed soil samples taken from four different land uses on the red loess soil and six different land uses on the yellow loess soil, and to quantify the relationships between soil detachment capacity and hydraulic parameters, soil properties, and root systems in the Loess Plateau. The collected samples were tested in a 4.0 m long, 0.35 m wide hydraulic flume under six different shear stresses (5.51–16.59 Pa). The result showed that both soil type and land use had significant effects on D c . For two tested soils, the mean D c of the yellow loess soil was 1.49 times greater than that of the red loess soil. For the red loess soil, D c of cropland was the maximum, which was 5.57, 5.85, and 34.08 times greater than those of shrub land, orchard, and grassland, respectively. For the yellow loess soil, cropland was much more erodible than other five land uses. On average, the ratios of the cropland D c to those of orchard, shrub land, woodland, grassland, and wasteland were 7.14, 12.29, 25.78, 28.45, and 46.43, respectively. The variability of D c under different land uses was closely related to soil properties, root systems, and tillage operations. Soil detachment capacity was positively related to silt content, and inversely related to sand content, cohesion, water stable aggregate, aggregate median diameter, organic matter, and root density. The measured detachment capacity could be well estimated by measurable parameters of stream power, slope gradient, soil bulk density, median diameter, silt content, cohesion, and root density (Nash–Sutcliffe efficiency = 0.89). [ABSTRACT FROM AUTHOR]

The Revised Universal Soil Loss Equation (RUSLE) was used in conjunction with geographic information system (GIS) mapping to determine the influence of land use and topography on soil erosion on the Loess Plateau during the period 2000 to 2010. The average soil erosion on the Loess Plateau was 15.2tha-1yr-1 in 2000-2010. Most of the Loess Plateau fell within the minimal and low erosion categories during 2000 to 2010. Forest, shrub and dense grassland provided the best protection from erosion, but the decadal trend of reduced soil erosion was greater for the lower vegetation cover of woodland and moderate and sparse grassland. Midslopes and valleys were the major topographical contributors to soil erosion. With slope gradient increased, soil erosion significantly increased under the same land use type, however, significant differences in soil erosion responding to slope gradients differed from land uses. The results indicate that the vegetation restoration as part of the Grain-to-Green Program on the Loess Plateau has been effective. [ABSTRACT FROM AUTHOR]

The soil carbon reservoir is the largest carbon reservoir in terrestrial ecosystems and consists of soil organic and inorganic carbon stocks. Previous studies have mainly focused on the soil organic carbon (SOC) stock, and limited information is available about the soil inorganic carbon (SIC) stock. The Chinese Loess Plateau (CLP), which is located in the arid and semi-arid region of China, is an important inorganic carbon reservoir, with a thick soil layer that is rich in calcium carbonate. However, there are few reports on the SIC stock and its spatial distribution in this region. In the current study, the SIC densities and stocks for various soil types and land use patterns were evaluated based on 495 profiles with 2470 soil samples across the CLP, which were collected from the Chinese Second National Soil Survey. The results showed that in the top 1m of soil across the CLP, the average SIC density is 17.04kg/m², and the total SIC stock is approximately 10.20 Pg C (1 Pg=1015g). The SIC stock of the CLP accounts for approximately 18.4% of the total SIC stock throughout China. The average values of the SIC stock in the 0-20, 20-50 and 50-100cm depths of the CLP are 2.39, 2.92 and 4.89 Pg, respectively. Under different land use patterns, the order of the average SIC density is farmland≈grassland > forest in all soil layers. For the various soil types, the SIC density in the 0-100cm layer is the highest in alkaline soil and lowest in subalpine meadow soil, whereas the SIC stock is highest in loessial soil, eolian sandy soil and sierozem, and the lowest in subalpine meadow soil. These differences are largely a result of the area occupied by each soil type and the climate conditions. The results of this study provide basic information about carbon reservoir in China and contribute to our understanding of the SIC stock on the CLP as it relates to the carbon balance of terrestrial ecosystems. [ABSTRACT FROM AUTHOR]