Guoce Xu

Capacity of soil loss control in the Loess Plateau based on soil erosion control degree

The capacity of soil and water conservation measures, defined as the maximum quantity of suitable soil and water conservation measures contained in a region, were determined for the Loess Plateau based on zones suitable for establishing terraced fields, forestland and grassland with the support of geographic information system (GIS) software. The minimum possible soil erosion modulus and actual soil erosion modulus in 2010 were calculated using the revised universal soil loss equation (RUSLE), and the ratio of the minimum possible soil erosion modulus under the capacity of soil and water conservation measures to the actual soil erosion modulus was defined as the soil erosion control degree. The control potential of soil erosion and water loss in the Loess Plateau was studied using this concept. Results showed that the actual soil erosion modulus was 3355 t∙km–2∙a–1, the minimum possible soil erosion modulus was 1921 t∙km–2∙a–1, and the soil erosion control degree was 0.57 (medium level) in the Loess Plateau in 2010. In terms of zoning, the control degree was relatively high in the river valley-plain area, soil-rocky mountainous area, and windy-sandy area, but relatively low in the soil-rocky hilly-forested area, hilly-gully area and plateau-gully area. The rate of erosion areas with a soil erosion modulus of less than 1000 t∙km–2∙a–1 increased from 50.48% to 57.71%, forest and grass coverage rose from 56.74% to 69.15%, rate of terraced fields increased from 4.36% to 19.03%, and per capita grain available rose from 418 kg∙a–1 to 459 kg∙a–1 under the capacity of soil and water conservation measures compared with actual conditions. These research results are of some guiding significance for soil and water loss control in the Loess Plateau.

Spatial variability of soil organic carbon in a typical watershed in the source area of the middle Dan River, China

Soil organic carbon (SOC) plays an important role in maintaining and improving soil fertility and quality, in addition to mitigating climate change. Understanding SOC spatial variability is fundamental for describing soil resources and predicting SOC. In this study, SOC content and SOC mass were estimated based on a soil survey of a small watershed in the Dan River, China. The spatial heterogeneity of SOC distribution and the impacts of land-use types, elevation, slope, and aspect on SOC were also assessed. Field sampling was carried out based on a 100 m by 100 m grid system overlaid on the topographic map of the study area, and samples were collected in three soil layers to a depth of 40 cm. In total, 222 sites were sampled and 629 soil samples were collected. The results showed that classical kriging could successfully interpolate SOC content in the watershed. Contents of SOC showed strong spatial heterogeneity based on the values of the coefficient of variation and the nugget ratio, and this was attributed largely to the type of land use. The range of the semi-variograms increased with increasing soil depth. The SOC content in the soil profile decreased as soil depth increased, and there were significant (P   forestland > cropland. Mean SOC masses of grassland, forestland, and cropland at a depth of 0–40 cm were 5.87, 5.61, and 5.07 kg m–2, respectively. The spatial variation of SOC masses under different land-use types was significant (P < 0.05). ANOVA also showed significant (P < 0.05) impact of aspect on SOC mass in soil at 0–40 cm. Soil bulk density played an important role in the assessment of SOC mass. In conclusion, carbon in soils in the source area of the middle Dan River would increase with conversion from agricultural land to forest or grassland.

Effects of freeze-thaw on soil erosion processes and sediment selectivity under simulated rainfall

The freeze-thaw (FT) processes affect an area of 46.3% in China. It is essential for soil and water conservation and ecological construction to elucidate the mechanisms of the FT processes and its associated soil erosion processes. In this research, we designed the control simulation experiments to promote the understanding of FT-water combined erosion processes. The results showed that the runoff of freeze-thaw slope (FTS) decreased by 8% compared to the control slope (CS), and the total sediment yield of the FTS was 1.10 times that of the CS. The sediment yield rate from the FTS was significantly greater than that from the CS after 9 min of runoff (P<0.01). Both in FTS and CS treatments, the relationships between cumulative runoff and sediment yield can be fitted well with power functions (R2>0.98, P<0.01). Significant differences in the mean weight diameter (MWD) values of particles were observed for washed particles and splashed particles between the CS and the FTS treatments in the erosion process (P<0.05). The mean MWD values under CS were smaller than those under FTS for both washed and splashed particles. The ratio of the absolute value of a regression coefficient between the CS and the FTS was 1.15, being roughly correspondent with the ratio of K between the two treatments. Therefore, the parameter a of the power function between cumulative runoff and sediment yield could be an acceptable indicator for expressing the soil erodibility. In conclusion, the FTS exhibited an increase in soil erosion compared to the CS.

Variations in runoff and sediment in watersheds in loess regions with different geomorphologies and their response to landscape patterns

In this study, two typical watersheds, i.e., the Dalihe watershed in the loess hilly–gully region of, and the Hailiutuhe watershed in the windy–sandy region of the Wudinghe Basin, were selected as study objects to evaluate the relationship between landscape indices and runoff and sediment, with the long-series data of runoff, sediment, and land use, using the GIS and Fragstats platforms. The results showed that between two watersheds showed that all of the contagion index, Shannon’s diversity index, and patch cohesion index exhibited an ascending trend in the Dalihe watershed, and a descending trend in the Hailiutuhe watershed. In the Dalihe watershed, only Shannon’s diversity index had a very significantly negative correlation with the runoff, whereas in the Hailiutuhe watershed, the contagion index had a significantly negative correlation with the runoff, and all of the Shannon’s diversity index, the Shannon’s evenness index, and the Simpson’s evenness index had a significantly positive correlation with the runoff. In respect of correlation of sediment with landscape pattern, the sediment had a very significantly negative correlation only with Shannon’s diversity index in the Dalihe watershed, whereas in the Hailiutuhe watershed, the sediment had a significantly negative correlation with all of the number of patches, the patch density, and the landscape shape index, and a very significantly positive correlation with the aggregation index. The importance of each landscape index in the regression equation and the positive or negative correlations indicated that erosion in watersheds could be reduced by strengthening the control function of the dominant patch, thoroughly improving the evenness of the landscape patch types, enriching the landscape types, reducing the physical connectivity between patches, and enhancing the degree of aggregation in landscape patches.

Distribution of soil organic carbon impacted by land-use changes in a hilly watershed of the Loess Plateau, China

Vegetation restoration, terrace and check dam construction are the major measures for soil and water conservation on the Loess Plateau. These effective measures of stabilizing soils have significant impacts on soil organic carbon (SOC) distribution. However, following ecological construction, whether the hilly watershed acts as a source or a sink of soil carbon is still unknown. To understand the impact of land-use changes combined with check dam construction on SOC distribution, 1060 soil samples were collected from a 100 cm soil profile across a watershed on the Loess Plateau. The soils in the 0-20 cm layer had a higher SOC concentration than those of the 20-40, 40-60, 60-80 and 80-100 cm layers. Forestland, shrubland and terrace had significant higher SOC concentrations in the 0-20 cm soil layer than that of sloping cropland and dammed farmland (p < 0.05). SOC densities (0-100 cm) in terrace, forestland, shrubland, grassland, sloping cropland and dammed farmland were 12.09, 11.99, 11.89, 11.77, 11.41 and 10.11 kg m-2, respectively. These estimations suggested that SOC was redistributed in the watershed through land-use changes. Topographical factors, including altitude, aspect and slope had impacts on SOC concentrations. The application of hydrological controls to hillslopes and along river channels should be considered when assessing carbon sequestration within the soil erosion subsystem.

Spatial and temporal stability of temperature in the first-level basins of China during 1951–2013

In recent years, global warming has attracted great attention around the world. Temperature change is not only involved in global climate change but also closely linked to economic development, the ecological environment, and agricultural production. In this study, based on temperature data recorded by 756 meteorological stations in China during 1951–2013, the spatial and temporal stability characteristics of annual temperature in China and its first-level basins were investigated using the rank correlation coefficient method, the relative difference method, rescaled range (R/S) analysis, and wavelet transforms. The results showed that during 1951–2013, the spatial variation of annual temperature belonged to moderate variability in the national level. Among the first-level basins, the largest variation coefficient was 114% in the Songhuajiang basin and the smallest variation coefficient was 10% in the Huaihe basin. During 1951–2013, the spatial distribution pattern of annual temperature presented extremely strong spatial and temporal stability characteristics in the national level. The variation range of Spearman’s rank correlation coefficient was 0.97–0.99, and the spatial distribution pattern of annual temperature showed an increasing trend. In the national level, the Liaohe basin, the rivers in the southwestern region, the Haihe basin, the Yellow River basin, the Yangtze River basin, the Huaihe basin, the rivers in the southeastern region, and the Pearl River basin all had representative meteorological stations for annual temperature. In the Songhuajiang basin and the rivers in the northwestern region, there was no representative meteorological station. R/S analysis, the Mann-Kendall test, and the Morlet wavelet analysis of annual temperature showed that the best representative meteorological station could reflect the variation trend and the main periodic changes of annual temperature in the region. Therefore, strong temporal stability characteristics exist for annual temperature in China and its first-level basins. It was therefore feasible to estimate the annual average temperature by the annual temperature recorded by the representative meteorological station in the region. Moreover, it was of great significance to assess average temperature changes quickly and forecast future change tendencies in the region.

Comparing watershed afforestation and natural revegetation impacts on soil moisture in the semiarid Loess Plateau of China

Two contiguous watersheds in the Loess Plateau in China that differed in the way their vegetation had been restored—afforestation or natural revegetation—differed in their consumption of soil moisture: the afforested watershed consumed more soil moisture, although the difference was significant only in wet years. Yet, both the afforestation and natural revegetation did not induce the soil desiccation in the study area. In the afforested watershed, soil moisture was depleted even beyond a depth of 100 cm, whereas in the grassland (natural revegetation), the depletion was confined to a layer less than 60 cm deep. Rainfall in the growing season accounted for 46–60% of the variation in soil moisture in the 0–60 cm layer in the grassland, but only 22–39% of that in the forest land. Overall, afforestation is the better option for the Loess Plateau only in areas where the annual rainfall is more than 500 mm. In any attempt at revegetation, the choice of tree species and planting densities should match the carrying capacity of the region’s water resources.