Changes in sediment discharge in a sediment-rich region of the Yellow River from 1955 to 2010: implications for further soil erosion control

The well-documented decrease in the discharge of sediment into the Yellow River has attracted considerable attention in recent years. The present study analyzed the spatial and temporal variation of sediment yield based on data from 46 hydrological stations in the sediment-rich region of the Yellow River from 1955 to 2010. The results showed that since 1970 sediment yield in the region has clearly decreased at different rates in the 45 sub-areas controlled by hydrological stations. The decrease in sediment yield was closely related to the intensity and extent of soil erosion control measures and rainstorms that occurred in different periods and sub-areas. The average sediment delivery modulus（SDM） in the study area decreased from 7,767.4 t/（km^2·a） in 1951–1969 to 980.5 t/（km^2·a） in 2000–2010. Our study suggested that 65.5% of the study area with the SDM below 1,000 t/（km^2·a） is still necessary to control soil deterioration caused by erosion, and soil erosion control measures should be further strengthened in the areas with the SDM above 1,000 t/（km^2·a）.

Decoupling effects of driving factors on sediment yield in the Chinese Loess Plateau

Investigations of runoff and sediment yield changes and their relationships with potential driving factors provide good insights for understanding the mechanisms of hydrological processes.This study attempted to present a comprehensive investigation on the spatiotemporal variations of sediment yield in the Loess Plateau using continuous observed data at 46 hydrological stations during 1961-2016,and its responses to changes of precipitation,land use/cover and vegetation cover were analyzed by using the Partial Least Squares-Structural Equation Model(PLS-SEM).The results indicated that sediment yield reduced pro-nouncedly during 1961-2016 in the Loess Plateau,and 77.9%of this variation was explained by the combined effects of precipitation,land-use change,vegetation dynamics and runoff reduction.Indirect effects of precipitation,land-use change,and vegetation cover on sediment yield were 0.242,-0.528 and-0.630(P<0.05),respectively,and direct effect of runoff on sediment yield was 0.833(P<0.05).According to the Pearson Correlation Coefficient,the strongest positive correlation existed between annual sediment yield and runoff(r=0.88,P<0.05),followed by vegetation cover(r=-0.47,P<0.05)and land-use change(i.e.forest land and grassland)suggesting their significant trapping effects on soil erosion.However,lower correlations were examined between sediment yield and precipitation indices(-0.14<r<0.34),and a relatively higher relationship was examined between sediment yield and heavy rainfall(P_(25))(r=034).Overall,changes in runoff and land-use/vegetation cover well explained varia-tions in sediment yield in the Loess Plateau.The findings are expected to provide scientific and technical support for future soil and water conservation planning in the Loess Plateau,and are valuable for sus-tainable water resources and sediment load management in the Yellow River Basin.

Gully erosion and expansion mechanisms in loess tablelands and the scientific basis of gully consolidation and tableland protection

Gully erosion is serious in the tableland area of the Loess Plateau due to high-intensity human activities and extreme rainfall, which cause serious soil loss and an increasing tableland shrinkage rate. Severe gully erosion has exerted a notable negative impact on local agriculture, human life and socioeconomic development. In recent decades, progress has been made in soil and water conservation with the goal of reducing soil erosion and protecting loess tableland, but basic research on gully consolidation and tableland protection(GCTP) is lacking, especially regarding the mechanisms of gully erosion and expansion in loess tableland under the interactive impacts of hydrodynamics and human activities. In addition, there is a lack of a deep understanding of the underlying mechanisms of soil-water disasters and controlling factors of unreasonable GCTP projects.Currently, the problems of headcut erosion and tableland fragmentation remain serious. Based on this situation, the Dongzhi tableland, the largest tableland on the Loess Plateau, was adopted as an example, and we studied gully erosion and expansion mechanisms in the loess tableland and the scientific basis of GCTP projects. We obtained a series of novel findings, including the following:(1) vertical joints are widely developed in loess and impose a controlling effect on tableland edge erosion;(2) rapid urbanization and road network expansion intensify headcut erosion and are the main reasons for severe erosion and tableland shrinkage in the Dongzhi tableland;and(3) unreasonable drainage of surface runoff and a rise in the groundwater level are the key factors affecting GCTP project stability. Moreover, the mechanisms and modes of erosion disasters in the project driven by these two factors were explained. The systematic remediation idea of retention, storage, drainage and consolidation for the GCTP project was introduced, and the core is water control, which emphasizes the combination of soil and water conservation and geohazard prevention measures. As a systematic remediation project, GCTP in loess tableland requires multidisciplinary and multimethod approaches and multiple measures involving ecology, soil and water conservation, geology and engineering to ensure project feasibility and sustainability.

Explaining the evaporation paradox in Jiangxi Province of China:Spatial distribution and temporal trends in potential evapotranspiration of Jiangxi Province from 1961 to 2013

Evaporation acts as an important component and a key control factor in land hydrological processes.In order to analyze the trend of change on potential evapotranspiration from 1961 to 2013 and to discuss the existence of the evaporation paradox in Jiangxi province,China,monthly meteorological data spanning the years 1961–2013 were analyzed in this study,where the data were collected from 15 national meteorological stations in Jiangxi Province.The Penman–Monteith equation was employed to compute the potential evapotranspiration(ET0).Spatial interpolation and data mining technology were used to analyze the spatial and temporal changes of ET0 and air temperature,with the effort to explain the evaporation paradox.By solving the total differential and the partial derivatives coefficients of the independent variables in Penman–Monteith equation,the cause of the paradox was quantitatively evaluated.The results showed that the annual ET0 had been decreasing significantly in Jiangxi Province since 1979,whereas the air temperature had been rising significantly,presenting the evaporation paradox.The decreases in sunshine duration and wind speed reduced ET0 by 0.207 mm and 0.060 mm,respectively,accounting for 92.3%and 26.7%of the total ET0,respectively.It is concluded that sunshine duration and wind speed are the main causes to the decrease in potential evapotranspiration in Jiangxi Province.