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Understanding the characteristics of the precipitation-use efficiency (PUE) of grassland ecosystems and its drivers is critical for predicting how ecosystem functions will respond to future climate change. In this study, we investigated several covarying biotic and abiotic factors (e.g., biomass, coverage, diversity, precipitation, temperature, and humid index (HI)) of 81 sites across a broad natural grassland gradient in the Loess Plateau of China to determine how PUE changes along a precipitation gradient and to assess the effects of biotic and abiotic factors on PUE. Our results showed that HI, below-ground biomass (BGB), vegetation coverage, and species diversity were the most important biotic factors in controlling PUE. HI had a higher positive indirect effect on PUE mainly through its influence on community characteristics. Our results suggest that precipitation and community characteristics are both important for the precipitation-use efficiency of natural grasslands across the arid and semiarid areas of the Loess Plateau. Additionally, improving the vegetation structure and increasing species diversity can help enhance the adaptability of grassland ecosystems to climate change. [ABSTRACT FROM AUTHOR]

Understanding the link between extreme precipitation and changes in runoff and sediment yield is of great significance for regional flood disaster response and soil and water conservation decision-making. This study investigated the spatial and temporal distribution of extreme precipitation (characterized by 10 extreme precipitation indices recommended by the Expert Team on Climate Change Detection and Indices) in the Toudaoguai–Longmen section of the middle Yellow River from 1960 to 2021 and quantified the effects of extreme precipitation on runoff and sediment yield based on the method of partial least squares regression (PLSR). The extreme precipitation index showed an obvious upward trend in the last 20 years, with the increases in the central and northern regions (upstream) being stronger than the increase in the southern region (downstream). However, the runoff and sediment yield decreased significantly due to the implementation of large-scale soil and water conservation measures on the Loess Plateau, with average rates of 94.7 million m3/a and 13.3 million t/a during 1960–2021, respectively. The change points of runoff and sediment yield change occurred in 1979. Compared with those in the period from 1960 to 1979, the reductions in runoff and sediment yield in the years 1980–2021 were 52.7% and 70.6%, respectively. Moreover, extreme precipitation contributed 35.3% and 6.2% to the reduction in runoff in the 1980–1999 and 2000–2021 periods, respectively, and contributed 84.3% and 40.0% to the reduction in sediment yield, respectively. It indicated that other factors (such as large-scale soil and water conservation construction) played main roles in the decrease in runoff and sediment yield in the study area in recent 20 years. [ABSTRACT FROM AUTHOR]

• Sand cover delayed the runoff initiation times; increased soil loss significantly. • Sand cover changed runoff from infiltration- excess to saturation- excess. • Sand mulch on the slope accelerated rill formation and development. 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. [ABSTRACT FROM AUTHOR]

Abstract Revegetation and check dam construction are two widely applied soil erosion control measures on the Loess Plateau of China. They play important roles in sediment yield reduction. However, it remains unclear how these large-scale land-use changes and in-channel structures affect water yield and sediment load on the watershed scale. A combination of field work and modeling exercises were used to quantitatively assess the effects of land-use changes and check dam construction on hydrological processes in the Wuding River watershed. The study area suffered important land-use changes with increases in forestland and grassland, coupled with decreases in cropland, from 1980 to 2010. A large number of check dams were constructed from 1970 to 1980. Runoff and sediment yield in the watershed showed significant decreasing trends (P < 0.01), with change points occurring in the early 1970s. Human activity contributed to 75% and 89% of runoff and sediment changes, respectively. The simulations showed that in a scenario without check dams, runoff and sediment increased by 12% and 11.7%, respectively. Vegetation recovery reduced runoff and sediment yield. 'Grain for Green' resulted in decreasing runoff and sediment levels, and reforestation had more hydrological regulatory effects compared with scenarios involving the conversion of cropland to grassland. Moreover, the combination of revegetation and check dam construction had a greater impact on water yield and sediment transportation. Check dams provide short-term flood control and sediment reductions, whereas land-use changes are long-term sustained soil erosion control measures. It may be more efficient to combine check dam construction with revegetation strategies. Graphical abstract Unlabelled Image Highlights • Check dams decreased runoff and sediment yield by 12% and 11.7%, respectively. • Reforestation resulted in more runoff and sediment reduction than grassland. • Revegetation of slopes and check dam construction should be combined. [ABSTRACT FROM AUTHOR]

Grazing exclusion is often implemented as an effective management practice to increase the sustainability of grassland ecosystems. However, it remains unclear if grazing exclusion can improve ecosystem services related to carbon (C) and nitrogen (N) sequestration in grassland ecosystems. We investigated the effects of 11 years of grazing exclusion on plant biomass and diversity, soil properties (pH, soil water content (SWC), bulk density (BD), soil organic carbon (SOC), total nitrogen (TN), and C/N ratio), and the C and N stocks of plants and soils in a desert grassland of Northwest China. Grazing exclusion improved plant aboveground biomass and diversity, as well as SWC, SOC, and TN contents, but lowered the belowground biomass, root/shoot ratio, pH, and BD. Moreover, grazing exclusion strongly influenced the C and N stocks of the ecosystem, and the annual mean ecosystem C and N sequestration rates were 0.47 and 0.09 Mg ha − 1 yr − 1 , respectively, over 11 years of grazing exclusion. Soil C stocks were most dynamic in the top 30 cm of the soil, and N stocks mainly changed in the top 20 cm after grazing exclusion. Our results indicated that grazing exclusion is an effective measurement on improving the ecosystem C and N pools in desert steppe of Northwest China. [ABSTRACT FROM AUTHOR]

Abstract The seasonal freeze–thaw process affects soil water migration, which influence spring planting, especially in arid and semi-arid regions that cannot be irrigated on the Loess Plateau. This study was conducted to evaluate differences in the freeze–thaw process and water migration between dam farmland (DF) and slope farmland (SF). To accomplish this, two typical agricultural soils (DF and SF), soil water content (SWC) and soil temperature (ST) were monitored at different depths (15, 30, 60 and 90 cm), were investigated under freeze–thaw conditions from November 2015 to April 2016 in the Northwest China. The results showed that different freeze-thaw process between dam farmland (DF) and slope farmland (SF). The DF can keep soil water content resulting from longer frozen period. Thermal transmission between soil and air in SF is greater than that in DF. The SWC values in DF were higher than in SF at each depth layer under similar soil temperature. Migrated and incremental SWC in the DF is greater than that in SF during the freeze-thaw process. The initial SWC is the main impact on freeze–thaw process in this study. This research can provide useful information to guide the water management of seasonally frozen agricultural soil. Graphical abstract Unlabelled Image Highlights • The freeze-thaw process differed between dam farmland (DF) and slope farmland (SF). • The migration and increment of soil water content (SWC) in DF are larger than in SF. • The freeze–thaw process was mainly affected by initial SWC in this environment. [ABSTRACT FROM AUTHOR]

Abstract The sediment-reducing effect of check dams and the safety issues following dam breaks are long-standing concerns. This study analyzed the runoff change and sediment source during rainstorms in a small watershed using a multivariate mixed model and a comparative analysis of watersheds. The problem of sediment loss from dammed farmland following check dam break during rainstorms was evaluated. The results showed that the flood peak lag time (PLT) was significantly influenced by pre-soil moisture in cases of small amounts of rainfall but not during rainstorms. Ecological construction significantly reduced the linear correlation between rainfall and runoff modulus (RM). The reduction in sediment delivery modulus (SDM) due to the check dam was more significant than that in RM. The reduction in RM and SDM under rainstorm conditions were 16%–74% and 53%–93%, respectively. The contributions of inter-gully and gully lands to the sediment deposited in dammed farmland during a large rainstorm on July 26, 2017 were 38.07% and 61.93%, respectively. Soil erosion remained significant during large rainstorms. The increase in vegetation coverage on the hill slope increased the amount of sediment from gully lands. Check dam breaches have accounted for a loss of only 1.2% of the total area of the dammed farmland, and thus have not caused a large loss of sediment. However, breaches in them clearly increased the coefficient of variation of RM and SDM. Therefore, check dams have a critical effect on controlling sediment delivery at the watershed scale. Dam breaks do not result in a large percentage of sediment loss in the dammed farmland. Graphical abstract Unlabelled Image Highlights • We investigate sediment source during heavy rainstorms. • Assess the effects of soil and water conservation measures on runoff and sediment • Examined the changes to check dam breaches [ABSTRACT FROM AUTHOR]

Abstract 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. Graphical abstract Unlabelled Image Highlights • The revegetation and terrace on the slope increased SOC. • SOC distribution was effected by land use changes and check dam. • Topographical factors had impacts on SOC concentrations. [ABSTRACT FROM AUTHOR]

Abstract Surface water quality has a vital role in determining the ecological environment, public health, and social and economic development. This study analyzed the spatial and seasonal differences in surface water quality in the Dan River basin based on three monitoring sections over the period of 2009–2015. The main influencing factors and their contributions to water quality in different seasons were determined using statistical analysis, Hurst exponent and redundancy analysis. Results indicated that vegetation coverage in the Dan River basin increased substantially from 2009 to 2015, particularly forested land. Higher concentrations of major water pollution indicators were recorded in the downstream monitoring sites. Nitrate nitrogen (NN) and total phosphorus (TP) made the largest contributions to the pollution of water quality and indicated spatial and seasonal changes. Lower NN concentrations were more frequent during the summer, whereas TP concentrations were higher during the spring. Thus, the factor making the largest contribution to water quality varied with the season. The contribution of the normalized difference vegetation index (NDVI) to water quality gradually decreased from spring to winter, whereas contributions of land use to water quality gradually increased from spring to winter. Analyses of landscape metrics suggested that patch connectivity was the primary factor influencing water quality in the different seasons. Water level was the main hydrological parameter impacting stream water quality. These results suggested that seasonal differences in the major factors influencing water quality should be taken into account for effective water management. Highlights • The time series of vegetation coverage was a consistent sequence in Dan River. • Factors making the largest contribution to water quality varied with the season. • Patch connectivity was the primary factor influencing water quality. • Water level was the main hydrological parameter impacting stream water quality. [ABSTRACT FROM AUTHOR]

Ren, Z.; Feng Z.; Li, P.; Wang, D.; Cheng, S., and Gong J., 2017. Response of runoff and sediment yield from climate change in the Yanhe watershed, China. In: Zhi, Y. and Guido Aldana, P.A. (eds.), Sustainability of Water Resources and the Development of Coastal Environments: Select Proceedings from the 2016 International Conference on Water Resource and Environment (WRE2016). Journal of Coastal Research, Special Issue No. 80, pp. 30-35. Coconut Creek (Florida), ISSN 0749-0208. Changes in temperature and precipitation in the Loess Plateau, China have been studied for many years. The runoff and sediment yield in the Loess Plateau are sensitive to global climate change. Understanding the characteristics of runoff and sediment will be of great importance in the future. The Soil and Water Assessment Tool (SWAT) was used to simulate the runoff and the sediment yield in the Yanhe watershed, a typical water basin with soil erosion in the Loess Plateau. The resulting statistics of the SWAT simulation of the runoff and sediment yield were acceptable. The rainfall for the period from 2010 to 2099, as predicted by the Statistical Down Scaling Model (SDSM), was used to simulate the runoff and sediment yield in the future, using SWAT. Compared with the period from the 1980 to 2000, the annual precipitation increased by 9.2% to 16.4%. Under simulated future climate change, the annual runoff of the Yanhe watershed changes averaged −2.6% to 52.7%, compared with the baseline period. In the context of future climate change, in general, the runoff distribution was more even within the year when it increased significantly from March to May and decreased from July to August. The variations of the sediment yield for the watershed were −31.3% to 62.5% compare with the period from the 1980 to 2000. Overall, the trends of the sediment yield for the watershed were consistent with the runoff. [ABSTRACT FROM AUTHOR]

Soil respiration is a large carbon flux from terrestrial ecosystems to the atmosphere, and small variations in soil respiration can prominently influence the global carbon (C) cycle. The vegetation changes could directly affect soil respiration. The large-scale "Grain for Green" project carried out on the Loess Plateau, China has importantly affected the contribution of soil respiration to atmospheric carbon dioxide (CO 2). Therefore, it is important to study the effects of vegetation restoration on soil respiration. We selected four land-use types: crop, forest, shrub, and grassland in the Zhifanggou watershed to analyze variation in soil respiration during dry and rainy seasons. Furthermore, the source of CO 2 emissions from soil respiration was identified using isotopes. The results showed that soil respiration in the rainy season was significantly higher than that in the dry season (P <.05). Soil respiration in the dry season was as follows: shrubland (1.04 μmol m−2 s−1) > cropland (0.72 μmol m−2 s−1) > forestland (0.44 μmol m−2 s−1) > grassland (0.33 μmol m−2 s−1). However, grass and forestland had significantly higher soil respiration than shrub and cropland in the rainy season (P <.05). Roots were the main source of soil respiration in cropland, which contributed >70% of CO 2 emissions. Following revegetation, litter contributed more to soil respiration than roots or soil microorganisms at >68% of soil respiration. Our results provide a theoretical basis for assessing C balance in terrestrial ecosystems. Unlabelled Image • Soil respiration in the rainy season was higher than that in the dry season. • Vegetation restoration increased soil respiration in the rainy season. • Roots were the main source of soil respiration in cropland. • Litter was the most important source to soil respiration in the vegetation land. [ABSTRACT FROM AUTHOR]

• Difference erosion process of unfrozen, shallow-thawed and frozen soils under different meltwater flow. • The sediment yield capacity is not a constant value for the two kinds of soil structures. • Runoff energy consumption can well predict soil erosion rate. The processes of rill erosion and overland flow are significantly affected by freeze-thaw cycles. Meltwater concentrated flow laboratory experiments were carried out to assess the soil erosion of different frozen conditions based on the runoff energy consumption process which own to runoff energy against the sediment transportation and terrain evolution. The experiments were performed over frozen, shallow-thawed, and unfrozen soil-filled flumes under 1, 2, and 4 L/min flow rates with the temperature around 5 °C. The results imply that soil erosion became more severe with increasing flow rate. Variation rate of the soil erosion rate of frozen slope was highest under 1 and 2 L/min flow rates due to lower infiltration of water into soil. Variation in runoff energy consumption variation with flow time presented significant differences under unfrozen, shallow-thawed, and frozen slopes at equal runoff rate (p < 0.05). Compared with shallow-thawed and unfrozen slopes, frozen slope displayed the highest runoff energy consumption and sediment yield capacity at the equal flow rate. Sediment yield capacity was constant regardless of soil condition except in shallow-thawed soil. The sediment yield capacity under 4 L/min flow rate was different from that under 1 and 2 L/min flow rates for shallow-thawed slopes. Soil erosion rates were predictable using runoff energy consumption under one soil condition. The results of this research would provide specific implications about meltwater erosion process and hydrodynamic conditions for improving the erosion model. [ABSTRACT FROM AUTHOR]

Revegetation and check dam construction are two widely applied soil erosion control measures on the Loess Plateau of China. They play important roles in sediment yield reduction. However, it remains unclear how these large-scale land-use changes and in-channel structures affect water yield and sediment load on the watershed scale. A combination of field work and modeling exercises were used to quantitatively assess the effects of land-use changes and check dam construction on hydrological processes in the Wuding River watershed. The study area suffered important land-use changes with increases in forestland and grassland, coupled with decreases in cropland, from 1980 to 2010. A large number of check dams were constructed from 1970 to 1980. Runoff and sediment yield in the watershed showed significant decreasing trends, with change points occurring in the early 1970s. Human activity contributed to 75% and 89% of runoff and sediment changes, respectively. The simulations showed that in a scenario without check dams, runoff and sediment increased by 12% and 11.7%, respectively. Vegetation recovery reduced runoff and sediment yield. 'Grain for Green' resulted in decreasing runoff and sediment levels, and reforestation had more hydrological regulatory effects compared with scenarios involving the conversion of cropland to grassland. Moreover, the combination of revegetation and check dam construction had a greater impact on water yield and sediment transportation. Check dams provide short-term flood control and sediment reductions, whereas land-use changes are long-term sustained soil 24 erosion control measures. It may be more efficient to combine check dam construction with revegetation strategies. [ABSTRACT FROM AUTHOR]