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The erosion, transport and redeposition of sediments shape the Earth's surface, and a ect the structure and function of ecosystems and society 1,2 . The Yellow River was once the world's largest carrier of fluvial sediment, but its sediment load has decreased by approximately 90% over the past 60 years 3 . The decline in sediment load is due to changes in water discharge and sediment concentration, which are both influenced by regional climate change and human activities. Here we use an attribution approach to analyse 60 years of runo and sediment load observations from the traverse of the Yellow River over China's Loess Plateau -the source of nearly 90% of its sediment load. We find that landscape engineering, terracing and the construction of check dams and reservoirs were the primary factors driving reduction in sediment load from the 1970s to 1990s, but large-scale vegetation restoration projects have also reduced soil erosion from the 1990s onwards. We suggest that, as the ability of existing dams and reservoirs to trap sediments declines in the future, erosion rates on the Loess Plateau will increasingly control the Yellow River's sediment load.Change of soil erosion and the resulting river sediment transport are important components of global change, so understanding the mechanisms behind such change is crucial to developing strategic plans for the sustainable management of catchments 4,5 . In recent decades, significant decreasing trends in river sediment loads have been observed in approximately 50% of the world's rivers 6,7 . The benefits and risks of the change in river sediment load largely depend on the baseline load and the scale of the change 8,9 . Hence, it is important to quantify the change of river sediment loads through time, and to understand the drivers and mechanisms behind them 2,5 .The Huang He, or Yellow River (YR) (Fig. 1), was the most sediment-laden river in the world, but its annual sediment load has continually decreased since the 1950s (refs 10-13). The yearly sediment loads at the main gauging stations along the YR, all show significant decreasing trends (p < 0.01) over the past six decades (Fig. 1b). Sediment load increases most suddenly in the middle reach of the river, when crossing the Loess Plateau (LP), between the Toudaoguai gauging station (TDG) (0.07 Gt yr −1 ) and the Tongguan station (TG) (0.63 Gt yr −1 ), and then gradually declines in the lower reach (Fig. 1b, top right inset). The LP is thus the largest sediment source, nearly 90% (refs 3,11) for the YR, and we therefore focus on this part of the river's catchment. A mass budget over the middle reach of the YR can be obtained from the difference of measured sediment flux and water discharge at TG and TDG (Fig. 1). Both the river discharge and sediment load across the LP show significant decreasing trends (−0.25 km 3 yr −2 , p < 0.001; and −0.02 Gt yr −2 , p < 0.001, respectively) over the past six decades, whereas precipitation decreased slightly (−1.2 mm yr −2 , p = 0.015). As Fig. 2a shows two abrupt falls in sed...

As one of the key tools for regulating human-ecosystem relations, environmental conservation policies can promote ecological rehabilitation across a variety of spatiotemporal scales. However, quantifying the ecological effects of such policies at the regional level is difficult. A case study was conducted at the regional level in the ecologically vulnerable region of the Loess Plateau, China, through the use of several methods including the Universal Soil Loss Equation (USLE), hydrological modeling and multivariate analysis. An assessment of the changes over the period of 2000–2008 in four key ecosystem services was undertaken to determine the effects of the Chinese government's ecological rehabilitation initiatives implemented in 1999. These ecosystem services included water regulation, soil conservation, carbon sequestration and grain production. Significant conversions of farmland to woodland and grassland were found to have resulted in enhanced soil conservation and carbon sequestration, but decreased regional water yield under a warming and drying climate trend. The total grain production increased in spite of a significant decline in farmland acreage. These trends have been attributed to the strong socioeconomic incentives embedded in the ecological rehabilitation policy. Although some positive policy results have been achieved over the last decade, large uncertainty remains regarding long-term policy effects on the sustainability of ecological rehabilitation performance and ecosystem service enhancement. To reduce such uncertainty, this study calls for an adaptive management approach to regional ecological rehabilitation policy to be adopted, with a focus on the dynamic interactions between people and their environments in a changing world.

Restoring disturbed and over-exploited ecosystems is important to mitigate human pressures on natural ecosystems. China has launched an ambitious national ecosystem restoration program called Grain to Green Program (GTGP) over the last decade. By using remote sensing techniques and ecosystem modelling, we quantitatively evaluated the changes in ecosystem carbon sequestration since China's GTGP program during period of 2000–2008. It was found the NPP and NEP in this region had steadily increased after the initiative of the GTGP program, and a total of 96.1 Tg of additional carbon had been sequestered during that period. Changes in soil carbon storage were lagged behind and thus insignificant over the period, but was expected to follow in the coming decades. As a result, the Loess Plateau ecosystem had shifted from a net carbon source in 2000 to a net carbon sink in 2008. The carbon sequestration efficiency was constrained by precipitation, and appropriate choices of restoration types (trees, shrubs, and grasses) in accordance to local climate are critical for achieving the best benefit/cost efficiency.

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a b s t r a c tAs an important part of the strategy of Western development, the Grain-for-Green Program (GFGP) was initiated to protect the environment and mitigate disasters. Ecosystem services and their dynamics are considered emerging features of ecological quality and the change in direction by many scholars and practitioners. Extending from ecosystem services (ESs) modeling, we propose a simple and feasible framework for quantitatively assessing the benefits and equilibrium of the consequences of the GFGP. Our starting evaluation shows that ESs has changed dramatically in the GFGP area. By fitting pair-wise ESs' spatial concordances at the grid-cell level, we have revealed the tradeoffs between provisioning and regulating services and the synergies between the regulating services. The analysis of the variability of the relationship between ESs on different land cover types clearly identifies the vegetation that has produced exceptionally strong ESs. Our findings suggest that quantifying the interactions between ESs may improve the ecosystem-based management practices and support policy-making to address the challenges of the sustainable use of natural resources. The framework designed for regional-scale analysis can help in clearly understanding the interrelations of ESs and make natural resources related decisions more effective and efficient, although this framework still needs to move beyond these fundamental and illustrative analyses to more fully explain the synergies and tradeoffs.

Ecological conservation and restoration are necessary to mitigate environmental degradation problems. China has taken great efforts in such actions. To understand the ecological transition during 2000–2010 in China, this study analysed trends in vegetation change using remote sensing and linear regression. Climate and socioeconomic factors were included to screen the driving forces for vegetation change using correlation or comparative analyses. Our results indicated that China experienced both vegetation greening (restoration) and browning (degradation) with great spatial heterogeneity. Socioeconomic factors, such as human populations and economic production, were the most significant factors for vegetation change. Nature reserves have contributed slightly to the deceleration of vegetation browning and the promotion of greening; however, a large-scale conservation approach beyond nature reserves was more effective. The effectiveness of the Three-North Shelter Forest Program lay between the two above approaches. The findings of this study highlighted that vegetation trend detection is a practical approach for large-scale ecological transition assessments, which can inform decision-making that promotes vegetation greening via proper socioeconomic development and ecosystem management.

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