Spatiotemporal Evolution Characteristics and Trade-offs/Synergies of Water Yield, Soil Conservation, and Carbon Storage Ecosystem Services in the Beiluo River Basin from 1970 to 2020

This study aimed to investigate the spatiotemporal changes and trade-offs/synergies of ecosystem services within the Beiluo River Basin to provide a scientific foundation for rational resource allocation and sustainable development. Utilizing multi-source data and models, such as InVEST and CSLE, to quantitatively assess and analyze the spatiotemporal variations and trade-offs/synergies of three key ecosystem services—water yield, soil conservation, and carbon storage—across different periods. These periods include the relatively stable land use period from 1970 to 1990, the transitional period around 2000, and the ecological restoration period from 2010 to 2020. This study showed that：1) The overall water yield of the basin initially showed an increasing trend, followed by fluctuating decline, bottoming out in the 2000s. During the first period, the average water yield was 10.16×10⁸ m³ (37.75 mm), which decreased by 36.9% during the second period and by 25.53% during the third period compared to the initial period. Among the three land use types of forests, cropland, and grassland, the total water yield and water yield depth of cropland are always the highest, while the water yield depth of forest was always the lowest. 2) The total soil conservation displayed an upward trend with fluctuations, peaking in the 2010s. Over the first period, the average annual soil conservation was 305.62×10⁶ t (113.57 t/hm²), which increased to 364.52×10⁶ t in the transition period and significantly increased to 426.19×10⁶ t (157.75 t/hm²)during the third period. The soil conservation capacity of forests was significantly greater than that of cropland, and the construction of terraces and other engineering measures have greatly enhanced the function of cropland.3) The total carbon storage remained stable and then continued to increase, with a notable increase from the 2000s onwards, and a 24.09% increase in the 2020s when compared with the 1970s. Forests were the main carbon reservoirs, with their carbon storage significantly increasing, whereas that in grassland and cropland have decreased due to the reduction in their areas.4) Regarding changes in the spatial pattern, the areas experiencing a decrease in water yield and an increase in soil conservation and carbon storage were mainly concentrated in the high plateau and gully areas, as well as the hilly and gully regions. 5) At the basin scale, there was a trade-off between water yield and soil conservation, as well as carbon storage. Soil conservation and carbon storage, however, exhibited a synergistic relationship. The degree of synergy between soil conservation and carbon storage decreased over time, while the trade-off between water yield and the other two remained relatively stable. With the restoration of vegetation, the three key ecosystem service exhibited significant temporal and spatial variation characteristics, possessing relatively stable trade-off and synergistic relationships. The research results can provide a scientific basis for enhancing the comprehensive benefits of ecosystem services on the Loess Plateau.

Keywords: ecosystem services; InVEST Model; CSLE Model; trade-offs and synergies; Beiluo River Basin