Sustainability of soil organic carbon in consolidated gully land in China's Loess Plateau

Massive gully land consolidation projects, launched in China's Loess Plateau, aim to restore 2667 km(2) agricultural lands in total by consolidating 2026 highly eroded gullies. This effort represents a social engineering project where the economic development and livelihood of the farming families are closely tied to the ability of these emergent landscapes to provide agricultural services. Whether these 'time zero' landscapes have the resilience to provide a sustainable soil condition such as soil organic carbon (SOC) content remains unknown. By studying two watersheds, one of which is a control site, we show that the consolidated gully serves as an enhanced carbon sink, where the magnitude of SOC increase rate (1.0 g C/ m(2)/ year) is about twice that of the SOC decrease rate (- 0.5 g C/ m(2)/ year) in the surrounding natural watershed. Over a 50-year co-evolution of landscape and SOC turnover, we find that the dominant mechanisms that determine the carbon cycling are different between the consolidated gully and natural watersheds. In natural watersheds, the flux of SOC transformation is mainly driven by the flux of SOC transport; but in the consolidated gully, the transport has little impact on the transformation. Furthermore, we find that extending the surface carbon residence time has the potential to efficiently enhance carbon sequestration from the atmosphere with a rate as high as 8 g C/ m(2)/ year compared to the current 0.4 g C/ m(2)/ year. The success for the completion of all gully consolidation would lead to as high as 26.67 Gg C/ year sequestrated into soils. This work, therefore, not only provides an assessment and guidance of the long-term sustainability of the 'time zero' landscapes but also a solution for sequestration CO2 into soils.