Spatiotemporal features of the hydro-biogeochemical cycles in a typical loess gully watershed

Hydrological and biogeochemical processes are essential for material and energy exchange among climate-soil-plant systems and, thus, play an important role in terrestrial ecosystems. In particular, the water-carbon dynamics determine the status and change of ecosystems. Therefore, understanding the spatiotemporal features of the water and carbon cycles is of great importance for watershed ecosystem management. This study employed a newly coupled hydro-biogeochemical model (SWAT-DayCent) to investigate the spatiotemporal characteristics and evolution of the water cycle (evapotranspiration (ET), soil water, and water yield) and carbon cycle (net primary productivity (NPP), soil organic carbon (SOC)) in a typical loess gully watershed (the Jinghe River Basin, JRB) on the Loess Plateau of China during the period of 2000–2010. The satisfactory performance of the coupled model demonstrates that the SWAT-DayCent model is capable of simulating hydro-biogeochemical processes at the watershed scale in the Loess Plateau region. The spatial distributions of hydro-biogeochemical components varied significantly over the JRB—a decreasing gradient from south to north in hydrological variables and NPP, a higher SOC in the western margin than other parts, and a general increasing trend for all the five components in the southeastern part. Temporally, the hydrological variables showed a slightly decreasing trend, the NPP underwent a slight upward trend, but the SOC decreased significantly in the whole basin under the current climate conditions. The correlation analysis between hydrologic components and carbon cycle indicated that the water cycle may have synergies with NPP but may exert little influence on SOC. Overall, our quantitative analyses over time and space can be informative in soil and water conservation practices and ecosystem service enhancement in the JRB specifically and other parts of the Loess Plateau region as well.