Mediation effect as the component to ecosystem? Establishing the chain effect framework of ecosystem services across typical karst basin in China

Ecosystem services exist trade-off or synergistic relationships. Ignoring the relationship between ecosystem services can lead to the decline for the supply of ecosystem services, and even threaten ecosystem security. However, the chain effect of multiple ecosystem services is not very sufficient. Therefore, this study took Sancha River Basin (SRB), China, as the study area, simulating the important ecosystem services including surface runoff, sediment yield, and net primary productivity (NPP), analyzing the characteristic, influence factors and chain effect of ecosystem services using geostatistical methods from 1999 to 2018. The results showed trade-off and synergistic relationships between sediment yield, surface runoff and NPP. Elevation and lithology were sensitive factors affecting the spatial relationship of ecosystem service variables, and the highest explanatory power of interaction exceeded 15 %. In the SRB, sediment yield as the mediation variable indirectly affected the change of the relationship between surface runoff and NPP, the mediation effect was 12.50 %. Under different gradients of sensitive factors, the mediation effects of ecosystem service variables differed. When the elevation exceeded 1600 m, the mediation effect increased with the increase of elevation. For the mediation effect divided by the lithological gradient from 1999 to 2018, the mediation effect of interbedded dolomite and clastic rocks was the highest, with more than 40 %. We suggest that karst ecological protection strategy should comprehensively consider the chain relationship between multiple ecosystem services led by diverse natural environmental factors, which can make scientific decisions under the regional sustainable development framework.