Impact analysis of expressway construction on ecological carrying capacity in the Three-River Headwater Region

The construction of expressways has a variety of impacts on the ecologically fragile and sensitive Three-River Headwater Region and causes changes in the structure and carrying capacity of the ecosystem. To assess the impact of expressway construction on the ecological carrying capacity of the regional natural system, net primary productivity (NPP) was used as the quantitative index to indicate the efficiency of the regional ecological environment to fix and transform photosynthesis products. In this study, trend analysis and buffer zone analysis were used to quantitatively analyze the spatial and temporal characteristics of NPP in the study area from 2006 to 2015 based on the MOD17A3/NPP dataset. In addition, the spatial-temporal effects of expressway and interchange construction on NPP in buffer zones were studied using GIS spatial analysis. The summarized results are as follows. (1) The multi-year average NPP in the study area is 137.9 gC/m², indicating a slight downward trend; spatially, the overall NPP shows a downward trend from east to west. (2) The impact of expressway construction on NPP in buffer zones will last for more than two years, generally presenting greater NPP further from the expressway. (3) After completion of the interchange, the NPP decreases significantly within its radiation radius; at a distance of 6 km, the NPP gradually stabilizes. (4) The influence law of expressway construction and interchange construction on NPP is approximately the same in the respective buffer zones.