Temporal changes in vegetation around a shale gas development area in a subtropical karst region in southwestern China

Abstract

Over the past decade, various aspects of China's fragile karst environments, including net primary productivity (NPP), have been changed or threatened by shale gas development. This industry is still developing, so it is important to understand what drives environmental changes, particularly in NPP, when shale gas pads are constructed in sensitive areas. Few previous studies have addressed this issue, so we quantified how the NPP changed, and what drove the changes, when a large shale gas area was developed at the end of 2012 in a mountainous karst area in Sichuan Province. We calculated the trend in the normalized difference vegetation index (NDVI) from 2012 to 2017 and used the Carnegie-Ames-Stanford Approach (CASA) model to calculate the changes in NPP at different distances from the pads using remote sensing images for July 2012 and July 2017 and field survey data from July 2017. We then identified the factors that drove the changes with Geodetector. The results showed that the NDVI increased across 64.2% of the shale gas development area from 2012 to 2017 because of climate change, and only showed a significant decrease across 0.3% of the area, mainly because of the shale gas development. The NPP decreased by 110.1 t because of the shale gas development in July 2017, or by about 0.35% of the total NPP. Of this, 93.8 t were associated with the pad construction areas, and 16.3 t were associated with the area around the pads. The changes in NPP around the shale gas pads were mainly confined to within 150 m during the construction phase and 90 m once the construction was completed. The NPP at different distances from the pads during the construction period was related to the distance from the pad, slope, and land use. Once completed, the NPP mainly varied with distance, land use, and the distance from the pad to rural settlements. The NPP was most strongly influenced by the distance from the pad and the area of the pad. We suggest that, when planning the construction of shale gas pads, the pads should be sited on gently sloping areas, the number of wells on each pad should be optimized, land use type changes outside the pad should be limited, and the land beyond the pads should be reclaimed in a timely manner to allow the NPP to recover.

Keywords: Distances from the pad; Geodetector; NPP; Shale gas pad development.