Impact of mining activities on the degradation of hydro-ecological networks in resource-based cities

Mining activities have posed a great challenge on the landscape patterns and aquatic ecology in the resource-based cities. While existing research focused mainly on the impacts of the mining on the individual aquatic ecological elements. It is still lacking on the aquatic ecological degradation under an integrated "sources-corridors" network. This study aims to explore the impact of the mining activities on the hydro-ecological network evolution in resource-based cities. The field test was conducted in Changzhi City, Shanxi Province, China. A hydro-ecological ecological network was constructed using the Normalized Difference Water Index (NDWI), InVEST 3.8.0, Fragstats 4.2, and water network pattern indices. Its spatiotemporal evolution was then analyzed from 1990 to 2020. Then there were the spatial conflicts between the mining activities and hydro-ecological sources or the river corridors. The structural evolution and functional responses of the ecological network were finally examined under mining disturbance. The results showed that: (1) The hydro-ecological network exhibited the significant spatiotemporal evolution. Hydro-ecological sources were primarily concentrated in the eastern Taihang Mountains and western Taiyue Mountains, with a total area increase of 1 273.14 km². The fragmentation of the landscape decreased generally at regional scale. But there was the high spatial heterogeneity. The expansion of the patch number and increasing shape complexity were dominated in the eastern ecological sources. While the patch area consolidation was reduced the fragmentation in the west. The area of the river corridors increased, with the water surface ratio rising by 4.8%, predominantly in the mining-intensive central-south region. Stream network density attenuation was concentrated in the low-order tributaries, whereas the regulation capacity of the main streams was improved notably. A pattern of the tributary was reduced, whereas the main stream regulation was enhanced. (2) Mining disturbances were triggered a cascading effect on the hydro-ecological sources: "spatial intrusion-structural fragmentation-functional degradation". The overlapping area between mining zones and ecological sources was expanded continuously, with a higher growth rate in the east. This intrusive disturbance was exacerbated the fragmentation within the overlapping zones. The capacity of water conservation was also diminished. Notably, there was the minimal difference of the Normalized Difference Vegetation Index (NDVI) between overlapping zones and the overall ecological sources; Both indicators exhibited an initial decline followed by an increase. This pattern was attributed to the deep coal seams, the coal pillar support techniques, and the ecological projects, like forest tending and degraded forest restoration. (3) Mining activities were imposed the compound stresses on the river corridors: "spatial encroachment-runoff reduction-morphological alteration-connectivity decline". Spatially, 81 mines were overlapped with the river corridors. The highest density was found in the Southern source of the Zhuozhang River, where the runoff attenuation exceeded 30%. Coal mining subsidence areas were altered the river morphology: 15, 21, and 8 subsidence areas were located on the main stems, tributaries, and near-water isolated zones, respectively. The flow directions were altered in the sections of the rivers, like the Taoqing and Jiang Rivers. The flood risk increased in the adjacent areas. While the topological connectivity index of the river network shared an overall increasing trend, local degradation-including channel discontinuity and reduced water conveyance capacity-occurred in the specific river segments. A paradoxical pattern was enhanced the connectivity in the river corridors under mining disturbance. Since mining activities drove the water ecological network degradation, the differentiated strategies were provided to coordinate the resource and ecological conservation.