Study on the habitat evolution pathways of coal mining subsidence wetlands in the Huang-Huai-Hai Plain

The Huang-Huai-Hui Plain is a typical coal-grain composite production area, where coal mining subsidence creates wetlands through water accumulation. However, these newly formed wetlands are susceptible to threats from agricultural wastewater, resulting in sensitive and unstable ecosystems. Based on field surveys, sampling, and laboratory testing data from the Huang-Huai-Hai Plain, this study selects six coal mining subsidence wetlands and one natural wetland in Xuzhou City （Jiangsu Province）, Zoucheng City （Shandong Province）, and Huaibei City and Huainan City （Anhui Province） as research subjects to analyze the evolution characteristics of wetland habitats and explore the evolutionary patterns and formation mechanisms of coal mining subsidence wetlands. The study finds that plant species composition in subsidence wetlands evolves synchronously with habitat conditions, progressing from initial xerophytic weeds to hygrophytic herbs and shrubs, with plant biomass following a pattern of rapid growth, stable maintenance, and gradual differentiation. Significant differences in water physicochemical properties are observed among wetlands with varying restoration durations （P＜0.05）, with chemical oxygen demand, total dissolved solids, and electrical conductivity all exhibiting an evolutionary pattern characterized by initially high values, mid-term peaking, and subsequent decline and stabilization. The physicochemical properties of wetland sediments, enzyme activities, microbial diversity, and species composition follow a succession logic of disturbance-degradation-restoration-convergence toward natural conditions. The contents of soil organic carbon, dissolved organic carbon, microbial biomass carbon, and particulate organic carbon show minor fluctuations during the early restoration stage, followed by a gradual increase to stability. Also, significant differences in bacterial and fungal α-diversity are detected in subsided wetland sediments under different restoration years （P＜0.05）, displaying a temporal trend of initial decline, subsequent increase, and ultimate stabilization with prolonged restoration duration. Furthermore, microbial community composition varies significantly across restoration durations, with distinct response patterns observed between bacterial and fungal communities. Within bacterial communities, Chloroflexota, Acidobacteriota, Actinomycetota, Bacillota, and Pseudomonadota dominate in wetlands with restoration durations of less than 30 years. Ascomycota, Basidiomycota, and Mortierellomycota are the dominant fungal phyla across different restoration durations. However, a general trend of increasing Ascomycota and decreasing Basidiomycota with prolonged restoration is observed, ultimately approaching stability. Overall, coal mining subsided wetlands restored for over 30 years achieve or asymptotically converge to native wetland levels in terms of vegetation communities, aquatic environments, soil environments, and microbial communities.