Effects Of Coal Mining Underlake On Wetland Plant Community And Control Strategies

Coal mining under the lake has a long history and is spread throughout the north and south of China.However,with the increasingly strict protection of the ecological environment,coal mining under the lake is highly controversial.The reason for this is that the mechanism of coal mining under the lake on the ecosystem is unclear,the degree of impact is unclear,and the positive and negative effects is controversial.Clarifying the mechanism of coal mining on the lake ecosystem can not only provides theoretical guidance for the design of protective mining under the lake,but also has practical value for the protection and management of the lake ecosystem in mining areas.Therefore,this study takes coal mining under the Nansi lakes in Shandong Province as the study area,takes changes in wetland plant communities as a breakthrough point,and uses methods such as on-site investigation,remote sensing technology,and geographic information technology to quantitatively evaluate the impact of coal mining on wetland ecosystems through comprehensive investigation and systematic analysis.The aims including to clarify the ecological effects of coal mining under the lake and reveal the evolution characteristics of wetland plant communities driven by coal mining activities,establish a comprehensive assessment system for wetland plant community changes and quantitatively evaluate the degree of impact,and propose strategies for wetland plant community protection.Research has shown that:(1)The change of ecosystem in the Nansi Lake Nature Reserve is the result of multiple factors.Natural environmental factors such as precipitation and temperature,as well as human activities such as reclamation and breeding,coal mining,shipping,sand mining,and residents’production and living activities,can all have negative impacts on the succession of the ecological environment.On a regional scale,the most significant change in the past 30 years in Nansi Lake has been the transformation of natural wetlands dominated by marshes into artificial wetlands dominated by platform fields and fish ponds.The proportion of natural wetland area has decreased from 80%in 1985 to 38%in 2022;the proportion of artificial wetland area has increased from 7%in 1985 to 56%in 2022.The grey correlation degrees between coal mining subsidence and natural wetland area,lake area,vegetation coverage,water area,average patch area,and maximum patch index are 0.42,0.25,0.20,0.25,0.33,and 0.28,respectively.All of them are low degree of correlation and suggest a certain impact of coal mining subsidence.(2)The vegetation coverage area in the Nansi area has increased overall,but fluctuates greatly and is highly correlated with changes in water area.There is no significant correlation between coal mining and vegetation coverage.The vegetation coverage shows an decreasing trend from the lakeside to the lake center,and the vegetation coverage area is mainly affected by rainfall and water level.When the lake has sufficient water,the open water surface area significantly expands,and the vegetation coverage decreases.Aquatic plants have a significant threshold effect on water depth changes.As the water depth increases,vegetation coverage decreases.When the water depth is 0.5 meters,vegetation coverage significantly decreases.When the water depth is 2.4 meters,vegetation can no longer be observed using remote sensing images,indicating that 2.4 meters is the threshold for the growth of aquatic plants in Nansi Lake.(3)The impact of coal mining under the lake on wetland plant communities is both positive and negative,and the transfer mechanism is"coal mining subsidence-deformation of lake topography-adaptive changes in plant communities".After coal mining under the lake,the bottom of the lake slowly sinks,gradually forming a flat concave bottom subsidence basin under the hydrodynamic and sedimentation effects of the lake,which then causes changes in water depth.After the changes in water depth,plants adapt to the environment by changing the morphological and physiological characteristics at three scales including individuals,species,and communities.Vegetation coverage has a certain resistance to coal mining under the lake.Coal mining under the lake has increased the habitat area of wetland plants,while the overlapping areas of Nansi Lake and coal mining have increased the habitat area of phytoplankton,emergent plants,floating leaf plants,and submerged plants by 0.06 km~2,0.33 km~2,0.26km~2,and 0.15 km~2,respectively.(4)By using the developed"Status-Habitat-Potential"(SHP)evaluation model based on long-term remote sensing data,the SHP index of plant communities were measured.The results indicate that the SHP index of Nansi Lake ranges from 0 to 0.59,with an overall low level,especially in the lakeside buffer zone that is suitable for plant community.This is mainly due to the water level fluctuations caused by agricultural cultivation,construction and development,fisheries and aquaculture,as well as inter-annual climate change,which makes it difficult to form stable plant communities on the lakeside.The SHP index of plant communities in the subsidence area and the control area are 0.34±0.12 and 0.32±0.1,respectively,with no significant difference.This indicates that the impact of coal mining at the lake bottom on plant communities is not significant at the regional ecosystem scale.(5)The strategies for effectively reducing the impact of coal mining under water bodies on wetland plant communities include four aspects:ecological conservation mining,orderly exit of coal mines,wetland ecological restoration,and strengthening wetland ecological supervision.According to the long-term practice of Nansi Lake,ecological protection mining methods include strip mining technology and filling mining technology.The orderly withdrawal of coal mining requires adjusting the coal resource development plan,and following the basic principles of legality,differentiation,orderliness,and protection of legitimate rights and interests.The wetland vegetation restoration strategy in the mining area is applicable to wetland areas with less damage,and the ecological pond-artificial ecological island construction technology can be used.The study shows that the ecological effects of coal mining under lake are different from those of onshore underground coal mining.Coal mining subsidence can effectively expand water area,increase water depth,and increase wetland plant habitat.The bottom topography of the lake is not only affected by subsidence,but also by sedimentation under the hydrodynamic action of the lake.Aquatic plants have a significant threshold effect on water depth changes.When water depth changes,plants adapt to the environment by changing the morphological and physiological characteristics at three scales including individuals,species,and communities.This study indicates that at the regional ecosystem scale,the impact of coal mining under the lake on wetland plant communities is not significant.