Study On The Impact Of Surface Water Quality By Ecological Rehabilitation In Subsidence Area With High Phreatic Water Level

Most of the coal in China is mined by underground mining,but underground mining can easily lead to surface subsidence,which leads to the continuous deterioration of the ecological environment of the mining area,especially the high phreatic water level mining area.The coal mining subsidence in this area not only changed the original topography,resulting in surface movement and deformation,damage to cultivated land,damage to ground building foundations and water levels,but also changed the regional water system,affecting surface water quality and water resources circulation,and further aggravating agriculture Non-point source pollution and deterioration of water environment.This study took the subsidence water area in the Peibei mining area of Xuzhou as the research object,and used the methods of single factor evaluation,Nemerow comprehensive index evaluation and comprehensive nutrient state index evaluation to evaluate the surface water before and after coal mining collapse and before and after three different ecological restoration methods.Carry out sampling analysis and evaluation on changes in water quality indicators.Based on the surface water quality index before and after ecological restoration in the subsidence area,analyze the impact of different ecological restoration methods on the surface water quality in the subsidence area,evaluate the improvement effect of different ecological restoration methods on the surface water quality,and propose corresponding project improvement ideas.The main conclusions reached are as follows:（1）Coal mining subsidence has great influence on regional water resources and water quality.Coal mining subsidence has changed the regional surface landscape structure,resulting in subsidence of water,river stoppage,etc.,which accelerates the accumulation of regional precipitation and surface runoff,and is prone to flooding and disasters.At the same time,affected by the accumulation of agricultural non-point source pollution in the subsidence water area,the content of total phosphorus and total nitrogen increased,but the comprehensive index of surface water quality and nutritional status in the subsidence water area was basically between 60 and 70,which belonged to moderate eutrophication,and the permanganate index(COD_Cr)averaged96.2,which was the largest contributor to pollution.（2）According to the actual situation of the Peibei mining area,the ecological annular ditch type should be selected to improve the water by drought and dig deep and shallow to remediate according to local conditions.Applying the"4R"water ecological restoration theory,combined with the current main technical means of ecological restoration,to analyze the serious subsidence and shortage of funds in the current ecological restoration in the study area,and select the ecological restoration with less economic cost and more economic benefits.Circular ditch type drought to water,combined with deep digging technology,so as to achieve the coordinated development of food security and regional ecological environment protection.（3）The ecological restoration of the mining area has significantly improved the water quality of the subsidence area and produced good economic,social and ecological benefits.The nitrogen and phosphorus content of the regional surface water was significantly reduced,but the removal effect of COD and BOD₅was not obvious.The nutrient status index of water quality in the subsidence area after water ecological restoration was between 40 and 50,but the permanganate index(COD_Cr)was still the largest contributor to water pollution.The evaluation level of water quality improvement effect of water ecological restoration was raised from"very poor"to"good",with an improvement rate of 73%.In view of the situation that the improvement effect of some water quality indicators is not obvious,based on the"4R"theory,a four-point improvement strategy is proposed,and three opinions are put forward from the perspective of government planning and implementation,including:strengthening the reduction of pollution sources,improving the blocking of pollution processes,Implement the cascade utilization of nutrients and scientifically reconstruct the ecosystem;the government departments rebuild and improve the institutional system to improve the efficiency of planning implementation;strengthen departmental collaboration,strengthen planning supervision and management;expand funding channels to ensure funding for planning implementation.