Environmental Impact And Evaluation Of Line Project On Turfy Wetland In Seasonal Frozen Area

Turfy wetland is a unique type of swamp wetland,which is widely distributed in mountain Interval of perennial standing water,vegetation development and low-lying terrain,such as Changbai Mountain area,Xing'an Mountains,Qinghai Tibet Plateau,Yunnan Plateau,Zoige Plateau and some mountain areas in Xinjiang Province,etc.Due to the interaction of topography,climate,hydrology and vegetation,the formation of turfy wetland has special environmental functions,such as water conservation,climate regulation,pollution degradation,environmental beautification and rich gene pool.However,in recent years,with the development of social and economic construction,a large number of new line projects have inevitably invaded the area of the turfy wetland,resulting in various threats to the ecological environment of the turfy wetland,such as the decline of wetland area,vegetation damage,water resources loss and environmental pollution.The destruction of ecological environment of turfy wetland means that its biological support,stable climate and ecological balance are seriously disturbed,which will cause incalculable losses to the local economic environment and human life.Therefore,it is necessary to explore the impact mechanism of the line project on the ecological environment of the turfy wetland and evaluate its impact degree,so as to protect the unique ecological environment function.Based on the above reasons,this paper chose three turfy wetlands affected by the line project in Jiangyuan,Longquan and huangsongdian as the research object,and studied the impact mechanism of the line project on the soil environment,plant environment and water environment of the turfy wetland through the experimental scheme design,field survey sampling and indoor test,mainly including the following contents:?1?the impact of the line project on the physical and chemical properties of the soil;?2?the impact of the line project on the heavy metal concentration of the soil in the turfy wetland;?3?the impact of the line project on soil microorganism in turfy wetland;?4?the influence of the line project on the plant community structure of the turfy wetland;?5?the influence of the line project on the heavy metal enrichment characteristics of the plants in the turfy wetland;?6?the influence of the line project on the water level,water temperature and water quality of the turfy wetland.Based on the above research content,the evaluation index system and evaluation method of the environmental impact of the line project on the turfy wetland are established and verified by Jiangyuan,Longquan and Huangsongdian example.The mainly conclusions are as follows:1.From the study of the impact mechanism of the line project on the soil environment of the turfy wetland,it can be concluded that:?1?The soil physical and chemical properties of turfy wetland have the distribution rule of vertical depth profile,that is,soil organic carbon?SOC?,total nitrogen?TN?,water content?WC?,void ratio?VR?decrease with the increase of sample depth,and soil bulk density?BD?increases with the increase of sample depth.The disturbance of the line project only affected the physical and chemical properties of the surface soil?0-20cm?of the turfy wetland,such as reducing the SOC,TN,TK,WC and VR of the surface soil,and increasing the soil BD?p<0.05?.?2?Cr,Zn,Cu and Cd are the main traffic-related heavy metal pollutants in the soil of turfy wetland,and their concentrations decrease with the increase of distance,and tend to be constant at 30m away from the road.The results of I_geo and EF calculating indicated that the pollution degree was between no pollution and serious pollution,and Cd pollution is the most serious.?3?The microbial diversity and richness of top soil were significantly higher than that of deep soil?p<0.05?.The microbial diversity index OTU,Ace,Chao,Shannon decreased with the increase of sampling depth,while Simpson index increased with the increase of sampling depth.For community composition,at the phylum level,the relative abundance of Proteobacteria decreased with the increase of depth,while the relative abundance of Bacteroidetes and Chloroflexi increased with the increase of depth;At the genus level,the relative abundances of Geobacter,Syntrophus,Escherichia,Syntrophorhabdus,Syntrophobacter,Smithella,Methylobacter and Methylotenera decreased with the increase of depth,while the relative abundances of Longilinea and Terrimonas increased with the increase of depth.?4?The disturbance of the line project has no impact on the soil microbial diversity of the turfy wetland,but it has changed the composition of the microbial community,especially for the species at the level of bacterial genera,such as the relative abundances of Geobacter,Syntrophus,Escherichia,Syntrophorhabdus,Syntrophobacter,Smithella,Methylobacter,Methylotenera and Longilinea in the surface soil of the impact area were significant lower than those in control area,and the relative abundance of Terrimonas in affected area increased significantly?p<0.05?.?5?The change of soil microorganism in turfy wetland was affected by both soil depth and drainage activity,and soil organic carbon and total nitrogen are the key factors to control the change.Road drainage resulted in the loss of soil nutrients on the surface soil of wetland,thus affecting the C and N cycle related microorganisms?Geobacter,Syntrophus,Syntrophorhabdus,Syntrophobacter,Methylobacter?and changing the composition of soil bacterial community.2.From the study of the impact mechanism of the line project on the plant environment of the turfy wetland,it can be concluded that:?1?The plants of turfy wetland have the characteristics of complexity and diversity,and it consists of 24 species,24 genera,23 families,of which the species distribution is mostly 1 family,1 genus and 1 species,accounting for 91.3%of the total species.The disturbance of the line project did not change the plant community composition,and the dominant species were still Carex meyeriana Kunth,Thelypteris palustris.var.pubescens Fernald,Caltha membranacea?Turcz.?Schipcz,Lythrum salicaria Linn.,Pedicularis resupinata L.,etc.,but it had an impact on the distribution pattern of the importance of the dominant species,that is,the number of Carex meyeriana Kunth near the road increased,while the number of some minor dominant species decreased.In addition,two kinds of alien Dysphania ambrosioide and Medicago sativa L.were found in the turfy wetland,with an invasion range of50m.?2?The disturbance of line project affected the?diversity of plant community,especially Shannon-Wiener index,Pielou evenness index and Simpson index,Shannon Wiener index and Pielou evenness index increase with the increase of distance,while Simpson index decreases with the increase of distance,while the?diversity of plant was not affected by the line project.?3?The line project had a significant impact on the heavy metal accumulation characteristics of Carex meyeriana Kunth and Thelypteris palustris.var.pubescens Fernald in turfy wetland,They can absorb heavy metals from highway sources through soil and atmosphere,and accumulate them in roots and stems,which is similar to the distribution characteristics of heavy metals in soil.The concentration of heavy metals in roots and stems of plants decreases exponentially with the increase of distance.Modelcan accurately describe the distribution characteristics.According to the model,it can correct the impact distance of the line project on the soil plant heavy metals to the range of 100m.?4?In the soil-plant system of turfy wetland,the dynamic characteristics of heavy metals change with species and elements.Thelypteris palustris.var.pubescens Fernald mainly absorbed Cr,Cu,Cd from the soil,Pb from the atmosphere and Zn from the soil and the atmosphere,while Carex meyeriana Kunth absorbed Cr,Cu,Cd from the soil and the atmosphere and Pb from the atmosphere.The calculation results of plant bioaccumulation factor?BF?,transfer factor?TF?and enrichment factor?EF?indicated that the enrichment and transfer ability of heavy metals in plants in turfy wetland is related to the diffusion mode of traffic-related heavy metals.The average values of all factors outside the impact range were calculated and found that the BF?1.34?of Carex meyeriana Kunth to Cd and TF?1.13?of Thelypteris palustris.var.pubescens Fernald to Zn were more than 1,which means Carex meyeriana Kunth is an ideal plant for absorbing Cd in soil,while Thelypteris palustris.var.pubescens Fernald is a suitable plant for transferring Zn.3.From the study of the impact mechanism of the line project on the water environment of the turfy wetland,it can be concluded that:?1?The excavation of the drainage ditch reduces the groundwater level near the wetland road area,and the water temperature near the road area slightly increases due to the long-term driving of vehicles and the heat dissipation of the road surface;?2?Only Cu?Pb?Zn?Cr?Cd?Na⁺?K⁺?in the 19 water quality indexes of turfy wetland are greatly affected by the line project,and each index follows the same distribution model as soil-plant heavy metal in the distance profile,with the influence range of 15-100m,and the background content of Cu?Pb?Zn?Cr?Cd?Na⁺?K⁺?in the underground water is 36.8?g L^-1?17.5?g L^-1?96.9?g L^-1?1.4?g L^-1?4.9?g L^-1?2.5?g L^-1?1.0?g L^-1?4.8?g L^-1.?3?The heavy metal pollution index HPI<100 and<0 of groundwater indicated that the water quality is in a no polluted state,which conformed to the water quality grade of the water source area.However,the correlation analysis results show that the main contribution factors of HPI and are Cu,Pb,Zn,Cr,Cd,and the two indexes also have the distribution pattern of exponential decline,indicating that the impact of the line project on the accumulation of heavy metals in the groundwater of the turfy wetland can't be ignored.4.Combined with the principle of index selection,the evaluation index system of the impact of the line project on the environment of the turfy wetland is established.There are 24 indexes in total,which are as follows:heavy metal pollution index?Cr,Cu,Cd,Zn,Pb?,chemical index?SOC,TN,TK?,physical index?BD,WC,VR?,microbial index?Proteobacteria relative abundance?in the soil environment;heavy metal pollution index?Cr,Cu,Cd,Zn,Pb?,general chemical indexes?Na⁺?K⁺??in the water environment;?diversity indexes?Species richness,Shannon-Wiener index,Pielou index,Simpson index?,and the number of Carex meyeriana Kunth in plant environment.5.From the two aspects of environmental quality and ecological response of turfy wetland,the soil environmental impact assessment method based on soil quality index?SQI?,water environmental impact assessment method based on normal cloud model theory and plant environmental impact assessment method based on plant response index?PRI?were established.Finally,based on the multi-dimensional cloud model theory,the evaluation method of the comprehensive environmental impact of the line project on the turf wetland was established,and the actual monitoring values of Jiangyuan,Longquan and Huangsongdian turfy wetland were evaluated.The results showed that the evaluation results based on the established index system and the evaluation method are basically consistent with the actual wetland conditions.Under the background of project construction and wetland protection,from the perspective of system mechanism,this paper makes a detailed investigation of the impact mechanism and degree of the line project on the wetland ecological environment when it passes through the turfy wetland,which has important basis for taking effective measures to ensure the safety and stability of the line as well as the reducing impact on the wetland ecological environment.Moreover,the establishment of a complete set of evaluation index system and evaluation method for the environmental impact of the line project on the turfy wetland can provide reference for the construction of other wetland regional line projects.