The Study On Evaluation And Tradeoff Of Ecosystem Services In The Hegang Mining Area

Coal mining promoted the national economic development,however,also caused huge negative impact on the natural environment.Coal mining disturbed the ecosystem in mine area,caused the changes of land utilization type,environmental pollution,water and soil erosion and so on.Hegang coal mine started in 1917,was a typical old multiple seam coal mine in northeast China,has been mined for a century.It was composed by 9 underground mines from north to south:Xingshan mine,Yixin mine,Zhenxing mine,Niaoshan mine,Nanshan mine,Xinlu mine,Fuli mine,Xingan mine and Junde mine.Zhenxing mine has the least coal seam（13 seams）,and Yixin has the most coal seam,reach to 36 seams.In these 9 mines,the amount of coal seam that still available was 6³4.The average service life was 49 a,and the longest could reach to128.9 a.Total area of Hegang mine was 9933.68 hm².The subsidence area reached to7932.12 hm² by 2013 a,which restricted the economic development of Hegang.Ecosystem service was closely related to human well-being.The ultimate aim of environmental management in mining areas was to restore the ecosystem services.Since the 1990s,ecosystem service has become a frontier research in ecology and the related disciplines.The research content of ecosystem services towarded analysing the relationship between multiple ecosystem services from the evaluation of ecosystem service.The tradeoff and synergies of ecosystem services was a key point of the relationship between multiple ecosystem services.Understanding the relationship of tradeoff and synergies between different ecosystem services was useful to evaluate the effects of mining activities on the ecological environment.It also could provide scientific basis for mine land reclamation,ecological restoration and the establishment of management policies.Meanwhile,it has important practical significance for mining area ecological civilization construction,and could promote the harmonious and sustainable development of mine area.The research progress of ecosystem services,quantitative estimation of ecosystem services,the tradeoff and synergies of ecosystem services and the ecological efficiency of coal mining were reviewed.Based on the major characteristics of coal mining subsidence land,land use change,climate and soil in Hegang mine area,the estimation method of ecosystem services in coal mining area was determined.Then,the ecosystem services of water yield,soil conservation amount,plant net primary productivity and food supply in Hegang old multiple seam mining area were estimated.In VEST model（Integrated Valuation of Ecosystem Services and Trade-offs）was used to estimate the water yield and soil conservation amount;CASA model（Carnegie-Ames-Stanford Approach）was used to estimate the plant net primary productivity;food production or grazing capacity was used as a representation indexes of food supply to evaluate the ecosystem services,and the results was corrected by NPP.In order to ensure accuracy of the ecological services estimation in Hegang mining area,the model parameter was amended.Base on the estimation on water yield,soil conservation amount,plant net primary productivity and food supply in Hegang old multiple seam mining area,the space-time change characteristics and the primary driving factors of these 4 ecosystem services were analysised.However,these ecosystem services were not isolately,they have interaction effect on each other.In this research,logistic regression model was used to analyze the space relationship of tradeoff and synergies between the ecosystem services of water yield,soil conservation amount,plant net primary productivity and food supply in 1993,2000 and 2013,and that was useful to understand the effect of coal mining on the relationship among ecosystem services in Hegang coal mine subsidence.Meanwhile,the future subsidence situation of Hegang mining area was predicted,and the future damage degree of subsidence was also evaluated.According to the land damage degree and subsidence land sinking characteristic in current and future,suitable land reclamation planning scenarios were established.Scenario analysis method was used to investigate the time tradeoff and synergies relationship between food supply,soil conservation and water yield.According to the tradeoff and synergies relationship between ecosystem services in different scenario and land subsidence conditions,the effect of coal mine land subsidence on ecosystem services and the relationship among each ecosystem services was investigated.The future reclamation planning was corrected in the perspective of ecosystem service.The results showed:（1）The main land use types were cropland and construction land with the proportion of 47.21%and 44.87%,and forest land,grassland,water land and unused land accounted for a small proportion of 7.92%in Hegang mining area.Cropland and construction land had the greatest change from 1993 to 2013.Cropland area had dropped by 910.17 hm² during the last two decades whose variance ratio was-14.99%;construction land area had increased 776.68 hm² whose variance ratio was 15.98%.Further analysis of transfer matrix of land use showed that cropland was most driven by construction land and there were 1078.91 hm² cropland transformed into construction land in 2013 a.（2）The mining subsidence area was enlarging with the increasing of coal mining in Hegang mining area,the NPP,soil conservation,water yield and food supply service showed obvious spatial differences from 1993 to 2013.The annual average value of water yield in subsidence area was higher than non-subsidence area,and the annual average values of soil conservation,NPP and food supply were lower in subsidence area compared to non-subsidence area.The annual average of the NPP has dropped from 57.89 g C·（m²·year）to 36.42g C·（m²·year）during the last twenty years and because of increasing construction land and the area of subsidence land,the NPP was decreases on 72.03%of total areas,which indicated that the eco-environment in Hegang mining area has continuously deteriorated after many years of extensive and substantial mining operations.The annual average value of water yield increased from339.66 mm in 1993 a to 465.58 mm in 2013 a,which had a close relationship with precipitation（R²=0.994）and the change of land use type caused by coal mining.The variation of soil conservation was similar to water yield,and the annual average quantitys of soil conservation in 1993,2000 and 2013 was 129.73,77.54 and190.08t·hm^-2·a^-1 respectively,that was due to the precipitation（R²=0.947）and the coal mining（R²=0.30）.（3）In the view of spatial pattern,NPP was higher in the eastern of Hegang coal mining subsidence land than those in the western from 1993 to 2003,and the lower area of NPP gradually increased and expanding to the eastern region,because construction land and subsidence area gradually increased to the eastern region with the cultivated land decreased.The water yield is higher in the western than eastern,which is related to the distribution of rainfall,subsidence area and the continually expanding of construction land in Hegang mining area.In the southwest of Hegang mining area,the soil conservation is relatively lower.With the expanding of subsidence area,the region with soil conservation more than 300t·hm^-2·a^-1 increased steadily.The reduction of food supply area was caused by the gradually expanding of sunbisidence area from west to east.（4）The analysis results of ecosystem services tradeoff and synergies relationship in Hegang coal mine subsidence showed that the NPP and soil conservation amount have a synergic relationship,NPP and water yield have a tradeoff relationship in space in1993,2000 and 2013.Compared with other scholars’research conclusion,the degree of space synergies relationship between NPP and soil conservation amount and the space tradeoff relationship between NPP and water yield was lower.That was due to the proportion of construction land and cultivated land is larger.The results could reflect that the ecological environment in Hegang mine area is fragile,protection measure should be taken to recover forest land and grassland,and reduce soil loss.Hot spots method was used to identify the distribution of ecosystem services in Hegang mining area,the core area of multiple services hot region was found in agricultural region,northeast and middleeast of research area.In this region,food supply and NPP were the major ecosystem services.In 1993-2013,with the contiously expanding of subsidence area from west to east,the scope of multiple services hot region showed a sustained decrease.（5）Based on the multi-period subsidence prediction,a division method of different land use situation of subsidence land was built.The damage degree and sinking sequence of subsidence land in Hegang mining area in 2013,2014-2020 and2021-mine closure were analyzed and the Hegang coal-mining subsidence was divided into stable region,temporary stable region,dynamic region,future subsidence region.Combined with four divided regions above,four different land use scenarios in future（2020 a）were constructed:farmland protection scenarios,urban development scenarios,ecological protection scenarios and farmland-city-ecological combined scenarios.（6）Under the cultivated land protection scenarios,city development scenarios,ecological protection scenarios and farmland-city-ecological combined scenarios,coal mining subsidence will influence the food supply and soil conservation amount.After mining,with the surface subsidence depth increases,the food supply and soil conservation amount per unit area will decrease.Surface subsidence value did not affect the water yield,results showed surface subsidence depth increase 7 m,the water yield did not change.Additionally,the order of the food supply and soil conservation amount per unit area in different land use scenario was urban development scenario>ecological protection scenario>farmland-city-ecological combined scenario>farmland protection scenario.The order of the water yield per unit area was ecological protection scenario>farmland-city-ecological combined scenario>urban development scenario>farmland protection scenario.The increase of farmland in the mining area could probably induce soil erosion.（7）The surface subsidence will affect the tradeoff and synergies among food supply,soil conservation and water yield in different land use scenarios.In these 3scenarios of farmland protection scenarios,city development scenarios and farmland-city-ecological combined scenarios,with the increase of surface subsidence depth,the relationship between soil conservation amount and water yield changed from synergies to tradeoff.With increase of subsidence depth,soil conservation amount decreased,water yield increased,caused soil erosion and water loss,and the ecological environment is deteriorating.Under ecological protection scenarios,the relationship between soil conservation amount and water yield changed from tradeoff to synergies.However,the water yield per unit area decrease greatly,which will be make the ecological environment in Hegang coal mining subsidence land better.By analyzing tradeoff of ecosystem services,farmland-city-ecological combined scenarios was the optimal land use style in large food demand condition,and ecological protection scenarios was the most conducive to the long-term development of Hegang mining area in the future.