| Long-term coal mining activities have made important contributions to the national economy,but also have caused widespread destruction of the regional ecological environment,which had a significant regional eco-environment effect on its basin.Coal mining subsidence watersheds have been formed in high phreatic areas,which has changed the original micro-geomorphology and land use types of the mining area.In this study,the Landsat remote sensing image maps of the Xifei River Basin in1980,1990,2000,2010 and 2015 were selected.The multi-scales segmentation object-oriented classification method was used to interpret the land cover types and classify the land use types,including cultivated land,construction land,forest land,traffic land and water.The land use change matrix was used to analyze the land use changes and the conversion of land use types.Based on above data processing,the impacts of land use changes on the regional landscape pattern were analyzed.In addition,a monitoring station was set up at the exit of the river basin to monitor the output characteristics of non-point source pollution load in a two-year period,and the SWAT ecological hydrological model was developed to simulate the runoff and non-point source pollution load in the study area.The effects of land use change on watershed runoff and non-point source pollution load output were estimated.The main findings are as follows:(1)The land use structure of the Xifei River Basin changed greatly from 1980 to2015.The area of cultivated land decreased from 1532.3km~2 in 1980 to 1270.0km~2 in2015,with 262.3km~2reduced.Accompanied by the acceleration of urbanization,the construction land area increased from 226.3km~2 in 1980 to 417.4km~2 in 2015,and the increment was 191.1km~2.Meanwhile,the traffic land increased by 26.6km~2.Coal mining activities led to the collapses of large area villages and cultivated land,and the area of waters increased continuously from 68.1km~2 in 1980 to 113.7km~2 in 2015,with an increase of 45.6km~2.Besides,the cultivated land was mainly converted into construction land and waters which could be observed from the land use transfer matrix.(2)Changes in watershed landscape were caused by land use change.From 1980to 2015,the number of landscape patches and the separation index increased,the landscape pattern of the basin became broken,and the phenomena of other landscape was embedded in landscape patches became more and more common.And the types of plaques were much more dispersed due to the intensive disturbance of human activities.In the past 35 years,the diversity index and evenness index increased by 0.26 and 0.16,respectively.And the dominance of cultivated land landscape decreased.The roles of construction land and water landscape in the landscape pattern of the basin were more and more important,and the landscape distribution of the basin was more diverse and balanced.(3)The non-point source pollution in the Xifei River Basin has obvious seasonal changes.The main reason was that the large rainfall in summer and it was easy to form strong rainfall runoff and result in more surface and farmland pollutants enter the river and cause the higher concentration of non-point source pollution.In March,the rainy season in the basin begins,the early scouring effect was obvious and the N and P pollution concentrations show significant peaks.Sewage and manure were the main factors affecting the N element pollution output in the Xifei River Basin.The increase of N nutrient concentration in the river water was caused by the untreated sewage discharge point and the diffuse source from manure cause.(4)In the study,three land use scenarios were set to simulate the effects of land use changes in the basin to the hydrological process and the non-point source pollution load in the basin.In scenario 1,the land and waters would be restored to cultivated land.In scenario 2,waters would be replaced by cultivated land.In scenario 3,the construction land would be restored to cultivated land.The simulation results show that the annual average runoff was 20.61m~3/s,22.0m~3/s,20.17m~3/s.Scenario2>Scenario 1>Scenario 3.When the cultivated land was converted into construction land and the construction land increased by 417.4km~2,the annual average runoff would increase by 6.3%.The construction land could promote the generation of annual runoff,and the contribution to the increase of runoff was greater than cultivated land.When113.7km~2of cultivated land was converted into waters,the annual average runoff in the Xifei River Basin decreased from 20.61m~3/s to 20.17m~3/s,and the decrease was 2.2%.(5)In the three land use scenarios,the annual average load output per unit area of TP was 59.10kg,57.56kg,55.26kg,and scenario 1>scenario 2>scenario 3.When the cultivated land area was the largest,the TP load output was the largest.The production of crops consume a large amount of fertilizer,and the cultivated land was the most significant contribution to the TP load output,and followed by the construction land and waters.In the three types of land use scenarios,the annual average load output per unit area of TN was 357.66kg,450.45kg,and 329.19kg,respectively.When the construction land was the largest,the annual average load output of TN was the largest.And the construction land led the contribution rate to TN,and the next one was the cultivated land.The water area and the water area contribute slightly to the N and P load outputs.Cultivated land and construction land are the mainland types for non-point source pollution load output in the Xifei River Basin.Figure 26 Table 14 reference 25... |
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