| Land-use change and land-cover change is a core field of global environmental change research.Study on land-use and land-cover change of different spatial and time scale is also one focus of geography recently.Land-use change,due to modern agriculture development,industrialization and urbanization,has lots of impacts on water balance and environment,such as increasing downstream flooding,decreasing groundwater supply, drying wetlands,soil erosion,non-point source pollutant increasing and so on.Soil erosion and non-point source pollution are two serious environmental issues.So it is very important to analyze water environment impacts and soil loss of land use change for land use plan and watershed management.By selecting Qilu lake basin as study area,this paper analyzed the land use change of the basin and found the key driving forces in 17 years firstly.Secondly landscape patterns and its environmental effect were analyzed,then,under the support of technology of remote sensing and geographical information system,this paper analyzed the land use changes and its non-point source pollutant in 1989 and 2005.Finally,to use modified pressure-status-response(P-S-R) model,ecological security status of Qilu lake basin was qualitatively assessed.The land map of 1989 and 2005 are acquired by explaining the TM image.Some conclusions are drawn out.The land use had changed greatly from 1989 to 2005 in Qilu lake basin.Agricultural land and waste-grassland areas reduced largely,forest land and construction-use land increased considerably during the period.The land use changes speed is higher than other Yunnan plateau lake basin's,such as Erhai basin,and its changes ratio is 0.66%annually. So far as the dynamic degrees of certain land types are concerned,forest land areas' annual change ratio is the maximum,the second is construction-use land areas,then are shrub land and agricultural land,the minimum is waste-grassland and water-body.As far as land-use conversion target is concerned,forest land converted to shrub land mainly,shrub land converted to forestland,waste-grassland to shrub land,water body converted to agricultural land lightly.Agricultural land area change is the maximum and it convened to construction-use land.So far as the source is concerned,forestland area increase is due to shrub protection and forestation on waste-grassland,the part of shrub land was destroyed and convened to waste-grassland.Agricultural land and waste-grassland area decrease are the major contributors to construction-use land area increase because of population increase and economic growth.In the relatively small region,Qilu lake basin,nature driving forces had little effect on land-use change during 17 years.By the methods of Factor Analysis,it is found that there are several main human factors including population growth,economic growth and fast urbanization process.Landscape patterns changed with land use/cover changes because of human activities. The landscape diversity index and evenness index increased,dominance index and fragmentation index decreased from 1989 to 2005.The total patch density decreased because that some similar patch in forest land and construction-use land combined to a bigger patch.Landscape diversity index increased because of agricultural land and shrub land area decrease greatly,in addition forest land,construction-use land and waste-grassland area increase.The degree of every landscape types' control decreased and the evenness index increase.The degree of landscape fragmentation decreased was due to the number of all land-use patch decrease.As far as landscape structure and change feature was concerned,fragmentation degree of construction-use land is the quickest decrease because of urbanization and economic development,and fractal dimensions is increasing with the constant strengthen of human activities.Vegetation restoration and lake environmental protection made forest land have concentrated continuous tendency,moreover,agricultural land and shrub land trended separated tendency as human activities.As a result of landscape element changes,shortage of water resources,serious water pollution,water degradation,humid area decrease,loss in ecological function of wetland and serious soil erosion etc,these ecological environment effects lead the ecological services function decreased.The total ecological services value of Qilu lake basin is 2.37×10~8 yuan,which decreased by 24.15 percentage than 1989.In general,the system services function decreased.Using precipitation daily serial(from 1985 to 2004),and soil category map,the average annual runoff of 1989 and 2005 can be stimulated based on different land use distribution by L-thia(Long-term Hydrologic Impact Assessment ).The model result express there is prominence pollution impacts of land use change.The runoff in 1989 is 9599.52×10~4m~3,and 9344.43×10~4m~3 in 2005.The total nitrogen and total phosphorus of agricultural land and constructional-use land are the main contributor to the non-point source pollution.The simulated pollutant loads of different land use result show that the total nitrogen and total phosphorus loads is most serious in agricultural land, constructional-use land take the second place.Forest land and waste-grassland can prevent pollutant to a certain extent.The ecological security assessment result showed that Qilu lake basin located unsafe status both 1989 and 2005.The main reason is that humanity pressure increased.Human activities changed the land use construction,and the bearing capacity of the ground is limited.Although economic growth can ease the conflict between land and ecological environment to a certain degree,there is still some measure to promote ecological security construction of Qilu lake basin. |
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