| With the development of urbanization, water pollution has become more and more serious, which is one of the urgent problems need to be solved. As different land use types have different pollutant export coefficient and evapotranspiration coefficient, land use changes will change the amount of pollutants’ loss, which will lead to a large area of nonpoint source pollution.Nonpoint source pollution will not only destory surrounding ecological environment,but also threaten human life and health. Therefore,it is very necessary to understand and explore the methods to improve future water purification function of ecosystem by using existing land use model and ecosystem service model.In this study, the function of water quality purification in 2010 was simulated by In Vest model, and the accuracy of the model was calculated by using the data of 2010.This research used the land use map in 2000 forecasted the land uses in 2010 by CLUE-S model. Actual land uses in 2010 were used to vertify the driving factors.Then, the land use data in 2020 were simulated using driving factors had verified already. And the study got the land uses in 2020 natural development scenario, ecological red line protection scenario and ecological red line+ riparian zone scenario by combining with ecological red line and riparian zone.Finally,the research used Invest model to simulate the function of future water quality purification in three scenarios in Nanjing.The results showed that:(1) The simulation accuracy of InVest model for water production and function of water purification is higher, which is in accordance with the requirements of this study.(2) In Nanjing, water purification function of forest is the highest, followed by the shrub, wetland, grassland, urban, water purification function of farmland is the lowest., the total amount of N, P exportation and retaining was 829.09t,189.53t, 3533.14t and 850.23t in 2010.(3)The simulation precision of CLUE-S model is 0.75, and the model has high reliability.Under the natural development scenario,compared with 2010, areas of urban increased 46.39%, areas of farmland decreased 28.15%, this situation will lead to food security and a series of environmental problems;In ecological red line protection scenario,compared with natural development scenario,areas of farmland increased 8.3%, areas of urban decreased 6.54%, food security will be significantly better than that in natural development scenario;In ecological red line+riparian zone scenario,compared with ecological red line protection scenario,areas of forest increased 16.08%,areas of wetland,farmland,shrub and urban decreased 3.27%, 2.04%,0.44% and 0.17% respectively,the ecological environment situation in this scenario is better than that in the ecological red line protection scenario.(4) the amount of N, P exportation and retaining is 818.94t,173.35t,2887.72t and 640.46t in natural development scenario. The amount of N, P exportation in ecological red line protection scenario is 5.48t and 1.27t less than that in natural development scenario, the amount of N, P retaining is 134.92t and 44.65t more than that in natural development scenario.Among them, the urban’s N, P exportation and retaining is reduced by 24.51t,3.69t,0.5T and 16.66t, farmland’s N, P exportation and retaining is increased by 19.81t,2.4t,132.33t and 37.11t,the function of water purification is significantly higher than that of natural development scenario.The amount of N, P exportation in ecological red line+riparian zone scenario is 46.93t and 4.81t less than in ecological red line protection scenario, the amount of N, P retaining is 34.6t and 3.49t more than that in ecological red line protection scenario. Among them, the urban’s N, P exportation and retaining is reduced by 22.84t, 1.1t, 8.966t and 1.35t, farmland’s N, P exportation and retaining were reduced by 24.62t, 3.72t,43.69t and 10.58t, forest’s N, P exportation and retaining is increased by 4.76t, 0.03t,111.72t and 20.06t, the function of water quality purification is more higher than that in ecological red line protection scenario.And the function of water purification in ecological red line protection scenario is higher than that in natural development scenario. Therefore, in order to better protect the river,control water pollution and improve water safety in Nanjing, as control measures,ecological red line should be executed strictly,and at the same time,the river banks of forest of proper width should be set. |
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