Simulation Of Non-point Source Nitrogen Export In Jiulong River Watershed Under Different Land Use And Climate Change Scenarios

Water purification is one of the most basic ecosystem services provided by the terrestrial ecosystem.With the development of global society and economy,the changes in land use land cover,and patterns of precipitation resulting from global climate change over time and space,have caused the changes of regional hydrologic cycle process,leading the crisis of water resources and water pollutions increasingly becoming the issues facing by the countries around the world.Studying and exploring the influences of land use land cover and climate change on the water ecological environment are one of the core issues in mitigating the current crisis of water resource and water pollutions.Non-point source pollution is one of the typical ecological process,which is affected by varieties of natural and anthropogenic factors.It has very important theoretical and practical significance for decision-makers to prevent and control non-point source pollution and environmental management in watersheds from the perspective of the land use land cover and climate changes.In this study,Jiulong River Watershed was taken as the research area,which is in the south of Fujian Province.Based on the review of research processes of ecosystem services assessment,In VEST(Integrated Valuation of Ecosystem Services and Tradeoffs)model and scenario building,NDR(Nutrient Delivery Ratio)module and scenario generator tool of In VEST were used to explore the non-point source nitrogen export to Jiulong River,and its response of water purification service to land use land cover and climate change in the watershed,hoping to provide managers with references about land use planning,water resources protection.The main contents and conclusions are as follows:(1)Based on the NDR module of In VEST,the spatial pattern of export of non-point source nitrogen within Jiulong River Watershed was simulated,the results of which was used to calibrate and verifies the model.Result shows that through adjusting parameters,the NDR module has a better applicability and reliability in the assessment and simulation of non-point source nitrogen export in the Jiulong River Watershed.Non-point source nitrogen export to Jiulong River is 12568.54 t/a.And the amounts of non-point source nitrogen export vary to some extent,accounting for the varieties of types of land use land cover.Agricultural land shows the highest non-point source nitrogen export per km2,which makes the southeastern part of Jiulong River Watershed is the main source of non-point source nitrogen pollution.Also,the administrative in this area,such as Zhangzhou,Changtai,show higher non-point source nitrogen export rate.(2)Maps of land use land cover scenarios were simulated by Scenario Generator Tool and ArcGIS Tools,based on the current land use land cover map.Combined with the Plan for Land Utilization of Fujian Province(2006-2020)and the establishment of constructed wetlands within the riparian buffers,three possible land use land cover scenarios were built:policy-based scenario,managed scenario and grain for green scenario.Compared with the current situation,the areas of different land use land cover types vary slightly.Forest are the largest,followed by the agricultural land.(3)Non-point source nitrogen export under different land use land cover scenarios,and climate change scenarios based on three representative concentration pathways,were simulated by NDR module.The analysis of non-point source nitrogen export within Jiulong River Watershed under different scenarios shows that the establishment of constructed wetlands within riparian buffers,grain for green and reduce the amount of fertilizer can improve the ability of water purification as for the whole watershed,and the climate change will,in some cases,increase the nitrogen export from non-point source and deteriorate the water quality.Under the synergistic effects of land use land cover and climate change,water purification in the southeastern of Jiulong River Watershed has improved even more significantly.(4)According to the results of scenario analysis,strategies to reduce non-point source nitrogen pollution in Jiulong River Watershed was purposed,and the efficiency of which was also simulated.The priority management area of in Anxi,Changtai and Zhangpu were taken as the prior areas to reduce the non-point source nitrogen export caused by soil and water loss.Zhangzhou,Zhangpu,Longhai and Changtai were taken as the prior areas for fertilizer application.Longhai,Zhangpu,Nanjing,Changtai and Zhangzhou were taken as the prior areas for riparian buffers.Result shows that it is very effective in the areas such as Zhangpu and Changtai.At the same time,the regions identified to take measures to reduce non-point source nitrogen first in this study that are also sensitive to climate change.Thus,the plan can also mitigate the effects of climate change on water ecosystem.