| With the effects of global climate change and human activities, the crisis of water resources and water environment pollution has become an urgent issue to be solved in the world. Under the background of climate change, the spatial and temporal heterogeneity of precipitation, temperature, and other climate factors, will inevitably lead changes in water cycle process and the ecological environment. Meanwhile, due to the strong influence of human activities, especially land use/cover change, making the mechanism of the runoff yield in watershed changed, thereby causing changes in basin water environment. Non-point source pollution (NPS), as a typical ecological processes, was affected by the combined effects of natural factor and human factors. Miyun Reservoir, as the only surface water sources, has important strategic significance for water surply of Beijing city. Researches showed that NPS pollution has become an important source affecting the quality of the Miyun Reservoir water environment. Therefore, exploring the impact of climate and land use change on NPS pollution, has important practical implications for cognitive non-point source pollution process and its management.In view of this background and condition, this dissertation took the Miyun Reservoir watershed as the study area, to carry out research in the response of non-point source pollution to land use and climate change. This study used three period land use data of1995,2000,2005and adopted Soil and Water Assessment Tool (SWAT), Canonical Correspondence Analysis (CCA) and Path Analysis to explore the relationship between land use change and non-point source pollution loads on a series of spatial seale. Based on the long time series of meteorological data, Global Climate Models (GCMs), Statistical Downscaling Model (SDSM) and Weather Generator (NCC/GU-WG) were used to predict the future climate change scenarios. Combined with SWAT model, then, the trends of future NPS pollution loads was estimated. The main contents and conclusions are listed as follows:(1) The SWAT model was applied for NPS pollution simulation in the Miyun Reservoir watershed. The model were calibrated and validated with monthly observed data from1995to2004. The results showed that Nash-Suttcliffe coefficient (Ens) was greater than0.8for runoff simiulation, and greater than0.5for TN and TP, which suggested a good agreement between observed and simulated runoff and water quality. The results suggested that SWAT model was suitable for the study area. The pollution loads simulation showed that, TN and TP loads decreased with the rainfall varies from1995to2005, indicating that rainfall has important impact on the temporal variability of pollution loads, and its impact on TN loads was greater than TP loads. The spatial distribution of TN and TP loads were significantly affected by the comprehensive influence of rainfall and land use. The high-risk areas were mainly located in Chicheng, Chongli, and Fengning County.(2) Analysis and compare land use change of Miyun Reservoir watershed between1995,2000, and2005. By applying landscape metrics method, quantitative analysis of the spatial and temporal variation of land use pattern was carried out. It showed that land use occurred significantly change between the10years. From1995to2000, the forestland area reduced remarkably, and grassland, arable land area correspondingly increased. The changes mainly occured in the transitions of forest land, grassland and arable land. Land use change from2000to2005maintain stability, and fluctuate slightly btween different land use types. The characteristic of spatial pattern of land use in the10years tended to be more fragmentation, diversity, and more complicated shape. Land use patterns was closely associated with the spatial scale. With the increase of scale, landscape diversity and fragmentation were reduced, patch shape became complicated, and the agglomeration level enhancement. (3) Canonical correspondence analysis (CCA) and path analysis method were used to explore the relationship between land use change and NPS pollution loads at different scales. The results showed that, there was a significant correlation between NPS pollution loads and landscape characteristics in the study area. Landscape variables can explain56%variation of nutrient loads. At the landscape level, the fragmentation metrics, and shape metrics were the main pattern indices effectively affecting the variation of nutrient losses. At the patch-class level, landscape metrics affecting the spatial variation of pollution process varied with land use types. The result of path analysis suggested that the proportion of arable land and forest land area, patch density, and shape index were the main pattern indices effectively affecting the nutrient pollution process. The interpretation capacity of proportion of arable land and shape index to TN and TP loads was greater than the other indicators. The relationship was closely associated with the spatial scale. With the spatial scales increased, the interpretation capacity of landscape variables reduced. The first grade protection zones had the highest interpretation capacity, which reached62.9%, indicating that the area around the reservoir area should be highly valued for the prevention and treatment of NPS pollution.(4) Based on the long time series of meteorological data, Statistical Downscaling Model (SDSM) and Weather Generator (NCC/GU-WG) were simulated and compared. The results showed that the two statistical downscaling methods both had achieved satisfactory results, and the simulation of temperature was better than precipitation. NCC/GU-WG has certain advantages at simulating amount of precipitation, while SDSM was better at simulating variability of precipitation and temperature.(5) Under GCMs A2, B2and NCC/GU-WG climatic scenarios, the change of precipitation and temperature in the Miyun Reservoir watershed during2021to2050were predicted. The results showed that there were significant increasing trends for the precipitation and temperature in this area. Future climate change simulated by B2 scenario was significantly higher than that of other scenarios. Impacts of climate changes on pollution loads were simulated by using SWAT model with input downscaled climate variables. Runoff, TN and loads showed increasing trends in the next30years. Runoff would increase significantly in the period of2021to2050compared to the period of1961to2000, which had an increase of15%. The inerease of TN and TP loads were relatively smaller than runoff, but had larger interannual fluctuations. |
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