| Water quality deterioration has been one of the most serious water issues in watershed management around the world, and has been a great threat to global water security. Recently, the integrated water quality and quantity management has been one of the hot topics in addressing global water pollution. Moreover, it is of great significance to accrurately depict the hydrological and water quality processes at basin scale in the integrated water quality and quantity management and water quality improvement. Whereas, the inherent nonlinearity and time-variation in hydrological processes become increasingly significant with intensive anthropogenic activities and climate change forcing. Thus, the hydrology statistical models, hydrological models, hydrodynamic models and water quality models, etc. should be made full use of, so as to accurately describe the variations in hydrological factors and water quality elements at basin scale, and identify and quantify the flow regime changes and underlying water quality problems due to anthropogenic activities and climate change.Supported by the National Grand Science and Technology Special Project of Water Pollution Control and Improvement (2014ZX07204-006), the study was carried out on the basis of watershed hydrology theory, and made use of knowledge on pollutants migration and transformation, hydrodynamics and systematic hydrology and so on. Thus, the variations in hydrological and water environmental factors were detected, and the anthropogenic factors closely related with water quality changing were identified; an mathematical model describing hydrological and water quality processes was established, and the influences of climate change and anthropogenic disturbances were quantified. Moreover, Huai River Basin and Xin’anjiang Catchment in China were selected for case study. The main work includes:(1) The significances of the research on the numerical simulation of watershed environmental hydrological processes in a changing environment were discussed, and the research progresses on water cycle, environmental hydrology and the integrated simulation of water quality and quantity processes in a changing environment were reviewed around the world.(2) The mechanisms of environmental hydrology at basin scale were clarified, along with the influences of climate change and anthropogenic interferences. Moreover, the study framework was proposed, including a) the assessment of hydrological and water quality variations using multi-statistical analyses and indentification of the factors closely related with water quality variations, b) the construction of an integrated model incorporating hydrodynamic, hydrology and water quality modules at basin scale in a highly regulated basin, and assessment of the hydrological and water quality responses to dam regulations and point source emissions, c) the establishment of a non-point source pollution model based on the Soil and Water Assessment Tool in a watershed with multiple pollution sources, and evaluation of the hydrological and non-point source pollution responses to climate change, which was projected through the coefficient adjustment method with the future climate scenarios.(3) The Huai River Basin was selected as the research area representative of the highly regulated and polluted basins for water quality variation analyses. The results showed that:a) water quality deterioration at basin scale was ameliorated from 1994 to 2005, b) CODMn and NH3-N concentration presented spatial autocorrelation although their spatial structures varied, specifically, the high pollution cluster center of CODMn from 2000 to 2005 was coincided with that of NH3-N, which was aggregated at Fuqiao, Huangqiao and Jialuhe, c) the variations in water quality was significantly related with point source pollutions, flow regulation, water temperature and land use variations, and so on.(4) Moreover, an integrated numerical model was constructed in the upper and middle regions of the highly regulated Huai River Basin, incorporating the hydrological module, hydrodynamic module, water quality module and a dam regulation module. The water level, water discharge, CODMn and NH3-N concentrations, CODMn and NH3-N loads in 2007 were used for model calibration, and those in 2004 and 2008 were for model validation. The relative errors for the six hourly series were within ±1.80%, ±30%,±15%,±50%, ±18% and ±45%, respectively, the average correlation coefficient were 0.96,0.97,0.61,0.81,0.91 and 0.67, respectively, and the average Willmott index were 0.97,0.98,0.91,0.71,0.74 and 0.56, respectivey. Furthermore, the average Nash-Sutcliffe coefficient were 0.87,0.93,0.81 and 0.33 for water level, water discharge, CODMn and NH3-N loads processes. Thus, the integrated model could well reflect the flow regime and water quality variations in regulated river basins. Besides, Fuyang, Huaidian and Linhuaigang dams promoted water quality improvement, while the regulation rules at Yingshang and Bengbu dams played negative roles in water quality improvement under the current point source emissions scenarios. And dam regulation and point source emissions contributed 56% and 44% for CODMn deterioration, and 40% and 60% for NH3-N deterioration at Yingshang, and contributed 30% and 70% for CODMn deterioration, and 25% and 75% for NH3-N deterioration at Bengbu station, respectively.(5) The influences of various factors on hillslope water and pollutants migration were quantitatively analyzed through the nonlinear precipitation-runoff-pollutant response function, including the precipitation amount, antecedent precipitation index, underlying property and pollution loads in soil surface. Moreover, the contributions of hillslope pollutants for instream water quality variation were identified. The hillslope contributed no more than 25% and 8% pollutants for CODMn and NH3-N concentration variations in the regulated Huai River.(6) SWAT model was established in the Xin’anjiang Catchment. The average absolute relative error, correlation coefficient and Nash-Sutcliffe coefficient were 0.05, 0.95,0.90 and 0.07,0.84,0.65, respectively for monthly water discharge and sediment load processes during both the calibration (2001-2007) and validation (2008-2010) periods, and the average relative error and correlation coefficient were 0.04,0.46 and 0.08,0.73, respectively for total nitrogen and total phosphorous load processes. Thus, SWAT can be a good estimator for the identification and quantification of non-point source pollution at catchment scale, and the assessment of climate change influences. She and Xiuning County contributed more than 50% of the catchment pollutions. At the catchment scale, rice land contributed the most for nutrient loads generation, followed by tea garden, winter wheat land, forest and grassland. Besides, the future daily climatic variables driving the established model were derived from the average of the 21 CMIP5 global climate models using the coefficient adjustment method. The results showed that:in comparision of the conditions during 2000-2010, both water discharge and sediment load tended to increase and decrease, respectively under the RCP4.5 and RCP8.5 scenarios, while they tened to decrease and then increase under RCP2.6 scenario; while various changing patterns exited in the total nitrogen and total phosphorous load distributions under the three scenarios. |
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