Environmental Behavior, Simulation And Prediction Of Nonpoint Source Nitrogen And Phosphorus In Cold Regions

Fresh water is a fundamental resource, integral to all ecology and societal activities. Drinking water security is important to human health and the national economy. China is one of the fifteen countries who face the most serious water crisis. Yet fresh water resources are unevenly and irregularly distributed, the cold regions faced the program of extremely water short and poor water quality. Due to the nonpoint source pollution, these regions face the serious crisis of the water resource shortage and water pollution. For the cold regions, the long winter processes have strong effects on environmental behavior of nonpoint source pollution. In this study, the nonpoint source pollution affect by winter process, the nitrogen and phosphorus budget, and the physically based model (SWAT) were investigated in DRW, respectively. Finally, the simulation and prediction of water resources and quality were conducted to study the influence of water diversion project and future climate change.First, a series of experiments using the rainfall simulator in small plots were conducted to investigate nonpoint source nutrients influenced by winter processes. At all sites, there was a great deal of variation in nutrient concentrations before and after winter. In arable land and grassland, the nitrogen loss was raised both, particularly in interflow. In contrast, the phosphorus concentrations were reduced both in surface runoff and interflow. The results were mainly attributed to winter processes effects on nutrient accumulation and transformation, soil structure, and hydrological condition. Greater TN and TP concentrations in soils were observed after winter processes, which were resulted from soil frost, runoff lacking and decreasing nutrients uptake by vegetation. The winter processes also disturb the nutrient transformation in soil. Further, freeze-thaw cycles caused the disruption of soil structure, and induced more micro-aggregates. This effect released more nitrogen from the destroyed aggregate, and obviously increased TN losses in interflow. On the contrary, the TP loss was decreased owing to the increasing sorption of exposed new surfaces and the high sorption capacity of the dissolved phosphorus. Finally, hydrological conditions impacted by snowpack and frozen soil layer, might trigger more serious NPS nutrient losses in the first flush. This study suggests that losses of the NPS nutrient are obviously disturbed by winter processes in the cold regions, and the interflow could be considered as an important component of nitrogen loss after winter processes.Second, the nitrogen and phosphorus budgets in DRW were constructed to investigate the temporal and spatial distribution. The result indicated that the nitrogen and phosphors budget were both obviously changed from1985to2004. The whole trends were increased noticeably in the early period, and decreased slowly in the later period. But there was a break in1995. The change of nitrogen and phosphorus was both influenced by the net food and feed input, and fertilizer use. The mutation of hydrology induced the break of the budget in1995. Further, the temporal and spatial distribution of budgets were investigated. The result indicated that the nitrogen and phosphors budget were both increased in the entire watershed from1985to1999, especially in the upper watershed in Qingyuan country and Xinbin country. In the period of2000-2004, the budgets of these regions were decreased, but the budgets in surrounding countries of the reservoir were increased obviously. It also was found that there was a close relationship between nitrogen and phosphorus budget and TN and TP concentration in the reservoir, respectively. However, for2003-2004, TN and TP concentrations were increased may be influenced by the spatial distribution change of budget.Third, SWAT model was used to investigate the efficiency applied in cold regions. The environment behavoir of nonpoint source nitrogen and phosphorus was also demonstrated in this study. It was found that there was higher simulation accuracy for flow, sediment and nutrients in the watershed. However, there was lower simulation accuracy for the nutrients in the reservoir. The reason was found that the reservoir model party of SWAT was established based on the smaller reservoir, which is not competent for the broad valley reservoir. The environmental behavior of nonpoint source nitrogen and phosphorus was special in cold regions. There were60%nutrients output focused in the rainy season (Jun-Sept). Large amounts of nutrient losses in March were found due to the effect of the winter process in cold regions. Hydrological conditions impacted by snowpack melt and frozen soil layer triggered more serious NPS nutrient losses in the first flush due to larger amounts of nonpoint source pollution accumulated in the watershed. It was found that the reservoir in the upper watershed may reduce the export of nonpoint source pollution in dry seasons. This effect reduced the export of nitrogen and pollution in Suzi River.Finally, SWAT was investigated the water resource and quality changes in the reservoir influenced by the water division project and climate change. For the water division, the water resource was perceptibly increased. In contrast, the nitrogen concentration was increased owing to there was higher TN concentration in the source of water division. For the climate change, there was a decreased trend in flow, nitrogen and phosphorus load. The reduced flow was reduced by the higher temperature and evaporation. The decreased nitrogen and phosphorus loads were subject to reduced soil erosion of surface runoff and higher nutrients uptake. For the distribution of months, the load of flow and nutrients in Feb to Nov was reduced, and the left months were increased. The increased trend in Dec and Jan was attributed to the increased temperature and extreme weather, which made the snowpack melted earlier.In summary, this study will help to understand the environmental behavior of nonpoint source nitrogen and phosphorus in cold regions, and provide scientific support for the nonpoint source pollution control and water resource protection currently and in the future.