流域人类活动净氮输入的时空变化及其对河道水质的影响

发布时间：2018-01-28 14:02

本文关键词： 净氮输入 GBNP模型氮素入河负荷入河系数河道水质　出处：《清华大学》2016年博士论文　论文类型：学位论文

【摘要】：人类活动使流域中的氮输入量不断增加,由此引发了一系列的水环境问题。本文以新安江流域上游和长江流域上游为研究对象,分析人类活动净氮输入及其在流域中的时空分布特征;采用分布式流域非点源污染模型GBNP,模拟氮素在流域中通过水文过程对河道的补给,分析入河氮素的时空特征;模拟氮素在河道中的迁移转化过程,分析入河氮素对河道水质的影响。基于社会经济统计资料,论文首先分析了新安江流域上游和长江流域上游自上世纪90年代以来的人类活动净氮输入量的时空分布与变化情况;然后,在两个流域分别构建了分布式非点源污染模型GBNP,模型的率定与验证结果显示,模型在两个流域适用性良好;最后,基于模拟结果,分析了流域中的入河氮素负荷与河道水质的时空变化,并以新安江流域为例,探讨了河网系统中氮素滞留的影响因素;以长江流域上游为例,探讨了人类活动对氮素负荷和河道水质的影响。在新安江流域的研究结果显示,流域的主要氮素来源均为农田氮肥施用和大气氮沉降,人类活动净氮输入量较高的区县主要包括屯溪区、歙县和绩溪县。人类活动净氮输入与城镇与农田的面积呈显著正相关,与森林面积则呈显著的负相关关系。GBNP的模拟结果显示,流域年均入河总氮负荷强度约为1.16 ton/km2,5-8月入河总氮负荷量约占全年总负荷量的57.7%,流域总氮入河系数约为0.16;入河总氮负荷量主要取决于人类活动净氮输入,并受降雨量和降雨强度及流域下垫面条件的影响。流域河道水质整体良好,汛期总氮浓度低于非汛期,年均氮素滞留率约为80%;氮素在河网系统中滞留率从一级河道(河源)至干流河道递减。在长江流域上游的研究结果显示,流域中氮素来源主要为氮肥施用和大气氮沉降,食品/饲料氮净输入量所占比例也较高,其中成都平原地区人类活动净氮输入量最高;城市化通过改变城市及周边地区的种植方式与养殖类型,增加了人类活动净氮输入量。GBNP的模拟结果显示,流域年均入河总氮负荷强度约为1.50ton/km2,其中7、8月份的入河负荷量约占全年总负荷量的65%以上,流域年均总氮入河系数约为0.26。在氮素供给充足的区域,流域总氮输出量主要受降雨-径流过程控制,反之,限制总氮输出量的主要因素则是流域中氮素累积过程。汛期的河道总氮浓度显著高于非汛期,流域年均氮素滞留率约为87%。情景分析结果表明,退耕还林和控制施肥能有效降低入河总氮负荷,减少氮素通过河道的输出量。
[Abstract]:Human activities make the input of nitrogen in the river basin increase, which leads to a series of water environmental problems. This paper takes the upper reaches of Xinanjiang River and the upper reaches of the Yangtze River as the research objects. The characteristics of net nitrogen input from human activities and its temporal and spatial distribution in the watershed are analyzed. A distributed watershed non-point source pollution model (GBNPP) was used to simulate the recharge of nitrogen to the river channel by hydrological process in the watershed and to analyze the spatio-temporal characteristics of nitrogen in the river. To simulate the process of nitrogen migration and transformation in river, and analyze the effect of nitrogen on river water quality. Based on social and economic statistics. Firstly, the temporal and spatial distribution and variation of net nitrogen input from human activities in the upper reaches of Xinanjiang River and the upper reaches of Yangtze River since -10s are analyzed. Then, a distributed non-point source pollution model (GBNPs) was constructed in two watersheds. The results of rate determination and verification showed that the model was suitable for the two watersheds. Finally, based on the simulation results, the temporal and spatial changes of nitrogen load and channel water quality in the river basin are analyzed, and the influencing factors of nitrogen retention in the river network system are discussed by taking the Xinan River basin as an example. Taking the upper reaches of the Yangtze River as an example, the effects of human activities on nitrogen load and river water quality were discussed. The results showed that the main nitrogen sources in the basin were farmland nitrogen application and atmospheric nitrogen deposition. The areas with higher net nitrogen input from human activities mainly included Tunxi County, Shexian County and Jixi County. There was a significant positive correlation between the net nitrogen input of human activities and the area of towns and farmland. The simulated results of GBNP showed that the average annual nitrogen load intensity was about 1.16 ton/km2. From May to August, the total nitrogen load of the river accounts for 57.7 percent of the total load of the whole year, and the coefficient of the total nitrogen into the river basin is about 0.16. The total nitrogen load mainly depends on the net nitrogen input from human activities, and is affected by rainfall, rainfall intensity and underlying surface conditions. The water quality of the river is good, and the total nitrogen concentration in flood season is lower than that in non-flood season. The average annual nitrogen retention rate was about 80%. The retention rate of nitrogen in the river network system decreases from the first class river (source) to the main stream. The results of the study in the upper reaches of the Yangtze River show that the main sources of nitrogen in the river network are nitrogen fertilizer application and atmospheric nitrogen deposition. The proportion of net input of food / feed nitrogen was also high, and the net nitrogen input of human activities was the highest in Chengdu plain. Urbanization increased the net nitrogen input of human activities by changing the planting patterns and breeding types in cities and surrounding areas. The average annual nitrogen load intensity is about 1.50 ton / km ~ (2), in which the inflow load in July and August accounts for more than 65% of the total load in the whole year. The average annual total nitrogen inflow coefficient is about 0.26. In the region with sufficient nitrogen supply, the total nitrogen output of the basin is mainly controlled by the rainfall runoff process. The main factor limiting the total nitrogen output is the accumulation of nitrogen in the basin. The total nitrogen concentration in the river in flood season is significantly higher than that in the non-flood season, and the average annual nitrogen retention rate is about 87. The results of scenario analysis show that the total nitrogen concentration in the river is much higher than that in the non-flood season. Returning farmland to forest and controlling fertilization can effectively reduce the total nitrogen load and the output of nitrogen through the river.
【学位授予单位】：清华大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：X52

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