平原城市河流面源污染研究范围及方法的选择与效果比较

The Studied area selection and result comparison of river non-point source pollution in plain urban area

由于平原城市地貌起伏不大,较难划分城市河流的流域范围,使得与河道面源污染相关的研究范围的边界确定存在一定的困难。针对这一问题,本文对比了基于缓冲区和排水区的两种研究范围及方法。根据遥感影像,利用GIS提取研究区内土地利用信息并与河流水质进行回归分析,对比两种范围及方法所得出的结果,试图为城市河道污染物的研究及管理提供方法支持和理论依据。本文选取了天津滨海地区11条河流进行研究,结果表明:(1)选取城市排水区作为土地利用数据的方法能够与河流中污染物的发生,迁移的真实情况相符合,能够综合考虑不同的景观格局分布对于水质的影响,结合平原城市的特殊性反映土地利用与河流污染物之间的相关关系,在机理严谨性上优于使用缓冲区范围,在整体性上更为完整;(2)基于缓冲区的研究方法能够在一定程度上解释在地表径流作用下,河流近岸不同距离的土地利用类型对河流污染物的影响,如耕地对污染物的影响,河流近岸100 m缓冲区的联合显著性为0.848,300 m缓冲区的仅为0.165;(3)土地利用类型对河流中污染物类型的贡献和消减趋势基本一致,城市居民点与工矿用地是河流当中重金属污染物如铅、汞的主要输入源;耕地对重金属等污染物有一定的截留消减作用,但在面积较大时增加了河流的有机污染物如氨氮;林地、园地、草地和水体对于城市河流污染物有一定的净化作用。两种方法结合起来可以得出更为详尽、客观的研究结果。

As the plain urban area doesn’t show much difference in topography conditions, the usage of traditional river basin concept applying in plain urban area is not convincing. Thus, it’s hard to make an identification of effective border of the land use that can impact the relevant river water quality. To solve this issue, this paper compares the final results based respectively on the traditional buffer zone and drainage area method. Using 11 rivers’ pollutants in Tianjin Costal region and RS image, this paper apply GIS to study the correlation between land use and water quality by analyzing land use buffer data along the river banks and selecting land use data in drainage area, trying to provide methods and theories support to analyze and manage the rivers’ pollutants in plain urban area. The preliminary results showed that （1）The drainage area method can better illustrate the relationship between water quality and urban land use by taking full consideration of urban specialties such as water pollutant occurrence, movement and the impact of different landscape on water quality. It’s more theoretically convincing and comprehensive compared with the buffer zone analysis.（2）The buffer zone analysis can explain the influence on water quality under the effect of surface runoff to a certain extent. The negative correlation between the distance of buffer zone and the joint significance level can be used to identify the key area. For example, the joint significance level for arable land within 100 meters buffer zone is 0.848 and that number decreases to 0.165 as buffer zone expands to 300 meters. （3） Both methods show the same pattern for the relationship between water pollutant and land type. Urban construction land use will increase the water pollutant such as Pb and Hg;the arable land can reduce the heavy metal pollutant but will increase the organic pollutants such as ammonia as the area of arable land gets bigger;the grass land and water body will serve as the cleaner of the pollutants and help to improve the water quality. The combination of these two methods can help to get the result more objectively and comprehensively.