资江尾闾集水区景观格局与非点源污染过程关系研究

Relationship between landscape patterns and non-point source pollution processes in the Zijiang catchment tail,China

为识别资江尾闾集水区非点源污染的关键源区并探究非点源污染过程与景观格局之间的关系,利用SWAT模型模拟非点源污染总氮、总磷的时空输出特征,选取景观格局指数定量描述景观格局特征,通过冗余分析(RDA)方法分别从景观、类型两个层次分析子流域尺度上非点源污染过程与景观格局的关系。结果表明:在率定期与验证期径流量、总氮、总磷的R^(2)与ENS均大于0.66,表明SWAT模型在研究区的适用性较好;总氮、总磷的关键源区空间分布上不完全一致,在非点源污染输出的关键时期,关键源区分别贡献了研究区非点源总污染的31.64%、43.73%。景观格局与非点源污染过程的联系密切,景观水平上,流域内景观越破碎、景观类型越复杂、人类活动对其影响越大,非点源污染负荷输出值越高;类型水平上,聚集度指数(AI)、最大斑块指数(LPI)、斑块平均面积(AREA-MN)、斑块边缘密度(ED)是对“源”“汇”景观具有显著影响的共性指标,其中“源”景观破碎度越大、斑块面积越大、聚集度越高越会加剧非点源污染负荷的输出,而破碎度小、景观形状复杂、斑块连通度高的“汇”景观则有利于阻截非点源污染物。研究表明,非点源污染过程与“源”“汇”景观格局存在明显的内在联系,合理布设“源”“汇”景观可以降低非点源污染风险,从土地利用角度为非点源污染防治提供了借鉴。

In order to identify the critical source areas of non-point source(NPS)pollution and explore the relationship between the NPS pollution process and landscape patterns in the Zijiang catchment tail,the SWAT model was applied to simulate the spatiotemporal output characteristics of NPS pollution for total nitrogen and total phosphorus.The landscape pattern metric was utilized to quantitatively assess the characteristics of the landscape pattern.The relationship between NPS pollution and the landscape pattern was analyzed by the redundancy analysis(RDA)method from the two levels of landscape and patch type at the sub-basin scale.The R2 and ENS values of runoff,total nitrogen,and total phosphorus were all greater than 0.66 in the periods of calibration and verification,thereby indicating that the SWAT model has good applicability in the study area.The spatial distribution of the critical source areas of total nitrogen and total phosphorus was not completely consistent.In the critical period of NPS pollution,the critical source areas contributed 31.64%and 43.73%of the total NPS pollution in the study area,respectively.The landscape pattern was significantly correlated with the NPS pollution process.At the landscape level,the RDA between the landscape metric and pollution load showed that the more fragmented the landscape,the more complex the landscape type,and the greater the impact of human activities on the landscape,the higher the output value of the NPS pollution load.At the type level,the aggregation index,largest patch index,average patch area,and patch edge density were the common indicators that had a significant influence on the source and sink landscapes;the larger the fragmentation degree,the larger the patch area,and the higher the aggregation degree,the stronger the output of the NPS pollution load.Meanwhile,the sink landscape with small fragmentation,a complex landscape shape,and high patch connectivity could help to intercept NPS pollution.The study shows that there is a clear internal relationship between the process of NPS pollution and the landscape pattern of sources and sinks,and the rational layout of the landscape of sources and sinks can reduce the risk of NPS pollution.This study provides a reference for the prevention and control of NPS pollution from the perspective of land use.