流域养分迁移过程对源汇景观格局动态的响应

The formation of non-point source pollution has a close relationship with the patterns of “source” and “sink” landscapes. However, the “source” and “sink” landscapes would change under different rainfall conditions such as rainfall amount, rainfall intensity, and rainfall duration, which make the processes of nutrient transportation more complicated. So, understanding the response mechanism of nutrient transportation processes to dynamics of “source-sink” landscape pattern is significant in revealing the forming mechanism of non-point source pollution. In this study, a typical small watershed of Danjiangkou Reservoir, which is the water source for the Middle Route Project under the South-to-North Water Transfer Scheme of China, is selected as the study area. Based on the historical measured data of typical runoff plots and slopes, the characteristics of “source” and “sink” landscape dynamics under different rainfall and surface conditions will be analyzed, and a system for the definition of “source-sink” landscape dynamics based on different rainfalls will be established. Continuous monitoring of water quality will be performed to study the dynamics and transportation processes of the nutrients. Then the quantitative analysis will been performed to analyze the responses of the nutrient export to the “source” and “sink” landscapes under different rainfall conditions based on rainfall-runoff processes, and to reveal the coupling mechanism between nutrient transportation processes and dynamics of “source-sink” landscape patterns. The results of this research will provide scientific bases for controlling non-point source pollution and protecting the water quality of drinking water reservoirs.

面源污染的形成与“源汇”景观的空间分布格局具有密切的联系。在次降雨过程中，面源污染的“源汇”景观会随着雨强、历时和降雨量等降雨条件的改变而发生变化，使得养分的迁移过程更加复杂化。因此，理解养分迁移过程对“源汇”景观格局动态的响应机制，对揭示面源污染的形成机理具有重要意义。本项目选择南水北调中线水源地丹江口库区典型小流域为研究区，利用径流小区与典型坡面历史观测数据，研究“源汇”景观在不同降雨和下垫面条件下的动态变化规律，建立基于不同降雨事件的面源污染“源汇”景观动态划分体系；通过对流域沟道水质的长期定位监测，研究养分的动态变化规律与迁移过程；在此基础上，结合降雨径流过程，定量分析不同降雨特征下流域养分输出与“源汇”景观格局的响应关系，揭示养分迁移过程对“源汇”景观格局动态的耦合机制，为面源污染治理与水源地水质保护提供科学依据。

流域“源汇”景观的空间分布格局对面源污染的形成具有重要的影响。本项目以南水北调中线水源地丹江口区域胡家山小流域为研究区，结合流域的土地利用、土壤等资料，在进行水质的长期定位监测及降雨过程监测的基础上，研究了养分的动态变化规律和迁移过程，揭示了“源汇”景观格局与流域养分迁移过程的耦合机制，通过研究发现：（1）将源汇景观格局指数与土壤侵蚀、土地利用数据相结合，有助于更精确的识别流域面源污染的关键源区；（2）常规水质监测结果显示，全氮和硝态氮是研究区主要的面源污染物，在雨季和旱季均表现出明显的空间变异特征，高浓度的全氮和硝态氮多分布在流域内耕地和居民地较为密集的南部地区；（3）在子流域及50m、100m、150m和200m缓冲区等不同尺度上，林地和汇景观比例在0.01水平上与水质指数（WQI）有显著的正相关关系，与全氮 和硝态氮之间有显著的负相关关系，与铵态氮、全氮、高锰酸盐指数的关系不显著，表明流域内林地及汇景观的比例对提升水质具有重要的影响，且汇景观比例的提升能显著降低全氮和硝态氮的浓度；（4）在干旱和湿润季节，全氮和硝态氮浓度与汇景观比例的均在200m缓冲区尺度上具有最优的拟合效果，因此，为了在保证农业正常生产的同时也能有效控制面源污染，可重点对200m缓冲区内的源汇景观比例进行优化；（5）源汇景观格局和降雨特征都会对养分的迁移过程产生影响。较高的汇景观比例能使有效降低径流中的养分浓度，短时强降雨类型所形成的超渗产流会促使径流中的养分浓度处于较高的水平。本研究结果补充了面源污染形成机理的研究内容，同时对水源地水质保护及流域面源污染的科学防治具有重要的借鉴意义。