基于非点源污染过程的景观源汇功能强度分布及其水质响应研究

Relationship between landscape pattern and ecological process is the key topic of landscape ecology. Landscape units are classified as "source" and "sink" according to landscape function to certain ecological process. "Source" landscape is recognized as contributing positively to the development of the ecological process while "sink" landscape is unhelpful. For non-point source pollution process, the "source" type was defined as where the pollutants outflows and the "sink" type was defined as where pollutants retained. The "source-sink" analysis method was widely used to related the landscape pattern with water quality. However, empirical coefficient was assigend to a certain landscape type to characterize the intenstity of the landscape function according to the relatively important of different landscape types without considering the variance of landscape function among the landscape units classified as the same type. The heterogeneity of landscape function was owed to the different amount of nutrient inputs, hydrological characteristic and vegetation quality. Therefore, the research focused on characterizing the distribution of the intensity of landscape function (source or sink) according to the "source-sink" theory based on comprehensive field investigation, hydrological analysis, remote sensing monitoring and so on. For the non-point source pollution process, the landscape function of source type for the contamination outflow during the rain event was calculated by nutrient inputs and topographic index, while the "sink" function for the migration of pollutants was calculated by slope and percentage of vegetation cover. After collecting several water samples in Xiang Xi River watershed upstream of the backwater area in the Three Gorges Reservoir, we will correlate the water quality with the new source-sink function distribution index. Then, the study explore the mechanism of the relativity distribution of source and sink function affecting on the water quality. It could identify the key region of non-point source pollution in a watershed and suggest a better govern plan.

格局与过程的关系研究是景观生态学的核心研究内容之一。将景观单元根据功能不同分为“源”、“汇”景观，并在此基础上建立的“源汇理论”在“景观格局—水质”关联研究中得到了广泛应用，已有的研究中，同一景观类型的源汇强度权重多采用相对重要性进行经验赋值，而忽略了由于养分投入、水文特征、植被生长状况等差异造成的同一景观类型的源汇功能强度的差异。本项目在源汇理论的基础上，综合野外调查、水文分析、遥感监测等手段，以养分投入、地形指数表征“源”景观在降雨产污过程中的源功能强度，以坡度、植被覆盖度等表征“汇”景观在污染物迁移过程中的汇功能强度，量化景观源汇功能强度在空间上的异质性，并以三峡水库香溪河回水区以上自然流域为研究区，探讨流域源汇景观强度分布对水质的作用机制，在源汇功能强度空间分布状况的基础上，为流域的非点源污染关键区域识别、治理提供直观依据。

以三峡水库支流流域为研究对象，基于多时相遥感影像，采用面向对象的方法监测获得研究区2012年和2016年的源汇景观类型分布。采用非点源污染输出系数法模型和牲畜数据收集，得到了2012年和2016年非点源污染源功能强度的分布，并根据不同时相遥感影像采用像元二分法反演了年均植被覆盖度，作为非点源污染汇功能强度分布。.构建了针对三峡水库的多光谱叶绿素a反演模型，并统计三峡水库175m蓄水位以来不同年份不同支流水质营养等级分布状况，可以发现大宁河、磨刀溪是水华发生最严重的支流，其次为神农溪、香溪河、小江，其它支流相对较好，但也有水华现象发生，对比库首库中地区7条主要支流的非点源污染负荷估算结果展开相关分析，可以看到富营养等级频次较高的流域非点源污染负荷较低，这表明，以叶绿素a为代表的支流水质状况不仅与流域单位面积污染物来源有关，同样与不同流域之间的水文水动力条件状况有关。.以香溪河、神农溪、小江3条支流共21个断面为出水口提取其汇水区域，并以水流路径距离为空间要素，通过缓冲区分析和源汇景观负荷对比指数的构建与计算，定量得到不同断面汇水区单元的景观格局，与对应的水质关联分析可以得到：.（1）TN、叶绿素a指标，农业用地尤其是近水体的农业用地对TN、叶绿素a的影响较大，但在水位变化期间和高水位枯水期，由于干流来水的补给，农业用地对TN、叶绿素a的影响程度降低，而在低水位汛期，则呈显著正相关关系；林灌草比例与TN指标呈显著负相关，离水体越近，相关性越强。在香溪河（受到上游截水影响）流域中，建设用地对TN的影响最大，叶绿素a与景观格局关联不大。.（2）TP与景观格局的关联性不强，2000m以内的建设用地比例与水体TP浓度呈显著的正相关，而在整体流域中相关性较弱，这表明，超过离水体2000m区域内的建设用地对水体TP的影响很小。.（3）基于源汇景观分类的负荷对比指数结果同样能较好的表征断面TN、叶绿素a浓度的高低，而在特殊的水文流域如香溪河中，则难以进行表征分析。