河岸带植被格局对土壤养分流失的“源－汇”效应及其机理

Exploring the relationships between land use structure and ecological processes is an important content of landscape ecology. Riparian in the landscape area is smaller, the attention of people to riparian is not enough, and the cognition of riparian ecological processes is fuzzy. Due to the disturbance of human activities strongly, the riparian vegetation types and its spatial configuration have occurred tremendous changes. According to preliminary studies, the riparian cultivated farmland and the bare land may play a "source" role in the process of nutrient loss. The riparian forestlands and grasslands which are located between the farmland and river channel may play the role of "sink" in the process of nutrient loss. However the interference of the riparian area is complex and changeable. How is the "source-sink" effect of different riparian vegetation types and its patterns on the process of soil nutrient loss？How to optimize the riparian vegetation pattern in order to achieve the balance of soil nutrients and reduce the pollution of the rivers? Therefore, six riparian vegetation patterns from the upland to the Yellow River channel were chosen in this study: grassland, cropland, forestland, cropland-grassland, bare land and forestland-cropland. We compared the effect of different riparian vegetation patterns on the process of soil nutrient loss and interception during the period of main rainfall. And analysis the dominant factor which impact the "source- sink" effect in the process of soil nutrient loss. In the view of soil nutrient balance, provides the basis for the riparian vegetation pattern optimization and the control of soil nutrient loss in riparian zone.

探究土地利用结构与生态过程的相互关系，是景观地理学研究的重要内容。河岸带所占的景观面积较小，人们对其的重视还不够，对其生态过程的认知还比较模糊。由于受强烈的人类活动干扰，河岸带的植被类型及空间配置均发生了巨大的变化。据前人研究，对于养分流失过程来说，河岸人工种植的农田和裸地等景观类型，可能起到了“源”的作用，而位于河岸农田和河道之间的林地和草地等景观类型，可能起到了“汇”的作用。但河岸区域的干扰是复杂多变的，不同的河岸植被类型及其格局在土壤氮磷流失过程中的“源－汇”效应和强度大小究竟如何呢？如何通过优化河岸带的植被格局，来实现土壤的养分平衡和减少河流的污染？为此，本项目拟以黄河下游的6个河岸植被模式为研究对象，比较不同植被模式在主要降雨期间的土壤养分流失和截留过程；分析影响土壤养分流失过程中的“源－汇”效应的主导因子。从养分平衡的角度，为河岸区域的土壤养分流失防治和植被格局优化提供依据。

河岸带是河流生态系统和陆地生态系统之间的生态交错带，也是一个敏感和脆弱的生态区域。由于受强烈的人类活动干扰，河岸带的植被类型及空间配置均发生了巨大的变化。通过对黄河沿岸河岸带的植被类型调查，明确了河岸带植被类型和植被格局的空间演变特征。分析了河岸带植被类型变化对土壤养分保持能力的影响，结果表明养分保持能力从高到低依次为：狗牙根群落＞看麦娘群落＞柽柳群落＞艾蒿群落＞白茅群落。评价了河岸带不同植被类型的土壤养分流失风险，结果表明非点源磷流失的风险从大到小依次为：果园（1.86）、黄豆地（0.55）、玉米地（0.39）、杨树林地（0.31）、荒草地（0.30）。通过对不同河岸带植被格局的生态要素采样分析，研究了不同河岸带植被格局的土壤养分流失风险。研究发现，对于河岸的林地-农田，土壤养分的流失风险最大，从河漫滩到河道的环境梯度上土壤全氮、全磷、有效氮、有效磷和土壤有机质均呈现逐步降低的趋势。对于林地-草地河岸带，从河漫滩到河道的环境梯度上，土壤养分在河岸断面上均呈现出波动或比较平缓的迁移趋势。对于农田-荒草地河岸带植被配置模式，结果表明处于下坡的荒草地可以起到固定和截留来自河岸断面上坡区域流失的土壤养分。研究表明河岸的植被缓冲带在农业面源污染防控中具有重要的作用，构建合适的植被配置模式可以有效的防治河岸区域的土壤养分流失。