【作者】 高常军；

【导师】 崔丽娟；

【作者基本信息】 中国林业科学研究院 ， 生态学， 2013， 博士

【摘要】 C、N和P等营养物质通过河流向下游水体输送及其对下游水生态系统的影响已经成为国际上流域生态学领域关注的重点问题。河流水体中C、N和P等营养物质的输移过程主要受流域内气候、地形地貌、土地利用及水文条件等因素影响。目前，以土地利用/覆被变化为标志的人类活动已经改变了47%的地球表面，导致全球河流营养盐迁移过程改变和输出量的增加，并危及下游水生态系统的健康状况。因此，系统分析流域土地利用对河流水体中碳、氮和磷等营养物质输出的调控机理是当前了解流域内各类营养物质经由河流向下游水体迁移的生物地球化学行为，及采取相关措施以减缓流域营养物质向下游水体输送，维护或恢复下游水生态系统健康所亟待解决的问题。苕溪作为太湖的主要供水和营养物质输入源头之一，对太湖水体富营养化甚至整个长江三角洲地区的水环境安全有着重要影响。本文选择苕溪流域作为研究区，以野外水质与水文监测数据、土地利用与DEM数据等为基础，同时结合遥感与GIS等空间信息技术，通过多步回归、冗余分析、空间多准则分析等典型数理统计方法，系统分析流域土地利用特征、水文过程对溪流水体中C、N、P迁移的调控作用及其影响力所表现出的时空尺度依赖性；评估土地利用综合特征影响下，流域内每个统计单元的C、N、P释放潜力等科学问题。通过研究得出以下主要结论：（1）西苕溪流域内某些景观特征对溪流水体中C:N、C:P和N:P三种营养元素生态化学计量比指标的季节变化有显著影响，而作为流域水文过程代理变量的溪流流量对流域景观特征与溪流水体中三种营养元素生态化学计量比指标之间的关系具有显著调节作用，且这种调节作用因流域景观组分及营养元素比种类的不同而因。同样地，西苕溪流域每条溪流中三种营养元素计量比（C:N、C:P和N:P）与其所在集水区内溪流流量之间的相关关系因不同集水区内景观结构特征的差异而有所不同。在各集水区之间，伴随某些景观类型面积的变化，其对三种元素计量比与溪流流量之间相关性的控制作用主要体现在影响两者间相关性的正负方向方面。（2）流域景观对溪流水体中营养物质影响的尺度效应分析表明：在苕溪流域中，与岸带和河段尺度相比较，溪流水体中C、N、P营养物质对来自集水区尺度上的自然环境与土地利用所产生的压力更为敏感。流域自然环境及三种空间尺度（河段、岸带和集水区）上的人为干扰变量对河流水体中C、N、P营养物质动态变化的相对影响力随季节更替而产生变化。特别是在雨季期间，流域尺度上自然环境与人为干扰变量所产生的影响力则有所下降，而岸带与河段尺度上人为干扰变量对溪流水体中营养物质变化的作用力显著升高。因此，溪流水体中C、N、P营养物质的动态变化是苕溪所在流域内不同空间尺度上自然环境与人为干扰变量联合作用的结果。其中集水区尺度所产生的影响力总体较大且相对稳定，而局部尺度（河段和岸带）所产生的影响力相对较小且会随季节更替产生显著变化。（3）苕溪流域碳、氮、磷释放潜力空间分布特征如下，总氮和总磷的释放潜力空间分布特征大致一致。释放潜力由低到高的分布区域分别为：苕溪流域内的水域分布区、位于上游高地的林地分布区、位于中下游的大型城镇居民点分布区、中下游河道两侧的耕地集中分布区。总有机碳释放潜力的空间分布特征与以上两种营养元素大致相反。总体表现为，流域内受人为干扰程度较低的森林分布区有机碳释放潜力较大，而流域中下游沿河两侧近岸区域内的城镇、农村居民点及水稻田等人为干扰程度较大的用地类型有机碳释放潜力较低。同时基于县域尺度的苕溪流域C、N、P营养盐释放潜力分析表明，尽管三种营养盐释放潜力值因县域不同而存在明显差异，但是该区域内所有县市均具有较高的C、N和P释放潜力，且三种营养物的释放潜力均值均在0.6以上。C、N和P的释放风险等级划分结果表明，苕溪流域内约有48.49%、31.34%和21.54%的区域分别为TN、TP和TOC的重要释放源区更多还原

【Abstract】 The elemental composition of particulate or dissolved matter (e.g., carbon, nitrogen orphosphorus), exported into downstream freshwaters or oceans (e.g., lakes and estuaries), hasimplications for downstream ecosystems. These relationships between riverine nutrientstransport and downstream ecoystems have been intensively studied by the global watershedecologists. Riverine nutrients export is mainly influenced by the climate, topography, geology,land use, and hydrology regieme of a catchment. Global human acitivities, indicated by landuse/land cover change, have made47%of the earth’s surface changed irreversibly, whichaffected not only the transport process of nutrients in streams but also downstream ecosystemshealth. Thus, throught profound analyses of influences of watershed land use pattern onriverine nutirents export, we will increase our ability to understand the biogeochemicalbehavior of kinds of nutrients from the watershed upland to downstream waters, and it isimperative for mangers to develop effective adaptation strategies to reduce riverine nutrientsexport and/or restore downstream ecosystems.The Tiaoxi Rvier, which is located in northern Zhejiang Province, typically contirbutedmuch of water and nutrients for the Taihu Lake. It not only led to the eutrophication in theTaihu Lake but also have implications for the water environmental security in the YangtzeRiver delta. In this study, the Tiaoxi River watershed was selected as the study region. Thewater quatliy indexes, river discharge and land use, incorportaing RS and GIS, and somestatistical methods, such as multistep regression, redundancy analysis and spatial multicriteriaanslysis, was used to analyze the influence of watershed land use patterns and hydrolgicprocesses on riverine nutrients export, and the scale dependence of these influences on riverinenutrients export, and the loss potential of C, N and P in each spatial unit in the Tiaoxi Riverwaterhed. Through the above research, we mainly obtained the follow conclusions: (1) Stream water C:N:P ratios were strongly related to several catchment landscapeproperties in the Xitiao River watershed. In addition, the relationships between C:N:P ratiosand catchment landscape properties were significantly affected by the variable hydrologiccondition, which was indicated by the river discharge in the Xitiao River watershed. Thestrength of these relationships changed depending on the element under consideration. Forexample, increasing river discharge was found to strengthen landscape (e.g., the percentage ofcropland)-C:P ratio relationships, but weaken landscape (e.g., percentage of waterbody)-N:Pratio relationships. Similarly, there were significant correlationships between stream waterC:N:P ratios and river discharge in each stream in the Xitiao River watershed. The direction(e.g., postive or negative) of these correlations were related with different landscape propertiesamong catchments from the Xitiao River watershed.(2) During the study period, variations of stream water nutrients (e.g., C, N and P) in theTiaoxi River watershed were more responsive to physiography vairables and catchment-scaleland use than to reach-scale anthropogenic variables and riparian-scale land use. In addition,the relative contribution of physiography variables and factors at different scales (e.g., reach,riparian and catchment) varied largely with seasons change. Especially in the rainy season, theinfluence of local-scale (e.g., reach and riparian scale) variables on variations of stream waternutrients in the Tiaoxi River watershed increased significantly and riparian was the greatestpowerful scale for the variation of nutirents in streams, while the relative influence oflarger-scale (e.g., physiography and catchment-scale) variables on variations of in-streamnutrients decreased during the same period. The results indicate that variations of nutrients (e.g.,C, N and P) in stream water of the Tiaoxi River watershed were controlled by the combinedeffect of local-scale and larger scale variables. The influence from catchment-scale variables onvariability of in-stream nutrients was large and relatively stable, while the impact from localscale (e.g., reach and riparian scale) variables to variability of nutrients was generally weak andvaried largely with seasons change. (3) Potential exports of total nitrogen and total phosphorus in the Tiaoxi River watershedgenerally followed the pattern of cropland> urban> forest> waterbody, while the losspotential of total organic carbon in the study region showed an opposite pattern as compared tothat of N and P. For example, forests distributed in the watershed upland showed generallylarger values than cropland or urban in the downstream regions. Althrough loss potentials fornutirents (e.g., C, N and P) in six counties in the Tiaoxi River watershed varied largely, therewere a relatively larger values of loss potential for nutrients and mean values of the three kindsof nutrients in each county were larger than0.6. Critical areas on large potential export of C, Nand P covered21.54%,48.49%and31.34%of the entire area in Tiaoxi basin.更多还原