三峡库区小流域土壤养分氮磷流失的景观控制机制研究

In past few decades, the exploitation of slope lands resulted in excessive, inappropriate and illegal land uses in the Three Gorges Reservoir area (TGR). Soil erosion and nutrient loss is a major agricultural and environmental problem in the watershed of TGR. Controlling soil and nutrient loss needs a solid scientific foundation, which includes coupled study between landscape pattern and soil and water loss in different scales. As one of ecological processes, soil and water loss has been paid much attention. Coupled research between landscape pattern and ecological processes is a key topic of landscape ecology. In theoretical studies, analysis of heterogeneity with respect to different components of the hydrologic processes often provides insight into the underlying controlling mechanisms, which is linked to heterogeneity in other related variables that describe underlying controlling processes. The relevance of spatial patterns to ecosystem process, depend on the process chosen and the spatial and temporal scales of interest. Spatial pattern or heterogeneity is important to hydrological process at all spatial scales from plot to watershed. Dealing with the scale issues should follow the deep understanding of interaction mechanism and scale characteristic between pattern and processes. These sites represent a variety of landscapes and are under a number of land uses representative of the Agroforestry region. Experimental plots were constructed in the Watershed of the Three Gorges Reservoir Area to evaluate soil erosion of traditional slope land farming and effects of soil conservation measures. Surface runoff and sediment from the watershed and each plot are collected and measured. For the soil and nutrient loss, a complicated process with spatial variation it shows a significant multi-scaling characteristic. The objective of the work is to evaluate and compare runoff and soil erosion field data collected in plots and hill slopes. The spatial configurations (i.e., patterns) of land uses at both landscape and patch levels are measured, focusing on nutrient levels (e.g., total nitrogen and total phosphorus). With scaling variation in landscape pattern or soil and nutrient loss, to analyze the mechanisms governing runoff generation and the effects of hydrological pathways on N,P loss. Our studies will provide much information in theory and methods to study the scaling landscape pattern and loss of soil and water and their relation to the influencing factors based on scale-pattern-process. However, it is scare though necessary to study the continuous scaling characteristics of soil and nutrient loss and their relation to the patches, mosaic and watershed factors. The effect of patch on annual runoff and sediment loss are investigated in three different patches along watershed in TGR. These researches will contribute to theory consummation of landscape ecology，and moreover, provide guidance for ecological construction in soil erosion area.

景观单元类型（斑块）及其镶嵌格局（坡面）如何影响小流域的土壤养分流失，调控小流域土壤侵蚀和养分流失，是景观格局与生态过程研究的关键科学问题。三峡水库小流域不合理土地利用活动引起土壤侵蚀、土壤养分（氮磷）输出是库区水体富营养化的主要因素之一。实施退耕还林工程等形成多种农林景观单元类型及空间镶嵌结构模式，直接影响土壤养分氮磷的运移过程，氮磷养分流失对径流、侵蚀过程的响应及景观格局控制机制是研究核心问题。本研究采用控制实验、对照实验、定位监测、格局分析和模型模拟等方法，在斑块、坡面和小流域尺度上，分析土壤养分氮磷的输移途径及其时空动态分布，土壤养分流失对径流和土壤侵蚀过程的响应特征，揭示景观单元类型、斑块镶嵌格局的土壤养分输出的控制机制，建立景观格局与土壤养分氮磷流失过程耦合关系，为三峡水库的植被结构优化配置提供理论与技术支撑。

三峡水库小流域不合理土地利用活动引起土壤侵蚀、土壤养分（氮磷）输出是库区水体富营养化的主要因素之一。实施退耕还林工程等形成多种农林景观单元类型及空间镶嵌结构模式。本研究在斑块、坡面和小流域尺度上，监测土壤养分氮磷的输移途径及其时空动态分布，建立景观格局与土壤养分氮磷流失过程耦合关系，揭示景观格局对土壤养分流失的控制机制及效应。结果如下：.1、退耕后土壤养分氮磷年流失量(包括随泥沙和地表径流流失的量)减少；与坡耕地比较，退耕还林(园地、林地)总氮、总磷年输出载荷分别减少了68.68%和81.75%。硝态氮、铵态氮主要通过地表径流输出，所占总量比例分别为91.4%和92.2%；总氮和总磷主要通过泥沙输出，所占总量比例分别为86.6%和98.4%。退耕还林地表径流以及土壤侵蚀输出明显减少，土壤养分流失得到有效控制。.2、集水区水体氮、磷等输出时空特征及土地利用景观格局对其产生的影响。流域总氮(TN)、总磷(TP)、硝态氮(NO3--N)主要来源于园地，6～9月汛期的氮磷输出显著大于1～5月的非汛期；非汛期铵态氮(NH4+-N)主要来源于住宅用地，汛期NH4+-N则来源于园地。PD与非汛期的氮素及汛期的NO3--N、NH4+-N显著正相关；CONT与汛期的氮素及非汛期的TP呈负相关；典型相关分析进一步显示，不同土地利用斑块类型导致的景观破碎化能较好解释氮磷输出的影响，两典范轴累积解释氮磷输出变量的90%，景观变量PD贡献最大，对流域水质评价与预测具有重要意义。.3、农林复合系统小流域为研究对象，小流域雨季输出总氮载荷为52.43 kg· hm-2，其中以硝态氮（30.26 kg· hm-2）和颗粒态氮（21.61 kg· hm-2）为主体；②丰水期强降雨是土壤养分输出的主要驱动，其降雨径流贡献了雨季88%的总氮和90%的总磷流失；③小流域土壤养分氮、磷主要经由降雨形成地表径流过程输出，占养分总流失量的68%和74%；④雨季流域水体总氮浓度超标，降雨或非降雨期间均属劣Ⅴ类水质。.本项目研究将提供大量的理论、技术和方法信息，用于研究尺度景观格局和土壤侵蚀和养分流失控制。这些研究将有助于景观生态学理论的完善，并为水土流失区的生态建设提供指导。