中文摘要：

本研究以亚热带红壤丘陵区为研究区域,选取10个典型小流域,根据土地利用和畜禽养殖密度分为4种类型（森林、森林-种植、养殖和种植-养殖小流域）,并基于近3年小流域把口站的原位观测数据,采用负荷历时曲线模型（LDC）计算了不同类型小流域水体总氮（TN）的最大日负荷（TMDL）,运用灰度分析法定量研究了不同流量阶段小流域主要因子对TN负荷消减率的影响.结果表明,小流域TN负荷特征与流域类型密切相关,10个小流域TN年均负荷为739.0~2798.4 kg·km-2·a-1,由小到大依次为森林、森林-种植、养殖、种植-养殖小流域,其中,养殖、种植-养殖小流域水质整体超标严重,且应针对中、低流量条件下（秋、冬季节）负荷进行消减,而森林-种植小流域TN负荷超标情况略好,但高流量阶段（春、夏）超标率过高.灰度分析结果表明,TN负荷消减率在高、中流量阶段下主要受农田面积比例影响,而低流量阶段受畜禽密度影响.农田面积比例对高、中流量段TN消减率影响显著,而畜禽养殖密度在低流量段具有更大影响,小流域景观越破碎、类型越丰富、斑块分布越零散、形状越复杂,TN负荷通量则越大.

英文摘要：

Agricultural non-point source pollution has become a great obstacle of modern agriculture and sustainable development of society. In this study,ten small watersheds, which were divided into 4 types（ forest, forest-dominated, livestock production-dominated and plant-livestock productionwatersheds） by the land use patterns and livestock production distribution in a subtropical region of southern China,were investigated to study total nitrogen（ TN） loads and their contributing factors. Load duration curve（ LDC） method was applied to estimate total maximum daily load（ TMDL） of TN under different flow conditions,and the key contributors of required load reductions were obtained by using by gray relational analysis（ GRA） method.The results showed,the characteristics of TN loads in small watersheds were significantly depended on the type of watershed. The annual TN loads varied from 739. 0 to 2798. 4 kg·km- 2among the different types of watersheds. There were forest,forest-dominated,livestock production-dominated and plantlivestock production watersheds in ascending order,that livestock production-dominated and plant-livestock production watersheds observably exceed the TN TMDL under high and mid-range flow conditions,while high flow conditions was the major hydrologic conditions during which TN loss occurred in forest-dominated watersheds. Results of GRA suggest that cropland was the most important factors impacting on watershed daily reduction rate（ DDR）under high and mid-range flow conditions,while livestock density was noticeable factors for DDR under low flow conditions. More fragmentation,diversity and scattered distribution of the landscape pattern would result in more TN losses at small watershed scale.