中文摘要：

以三峡支流澎溪河消落带为研究区域,采集澎溪河消落带上、中、下游3个水文断面,2个水位高程,5个深度的沉积物样品,结合沉积物颗粒分形理论探讨沉积物粒径组成与总氮（TN）、总可转化态氮（TF-N）、铵态氮（NH4^＋-N）、硝态氮（NO3^--N）含量和分布特征的关系。结果表明：澎溪河消落带沉积物粒径组成为砂粒（49.75%）〉粉粒（36.16%）〉黏粒（14.09%）,粒径分布具有分形特征,分形维数（Dm）在2.612～2.781之间,均值为2.727。随消落带水位高程下降、流域断面自上至下、深度由表至底,黏粒、粉粒比例、Dm降低,砂粒比例升高。TN、TF-N、NO3^--N含量分布与黏粒、粉粒、Dm正相关,与砂粒呈极显著负相关。Dm可作为判断沉积物粒径组成与氮含量关系的潜在指标。沉积物总体质地结构良好,但频繁的干湿交替使澎溪河下游和低水位高程沉积物保水保肥能力下降和砂质化,并通过改变粒径组成影响氮分布。落干期上游和高水位高程沉积物TF-N增加,提高了淹水期氮素进入水体并导致水体富营养化的风险。

英文摘要：

Since the special water storage regime in Three Gorge Reservoir,the periodic rise and fall of water table take place within 30m′s elevation difference. So,the different hydrological sections and water level elevations in the water level fluctuating zone of Yangtze River tributaries undergo a different dry-wet alternation. The dry-wet alternation make variable hydrological processes,regional climate,vegetation adaptability and particle size composition of sediment change obviously,which may transfer the role of sediment instead of a nitrogen sink into nitrogen source. The determined total nitrogen（TN）and inorganic nitrogen,such as ammonium-nitrogen（NH4^＋-N）and nitrate-nitrogen（NO3^--N）could reflect background level of nitrogen in sediment,whereas the measured total transformable nitrogen（TF-N）,weakly bonded with sediment lattice,was a good indicator for nitrogen cycle. Sediment is composed by different size particles. Since the larger particles are hardly broken down into small size for releasing the dissolved nitrogen into water,the absorbed nitrogen on the surface of the particles and the smaller particles would easily release into water. Frequent dry-wet alternation is a crucial factor affecting soil particle size composition. Sediment plays a key role as a source and pool in nitrogen recycling in water body. So it is important to understand the relationship between sediment particle size composition and nitrogen distribution in the water level fluctuating zone as affected by dry-wet alternation in elaborating mechanism of eutrophication of the water body in tributaries of the Three-Gorge Reservoir. The Pengxi River is a typical tributary of the Yangtze River in the Three-Gorge Reservoir Area. The water level fluctuating zone of the river was selected for the study. Sediment samples were collected,5 each sampling site,different in depth,at two water level elevations and the sampling sites were distributed at three hydrologic sections of the river,upper,middle and down streams of the river. P