近年来，除了湖泊和水库，河流的富营养化问题，在国内外也逐渐受到关注。河流水系中的营养盐来源很多，包括人为来源，如生活污水排放，工业污水排放，养殖的畜禽排放等，以及自然的大气输入，土壤侵蚀等。河流能够将污染物质向下游输移，最终影响到河口甚至是海洋环境与生态系统，并且输移过程中的一系列的生化物理因素限制了藻类的生长，所以河流的水质问题比湖泊和水库更为复杂。水利工程建设，这一人类活动，在给人类带来福祉的同时，也引起了河流的原有的水文条件、水质组分，甚至是生态环境的变化。本论文以长江干流宜昌站、汉口站、大通站的水文水质序列为研究对象，旨在分析对三站流量、溶解态无机氮的浓度和负荷的趋势变化，并分析三峡工程蓄水对三站点产生的的影响。论文采用水文分析工具（HAT）和统计方法，对三站月均径流量、日均流量极值进行分析，量化了三峡工程蓄水对其下游监测站点流量的影响。分析结表明：1）三峡工程的运行会引起宜昌站洪季最大流量的减小和枯水季最小流量的增加，其中，洪季的10月份和枯季的2月、3月最为明显；2）三峡工程蓄水后，下游三站10月份月均流量均有明显减小，但在枯季，宜昌站、汉口2、3月份有所增加，大通站却增加不明显；3）1950-2003年之间，三站10月、2月、3月有趋势变化，但变化显著年份不多，但在03年后，这三个月的趋势变化显著性年份增多。论文尝试利用TRAMO/SEATS和HP滤波等时间序列方法对三站溶解态无机氮浓度进行了趋势分析。分析结表明：1）从三站DIN浓度的变化看，1990-1994年底，三站均有浓度减小的趋势；随后在1995-2003年间，浓度随着农业生产活动的增大而增高；2）在三峡蓄水之后，宜昌站DIN浓度停止增加，转而缓慢下降，而汉口站增加趋势减缓，但大通站则不受影响，浓度依旧增加。三站的DIN浓度反映了三站上游流域农业活动状况，但三峡蓄水之后，则反映了二者的综合作用。论文引入美国USGS LOADEST负荷估算程序，对三站溶解态无机氮的负荷进行了估算，并对三峡工程建设前后，其趋势变化、年内分配及引起变化的影响因素进行了探讨。论文得到以下结论：1）宜昌和汉口站溶解态无机氮负荷在1998年之前，均经历了一个快速增加的过程，而1998年后又不再增加；而大通站在1998年之后，整体上依旧处于增加的状态。2）汉口-大通站之间河段部分的输入所占的大通站比重，在1998年之后，较1998年之前更小。大通站的负荷整体处于增加趋势，故而，汉口站上游地区（包括宜昌站以上）的溶解态无机氮的年负荷增加更为迅速。迅速增加的时间发生在1995-1998年4年间。这样的比例的变化进一步表明，虽然之前较为落后，但长江流域宜昌上游地区在1995年-1998年4年间，农业发展尤为迅速。之后，三个站点上游地区的发展的增加速度相当，从而硝态氮的负荷比值维持稳定。3）宜昌站流量在三峡工程蓄水之后，10月份有较大下降，溶解态无机氮负荷与流量呈现相似的变化。在旱季，尤其是一月和二月，随着农业灌溉和发电，流量与负荷的比例均有所增加。汉口和大通的溶解态无机氮年内分配无明显变化，但氨氮的比例在洪季明显减小。这表明，三峡蓄水，主要影响溶解态无机氮中的氨氮的比例。

Eutrophication research in streams and rivers has also been nonetheless of great concern worldwide besides lakes and reservoirs in resent years. Nutrients in the streams and rivers come from many sources including both human activities such as sewage discharges, industrial waste discharges, livestock emissions and natural sources such as atmosphere deposition, soil erosion. Streams and rivers will transport pollutions downstream affecting water quality of estuary ultimately, and during transportation a series of biochemical and physical factors will limit the growth of algae. Water quality problems in rivers are more complex. As a main anthropogenic source that affects water environment in streams and rivers, water projects constructions, on the one hand, bring people blessedness, but on the other hand, cause alteration in hydrology, water components, and even water ecosystem. In this thesis, the authors select three hydrological station-the Yichang station, the Hankou station, and the Datong station- downstream the Three-Gorges Dam (TGD) in the main stream of Yangtze River as objectives of study. Trend in daily average discharges, both concentrations and loads of dissolved inorganic nitrogen (DIN) are analyzed. Besides, influences caused by impoundment of TGD are discussed.The Hydrological Analysis Tools (HAT) and statistical methods was applied to analyze changes in Monthly Highest daily average flow (MH), Monthly Lowest daily average flow (ML), Monthly Magnitude of daily average flow at the selected stations. The results are shown below: 1) Operation of the TGD could result in both reduction in the highest flow discharges in the flood season, especially in October, and increase of the lowest discharges in the dry season, especially in February and March at the Yichang station; 2) Operation of the TGD have led to magnificent decrease in flow discharges at all the three stations in October, but when it comes to dry season, it made discharges increase only at the Yichang and Hankou stations, not at the Datong stations; 3) From 1950 to 2003, downward trend can be seen in all monthly average flow discharges at the three stations reduced, but the phenomenon are not significant in these years; but after 2003, more years can be detected. This thesis tried to apply TRAMO/SEATS program, combined with Hodrick-Prescott (HP) filter, to detect trends and potential change points in time series of DIN at three representative stations. The trend components were extracted, and two change points were successfully detected. The trend components revealed that: 1) After experiencing a slight downward trend in 1990 to 1994, DIN has been increasing at all the stations since the 1995. Changes visible before 2002 illustrate the differences in agriculture development among regions upstream from the stations. 2) The TGD also led to years of differing trends. The upward trending DIN began a slightly downward trend because of NH4+ depletion. Readings at the Yichang station-closest to the dam-revealed this trend most strongly; those at the Hankou station less so. The Datong station was far enough away from the impoundment of TGD so that no obvious effects were seen.Besides, the USGS LOADEST program was introduced to estimate nutrient loads at the stations. Trend analysis, monthly variability and their affecting factors in three sub-periods were discussed. The following results are listed: 1) DIN loads at both the Yichang station and the Hankou station increased rapidly before 1998, and after 1998, the trend halted. Those at the Datong station continued to increase all the time. 2) Percentage of DIN inputs from regions between the Hankou and Datong station become less after 1998 compared to before. Since continuous increase in loads at Datong stations, it is inferred that more DIN loads are from regions upstream the Hankou station (including upstream Yichang). It is from 1995 to 1998 that the extreme increase occurred. Furthermore, agriculture in both regions developed more faster during this period. After 1998, rates of development in the three regions are comparable which made the load ratios stable. 3) Monthly DIN at the Yichang station had the same variability with flow discharges between the three periods. Compared with the transition period, a most remarkable reduction occurred in October, when the TGD impounded. During the dry season, especially in January and February, the discharges and DIN percentages increased in good correspondence with the release of TGD waters for irrigation, flood control, and power generation. There are no obvious changes in monthly percentage of DIN loads at the Hankou and Datong stations, but percentages of ammonium in the flood season after impoundment of the TGD reduced, indicating affection by the TGD.