Abstract: There exists heterogeneity in water dynamics in different areas of the Three Gorges Reservoir tributaries after impoundment. In order to illustrate the processes of ecological hydrology in tributaries, a tributary (Zhuyi Bay) was chosen to analyze the spatiotemporal characteristics of hydrogen and oxygen isotopic compositions using isotope tracing technique. The water mass characteristics of endmember mixing process of the mainstreamtributary and sourcetributary was also revealed. The results showed that: (1) In backwater area of Zhuyi Bay, the δD values ranged from -84.1‰ to -54.4‰, and δ¹⁸O from -11.71‰ to -8.13‰. These values were respectively similar to those of adjacent water body in mainstream, while obviously less than those in source water of the tributary (δD: -49.6‰ to -46.1‰; δ¹⁸O: -7.61‰ to -7.19‰). (2) The rate of water recharge of the mainstream of Yangtze River to the backwater area of Zhuyi Bay was approximately 95% using binary linear mixed model. This value indicated that bay water was mainly affected by the backward flowing from the mainstream to the tributary. (3) The backward flowing from the mainstream of Yangtze River to Zhuyi Bay occurred in the middle layer of Zhuyi Bay estuary during preflood hydrofluctuation period and dry period, whereas in the uppermiddle layers during flood period and storage period. Hydrogen and oxygen isotope tracing technique has relatively good applicability in analyzing the mode of backward flowing. (4) Yangtze River locates in monsoon climate areas, and the main factors affecting hydrogen and oxygen isotope compositions of Zhuyi Bay in rainy season could be ordered in significance as: backward flowing > rain > isotope fractionation. However, this order changed as backward flowing > isotope fractionation > rain in dry season.

Key words: dry matter accumulation, fertilizer N maximum efficiency period, fertilizer N utilization, N accumulation, apple