| 摘要: |
| 梯级大坝的建设对河流水文循环和水生态环境产生了深远的影响。本文对金沙江下游4个梯级深大水库（水深>150 m），依次为乌东德、白鹤滩、溪洛渡和向家坝，丰水期热分层期间氢氧同位素值进行垂向测定，探究同位素指示下水源、分层动力学及气象等对河流水循环的作用。通过MixSIAR模型对研究区水体来源进行定量分析，得到偏枯年份（2023年）的丰水期大气降水和冰川融水为金沙江下游的主要水源补给，占比分别为89.8%和10.2%。水源的占比在丰、枯水年，以及年内的丰、枯水期发生变化，丰水期水库入流的氢氧同位素值相对高于枯水期，库区发生热分层，同时受蒸发、地下水和支流等因素的综合影响，同位素值在垂向剖面上呈现复杂的差异性。层化现象导致水体垂向交换减弱，通过垂向二维水动力水温数值模型反演，在通常的上层取水方式下，表温层的中下水域流动性快，携带丰水期水体信息，而深层的滞温层水体表现为混合期冬春季节枯水期水体的滞留特性。上游乌东德库区位于干热河谷区，表层水体的氘盈余（d-excess）均值低至-26.40 ‰，δ18O均值为-11.15 ‰，表层蒸发效应显著高于其余3个水库。此外，部分垂线底层δD值的变化，反映了乌东德水库坝前、白鹤滩近库尾及溪洛渡坝前的底层水体均受地下水入渗影响。大坝拦截增加了水体的水力停留时间（HRT），加强了蒸发富集作用，从库尾至坝前，乌东德、白鹤滩和向家坝水库的δ18O值均具有逐渐上升的趋势。梯级水库的累积效应主要表现为表层水体的δD均值从上游（-115.62 ‰）至下游（-100.66 ‰）逐渐升高，δ18O均值呈先减小后增大的波动增长的趋势，乌东德水库的δ18O均值最大，而白鹤滩水库的δ18O均值（-15.36 ‰）最小。本研究可为流域系统调度管理提供理论参考。 |
| 关键词: 梯级水库 氢氧同位素 分层效应 累积效应 分层水动力 蒸发富集 MixSIAR模型 |
| DOI： |
| 分类号: |
| 基金项目:(U2040211, U2340224, 42107283, 52309107),国家自然科学基金项目（面上项目，重点项目，重大项目） |
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| Hydrogen and oxygen Isotope indicated thermal stratification and accumulation effects of Cascade Reservoirs in Jinsha River |
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Zhou Rongdan1,2,3,2, Bao Yufei3, Wang Yu-chun3, Du Yanliang3, Wang Shiyan3, Liu Chang3, Bi Erping1, Wen Jie3
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1.: School of Water Resources Environment,China University of Geosciences;2.China;3.: China Institute of Water Resources and Hydropower Research
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| Abstract: |
| The construction of cascade dams had the profound impacts on the riverine hydrological cycle and ecological environment. In this study, vertical measurements of hydrogen (δD) and oxygen (δ18O) isotope were carried out in 4 deep reservoirs (water depth >150 m) in the lower Jinsha River, named Wudongde (WDD), Baihetan (BHT), Xiluodu (XLD), and Xiangjiaba (XJB), during the wet season with thermal stratification, to investigate the roles of water sources, stratification dynamics, and meteorology, as indicated by the isotope values. Based on the quantitative analysis of water sources area by using the MixSIAR model, the results showed that in the dry year (2023), atmospheric precipitation and ice-melt are the main water sources of the lower reaches of the Jinsha River, accounting for 89.8% and 10.2% respectively. The proportions of the two sources change in the wet and dry years, as well as the dry and wet seasons in a year. δ18O and δD in runoff were typically exhibit higher during wet seasons compared to dry seasons. The vertical profiles of these values display complex variability influenced by thermal stratification, evaporation, groundwater inflow, and tributaries. Thermal stratification weakens vertical exchanges. The 2D numerical model results indicated that the rapid flow in the middle and lower epilimnion carried the information of the wet period, while water in the hypolimnion reflected stagnant conditions of the previous months during dry seasons. WDD Reservoir, situated in a dry-hot valley, experienced significant surface evaporation effects. The average deuterium excess (d-excess) of surface water was low at -26.40 ‰, and the average δ18O was -11.15 ‰. The surface evaporation effect was significantly higher than other reservoirs. Additionally, changes in vertical δD indicated influence from groundwater infiltration in bottom waters near WDD Dam, reservoir tail of BHT, and XLD Dam. Dam interception increased hydraulic retention time (HRT) and enhanced evaporation. δ18O of WDD, BHT and XJB Reservoir gradually increased downstream from the reservoir end to the dam front. Cascade reservoirs cumulatively caused surface water δD to increase upstream (-115.62 ‰) to downstream (-100.66 ‰), while average δ18O initially decreased and then raised. WDD Reservoir had the highest average δ18O, with BHT Reservoir the lowest (-15.36 ‰). This study can provide theoretical references for the basin management of the Reservoir Regulations. |
| Key words: Cascade reservoirs hydrogen and oxygen isotopes stratified effect cumulative effect Stratified hydrodynamics evaporation enrichment MixSIAR model |
