Background

Seasonal variations of stable hydrogen and oxygen isotopes in river water can be used to indicate hydrological processes and the water cycle in the river basin. This study presents a high-resolution time series of stable oxygen isotopic record (δ¹⁸O) in the lower Changjiang (Yangtze) River mainstream and aims to investigate the regional water cycle concerning natural climate changes and anthropogenic activities.

Results

The river water δ¹⁸O shows apparent seasonal variations, which is overall higher during the dry season and lower during the flood season. This basin-scale seasonal variation of δ¹⁸O in precipitation over the Changjiang catchment is calculated based on the long-term meteorological and hydrological data. The seasonal variation of δ¹⁸O in the lower Changjiang river water is largely constrained by monsoon-induced precipitation, but is more directly controlled by the mixing of waters from the upper reaches and the tributary lakes in the middle valley.

Conclusions

The relative contributions of waters from the upstream and tributary lakes to the lower Changjiang mainstream have been considerably altered by the construction of Three Gorges Dam via the regulation of river discharges. A comparison of river water isotopic records with water discharges from the lakes suggests that it takes about 2 weeks (~ 17 days) for the Changjiang river water to circumvent the mid-lower reaches of the catchment before traveling to the sea. This study suggests that the stable hydrogen and oxygen isotopes can be harnessed as sensitive indicators for water cycling within a large catchment that is driven primarily by natural forcing though subject to substantial human impacts.

中文翻译：

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长江（长江）水中稳定同位素的季节性变化及其对自然气候和人为影响的影响

背景

河水中稳定的氢和氧同位素的季节性变化可用于指示流域的水文过程和水循环。这项研究提出了一个高分辨率的时间序列稳定氧同位素记录（δ ¹⁸ O）在较低的长江（长江）干流，旨在调查有关的自然气候变化和人类活动的区域水循环。

结果

河水δ ^18个ö显示明显的季节性变化，这是总体较高的旱季和汛期降低。的δ此流域尺度季节变化¹⁸ ○在降水长江集水是基于长期气象和水文数据计算。δ的季节变化¹⁸在下部大江水O的主要由季风诱导沉淀的限制，但更直接地通过水的从上游和中间谷支流湖泊混合控制。

结论

通过调节河水流量，三峡大坝的建设大大改变了上游和支流湖水对长江下游主流的相对贡献。将河水同位素记录与从湖泊中排放的水进行比较，表明长江水在流向大海之前要绕过集水区的中下游大约需要2周（〜17天）。这项研究表明，稳定的氢和氧同位素可以用作大型集水区水循环的敏感指标，尽管受人类的重大影响，但主要由自然强迫驱动。