Spatio-Temporal Variations of the Stable H-O Isotopes and Characterization of Mixing Processes between the Mainstream and Tributary of the Three Gorges Reservoir

Abstract

Understanding the runoff characteristics and interaction processes between the mainstream and its tributaries are an essential issue in watershed and water management. In this paper, hydrogen (δD) and oxygen (δ 18 O) isotope techniques were used in the mainstream and Zhuyi Bay (ZYB) of the Three Gorges Reservoir (TGR) during the wet and dry seasons in 2015. It revealed that (1) Precipitation was the main source of stream flow compared to the TGR water line with meteoric water line of the Yangtse River basin; (2) The δD and δ 18 O values exhibited a 'toward lighter-heavier' trend along mainstream due to the continuous evaporation effect in the runoff direction, and the fluctuations reflected incoming water from the nearest tributaries. The general trend of d-excess increased with increasing distance from the Three Gorges Dam, which indicated that kinetic fractionation was an important process affecting the isotopic composition. The enrichment effect of isotopes was found in the downstream of TGR; (3) Water mass from the TGR mainstream flowed backward to the confluence zone of ZYB via the middle and bottom layers in the dry season, whereas in the wet season, water reversed through the upper-middle layers due to thermal density flows. This study described and demonstrated that the water cycle of TGR was driven by natural environmental variability and operational system, which will provide valuable information for the water resource management and for controlling the algal blooms in the future.

Seasonal variability of stable isotopes in the Changjiang (Yangtze) river water and its implications for natural climate and anthropogenic impacts

“…The seasonal variations of δD and δ 18 O in river water from large rivers made a useful proxy to investigate the catchment hydrology, impacts of climate change and human activities on river discharges, and can be used to structure and validate on newly proposed hydrological models [22,51]. However, the reasonable interpretation of seasonal stable isotopes variation depends mostly on the understanding of the hydrological setting and meteorological conditions of the river.…”

“…A systematic investigation of H and O isotopes in the Changjiang river water was initiated in 2002 by a program namely "The isotopic tracing of hydrology processes in the Yangtze River basin", which was a joint-research with "Designing criteria for a network to monitor isotope composition of runoff in large rivers" by IAEA [10]. This investigation provides the first systematic analysis of stable H and O isotopes in the Changjiang River, which then inspired a series of investigations focused on spatial and temporal variations of stable isotopes [18][19][20][21][22][23]. These studies suggest that the δD and δ 18 O of the Changjiang river water increase gradually from the upstream to estuary due to reducing runoff influences from the alpine catchments [19], "continental effect" [24] of the local precipitation [10], and increasing water contributions from tributary rivers and lakes in the middle and lower reaches [19,25,26].…”

Seasonal variability of stable isotopes in the Changjiang (Yangtze) river water and its implications: natural climate and anthropogenic impacts

“…Our calculation on δ 18 The stable isotopes seasonal pattern in the large river made a useful proxy to investigate the catchment hydrology, impacts of climate change and human activities on river discharges, and can be used to structure and validate on newly proposed hydrological models [27,54]. However, the reasonable interpretation of seasonal stable isotopes variation depends mostly on the understanding of the hydrological setting and meteorological conditions of the river.…”

“…A systematic investigation of H and O isotopes in the Changjiang river water was initiated in 2002 by a program namely "The isotopic tracing of hydrology processes in the Yangtze River basin", which was a joint-research with "Designing criteria for a network to monitor isotope composition of runoff in large rivers" by IAEA [20]. This investigation provides the first systematic analysis of stable H and O isotopes in the Changjiang River, which then inspired a series of investigations focused on spatial and temporal variations of stable isotopes [21][22][23][24][25][26][27][28]. These studies suggest that the δD and δ 18 O of the Changjiang river water increase gradually from the upstream to estuary due to reducing runoff influences from the alpine catchments [23],"continental effect" [29] of the local precipitation [20] and increasing water contributions from tributary rivers and lakes in the middle and lower reaches [23,30,31].…”

Spatial Variation and Controlling Factors of H and O Isotopes in Lancang River Water, Southwest China

“…Cascade dams are massively constructed on the main stream and major tributaries of the Lancang-Mekong River, which may be accelerating and magnifying the long-term effect of climate changes and global warming [31]. The spatio-temporal variation of H and O isotopes reflects the effects of trapping the river and of water regulation in some rivers [32,33]. Regarding the damming effect, the seasonal distribution of stable oxygen isotopes in the Changjiang River water shows a time lag in responding to meteoric precipitation [34], and cascade dams increase the resident time of river water and change the isotopes of surface water, bottom water, and released water in the reservoirs, which indeed shows their influence on the water cycle [35].…”