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

Rong Jiang,Yufei Bao,Yong Shui,Mingming Hu,Zhenya Ye,Yuchun Wang,Aiming Cai,Pengcheng Du,Yao Cheng

doi:10.3390/w10050563

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 (δ18O) 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 δ18O 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.

Highlights

As one of the largest hydropower projects in the world, the Three Gorges Reservoir (TGR) is located at the upper and middle catchment of the Yangtse River
The spatial and temporal distributions of δD and δ18 O in the surface water of TGR mainstream in the wet and dry seasons were shown in Figures 2 and 3, respectively
The study presented water hydrogen and oxygen (H-O) isotopic compositions in the mainstream and a tributary (Zhuyi Bay) of the TGR in 2015 and showed that the H-O isotopes and d-excess can be used to indicate the water cycle of the reservoir and reveal the stratification phenomenon that occurred in the confluence zone between the mainstream and tributary

Summary

Introduction

As one of the largest hydropower projects in the world, the Three Gorges Reservoir (TGR) is located at the upper and middle catchment of the Yangtse River. It is about 660 km long and 58,000 km in the watershed area [1]. It is key to engineering the exploitation and harnessing of water resources of the Yangtse River, which brings many obvious benefits, such as electrical energy, flood control, drought relief and economic development. It has many negative effects on the environment and ecology [2,3]

Methods

Results

Conclusion