Spacial and temporal variation of H and O isotopic compositions of the Xijiang Rivers System

Abstract:

Pin Lv¹, Fushan Li², Yang Tang²

1. School of Water Resources and Environment, China University of Geosciences (Beijing), Beijing 10083, China
2. The State Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002, China

The H and O isotope compositions in the Xijiang River water was investigated on the sample collected from the mainstream and main tributaries in Aug. 2014 and in Jan. 2015. Large variation ranges were observed for δD with (-35.3‰ to -77.1‰ in summer, -31.3‰ to -76.6‰ in winter) andδ¹⁸O (-4.8‰ to -10.3‰ in summer, -4.5‰ to -10.3‰ in winter). From the river head to the river mouth, the H and O isotope compositions of the river water collected in the high-discharge and low-discharge period display always a similar variation pattern. On the basis of isotopic composition of river water, the Xijiang River may be separated by three subbasins including the upper basin, the middle basin and the lower basin. The upper reached river water contains relatively low values of δD and δ¹⁸O. The values of δD and δ¹⁸O in the middle reaches are quite variable because of the middle basin severely disturbed through water impoundments. The lower reaches river water contains high values of δD and δ¹⁸O. The differences of δD and δ¹⁸O compositions between various tributaries and its effect to the δD and δ¹⁸O of the mainstream reflects also the constraint of the meteoric water to the Xijiang River. Evaporation has also important effect to the H and O isotope compositions of the Xijiang River, and it is found that evaporation can also raise the δD and δ¹⁸O values of the water during the dry season. Our investigation indicates that the H and O isotope tracing method can play a key role in studying the interaction between river water and other waters, such as the meteoric water, underground water, and lake water. The combination of proper H and O isotope study with conventional meteoric and hydrological investigation can be very helpful to understand the variation trend of water resource in the Xijiang River.