QIU Xiaolong^{1, 2}, WANG Baoli^{1, 2}, LIANG Chongshan³, LANG Yunchao^{1, 2}, LIU Taoze³，LI Yajun^{1, 2}，XIAO Jing^{1, 2}

(1. Institute of Surface-Earth System Science, Tianjin University, Tianjin 300072, China;
2. Tianjin Key Laboratory of Earth Critical Zone Science and Sustainable Development in Bohai Rim, Tianjin 300072, China;
3. State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Science, Guiyang 550081, China)

Abstract: River water chemistry can be used to estimate the chemical weathering rate in the basin, and relative impact from damming was still unclear. In order to understand this impact, we have investigated water chemistry and rock weathering rate of the basin seasonally in the karst Sancha River and the Maotiao River. The average concentrations of Ca2+, Mg2+, HCO3- and SO42- were 1397, 429, 2359 and 832 μmol/L, respectively, indicating that the main water chemical composition was mainly controlled by the weathering of carbonate rocks. The sum of these four ions (MTDS) was relatively stable and had obvious seasonal variation in the reservoir, but in the river MTDS was irregular, indicating that the dam did impact the river water chemistry. After a river was dammed, velocity of water flow decreased, and water depth and biological activities increased. This resulted in the MTDS stratification in the reservoirs. Due to the deep water discharge for hydropower in the reservoir, the downstream water chemistry inherited characteristics of the reservoir bottom water, which led to about 20% difference between reservoir surface and the downstream of the dam for the chemical weathering rate calculated based on water chemistry.

Key words: hydrochemistry; chemical weathering rate; reservoir; karst; Wujiang.

EARTH AND ENVIRONMENT Vol.47, No.6, Tot No.332, 2019, Page 768-776