Impact of sulfuric acid on carbonate dissolution in the upper-middle reaches of Wujiang River

Institute of Karst Geology, Chinese Academy of Geological Sciences, Guilin 541004, China

^* Corresponding author: qbohuang@karst.ac.cn

Abstract

Due to rapid population and economic growth in recent years, the Wujiang River has been heavily impacted by anthropogenic activities. Of particular concern is the increase in SO₄^2- concentration of the river water from various anthropogenic sources. The results showed that the major cations of groundwater and surface water were Ca²⁺ and Mg²⁺ (>70% of the cation concentration), and the main anions were HCO^3-and SO₄^2-(>85% of the anion concentration). In groundwater, the contributions of carbonate dissolution to Ca²⁺+Mg²⁺ by sulfuric acid ranged from 20.6% to 92.9% (average 51.5%); and to HCO_3- from 11.5% to 86.7% (average 36.9%). In the surface water, the contributions of carbonate dissolution to Ca²⁺+Mg²⁺ ranged from 56.1% to 94.6% (average 76.9%); and to HCO3from 39.0% to 89.7% (average 64.2%). Our results demonstrate that besides carbonic acid, sulfuric acid also plays an important role on carbonate rock weathering, and influences the hydrochemistry of both groundwater and surface water in the Wujiang River drainage.