[Impact of Human Activities on Water-Rock Interactions in Surface Water of Lijiang River].

The influence of human activities on karst surface water quality has received increasing attention. To explore the impact of human activities on water-rock interactions in karst surface water, water samples were collected from July to November in 2016 in the Lijiang River, which is dominated by human activities. The samples were analyzed for the hydrochemistryand the characteristics of δC. The results show that:①The Lijiang River is mainly characterized by HCO-Ca chemical composition.. The SO and NO concentrations are inferior to HCO concentrations in the anion composition; besides, the concentrations of SO and NO in the river between Guilin and Yangshuo are higher than in the other sampling sites, caused by tourism and urban development. ②Equivalent ratios of[Ca+Mg]/[HCO] are between 1.01 and 1.51 and the equivalent ratios of[Ca+Mg]/[SO+NO+HCO] are between 0.85 and 1.12, indicating that the sulfuric acid and nitric acid have participated in the water-rock interaction. ③The proportions of carbonic acid dissolving carbonate rocks range from 32.10%-98.01% with an average of 75.89%. The proportions of sulfuric acid and nitric acid dissolving carbonate rocks vary from 1.99%-67.90% with an average of 24.11%. The proportions of sulfuric acid and nitric acid dissolving carbonate rocks in the rainy period with an average of 24.31% is higher than in the brief rain period with an average of 23.88%. In addition, the proportions of sulfuric acid and nitric acid dissolving carbonate rocks present a fluctuated increasing trend from upstream to downstream and the maximum strength and the minimum strength of the sulfuric and nitric acid dissolving carbonate rocks occur in Lingchuan and Huajiang, respectively. ④ HCO mainly originated from the carbonate rocks dissolved by carbonic acid, with an average of 83.58%, followed by the carbonate rocks dissolved by sulfuric acid and nitric acid, with an average of 14.24%. The contribution of carbonic acid weathering silicate rocks is the smallest with an average of 2.18%. ⑤ δC of the Lijiang River ranges from -11.95‰--7.61‰; the calculated δC using the mixture endmember model ranges from -14.24‰--7.23‰. δC is close to δC in the rainy period and δC is significantly higher than δC in the brief rain period. The difference between δC and δC is caused by the influence of aquatic photosynthetic organisms.