WEI Minjie^1,2, GUO Fang², JIANG Guanghui², JIA Yanan¹

(1. Chongqing Key Laboratory of Karst Environment, School of Geographical Sciences, Southwest University, Chongqing, 400715, China;
2. Key Laboratory of Karst Dynamics, MNR&GZAR, Institute of Karst Geology, CAGS, Guilin Guangxi 541004, China)

Abstract: The Zengpiyan cave site in Guilin is a typical representative cave site of the Neolithic Age in China. When pollutants enter the reductive environment of fracture-based groundwater, their properties may be changed and thus they may erode the cultural layer of the site. In this paper, by collecting H2S and CH4 gases at the water-air interface of groundwater and analyzing sulfur isotope δ34S-SO42-, dissolved organic carbon(DOC), chemical oxygen demand(COD), sulfate reducing bacteria (SRB) and other indicators, the generation mechanism of the corrosive gas H2S at the water-air interface of groundwater in the site was studied. The results showed that the concentration of SO42- in the water body of the Zengpiyan cave ranged from 0.57 mg/L to 131.00 mg/L, with an uneven spatial distribution, indicating that the effects from precipitation, oxidation of sulfide minerals and microbial sulfate reduction. The abundant organic matter provided enough energy for the sulfate reduction. The spatial distributions of concentrations of DOC and COD were different but their high values all showed in the upstream area of the runoff, which was affected strongly by human activities. Generally, SRB participated actively in the sulfate reduction, amounts of SRB trended as rainy season > dry season and surface water > groundwater, which was determined by temperature, precipitation and organic matter. The formation of H2S was promoted by higher temperature, SRB and degree of reduction environment affected concentrations of H2S and CH4. H2S is unstable and can be easily oxidized to sulfuric acid, which may aggravate the chemical erosion at the site if accumulated. It is suggested to increase the monitoring of pollutant transport and reaction products and to pay more attention to the preservation environment of the site.

Key Words: Zengpiyan; karst media; water-air interface; sulfate; corrosive gas

EARTH AND ENVIRONMENT Vol.48, No.6, Tot No.338, 2020, Page 689-697