Characteristics and controls of the hydrochemistry and carbon isotope of thespring water in the Hongjiadu Basin of Guizhou
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摘要: 泉水是洪家渡盆地居民的重要饮用水源，近些年随着人类活动的增强，泉水水质呈恶化趋势。为查明泉水中污染物来源及其地球化学过程，采集15组具有代表性的水样分析水化学、溶解无机碳（dissolved inorganic carbon，DIC）碳同位素(δ13CDIC)特征。结果显示泉水组分以Ca2+、Mg2+和HCO-3为主，富集SO2-4，硫酸、硝酸与碳酸共同参与了研究区碳酸盐岩风化。泉水Na+、Cl-、K+和NO-3主要来源于肥料（如化肥、粪肥）和污水，SO2-4主要来源于煤层中硫化物氧化、雨水和污水。S01和S09泉因NO-3超标已不可直接饮用。泉水δ13CDIC值主要受碳酸盐岩溶解和土壤CO2的控制，但硫酸、硝酸参与碳酸盐岩风化使泉水δ13CDIC值偏正，且SO2-4、NO-3浓度上升；而硫酸盐细菌还原作用和反硝化作用及人为输入污染物中有机质的降解导致泉水δ13CDIC值偏负。诸多因素导致泉水δ13CDIC值在-17.72‰~-8.74‰之间，平均值为-11.58‰。研究证实δ13CDIC与水化学相结合是探讨碳的生物地球化学过程及示踪岩溶区地下水污染物来源行之有效的方法。Abstract: Spring water is an important source of drinking water for the residents in the Hongjiadu Basin of Guizhou. However, with the rapid increase in human activities, the quality of the spring water has continuously degraded over recent years. To investigate the sources and geochemical processes of contamination in the springs, 15 representative water samples were collected for analyses of the characteristics of hydrochemistry and isotope of dissolved inorganic carbon (DIC). The spring water samples are dominated by Ca2+, Mg2+, HCO-3 and SO2- 4. Sulfuric and nitric acid, together with carbonic acid, are involved in the weathering of carbonate rocks. Spring S01 and S09 are considered unsuitable as drinking water sources due to exceeding concentration limit of NO-3. Na+, Cl- , K+ and NO- 3 in the springs mainly originates from sewage, fertilizer (e.g. chemical fertilizer and manure); SO2-4 originates from sulfide oxidation in coal seams, acid rain, and sewage. The characteristics of δ13CDIC in the Hongjiadu Basin are thereby considered to be mainly impacted from soil CO2 and weathering of carbonate rocks. Meanwhile, the participation of sulfuric and nitric acid in carbonate rock weathering leads to positive δ13CDIC values and increasing concentrations of SO2-4 and NO-3 in the spring water, whereas the degradation of anthropogenic organic matter, bacteria sulfate reduction and denitrification result in negative δ13CDIC values. These factors caused the δ13CDIC values of the spring water from the study area to fall within the range of -17.72‰ to -8.74 ‰ with a average of -11.58‰. This study confirms that the isotope of δ13CDIC, combined with hydrochemical analyses, is useful to examine the carbon biogeochemical processes and trace the pollutants sources in groundwater in karst areas.
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