我国北方小流域硫酸参与矿物化学风化过程研究

Mineral chemical weathering by sulfuric acid and its effects on global climate change have been focused by many scientists, but the mechanism of chemical weathering by sulfuric acid and therefore consumption amount of atmospheric CO2 had not been well illustrated. Acid pollutants induced by SO2 during coal burning and acid mine drainages during coal and sulfide minerals exploration were more serious in North China, but the influences of chemical weathering by sulfuric acid on regional carbon cycling had not been paid attention. To elucidate this acid process, two small drainage basins in North China were selected, which were two tributaries in the midstream of the Yellow River, named Qin River and Yiluo River with distinctive rock types, and had been heavily polluted by acid mine drainages from coal exploration and sulfide minerals exploration respectively. More carbonate minerals outcrop in the upstream and downstream of Qin River, and granite and quartz sandstone outcrop in the upstream and midstream of Yiluo River. Oxidation path of sulfide minerals was identified by oxygen isotope of sulfate and water, meanwhile sources of riverin sulfate and contributions of sulfide minerals were also elucidated by dual sulfate isotopes. With the determination of sulfuric acid participating in chemical weathering of carbonate and silicate minerals, the variations of CO2 consumption induced by sulfuric acid and carbon acid could been calculated and the effects of sulfuric acid on regional carbon cycling could be illustrated. Meanwhile the weathering process of carbonate minerals by sulfur acid was verified by carbon isotope of dissolved inorganic carbon. This program can contribute to understand the relationship of chemical weathering by sulfuric acid and regional carbon cycling and climate changes, and elucidate the detailed influence of chemical weathering by sulfuric acid on local carbon cycling in North China, to enrich the theory of global carbon cycling, and to provide scientific foundation for water resources protection in North China.

硫酸参与矿物化学风化对全球气候变化的影响越来越受到关注，但是硫酸风化机制以及对大气CO2消耗量的认识仍存在不足。我国北方燃煤活动以及煤炭资源和金属矿产资源开采过程排放大量酸性污染物，但北方地区硫酸风化过程对区域碳循环的影响的研究尚未得到重视。本研究以我国北方受煤炭资源开采和金属矿产资源开采影响的两个小流域（沁河和伊洛河）作为研究对象，借助水的氢氧同位素及硫酸盐硫和氧同位素辨识硫化物氧化过程，计算河水中来自硫化物的硫酸盐量。对比分析硫酸和碳酸参与碳酸盐矿物和硅酸盐矿物化学风化引起的大气CO2消耗量的变化，量化硫酸风化机制对区域碳循环的影响程度，结合河水溶解性无机碳碳同位素验证硫酸参与碳酸盐矿物化学风化过程。本项目的实施，有助于深刻理解硫酸风化机制对区域碳循环和气候变化的影响过程，阐明我国北方流域硫酸风化机制对区域碳循环的影响程度，丰富全球碳循环理论研究，同时为我国北方水资源保护提供科学依据。

大陆硅酸盐岩化学风化过程吸收二氧化碳(CO2)构成重要的碳汇，但硫化物氧化产生硫酸并侵蚀碳酸盐岩释放CO2构成重要的碳源，二者是控制区域大气CO2平衡的重要因素。但是硫酸参与岩石化学风化过程及其对区域大气CO2平衡的影响仍不清楚。选择我国北方两条小流域沁河和伊洛河作为研究对象，借助水化学组成、硫酸盐硫和氧同位素以及水体氢氧同位素来辨识硫化物矿物氧化过程，并用正演模型计算硫酸参与岩石化学风化速率以及CO2释放通量。结果表明：1) 硫化物矿物氧化过程在研究区广泛存在，产生的硫酸参与区内碳酸盐岩的化学风化过程；2) 碳酸盐岩主导的沁河流域硅酸盐岩和碳酸盐岩化学风化速率年均值为2.6t/km2/a和6.0t/km2/a，硫化物矿物风化速率年均值为1.5t/km2/a，硅酸盐岩主导的伊洛河流域硅酸盐岩和碳酸盐岩化学风化速率年均值为7.4t/km2/a和7.7t/km2/a，硫化物矿物风化速率年均值为1.6t/km2/a；3) 沁河流域硅酸盐岩和碳酸盐岩化学风化吸收大气CO2通量年均值为0.41×105mol/km2/a和0.77×105mol/km2/a，硫酸参与碳酸盐岩化学风化释放的大气CO2通量均值为0.06×105mol/km2/a；伊洛河流域硅酸盐岩和碳酸盐岩化学风化吸收大气CO2通量年均值为1.15×105mol/km2/a和1.00×105mol/km2/a，硫酸参与碳酸盐岩化学风化释放的大气CO2通量年均值为0.04×105mol/km2/a。研究结果证实硫酸广泛参与岩石化学风化过程，但因硫酸侵蚀碳酸盐岩而释放大气CO2通量仅为硅酸盐岩风化吸收大气CO2通量的1/8(沁河)和1/29(伊洛河)，显示研究区岩石化学风化过程是大气CO2重要的汇。本研究结果为全球大气CO2源汇关系研究提供重要科学数据，同时对于全球岩石化学风化与气候变化研究具有重要科学意义。