煤矿开采活动对黄河中游窟野河流域溶解性硫酸盐的影响

煤矿矿井水是河水溶解性硫酸盐(SO^2-₄)的重要来源,但黄土高原煤矿开采活动对河水溶解性硫酸盐的影响仍不清楚。煤矿矿井水硫酸盐主要来自煤中黄铁矿氧化以及含煤地层附近裂隙水中硫酸盐,地表水硫酸盐还受其他人为输入的影响。因此,煤矿矿井水与河水硫酸盐具有不同的水化学特征、硫酸盐硫同位素(δ³⁴S_SO4)与氧同位素(δ¹⁸O_SO4)以及氢同位素(δD_H2O)与氧同位素(δ¹⁸O_H2O)组成。基于上述不同可以判定煤矿开采活动对河水溶解性硫酸盐的影响。选取受煤矿开采活动影响的窟野河流域作为研究对象,系统采集河水、地下水、煤矿矿井水、大气降水和泉水等水体样品,结合前人研究资料,借助δ³⁴S_SO4、δ¹⁸O_SO4、δD_H2O、δ¹⁸O_H2O以及水体水化学组成,辨析煤矿矿井水对窟野河流域河水溶解性硫酸盐的影响以及流域煤矿矿井水溶解性硫酸盐来源,并依据贝叶斯同位素混合模型量化其贡献比例。结果表明:窟野河流域煤矿矿井水溶解性硫酸盐浓度、δ³⁴S_SO4和δ¹⁸O_SO4值分别为0.07～1 206.45 mg?L^-1、-2.7‰～32.9‰和-5.5‰～11.6‰,平均值分别为231.91 mg?L^-1、11.4‰和4.3‰; 窟野河流域河水溶解性硫酸盐浓度、δ³⁴S_SO4和δ¹⁸O_SO4值分别为73.23～171.83 mg?L^-1、4.3‰～13.0‰和-2.9‰～5.1‰,平均值分别为113.94 mg?L^-1、10.4‰和3.0‰,溶解性硫酸盐浓度平均值与区内煤矿矿井水存在差异,δ³⁴S_SO4和δ¹⁸O_SO4平均值与区内煤矿矿井水差异不显著(p>0.05); 贝叶斯同位素混合模型结果显示,煤矿矿井水对上游乌兰木伦河溶解性硫酸盐的贡献比例为30.3%±18.9%,对下游窟野河溶解性硫酸盐的贡献比例为12.5%±10.2%,同时煤矿矿井水溶解性硫酸盐受裂隙水汇入影响,贡献比例为34.6%±16.5%,窟野河流域河水下渗补给煤矿矿井水溶解性硫酸盐的比例为18.8%±16.5%。结合硫和氧同位素组成,验证了煤矿矿井水溶解性硫酸盐的来源及其对窟野河流域河水溶解性硫酸盐的影响,阐明黄土高原煤矿开采活动对黄河流域河水溶解性硫酸盐的影响途径和程度,为黄河流域生态保护和高质量发展提供科学依据。

Impacts of Coal Mining Activities on Dissolved Sulfate in the Kuye River Basin,the Midstream of Yellow River,China

Coal mining drainage(CMD)is dominant dissolved sulfate(SO^2-₄)source in river system; however, the impacts of CMD on riverine SO^2-₄ in the Loess Plateau are still unclear. The SO^2-₄ in CMD is primarily derived from coal-bearing pyrite oxidation and sulfate in fissure groundwater buried around the coal-bearing strata, and the SO^2-₄ in surface water is affected by variable anthropogenic activities. Hence the hydrochemical compositions, sulfate sulfur and oxygen isotope values(δ³⁴S_SO4 and δ¹⁸O_SO4), and water hydrogen and oxygen isotope values(δD_H2O and δ¹⁸O_H2O)are different in CMD and surface waters, and these characteristics could solve the impacts of CMD on riverine SO^2-₄. The Kuye river was selected due to the obvious CMD effects on river water hydrochemistry. Water samples were collected in the Kuye river basin, including river water, groundwater, CMD, atmospheric precipitation and spring water; and the sulfate δ³⁴S_SO4 and δ¹⁸O_SO4, water δD_H2O and δ¹⁸O_H2O, and the hydrochemistry of water samples were analyzed to uncover the impacts of CMD on riverine SO^2-₄ in the Kuye river and watershed coal mine water. Bayesian isotope mixing model(BIMM)was used to calculate the contribution ratios of CMD on riverine sulfate. The results show that SO^2-₄ concentrations, δ³⁴S_SO4 and δ¹⁸O_SO4 values in CMD range from 0.07 to 1 206.45 mg?L^-1 with a mean value of 231.91 mg?L^-1, from -2.7‰ to 32.9‰ with a mean value of 11.4‰, and from -5.5‰ to 11.6‰ with an average of 4.3‰. The Kuye river water has SO^2-₄ concentrations varying from 73.23 to 171.83 mg?L^-1 with an average of 113.94 mg?L^-1, δ³⁴S_SO4 values from 4.3‰ to 13.0‰ with a mean value of 10.4‰, and δ¹⁸O_SO4 values from -2.9‰ to 5.1‰ with a mean value of 3.0‰, respectively. These average δ³⁴S_SO4 and δ¹⁸O_SO4 values have no significant difference between CMD and Kuye river water(p>0.05); the average SO^2-₄ concentration of CMD is different from that of Kuye river water; the results of BIMM show that the contributions of CMD to riverine SO^2-₄ are 30.3%±18.9% in the upstream Wulanmulun river, and 12.5%±10.2% in the downstream Kuye river water. Meanwhile, the SO^2-₄ in CMD is also affected by both overlying fissure water, which contributes 34.6%±16.5% sulfate to CMD, and Kuye river water, which contributes 18.8%±16.5% sulfate to CMD. Combined with sulfur and oxygen isotopic compositions, the SO^2-₄ sources in CMD and their impacts on riverine SO^2-₄ in the Kuye river basin have been well confirmed, which also provide the evidences of CMD on riverine SO^2-₄ in the Yellow River Basin through the Loess Plateau.