农业活动干扰下地下水无机碳循环过程研究

为准确识别浅层地下水污染来源及污染过程,选择我国北方某集约化蔬菜种植基地浅层地下水作为研究对象,借助水化学组成、氢氧同位素以及溶解性无机碳(DIC)碳同位素组成,探讨浅层地下水来源以及DIC来源和迁移转化特征.结果表明:浅层地下水阳离子以Ca²⁺和Mg²⁺为主,阴离子以HCO₃^-和SO₄^2-为主,沿地下水流向,水化学类型由HCO₃^?-Ca²⁺-Mg²⁺型转变为HCO₃^--SO₄^2--Mg²⁺-Ca²⁺型;浅层地下水δD组成范围为-69.6‰~-52.7‰,均值为-63.5‰,δ¹⁸O组成范围为-9.29‰~-6.80‰,均值为-8.45‰.大气降水是浅层地下水重要补给来源,靠近河水的浅层地下水还接受地表水的补给;浅层地下水δ¹³C_DIC组成范围为-11.76‰~-5.85‰,均值为-10.43‰.浅层地下水DIC来源包括土壤CO₂、碳酸盐矿物以及有机质分解.河水DIC侧渗对局部浅层地下水DIC碳同位素造成影响,化学肥料引起的酸性物质参与碳酸盐矿物风化作用以及浅层地下水CO₂去气作用对地下水δ¹³C_DIC组成产生影响,在利用DIC碳同位素识别地下水污染来源时需要引起重视.

Inorganic carbon cycling in subsurface environment influenced by agricultural activities

To accurately elucidate the pollution sources and pollutant transformations in subsurface environment, shallow groundwater affected by intensive cultivation of vegetables on open land in North China was selected as objective. Hydrochemical compositions, hydrogen and oxygen isotopes, and dissolved inorganic carbon isotopes of shallow groundwater samples were utilized to delineate the sources of groundwater and to illuminate the sources and transformations of dissolved inorganic carbon. The results demonstrated that Ca2+ and Mg2+ were dominated cations, and HCO3- and SO42- were dominated anions in local groundwater. Along groundwater flow path, hydrochemistry types varied from HCO3--Ca2+-Mg2+ to HCO3--SO42--Mg2+-Ca2+; Hydrogen and oxygen isotope values of shallow groundwater varied from -69.6‰ to -52.7‰ with the average value of -63.5‰ and from -9.29‰ to -6.80‰ with the average value of -8.45‰, respectively. It could be found that atmospheric precipitation was the main recharge source of local groundwater, meanwhile shallow groundwater located near the river water were also recharged from surface water. Dissolved inorganic carbon isotope values of shallow groundwater varied from -11.76‰ to -5.85‰ with average value of -10.43‰. Dissolved inorganic carbon in local groundwater was mainly derived from soil carbon dioxide, carbonate minerals and organic matters. It also indicated that some groundwater samples had been influenced by infiltration of river water. Fertilizer-induced acid participating carbonate minerals weathering and CO2 outgassing in shallow groundwater were two important factors controlling inorganic carbon isotopic compositions in groundwater, which should be paid more attentions during identification of groundwater pollution sources by dissolved inorganic carbon isotopes.