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. ©, 2015, Chinese Society for Environmental Sciences. All right reserved.