Fractionation of inorganic carbon in the surface sediments of northern and western Bohai Bay
渤海湾北部和西部海域表层沉积物中无机碳形态研究

Fractionation of inorganic carbon (IC) in the surface sediments of northern and western Bohai Bay was extracted sequentially with solutions of sodium chloride (NaCl), ammonia (NH3·H2O), sodium hydroxide (NaOH), hydroxylamine hydrochloride (NH2OH·HCl), resulting in five fractions: the exchangeable fraction (NaCl fraction), weak alkali extractable fraction (NH3·H2O fraction), strong alkali extractable fraction (NaOH fraction), weak acid extractable fraction (NH2OH·HCl fraction), and residual fraction. Combined with other sediment geochemical parameters, the factors which affected the IC content were discussed. The results showed that in the surface sediments of the study area, the average contents of IC in different fractions, i.e. NaCl fraction, NH3·H2O fraction, NaOH fraction, NH2OH·HCl fraction and Residual fraction, were 0.66, 0.86, 0.23, 2.56 and 0.46 mg/g, respectively. The NaOH fraction accounted for the smallest proportion (about 5%) of the TIC. The NH2OH·HCl fraction ration was the largest, in the vicinity of 50%. Correlation analysis among different IC fractions and geochemical parameters indicated that the sediment moisture content, total nitrogen (TN), total organic carbon (TOC) and sediment fine fraction had a highly significant effect on the NH3·H2O fraction of IC; TN and TOC had a significant effect on the NaOH fraction IC; sediment moisture content had a significant effect on residual fraction IC; and there was no significant correlation between various sediment geochemical factors and the other two fractions. During early digenesis, there might be a certain transformation between the NaCl and the residual fractions of IC.