Changes in Chemical Fractions of Inorganic Carbon in Sediments of Hulun Lake and A Differential Analysis Study with Other Typical Lakes of China

As an important source, sink and pool of carbon, lake sediment plays an important role in carbon cycle. Inorganic carbon (IC) in lake sediment is abundant, however the role of inorganic carbon in lake systems in terrestrial carbon cycling remains less clear. In this paper, the spatial variations, source and transformation of IC in sediments of Lake Hulun were investigated and compared with typical lakes of Inner Mongolia Plateau by analyzing the influencing factors. The results showed that contents of total IC in surface sediment in Lake Hulun ranged from 17.2 to 66.7 mg g(-1) with a mean of 42.6 mg g(-1), and the pattern of spatial distribution showed obviously decreasing trend from southwest to northeast lake districts. The order size of IC fractions in surface sediment was in a sequence of EX (extracted by NaCl) < SAL (extracted by NaOH) < WAL (extracted by NH3 center dot H2O)- SAC (extracted by HCl) < WAC (extracted by HO-NH2 center dot HCl), the WAC and SAC fractions were the major fractions, accounted for 80% of total IC. In vertical distribution, the WAC and SAC fractions presented obviously opposite spatial distribution, indicted that these fractions could transform into each other in sediments. The ratio of IAP/Ksp in lake water ranged from 8.87 to 108.5, suggested that this lake had what it took to form the authigenic carbonate precipitation. A differential analysis study indicated that the mechanisms what made the difference of IC content in four lakes were multiple, the chemical properties and temperature of lake water, the defusion or dissolve of CO2, biomass and sediment environment were the key factors that might affect the contents of inorganic carbon in the lake sediment.