| 其他摘要 | For decades, the soil deterioration and pollution became urgent issues resulted from the increasing artificial activities in Karst area in southwestern of China. Humic substances (HS) are the major part of organic matters in soil and peat, which could improve the soil structure and influence the transportation, transformation and bioavailability of pollutants in ecosystem. For most of soils and peat, humic acids (HA) are the major part of HS. The study of HA in typical soils and peat could support the reconstruction of the damaged ecosystem and the risk assessment of typical pollutants of Karst area. This work was focus on HA from peat and major soils (yellow earth and limestone soil) in Karst area. First, sample the peat and soils by layer. Second, extract and purify the HA from the peat and soil samples. Third, use tangential ultrafiltration system to separate the HAs from peat and soils into different fractions with different nominal molecular weight. Last, characterize these HA and their size fractions by using the Elemental analysis, Potentiometric titration, UV-visible spectroscopy, Fourier transform infrared spectroscopy and Cross polarization-magic angle spinning 13C-nuclear magnetic resonance. In summary, the main conclusion and new insight about HA from peat, yellow earth and limestone soil and their size fractions are as follows: With increasing depth of peat, the amount of HA increase, as well the oxygen, aromatic components, carbohydrates, carboxyl, ketonic groups and total acidity of HA, while the nitrogen, hydrogen and aliphatic constituents of HA continue to decrease. It is expected by the analysis results, the degradation of HA is influenced by the oxygen content in the pore of peat. In yellow earth profile, with soil depth increase, the amount of HA decrease, as well the carbon, aliphatic constituents, aromatic components, carboxyl, phenolic hydroxyl, ketonic groups and total acidity of HA, while the nitrogen, hydrogen and carbohydrate components of HA increase. The results imply that, in soil, the activities of microorganism are not limited by oxygen concentration in the soil solution and that, in different soil horizon, the precursors and the degradation extent of HA are different. Comparing with the HA from peats and yellow earth, the HA from limestone soils are lower in the atomic ratio of C/N and higher in the atomic ratios of H/C and O/C. In limestone soil, the microbial activity could also be higher. From these two points, in limestone soil, the microbial degradation of HA could be fierce and results in the change in amount and properties of HA in the soil profile dramatically. However, in limestone soil, with soil depth increase, the amount of HA decrease slightly, and the carboxyl, phenolic hydroxyl, ketonic groups and total acidity of HA increase slightly, while the change in the nitrogen and hydrogen of HA is not significant. We propose that, in the limestone soil, the HA are preserved by the CaCO3 package or complexing with the calcium ions from uptake by microorganism. Using tangential ultrafiltration system, the three HAs from peats and the HA extracted from the upper horizon in yellow earth were separated into 8 fractions with different nominal molecular weight. The mass distribution of the size fractions indicates that HA from peats and yellow earth have preferential range of MW values. With the molecular weight decrease, the carbon, nitrogen and hydrogen of HA decrease, as well the aliphatic constituents, methoxyl and carbohydrates in HA, while the oxygen, aromatic constituents, carboxyl, ketonic groups and total acidity of HA increase. We propose that the smaller size fractions, which are higher in oxygen functional groups such as ketonic and carboxyl groups, are more polar and soluble, more easily uptaken by microorganisms. Therefore, the more degradable components (nitrogen-containing constituents and carbohydrate constituents) in smaller size fractions are assimilated by microorg |
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