三江平原典型湿地剖面有机碳分布特征与积累现状

PROFILE DISTRIBUTION CHARACTERISTICS AND ACCUMULATION OF ORGANIC CARBON IN TYPICAL WETLANDS IN SANJIANG PLAIN

研究了三江平原3类典型湿地(泥炭沼泽、腐殖质沼泽和沼泽化草甸)沉积物剖面有机碳的组分与分布特征。结果表明,泥炭沼泽、腐殖质沼泽和沼泽化草甸剖面有机碳分布具有明显的储碳层和淀积层。储碳层厚度分别约为110、60和15cm,有机碳平均含量分别为295、280和60g/kg(干物质重)。泥炭沼泽和腐殖质沼泽储碳层内,有机碳主要组分为分解程度低的轻组碳(约占总有机碳的70%以上),沼泽化草甸的储碳层内轻组碳约为16%。储碳层以下淀积层的有机碳含量都<30g/kg,轻组碳含量很少。3种类型湿地剖面轻组碳与总有机碳之间有着极显著的正相关关系(P=0.01)。初步建立了湿地有机碳储量的估算方法,得到3种类型湿地剖面1m内的有机碳储量分别为6.62×104、4.90×104和1.44×104t/km2,2m内分别为8.16×104、6.81×104和2.24×104t/km2。

Distribution and fractions of organic carbon (C) in sediment profiles of 3 types of wetland ecosystems (peat fen, humus marsh and marshy meadow) were analyzed. Data show that the sediment profiles of the wetlands can be divided into an organic C depositing horizon (the upper layers) and a mineral-illuvial horizon (the lower layers) based on the characters in the distribution of organic C and its compositions in the profiles. The organic C depositing horizon of peat fen, humus marsh and marshy meadow had a depth of 110, 60, 15 cm and contained about 295, 280, 60 g/kg (dry matter) of organic C on an average, respectively. Light fraction of organic C (P<1.7) accounted for up to 70% of the total organic C in the organic C depositing horizon of peat fen, humus marsh, but only to 16% in the same horizon of marshy meadow. For the 3 types of wetland ecosystems, the contents of organic C in the mineral-illuvial horizon were all smaller than 30 g/kg, which was little fractionated as the light fraction (<2%). It was also shown that for the layers of wetland sediment profiles with a content of organic C above 180 g/kg, there was a close correlation existing between total organic C and the content of the light fraction, and below that level, the content of light fraction was small (0.2～17 g/kg) and also showed little response to changes in total organic C. This indicated that the large presence of the light fraction determined the accumulation of organic C in the organic C depositing horizon of the wetland sediment profiles. Thus, all of the results presented suggest that the extent to which organic C decomposed (e.g., as indicated by the percentage of light fraction as total organic C) be the primary factor to determine the accumulation of organic C in the sediment profile of wetland ecosystems. A procedure was developed to estimate the stock of organic C accumulated in the sediment profile of wetland ecosystems. It was estimated that the stock of organic C was 6.62×10~4, 4.90×10~4, 1.44×10~4 t/km in the upper 1 m depth, and 8.16×10~4, 6.81×10~4, 2.24×10~4 t/km in 2 m in the sediment profile of peat fen, humus marsh, and marshy meadow, respectively.