城市土壤有机碳和黑碳的含量特征与来源分析

CONCENTRATION AND SOURCES OF ORGANIC CARBON AND BLACK CARBON OF URBAN SOILS IN NANJING

由于城市化过程中人为活动的深刻影响,城市土壤的一些性质被强烈地改变。城市土壤有机质由于来源的多样性和受到不同程度人为活动的影响,其组成和分布特征表现出异质性和多样性。本研究以南京市为对象,研究了功能区之间土壤有机碳和黑碳含量的差异。与郊区土壤相比,城市土壤的有机碳含量普遍较高。通过对有机碳组成的分析发现其中稳定的黑碳含量较郊区土壤明显偏高,且在不同功能区之间呈现差异性,体现了人为影响过程和污染来源的差别。同时发现路边绿化带土壤正受到来自交通环境的强烈影响,其有机碳和黑碳含量与其他功能区存在显著差异。不同功能区之间因人为影响的差异,土壤中黑碳含量与有机碳含量的比值表现出明显的不同,可以指示黑碳的可能来源。城市土壤环境中黑碳可能构成了总有机碳中的很大部分,这与自然土壤有明显的差别。

Soil properties change dramatically during urbanization. However, recent knowledge about properties of urban soils is still scarce. The purpose of this paper is to deliver some data of soil organic matter （SOM） properties of urban soils and to describe environmental consequences of human activities in urban environment. For the above objectives, organic carbon （OC） and black carbon （BC） were analyzed of 60 soil samples collected fromO - 10 cm and 10 - 30 cm soil layers in five different function zones in Nanjing city, China. The method used to analyze OC and BC is chemical oxidation treatment （acid dichromate）, in which removal of OC is a critical process in determination of BC. The results suggest that SOM （e.g. OC and BC） is significantly different among function zones in chemical nature and concentration. The highest concentration of OC reaches 29.09 g kg^-1（0 - 10 cm layer）, and the highest concentration of BC 13.67 g kg^-1（0 - 10 cm layer） in roadside soils, suggested its substantially different human activity and pollution source. Especially, pollution compounds emitted from gasoline and diesel vehicles are found to be the main source of BC in roadside soils. The BC/OC ratio may be related to changing pollution intensity due to local biomass and fossil fuel burning. Based on the present data, the high BC/OC ratios and BC concentrations observed in roadside soils indicate that they are the result of direct human activity （e. g. vehicles）. In other words, the BC/OC ratio in different functional zones may show different intensity of human activities. Further comparison shows that BC is probably the main part of total organic carbon in urban soils, contrary to that in natural soils. This knowledge is essential for qualitative assessment of SOM properties of urban soils and urban environment.