泥沙沉积层次对有机碳矿化和CO_(2)排放影响的模拟研究

Simulation Study on the Influence of Sedimentary Layers on Organic Carbon Mineralization and CO_(2)Emissions

[目的]探讨沉积区不同掩埋层位对CO_(2)在沉积剖面中产生和传输的影响,为定量评估黄土高原地区侵蚀-沉积环境下碳源/汇强度和功能提供理论依据。[方法]通过土柱回填控制性试验模拟沉积土层,在12 cm高土柱的顶部(2 cm)、中部(5 cm)和底部(9 cm)分别添加13 C标记的葡萄糖溶液,并设置3种13 C葡萄糖溶液浓度(26,52,104 mg C/kg),对比分析20℃恒温培养10 d期间,不同添加位置和葡萄糖溶液浓度对土柱表观CO_(2)释放速率的影响,并结合稳定性同位素示踪法,解析不同有机碳来源对表观CO_(2)的贡献,进而探讨不同掩埋层位对外源输入有机碳矿化的影响。[结果](1)低浓度葡萄糖添加处理下,外源添加葡萄糖的矿化程度在顶、中、底部分别为38.6%,65.1%,50.9%,存在显著性差异;而随着葡萄糖添加浓度的升高,各层位间的矿化程度趋于一致。(2)顶部添加葡萄糖后,表观CO_(2)中δ13 C峰值最大(376‰,1527‰,3176‰),出现最早(第1天),而添加葡萄糖位置越靠近底部,CO_(2)排放中δ13 C峰值越小(131‰、236‰、645‰),时间滞后(第2天),且添加层位对CO_(2)传输和排放的影响主要在低浓度葡萄糖添加处理时比较明显,高浓度时差异不大。[结论]沉积区掩埋层位可显著影响有机碳的矿化和CO_(2)的传输与排放,黄土高原地区碳源/汇强度的定量评估应明确侵蚀径流外源碳输入的层位和浓度的影响。

[Objective]The aim of this study is to explore the effects of different sedimentary layers on the CO_(2)production and transport in soil depositional profile,and to provide a theoretical basis for quantitative assessment of the intensity and function of carbon source/sink in the erosion-sedimentary environment in the Loess Plateau.[Methods]Soil columns were filled with sieved soil to simulate the depositional soil layer.Three concentrations of 13 C-labeled glucose solution(26,52,104 mg C/kg)were added to the top(2 cm),middle(5 cm)and bottom(9 cm)of the 12 cm high soil columns.During the incubation period of 10 days at 20℃,the effects of different adding positions and glucose solution concentrations on the apparent CO_(2)emission rates were compared and analyzed.The individual contributions from different organic carbon sources to apparent CO_(2)were analyzed by comparing the stable isotopic signature of the CO_(2)and soil,with the attempts to explore the effect of exogenous carbon input at different layers on the mineralization of sedimentary organic carbon.[Results](1)By adding low-concentration glucose,the mineralization degree of exogenous glucose was 38.6%,65.1%and 50.9%at the top,middle and bottom,respectively,with significant difference.However,with the increase of glucose concentration,the mineralization degree of each layer tended to be consistent.(2)When the glucose was added at the top layer,the peak value of theδ13 C in the apparent CO_(2)appeared the earliest on day 1 with the highest values(376‰,1527‰,3176‰).When the glucose was added to the bottom layer,smaller peaks ofδ13 C in CO_(2)emissions(131‰,236‰,645‰)were observed and consistently with a time lag on day 2.Moreover,the effects of different buried layer on CO_(2)transport and emission were more evident when the glucose concentration was low,whereas little difference was observed when the glucose concentration was high.[Conclusion]The sedimentary layers in depositional sites can significantly affect the mineralization of organic carbon and the transport and emission of CO_(2).The quantitative evaluation of carbon source/sink intensity in the Loess Plateau should clarify the influence of the sedimentary layers and concentration of exogenous carbon input from erosion runoff.