| 摘要: |
| 湖泊作为全球碳循环的热点区域，一方面通过浮游植物光合作用固定大气中的二氧化碳（CO2），另一方面又通过有机物的降解向大气中排放CO2和甲烷（CH4）。随着气候变化和人类活动的增加，湖泊中蓝藻水华频繁发生，但目前关于蓝藻水华对湖泊沉积物-水系统中碳的源汇效应的影响研究主要集中于藻类死亡降解对含碳温室气体排放的改变，对藻类光合固定大气中CO2的效应的研究较少，因此蓝藻水华引起的湖泊碳的源汇效应的尚不明确。本研究于2023年夏季采集太湖竺山湾的表层沉积物，添加不同生物量的蓝藻，进行室内恒温水浴培养模拟实验，定期封闭培养柱，采样测定顶空气体中CO2和CH4浓度及碳同位素丰度，研究蓝藻生长和衰亡对CO2和CH4产生途径及排放通量的影响。结果表明，蓝藻生长与衰亡阶段分别呈CO2吸收和排放状态，CO2通量随初始蓝藻添加量的增加而增加。蓝藻衰亡阶段CO2排放通量随着蓝藻的死亡分解逐渐增加，在第25天达到稳定。蓝藻生长阶段的CH4排放通量为0.022±0.011~3.159±0.51 μmol·m-2·h-1，在第7天达到峰值：蓝藻衰亡阶段的CH4排放显著升高，达到0.219±0.017~9.783±0.215 μmol·m-2·h-1并在第20天达到峰值。将CH4换算为CO2当量(CO2-eq)，各处理组总的CO2-eq排放通量在蓝藻生长阶段表现为“碳汇”（-451.82~-113.28 mmol·m-2·h-1)，而在蓝藻衰亡阶段表现为“碳源”（35.46~196.86 mmol·m-2·h-1）。整个实验周期净CO2-eq排放通量为-746.71 mmol·m-2·h-1，表现出强烈的碳汇效应。13C-CO2和13C-CH4稳定同位素结果显示，表观分馏因子αC值均小于1.06，表明蓝藻生长和衰亡阶段CH4产生途径主要以乙酸发酵为主。随着初始蓝藻添加量的增加，αC逐渐减小，表明蓝藻提高了乙酸发酵途径在CH4代谢中的占比。研究结果对于揭示蓝藻水华对富营养化化湖泊碳循环与源汇效应影响机制具有重要科学意义。 |
| 关键词: 甲烷 排放通量 碳同位素 蓝藻水华 |
| DOI： |
| 分类号: |
| 基金项目:(42271126),中国科学院南京地理与湖泊研究所自主部署科研项目(NIGLAS2022GS03)联合资助 |
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| Effects of growth and decline of cyanobacteria on CH4 and CO2 emission fluxes and their source pathways in sediment-water system of Taihu Lake,china* |
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wumingjie,Xu hai,Zhan xu,Qiu yu,Sun hongwei,Qin boqiang,Zhu guangwei,Zhang yunlin
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School of Environment and Ecology, Jiangnan University
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| Abstract: |
| Lakes are the hot spots of the global carbon cycle. On the one hand, carbon dioxide (CO2) is fixed in the atmosphere through photosynthesis of phytoplankton. on the other hand, CO2 and methane (CH4) are emitted into the atmosphere through the degradation of organic matter. With the increase of climate change and human activities, cyanobacterial blooms occurred frequently in lakes. However, the current research on the effect of cyanobacterial bloom on carbon source and sink is mainly focused on the effect of algae death and degradation on carbon-containing greenhouse gas emissions. There are few studies on the photosynthetic carbon sequestration effect of algae. Therefore, surface sediments effects of cyanobacterial blooms in lakes are not clear. In this study, surface sediments were collected from Zhushanwan, Taihu Lake in the summer of 2023. Add different biomass of cyanobacteria to conduct indoor constant temperature water bath culture simulation experiments. The concentrations of CO2 and CH4 and the abundance of carbon isotope in the headspace were measured by sampling in the culture columns. The effects of cyanobacterial bloom growth and decline on CO2 and CH4 production pathways and emission fluxes were studied.The results showed that the growth and decay stages of cyanobacteria exhibited CO2 absorption and emission states, respectively. The CO2 emssion flux increased with the increase of initial cyanobacterial addition. The CO2 emission flux during the decay stage increased gradually with the death and decomposition of cyanobacteria. The phenomenon reached stability on the 25th day. The CH4 emission flux in the growth stage was 0.022±0.011~3.159±0.51 μmol·m-2·h-1 reaching its peak on the 7th day. The CH4 emissions during the death stage increased significantly, reaching 0.219±0.017~9.783±0.215 μmol·m-2·h-1. The CH4 emission flux peaked on the 20th day. After converting CH4 to CO2 equivalent(CO2-eq) and summarizing, the total CO2-eq of each group showed as a "carbon sink" (-451.82~-113.28 mmol·m-2·h-1) during the whole experiment. However, it was a "carbon source" (35.46~196.86 mmol·m-2·h-1) during the death stage. The net CO2-eq emission flux during the whole experiment period was -746.71 mmol·m-2·h-1, The water columns exhibited a strong carbon sink effect. The results of 13C-CO2 and 13C-CH4 stable isotopes showed that the apparent fractionation factor αC were less than 1.06. This indicated that acetic acid fermentation was the main pathway of CH4 production in both growth and decay stages of cyanobacteria. αC gradually decreased with the increase of initial cyanobacteria supplement. This result indicated that cyanobacteria increased the proportion of acetic acid fermentation pathway in CH4 metabolism. The results of this study have important scientific significance in revealing the mechanism of cyanobacterial blooms on carbon cycling and source sink effects in eutrophic lakes. |
| Key words: methane discharge flux carbon isotope cyanobacteria bloom |
