有机碳沉积效率对湖泊富营养化的响应机制研究

Lake eutrophication and algal bloom significantly varied the carbon cycle in the lake itself and its role in the global carbon cycle. However, the responding mechanisms of organic carbon burial rate, mineralization rate and burial efficiency to the lake eutrophication have not been well addressed. Thus, the contribution evaluation of lake to the global carbon cycle was impeded during the process of global growth trend of lake eutrophication. In this study, the lake sediment is taken as the research sample and the input organic carbon from algae is treated as an inducement. The influencing mechanism of lake eutrophication to the organic carbon burial efficiency was revealed via the laboratory controlled experiment and in situ sampling. We will establish the dynamical mode of carbon fix rate during the algal growth as well as the mineralization rate of organic carbon for different sources (autochthonous and allochthonous). The interaction of autochthonous and allochthonous organic carbon during the process of mineralization also is developed through the trace of carbon isotope. As the research area, Dianchi Lake is an extremely eutrophication lake. The source of organic carbon in the lake sediment was identified by the molecule marker of n-alkanes. Combining the mineralization rate and interaction effect of autochthonous and allochthonous, the impacts of Lake eutrophication to the organic carbon burial rate, mineralization rate and burial efficiency are finally distinguished from terrestrial effect. This research, on the one hand, will settles the theoretical basis for the spatial and temporal variation of burial efficiency, on the other hand, will provides technical support to the evaluation of lake eutrophication to the global carbon cycle.

湖泊富营养化及其引起的蓝藻水华显著改变了湖泊自身碳循环模式及其在全球碳循环中的作用。但湖泊碳循环过程中有机碳的沉积速率、矿化速率和沉积效率对富营养化的响应机制并没有被充分的研究。在全球湖泊富营养化加剧的情况下，严重阻碍了湖泊在全球碳循环中的作用评估。本研究以湖泊沉积物为载体，藻类有机碳输入为诱因，结合室内控制实验和野外采样，揭示湖泊富营养化对有机碳沉积效率的作用机制。室内利用碳同位素示踪等方法，通过藻类生长固碳实验、内源和外源有机碳矿化实验建立藻类生长固碳和不同来源有机碳矿化速率及其相互作用动力模式。野外以滇池为研究区，利用沉积物中分子标识物和碳同位素示踪有机碳的来源，结合室内藻类培养、有机碳矿化实验结果，明确沉积物中有机碳来源及其对沉积速率、矿化速率和沉积效率的影响。该研究一方面为研究有机碳沉积效率时空差异奠定理论基础，另一方面也为评估富营养化在全球碳循环中的作用提供技术支撑。

本项目以云南省滇池和抚仙湖为研究对象，利用210Pb、137Cs确定沉积物年代，通过湖泊沉积物有机碳、碳氮同位素和正构烷烃分子标识物等建立有机碳来源示踪模型，精确解析富营养化和非富营养化湖泊和湖区有机碳来源历史演变，定量表征不同来源有机碳的沉积效率，通过室内藻类培养和沉积矿化实验，揭示藻类添加对沉积物有机碳矿化的影响。结果表明，滇池有机碳沉积速率从富营养化前的16.62±7.53 g.m−2yr−1增加到了富营养化后的54.33±27.29 g.m−2yr−1，而蓝藻水华的发生，使得有机碳沉积速率增加到了61.98 ± 28.94 g.m−2yr−1。蓝藻水华前后，有机碳沉积速率增加了4.55倍，但如果考虑有机碳的矿化，有机碳沉积速率增加了2.5倍，藻类的添加增加了沉积物有机碳的矿化速率。通过有机碳矿化模式，结合有机碳来源，建立有机碳矿化模型，表明有机碳的矿化速度呈现藻类源有机碳>水生植物有机>陆源有机碳，藻类有机碳的矿化时间约在1~20年间；而陆源有机碳矿化时间约在10~100年。目前，沉积有机碳仅仅区分了内源和外源有机碳，在研究中我们发现，沉积物中溶解有机碳和黑炭与内源和外源有机碳在迁移和矿化特性方面存在显著差别，沉积物中黑炭大约占到总有机碳的11.78 ± 2.84%，惰性强，难以矿化；溶解有机碳迁移将有机碳迁移到沉积物-水界面，并释放到水体中，进一步减少沉积物有机碳沉积量。