抚仙湖水生植物HCO^(-)_(3)利用效率及与之相关的内源有机碳沉积通量研究

STUDY ON THE UTILIZATION EFFICIENCY OF HCO^(-)_(3)BY AQUATIC PLANTS AND THE BURIED FLUX OF AUTOCHTHONOUS ORGANIC CARBON IN FUXIAN LAKE

因可能是全球“遗失碳汇”的重要组分,耦合生物碳泵效应的碳酸盐风化碳汇日益受到学界关注,并且其对不同时间尺度上的气候变化都可能产生重要影响。由碳酸盐风化产生的HCO^(-)_(3)能否形成稳定的碳汇尚缺乏足够论证,厘清这一问题的关键在于如何有效评估水生植物固定HCO^(-)_(3)的能力,尤其是植物残体进入沉积物后的实际碳固定量。本文基于已发表的抚仙湖数据,利用碳同位素端元模型估算了抚仙湖水生植物光合固定HCO^(-)_(3)碳量,发现无机碳源中约有57%是以HCO^(-)_(3)的形式被水生植物光合固定下来,碳汇通量达24.76 tC/(km^(2)·a)。而可能由于微生物分解等作用,抚仙湖现代沉积物中真正被埋藏下来的内源有机碳沉积通量,即耦合生物碳泵效应的碳酸盐风化碳汇通量仅为9.2~16.4 tC/(km^(2)·a),这大致相当于水生植物所固定HCO^(-)_(3)的一半。尽管如此,水生植物的光合作用和碳酸盐风化耦合作用仍表现出巨大的碳汇潜力。因此,在未来的全球碳循环和气候变化模型中需考虑碳酸盐风化碳汇的影响。

The carbon fixed by the coupled carbonate weathering with aquatic photosynthesis mechanism may account for a significant portion of global‘missing sink’.This mechanism is therefore playing an underestimated role in climate changes on various timescales,and is attracting increasing attention from the climate community.However,how much carbon can be fixed through this mechanism is still debated,in particular,whether carbonate rock dissolution derived bicarbonates(HCO^(-)_(3))can form a stable carbon sink is still not certain.To better quantify the carbon sink by the coupled carbonate weathering with aquatic photosynthesis mechanism,we need to evaluate the ability of aquatic plants in HCO^(-)_(3)fixation,especially the effective carbon sequestration resulting from plant residues burial.Here,based on published data,we calculated carbon budget within the characteristic Fuxian Lake catchment(24°17'~24°37'N,102°49'~102°57'E)utilizing the carbon isotope model.We have found that ca.57%of HCO^(-)_(3)is utilized by aquatic plants,and the carbon sink flux within the catchment reaches ca.24.76 tC/(km^(2)·a).However,nearly half of the carbon sink flux is compensated by microbial decomposition,and resulted burial flux of autochthonous organic carbon in the modern sediments,i.e.the carbon sink by the coupled carbonate weathering with aquatic photosynthesis mechanism,is reduced to ca.9.2~16.4 tC/(km^(2)·a).Nevertheless,our modeled results still show the great potential of the combination of photosynthesis and carbonate weathering in carbon sequestration.Therefore,atmospheric CO_(2)uptake by carbonate weathering should be included in the global carbon cycle and climate change model.