State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences (CAS), 99 Lincheng West Road, Guiyang 550081, China; Yunnan Key Laboratory of Earth System Science, Yunnan University, Kunming 650500, China.
Yunnan Climate Center, Kunming 650034, China.
Water Res. 2022 Aug 15;222:118907. doi: 10.1016/j.watres.2022.118907. Epub 2022 Jul 25.
The precipitation of carbonate minerals does not invariably result in CO emission to the atmosphere, because dissolved inorganic carbon (DIC) can be partially utilized by terrestrial aquatic phototrophs, thus generating an autochthonous organic carbon (AOC) sink. However, little is known about the potential effects of this mechanism on carbon cycles in DIC-rich lakes, mainly due to the lack of detailed documentation of the related processes, which limits our ability to accurately evaluate and predict the magnitude of this carbon sink. We conducted field observations in Fuxian Lake, a large and representative karst lake in the Yunnan-Guizhou Plateau, SW China. Continuous diel monitoring was conducted to quantitatively assess the coupled relationship between lake metabolism and DIC cycling and its influence on the carbonate weathering-related CO sink. We found that the diel physicochemical variations and isotopic characteristics were mainly controlled by the metabolism of aquatic phototrophs, evidenced by a significant relationship between net ecosystem production and diel DIC cycling, and demonstrating the significance of DIC fertilization in supporting high primary production in karst lakes. The data showed that a reduction in photosynthesis occurred in the afternoon of almost every day, which can be explained by the lower CO/O ratio that increased the potential for the photorespiration of aquatic plants, thus reducing photosynthesis. We found that a net autotrophic ecosystem prevailed in Fuxian Lake, suggesting that the lake functions more as a sink than a source of atmospheric CO. Considering carbonate weathering, the estimated AOC sink amounted to 650-704 t C km yr, demonstrating both the potentially significant role of metabolism in lacustrine carbon cycling and the potential of the combination of photosynthesis and carbonate weathering for carbon sequestration. Our findings may help to quantitatively estimate the future impact of lake metabolism on carbon cycling, with implications for formulating management policies needed to regulate the magnitude of this carbon sink.
碳酸盐矿物的沉淀并不一定会导致二氧化碳排放到大气中，因为溶解无机碳（DIC）可以被陆地水生光合生物部分利用，从而产生一个自生有机碳（AOC）汇。然而，由于缺乏对相关过程的详细记录，人们对这种机制对 DIC 丰富湖泊碳循环的潜在影响知之甚少，这限制了我们准确评估和预测这个碳汇的规模的能力。我们在中国西南云贵高原的大型代表性岩溶湖泊抚仙湖中进行了实地观测。进行了连续的昼夜监测，以定量评估湖泊代谢和 DIC 循环的耦合关系及其对与碳酸盐风化相关的 CO 汇的影响。我们发现，昼夜理化变化和同位素特征主要受水生光合生物代谢的控制，净生态系统生产力与昼夜 DIC 循环之间存在显著关系，证明了 DIC 施肥在支持岩溶湖中高初级生产力方面的重要性。数据显示，几乎每天下午光合作用都会减少，这可以用 CO/O 比值降低来解释，因为 CO/O 比值的降低增加了水生植物光呼吸的潜力，从而降低了光合作用。我们发现，抚仙湖存在一个净自养生态系统，这表明该湖更像是大气 CO 的汇而不是源。考虑到碳酸盐风化，估计的 AOC 汇量为 650-704 t C km yr，这表明代谢在湖泊碳循环中具有潜在的重要作用，以及光合作用和碳酸盐风化相结合进行碳固存的潜力。我们的研究结果可能有助于定量估计未来湖泊代谢对碳循环的影响，为制定调节这个碳汇规模的管理政策提供依据。
