Sakaguchi Jinichi, Nakayama Keisuke, Komai Katsuaki, Kubo Atsushi, Shimizu Taketoshi, Omori Junpei, Uno Kohji, Fujii Tomoyasu
Graduate School of Engineering, Kobe University, 1-1 Rokkodai-Cho Nada-Ku, Kobe City, 658-8501, Japan.
School of Earth, Energy and Environmental Engineering, Kitami Institute of Technology, 165 Koen-cho, Kitami, 090-8507, Japan.
Heliyon. 2023 Sep 20;9(10):e20322. doi: 10.1016/j.heliyon.2023.e20322. eCollection 2023 Oct.
Carbon capture and storage due to photosynthesis activities has been proposed as a carbon sink to mitigate climate change. To enhance such mitigation, previous studies have shown that freshwater lakes should be included in the carbon sink, since they may capture as much carbon as coastal areas. In eutrophic freshwater lakes, there is uncertainty about whether the equilibrium equation can estimate the partial pressure of carbon dioxide (pCO), owing to the presence of photosynthesis due to phytoplankton, and pH measurement error in freshwater fluid. Thus, this study investigated the applicability of the equilibrium equation and revealed the need to modify it. The modified equilibrium equation was successfully applied to reproduce pCO based on total alkalinity and pH through field observations. In addition, pCO at the water surface was lower than the atmospheric partial pressure of carbon dioxide due to photosynthesis by phytoplankton during strong stratification. The stratification effect on low pCO was verified by using the Net Ecosystem Production (NEP) model, and a submerged freshwater plants such as were found to have high potential for dissolved inorganic carbon (DIC) sequestration in a freshwater lake. These results should provide a starting point toward more sophisticated methods to investigate the effect of freshwater carbon on DIC uptake in freshwater stratified eutrophic lakes.
光合作用驱动的碳捕获与封存已被提议作为一种碳汇以缓解气候变化。为加强这种缓解作用，先前的研究表明淡水湖应被纳入碳汇，因为它们捕获的碳量可能与沿海地区相当。在富营养化淡水湖中，由于浮游植物光合作用的存在以及淡水水体中pH测量误差，平衡方程能否估算二氧化碳分压（pCO）存在不确定性。因此，本研究调查了平衡方程的适用性，并揭示了对其进行修正的必要性。通过实地观测，修正后的平衡方程成功用于根据总碱度和pH值再现pCO。此外，在强烈分层期间，由于浮游植物的光合作用，水面处的pCO低于大气二氧化碳分压。利用净生态系统生产（NEP）模型验证了分层对低pCO的影响，并且发现诸如[此处原文缺失某种沉水淡水植物名称]等沉水淡水植物在淡水湖中有很高的溶解无机碳（DIC）封存潜力。这些结果应为研究淡水碳对富营养化分层淡水湖DIC吸收影响的更复杂方法提供一个起点。
