Carbon dioxide uptake in a eutrophic stratified reservoir: Freshwater carbon sequestration potential

Jinichi Sakaguchi; Keisuke Nakayama; Katsuaki Komai; Atsushi Kubo; Taketoshi Shimizu; Junpei Omori; Kohji Uno; Tomoyasu Fujii

doi:10.1016/j.heliyon.2023.e20322

Carbon dioxide uptake in a eutrophic stratified reservoir: Freshwater carbon sequestration potential

Heliyon. 2023 Sep 20;9(10):e20322. doi: 10.1016/j.heliyon.2023.e20322. eCollection 2023 Oct.

Authors

Jinichi Sakaguchi¹, Keisuke Nakayama¹, Katsuaki Komai², Atsushi Kubo³, Taketoshi Shimizu⁴, Junpei Omori⁴, Kohji Uno⁵, Tomoyasu Fujii⁶

Affiliations

¹ Graduate School of Engineering, Kobe University, 1-1 Rokkodai-Cho Nada-Ku, Kobe City, 658-8501, Japan.
² School of Earth, Energy and Environmental Engineering, Kitami Institute of Technology, 165 Koen-cho, Kitami, 090-8507, Japan.
³ Department of Geoscience, Shizuoka University, 836 Ohya, Suruga-Ku, Shizuoka, 422-8529, Japan.
⁴ Water Quality Laboratory, Kobe City Waterworks Bureau, Kobe, Hyogo, 652-0004, Japan.
⁵ Department of Civil Engineering, Kobe City College of Technology, 8-3 Gakuenhigahimachi, Nishi-ku, Kobe City, 651-2194, Japan.
⁶ School of Science Education, Nara University of Education, Takabatake-Cho, Nara, 630-8528, Japan.

Abstract

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 (pCO₂), 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 pCO₂ based on total alkalinity and pH through field observations. In addition, pCO₂ 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 pCO₂ was verified by using the Net Ecosystem Production (NEP) model, and a submerged freshwater plants such as Potamogeton malaianus 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.

Keywords: Algae; Freshwater lake; Net ecosystem production; Stratification; pCO2.