Accumulation of Recalcitrant Dissolved Organic Carbon During Cyanobacterial Blooms in Meiliang Bay, Lake Taihu: Insights Into the Microbial Carbon Pump

Xiaohan Wu¹Xiaogang Chen²Dan Wu³Fenfen Zhang^1*Jinzhou Du¹

• ¹State Key Laboratory of Estuarine and Coastal Research, East China Normal University, Shanghai, China
• ²Key Laboratory of Coastal Environment and Resources of Zhejiang Province, School of Engineering, Westlake University, Hangzhou, China
• ³State Key Laboratory of Estuarine and Coastal Research, East China Normal University, shanghai, China

Cyanobacterial blooms are increasing in frequency, intensity, and duration in both freshwater and marine environments, potentially enhancing atmospheric carbon sequestration by producing substantial amounts of recalcitrant dissolved organic carbon (RDOC). To investigate this, the study conducted monthly analyses of dissolved organic matter (DOM) composition and bacterial community dynamics in Lake Taihu, China, a hotspot for cyanobacterial blooms. Concentrations of carboxyl-rich alicyclic molecules (CRAM), a molecular proxy for RDOC, increased from 51.86 ± 11.22 μM C in the non-bloom period to 60.80 ± 8.21 μM C during the bloom, representing an approximate 17% increase. The annual average RDOC concentration was 62.93 ± 10.66 μM C, accounting for approximately 16% of the total DOC. These results suggest substantial RDOC accumulation during bloom events. Labile DOC was metabolized by bacterial communities and transformed into more recalcitrant compounds through microbial carbon pump mechanisms. Specifically, the CL500-29 marine group and Sphaerotilus contributed to the degradation of protein-like DOM, while the CL500-29 and hgc1 clades played key roles in CRAM formation. The pronounced RDOC enrichment in eutrophic lakes compared to non-eutrophic lakes, rivers, and marine systems underscores the potential of eutrophic lakes to function as significant carbon sinks. Our findings highlight the need to integrate bloom-driven RDOC accumulation into carbon budget frameworks and to reassess the long-term carbon sequestration potential of eutrophic lakes.