Co-metabolic-like Effects Induced by Eutrophication-Intensified Cyanobacterial Blooms Enhanced Sediment Carbon Emissions in Shallow Lakes

Eutrophication-intensified cyanobacterial blooms are increasingly recognized as significant contributors to carbon emissions from shallow lakes, yet the underlying mechanisms remain poorly understood. Here, we combined basin-scale field surveys, satellite-derived floating algae index (FAI), and microcosm incubations to evaluate the effects of cyanobacterial blooms on carbon emissions and sediment carbon loss in seven shallow lakes of the middle and lower Yangtze River Basin. FAI-based analyses showed severe and spatially extensive cyanobacterial blooms, with maximum bloom coverage reaching approximately 68.8% of the lake area in Taihu and nearly complete coverage in Dianshan, while bloom intensity correlated positively with trophic level. Field observations revealed that hypereutrophic lakes with higher total nitrogen (TN), total phosphorus (TP), and organic carbon (OC) concentrations in the overlying water and sediments exhibited strongly elevated CH4 and CO2 fluxes; specifically, CH4 emissions in Taihu (248.6 mu g center dot m(-2)center dot min(-1)) exceeded those in the mesotrophic Lake Caizi (7.1 mu g center dot m(-2)center dot min(-1)) by over an order of magnitude. Furthermore, microcosm experiments demonstrated that cyanobacterial-derived labile carbon enhances the decomposition of macrophyte detritus via co-metabolic-like effect interactions: mixed cyanobacteria-plant treatments resulted in up to approximately 100% and 125% increases in CH4 and CO2 production, respectively, while sediment TOC loss exceeded theoretical expectations. These findings highlight that bloom-driven co-metabolic-like effect is a critical mechanism for amplifying carbon emissions and destabilizing sediment carbon pools in eutrophic lakes, highlighting the necessity of incorporating bloom dynamics and multi-source carbon interactions into regional and global lake carbon budgets.