Key roles of carbon metabolic intensity of sediment microbes in dynamics of algal blooms in shallow freshwater lakes

Inorganic carbon acquisition is essential to algal growth, while the limitations of dissolved inorganic carbon (DIC) on phytoplankton are still less known in lakes. Sediment is an active hot spot for microbial metabolism, driving the migration and transformation of elements in shallow lakes, which may control the DIC availability to influence algal spatiotemporal dynamics. Hence, we investigated the spatiotemporal changes of phytoplankton, DIC and sediment respiration rates in a eutrophic shallow freshwater lake under non-bloom conditions. There was a widespread deficiency of DIC in the lake, except the estuary. Sediment respiration was positively associated with changes in DIC concentrations, indicating that carbon metabolic activity of sedimentary microorganisms was an important inorganic carbon source for water columns. The availability of DIC in water columns regulated by sediment microbial respiration influenced the algal biomass, composition and productivity. The synergistic effects of seasonal temperature changes and sediment microbial respiration influenced the vertical distribution and migration of phytoplankton. Our results emphasized that carbon metabolic intensity of sediment microorganisms might play a key role in dynamics of phytoplankton, further impacting the spatiotemporal pattern and formation of algal bloom in eutrophic shallow freshwater lakes.