Effects of benthic bioturbation on phytoplankton in eutrophic water: A laboratory experiment

Planktonic and benthic habitats in a limnic ecosystem are tightly coupled. Benthic bioturbation plays an important role in the process across the sediment-water interface and directly and indirectly affects phytoplankton in eutrophic water. Using a combination of high-resolution technology (Mini-Peeper and Microelectrode), this 135-day laboratory study explored the characteristics and the driving factors of phytoplankton responses to the bioturbation of chironomid larvae, a typical and common gallery-diffuser species widely distributed in eutrophic lakes. Results showed that benthic bioturbation influenced the eutrophication of the phytoplankton mainly by increasing resuspension and affecting nutrients. Bioresuspension increased phytoplankton recruitment and dissolved silicon, but worsened turbidity and light conditions. Bioturbation also increased sediment oxygen uptake, consequently delaying phosphorus release and inhibiting nitrogen release. During the mid-late stage, the accumulated metabolites of benthic animals stimulated the alkaline phosphatase activity of microbes in the sediment, which accelerated phosphorus release. The phytoplankton also exhibited a self-adjusting mechanism. Meanwhile, the benthic ecosystem did not support a high phytoplankton biomass and chose r-selected meroplankty, opportunistic species, and pennate diatoms; thus, the colonial cyanobacteria lost their advantages. The morpho-functional group classification of phytoplankton was an appropriate tool.