Extreme stoichiometric gradients and B-vitamin effects on phytoplankton communities.

Eutrophication of natural waters is a major environmental detriment, leading to increased occurrence of harmful algal blooms and harmful cyanobacterial blooms. In addition to the nutrients nitrogen and phosphorous, micronutrients such as B vitamins can drive phytoplankton growth. To better understand the complex interactions between nutrient stoichiometry and B vitamin biogeochemistry in phytoplankton communities, a B vitamin bottle bioassay experiment was conducted in subsequent years with samples from a long-term shallow-lake mesocosm experiment set up with an extreme nutrient stoichiometry gradient. Vitamin additions did not have a significant effect on the phytoplankton community or their nutrient stoichiometry but halting N additions to shallow-lake mesocosms in 2023 led to an increase in community fraction and photosynthetic efficiency of green algae. The legacy of nutrient supply played a major role in the phytoplankton community and continued nutrient stoichiometry. Therefore, it is important to evaluate present and legacy loading in evaluating eutrophic systems.