Abstract
Nutrient supply is an important determinant of N fixation rates in pelagic cyanobacteria. In shallow aquatic ecosystems, benthic primary producers can affect nutrient release from the sediment to the pelagic zone, yet the relationship between benthic primary producers and pelagic N fixation is not well understood. Here, we explore the effect of benthic primary producers on benthic nutrient fluxes and pelagic N fixation rates in shallow, eutrophic Lake Mývatn, Iceland. In paired benthic nutrient flux and pelagic N fixation assays, we showed that sites with increased benthic phosphate release were associated with increased pelagic N fixation. In turn, during assays of flux rates, benthic phosphate release was negatively associated with dissolved oxygen concentrations at the sediment–water interface, which was positively associated with benthic primary producer abundances. Together, these relationships suggest that benthic primary producers influence variation in within-lake pelagic N fixation via their effects on benthic nutrient flux rates.