Upper Midwest lakes are supersaturated with N <sub>2</sub>
Brianna M. Loeks, James B. Cotner
Abstract
Significance Excess nitrogen (N) in freshwaters is problematic due to its impacts on eutrophication, biodiversity losses, and harmful algal blooms. Some microbial processes such as denitrification and anammox can remove N from systems while others such as N-fixation can add a usable form of N. However, not enough is known about when and where these competing processes are occurring in lakes, and understanding this can provide insight to management. Here, we determined that nearly all of the 34 lakes that we examined in the upper Midwest had a net loss of N 2 that must be compensated by watershed inputs to maintain steady state. These results suggest that N-fixation in these lakes was not enough to offset denitrification and anammox.