Nitrogen transformations differentially affect nutrient-limited primary production in lakes of varying trophic state

The concept of lakes “evolving” phosphorus (P) limitation has persisted in limnology despite limited direct evidence. Here, we developed a simple model to broadly characterize nitrogen (N) surpluses and deficits relative to P in lakes, and compared the magnitude of this imbalance to estimates of N gains and losses through biological N transformations. The model suggested that approximately half of oligotrophic lakes in the US had a stoichiometric N deficit, but almost 90% of the most productive lakes had a similar N deficit. Although reactive N appeared to accumulate in the most oligotrophic lakes, net denitrification perpetuated the N deficit in more productive lakes. Productive lakes tended to export reactive N via biological N transformations regardless of their N deficit. The lack of N accumulation through N fixation has important implications for our understanding of lake biogeochemistry, ecology, and eutrophication management.