IRON-DEPENDENT AMMONIA OXIDATION IN DEVIL’S BATHTUB, A FERRUGINOUS MEROMICTIC LAKE.

Meromictic lakes are permanently stratified with anoxic monimolimnia. Our study site, Devil’s Bathtub (DBT) in Rochester, NY, is a ferruginous meromictic lake with high concentrations of iron and nitrogen compounds in the monimolimnion. In contrast to the thermodynamic expectations, nitrate and nitrite exceed the ammonia concentrations. This suggests that ammonia oxidation to nitrate or nitrite is occurring, but the source is unexplained. Due to lack of oxygen in the monimolimnion, ammonia oxidation would require a different electron acceptor, which based on the redox state and availability could be Fe(III). Ferric iron is regenerated at the surface and sinks to the bottom which then could fuel the ammonia oxidation. We hypothesize that iron-dependent ammonia oxidation is responsible for the observed geochemical profiles and meromixis, either through feammox, an energy metabolism coupling these reactions, or by separate taxa carrying out iron-reduction and ammonia oxidation. To determine which taxa may be responsible, we extracted DNA from the water column for 16S rRNA gene sequencing to characterize the microbial community. We found the presence of Pirelullaceae, known ammonia oxidizers, and Geobacter, an iron reducer. Our next step will be to use RT-qPCR to assess expression of marker genes for iron reduction and ammonia oxidation. This relatively understudied redox pair may contribute to the biogenic meromixis of DBT and give us insight to a better understanding of iron-nitrogen interactions in eutrophic conditions. 

Primary Presenter: Bethany Mangioni, Niagara University (bethanyrose203@gmail.com)

Authors:

Cassandra Marnocha, Niagara University  (cmarnocha@niagara.edu)

William Edwards, Niagara University  (wje@niagara.edu)