Identifying rates and drivers of nitrogen fixation, a key component Lake Erie’s nitrogen cycle

Session: Nutrient Sources, Transport, and Internal Cycling (1)

Christopher Boehler, Kent State Univeristy, Department of Biological Sciences, [email protected]
Darren Bade, Kent State University, Dept. Biological Sci., [email protected]

Abstract

Cyanobacteria capable of fixing nitrogen gas (N₂) contribute to harmful algal blooms (HAB) in Lake Erie and surrounding waters.  Nitrogen fixation allows these cyanobacteria to bloom even under periods of low dissolved reactive nitrogen in the water.  Increasing our understanding of the underlying mechanisms responsible for nitrogen fixation may provide insight into HAB promoting conditions.  Here, we employed acetylene reduction assay (ARA) to estimate rates of nitrogen fixation in Lake Erie and Sandusky Bay.  Significant rates of nitrogen fixation were observed in surface water samples in the summers of 2015 and 2017, but not during the summer of 2016.  Rates of nitrogen fixation were correlated with several physical and chemical parameters including: chlorophyll-a (+), total phosphorus (+), and nitrite/nitrate (-).  In addition to surface water samples, ARA was used to estimate nitrogen fixation in lab nutrient bioassays during the summer 2015.  Nutrients added included: Phosphorus (P), Boron (B), and Iron (Fe).  The nutrient additions of +P, +P+B, and +P+Fe significantly increased rates of nitrogen fixation relative to the control, but were not significantly different from one another.  Overall, these results provide a further understanding of nitrogen cycling in Lake Erie.