Flume experiments elucidate relationships between microbial genetics, nitrogen species and hydraulics in controlling nitrous oxide production in the hyporheic zone

Wednesday, 17 December 2014
Annika M Quick1, Tiffany B. Farrell1, William Jeffery Reeder2, Kevin P Feris3, Daniele Tonina2 and Shawn G Benner1, (1)Boise State University, Department of Geosciences, Boise, ID, United States, (2)University of Idaho, Department of Civil Engineering, Boise, ID, United States, (3)Boise State University, Department of Biology, Boise, ID, United States
The hyporheic zone is a potentially important producer of nitrous oxide, a powerful greenhouse gas. The location and magnitude of nitrous oxide generation within the hyporheic zone involves complex interactions between multiple nitrogen species, redox conditions, microbial communities, and hydraulics. To better understand nitrous oxide generation and emissions from streams, we conducted large-scale flume experiments in which we monitored pore waters along hyporheic flow paths within stream dune structures. Measured dissolved oxygen, ammonia, nitrate, nitrite, and dissolved nitrous oxide showed distinct spatial relationships reflecting redox changes along flow paths. Denitrifying genes (nosZ, nirS, and nirK), determined using qPCR, were spatially associated with abundances of nitrogen species. Using residence times along a flow path, clear trends in oxygen conditions, genes encoding for microbial catalysis, and nitrogen species were observed. Hotspots of targeted genes correlated with hotspots for conversion of nitrogen species, including nitrous oxide production and conversion to dinitrogen. Trends were apparent regardless of dune size, allowing for the possibility to apply observed relationships to multiple streambed morphologies. Relating streambed morphology and loading of nitrogen species allows for prediction of nitrous oxide production in the hyporheic zone.