Do nitrogen fixation and denitrification co-occur across a gradient of stream nitrogen concentrations in a western watershed?

Document Type

Conference Proceeding

Publication Date



It is frequently assumed that N2 fixation and denitrification do not co-occur in streams because they are favored under different concentrations of reactive nitrogen, yet we cannot evaluate this assumption because both processes are rarely quantified in the same stream. We measured rates of each process, as well as N2 flux, in 7 southeastern Idaho streams encompassing a DIN gradient from 6 to 582 µg/L. N2 fixation rates measured using acetylene reduction were 0-198 µg/m2/hr while denitrification rates measured using acetylene block were 0.59-5.66 µg/m2/hr. The highest N2 fixation rates occurred when DIN < 13 µg/L, but low rates were observed with DIN > 200 µg/L. N2 fixation rates were not significantly related to P concentrations or N:P, but N:P was < 20 in all study streams. Denitrification was linearly related to DIN, but the trend appeared asymptotic. These results suggest stream nutrient concentrations alone cannot explain the distribution of N2 fixation and denitrification. We are exploring the role of small-scale variation in environmental conditions and microbial assemblages for facilitating the co-occurrence of these processes.

Publisher's Statement

© 2016 Aquatic Sciences Meeting. Publisher’s version of record: http://www.sgmeet.com/aslo/santafe2016/viewabstract.asp?AbstractID=27951

Publication Title

Association for the Sciences of Limnology and Oceanography Summer Meeting 2016