JAEL EDGERTONKENT STATE UNIVERSITY

Effects of Labile Carbon Addition on Denitrification and Denitrifiers in a

Headwater Agricultural Stream

Anthropogenic Changes to the Global N-Cycle

Human activities - increased inputs of fixed nitrogen Nitrogenous fertilizer runoff-Eutrophication HypoxiaDeadzone formation.

•Microbial Denitrification – stepwise reduction of NO3 to N2 by facultative anaerobes•Denitrification –returns biovailable N can to the atmosphere.

Labile Carbon Additions to a Midwestern Agricultural Stream

1. How tightly coupled are DOC and N cycling?2. How does denitrification in an agricultural stream

respond to changes in the pool of DOC?3. Is the response mediated through changes in the

microbial community?

•Formate:acetate coupled with 15-N tracer

•Whole stream uptake of C and N, and denitrification rate

•Microbial community structure

•Sensor technology -chemical and physical variables in the water column

Results

Effectively shifted the carbon dynamics of the stream Increased N-demand via assimilatory mechanismsDid not effect denitrification rateShifted the overall microbial community (as

demonstrated by 16S rRNA gene TRFLP profiles)

Assimilatory N-Uptake and Denitrification

Figure credit: Todd V. Royer

Why wasn’t Denitrification Affected?

Figure credit: Todd V. Royer

Future Directions

Location—sediment level, reducing conditions, hypoxiaScale- centimeter scale, millimeter scale, micrometer scale

R.L. Meyer et al. (2008). Marine Chemistry 110, 68–76.