Denitrification potential in three saturated riparian buffers

Authors: GROH, TYLER - Iowa State University; DAVIS, MORGAN - Iowa State University; ISENHART, TOM - Iowa State University; Jaynes, Dan; PARKIN, TIMOTHY - Former ARS Employee

Submitted to: Agriculture Ecosystems and the Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/19/2019
Publication Date: 12/1/2019
Citation: Groh, T.A., Davis, M.P., Isenhart, T.M., Jaynes, D.B., Parkin, T.B. 2019. Denitrification potential in three saturated riparian buffers. Agriculture Ecosystems and the Environment. 286(106656). https://doi.org/10.1016/j.agee.2019.106656.
DOI: https://doi.org/10.1016/j.agee.2019.106656

Interpretive Summary: Denitrification is a microbial process that removes nitrate from the environment improving water quality. One nitrate removal practice designed for tile drained fields is saturated riparian buffers (SRBs) which looks to maximize soil denitrification within permanently vegetated stream side buffers. The current study looked to test the hypothesis that older buffers are better at removing nitrate than newer ones due to a build up of old plant material and increase in soil carbon content. Using a series of soil cores taken from buffers of different ages, we showed that older, more established stream side buffers are better at removing nitrate than are newer ones. Thus, we conclude that SRB effectiveness will improve with age. This research further informs conservations, consultants and farmers about this conservation practice.

Technical Abstract: Denitrification is an anaerobic process that converts nitrate to predominantly either nitrous oxide or dinitrogen gas while using nitrate as a terminal electron acceptor. The requirements for denitrification include available nitrate and organic carbon, an anaerobic environment, and the appropriate microbial communities. The edge-of-field nitrate removal practice of saturated riparian buffers (SRBs) looks to maximize soil denitrification by saturating carbon-rich alluvial soils with nitrate-rich tile water. Our initial in situ denitrification study showed the possibility of a carbon limitation for BC-2, the youngest of our study’s SRBs. The current study looked to test this hypothesis using a denitrification potential experimental design by adding nitrate and carbon both individually and combined to portions of soil cores. BC-2 did seem to have a carbon limitation from 20 to 100 cm when assessing the nitrate and carbon separate additions against both the control and the combined nitrate and carbon maximum denitrification potential rate. Temperature also seemed to affect each SRB’s maximum denitrification potential, but to varying degrees. The highest subsurface maximum denitrification potential rate, achieved by adding both nitrate and carbon, at each temperature was achieved by BC-1, the oldest SRB with the highest in situ denitrification rates. Conversely, BC-2, the youngest SRB, had the lowest rate. Thus indicating a potential riparian age effect on denitrification beyond elevated increased labile carbon additions, hypothesized to be an increased soil aggregation effect on denitrification communities.