Degree Type

Dissertation

Date of Award

2018

Degree Name

Doctor of Philosophy

Department

Natural Resource Ecology and Management

Major

Environmental Science

First Advisor

Thomas M. Isenhart

Abstract

Nitrogen (N) losses from the Mississippi River Basin contribute to the hypoxic zone in the Gulf of Mexico, and NO3 concentrations in surface waters often exceed the USEPA’s drinking water standard of 10 mg-N L-1. Nitrate from artificial subsurface drainage (tiles) underlying agricultural fields can be a major source of reactive N in surface waters. Reducing N flux from agroecosystems is complex and difficult to manage at the watershed scale, as N management alone will not significant reduce N flux. One method for N removal is enhanced microbial denitrification in edge of field practices. Microbial denitrification is an anaerobic process that reduces NO3 to N2 gas. Nitrogen gas released to the atmosphere in a non-reactive state. However, incomplete denitrification can result in nitrous oxide (N2O) production. Nitrous oxide is the third largest contributor to radiative forcing and global climate change. Furthermore, other forms of anaerobic respiration producing greenhouse gases, like methane, can occur in environments designed for denitrification. The studies presented in this dissertation improve greenhouse gas sampling methodology and advance understanding of the effects of enhanced denitrification technologies on greenhouse gas emissions. The Chamber Automated Sampling Equipment (FluxCASE) to measure soil gas flux was found to be accurate and precise compared to manual sampling and improved sampling efficiency. The FluxCASE system was utilized to maximize coverage of spatial variability associated with gas flux from soil surfaces of saturated riparian buffers (SRBs) and woodchip bioreactors. Nitrous oxide emissions from SRBs were compared to traditional buffers and corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] agriculture. Nitrous oxide emissions from SRBs were similar to traditional buffers and lower than crop fields. Nitrous oxide and CH4 production was measured at three hydraulic retention times (HRTs) from pilot scale (5.8  1.0  1.1 m) woodchip bioreactors. Nitrous oxide production increased with decreasing HRT and CH4 increased with increasing HRT. The lowest HRT had the greatest global warming potential. Edge of field practices designed to enhance microbial denitrification are integral strategies to reduce NO3 loss to surface waters, and have the potential to also reduce greenhouse gas emissions from agricultural landscapes.

DOI

https://doi.org/10.31274/etd-180810-5970

Copyright Owner

Morgan Davis

Language

en

File Format

application/pdf

File Size

88 pages

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