Date of Award

12-2017

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Forestry and Natural Resources

Committee Chair

Jeffrey S. Dukes

Committee Member 1

Cliff T. Johnston

Committee Member 2

Ronald F. Turco Jr.

Abstract

Climate change has altered precipitation regimes in many regions of the world. In the Midwestern United States, the intensity of precipitation events had increased, and the periods of drought between them have lengthened. Since the Industrial Revolution, nitrogen (N) deposition has increased and may further increase in response to growth in fossil fuel consumption and fertilizer use. Continuing changes in precipitation variability and N inputs will impact carbon (C) and N-cycling processes and atmospheric levels of greenhouse gases (GHG). Controlled by a variety of processes, soil GHG (CO2, N2O, and CH4) fluxes play a large role in determining atmospheric GHG levels. In a restored tallgrass prairie, I investigated responses of soil GHG fluxes to simulated increases in precipitation variability and N deposition over a single growing season. Precipitation variability was increased using rainout shelters, which diverted 50% of incoming precipitation from the experimental plots. The amount of precipitation diverted each month was returned to the plots in one large artificial rainfall event each month. This increased precipitation variability treatment was crossed factorially with an increased N deposition treatment (applied as slow-release urea, 50 kg ha-1 yr-1).

While the treatments did not directly alter the rate of soil respiration, CO2 emissions responded over time to seasonal changes in soil moisture and temperature. The precipitation variability treatment heightened the sensitivity of respiration to soil moisture and marginally to soil temperature. N2O emissions were highly variable but increased in response to the combination of precipitation variability and N addition. This prairie ecosystem was consistently a CH4 sink throughout the experimental period, with the precipitation variability treatment weakening the sink. The treatments did not affect contributions of this ecosystem to global warming potential (GWP). This study responds to calls for further research into precipitation variability combined with changing environmental variables and adds to the growing body of research that can be used for modeling soil GHG in differing ecosystems.

Download

Share

COinS