Date of Award
M.S. in Biological Science
Marjorie M. Holland
Justin N. Murdock
Richard E. Lizotte
Methane (CH4), nitrous oxide (N2O), and carbon dioxide (CO2) fluxes from agricultural landscapes may contribute significantly to regional greenhouse gas budgets due to stimulation of soil microbial activity through fertilizer application. Few studies have made measurements of CH4, N2O, and CO2 from the dominant landscape features of the agricultural landscape: farmland, riparian zone, and wetland habitat. This study assessed gas emission variability from the Mississippi Delta agricultural landscape and explored the effects of hydrology and hydrophytic vegetation on gas emissions.
Gas collection chambers were utilized to make gas measurements from soybean and corn farmland, vegetated riparian buffer, and two vegetated wetlands in summer of 2013. CH4 emissions were highest in the wetland, CO2 emissions were highest in the riparian zone, and N2O emissions were highest in the farmland. Percent soil moisture was lowest in the farmland and increased into permanently-flooded wetlands. CH4 emissions were positively-correlated with soil moisture (R2=0.31), while N2O emissions were negatively-correlated (R2=0.29). CO2 emissions, fit with a polynomial trendline, were significantly-correlated with soil moisture (R2=0.33).
To assess the effect of hydrophytic vegetation on wetland and riparian zone gas emissions, aboveground vegetation was clipped at the soil surface prior to gas sampling and compared to vegetated chambers. Wetland vegetation had no effect on gas emissions, while riparian zone vegetation had a slight inhibitory effect on gas emissions.
Gas emissions were compared between two wetlands with contrasting hydrologic regimes, yet existing in the same drainage system. One wetland was used for agricultural irrigation and thus experienced fluctuating water levels, while the other wetland had stagnant conditions due to upstream beaver activity and impoundments. CH4 emissions were higher under stagnant hydrologic conditions, whereas CO2 emissions were identical between the two. N2O consumption occurred under stagnant conditions, and N 2O emission occurred under fluctuating hydrologic conditions.
This study indicates that gas emission hotspots exist on the agricultural landscape and are influenced by distinct habitat soil moisture levels. Hydrophytic vegetation did not play an important role in gas emissions, but hydrologic variability was important in creating conditions suitable for microbial gas production and emission.
Keating, Michael P., "Location, location: Factors influencing greenhouse gas fluxes from the Mississippi Delta agricultural region" (2014). Electronic Theses and Dissertations. 1284.