Abstract

Wetlands have been identified as one of the largest sources of atmospheric methane (CH4), an important greenhouse gas with 28 times the global warming potential of CO2. Due to the complexity of wetland ecosystems, they have also been identified as one of the largest sources of uncertainties in the global CH4 budget. Net CH4 emissions are controlled by microbial production, consumption by methanotrophs, and transport to the atmosphere through diffusion, ebullition, and plant-mediated transport. Herbivory has the potential to alter these processes, with recent studies showing both positive and negative effects of herbivory on emissions and uncertainty in which components of the CH4 cycle are most impacted by grazing. To examine the effects of herbivory on CH4 emissions in wetlands, we completed an ¬in situ study and a simulated greenhouse herbivory study. The in situ study, completed at High Acres Nature Area (Perinton, NY), included pairs of plots protected from- and open to grazing, where we quantified CH4 flux, primary production, vegetation cover, porewater CH4 concentrations, and potential rates of CH4 production and oxidation. The simulated herbivory experiment included clipping the stems of Typha latifolia and Sagittaria latifolia at multiple levels of damage above- and below the water level to examine the impact of plant damage and biomass removal on emissions. The results of our study showed significant effects of herbivory, in situ emissions were 1-4 times higher in ungrazed plots compared to grazed plots. Changes in vegetation cover, emergent cover was 1.7-2.9 times higher in caged plots than uncaged plots, likely played an important role in the observed differences in CH4 emissions. Higher vegetation cover facilitates CH4 movement through plants, increasing net emissions. In the greenhouse, we observed increased emissions when plants were clipped above the water level and decreased emissions when plants were clipped below the water level, consistent with the key role plant transport plays in CH4 emissions. We also observed a significant effect of species on CH4 emissions, emissions from Sagittaria latifolia were 2-6 times that of Typha latifolia. We conclude that herbivory has a significant effect on CH4 emissions, where plant damage caused by grazing can yield an immediate increase in emissions, as observed in our clipping experiment, however, long-term herbivory reduces plant cover, resulting in lower substrate for CH4 production and fewer opportunities for transport through plants, leading to a net decrease in emissions, as captured in our ¬in situ measurements.

Library of Congress Subject Headings

Constructed wetlands--Environmental aspects; Constructed wetlands--Management; Grazing--Environmental aspects; Methane--Detection; Herbivores--Ecology

Publication Date

8-6-2020

Document Type

Thesis

Student Type

Graduate

Degree Name

Environmental Science (MS)

Department, Program, or Center

Thomas H. Gosnell School of Life Sciences (COS)

Advisor

Carmody McCalley

Advisor/Committee Member

Anna Christina Tyler

Advisor/Committee Member

Elizabeth Hane

Campus

RIT – Main Campus

Plan Codes

ENVS-MS

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