Abstract

Wetlands are frequently created to mitigate the loss of natural wetlands due to commercial expansion. However, wetland ecosystem function is determined by complex abiotic and biotic interactions that are not well understood in natural wetlands, and even less so in created wetlands. This lack of understanding may lead to shortcomings in meeting desired restoration outcomes. Key abiotic drivers in wetlands include hydrology and nutrient availability, while herbivory provides both direct and indirect controls on plant communities and biogeochemical cycling. I hypothesized that by decreasing emergent plant biomass and shifting plant community structure to favor submerged plants, large grazers such as geese would promote cascading impacts on nitrogen immobilization, denitrification, nitrogen fixation and sediment nutrient regeneration. To assess these effects, paired caged and uncaged plots were established in three created emergent freshwater wetlands in Western New York State. At the site with high waterfowl abundance, emergent macrophyte cover was reduced and there was a shift towards submerged plants. More complex impacts were observed at other sites where grazing pressure was lower: grazer exclusion substantially increased emergent growth at one site and had no effect where the dominant macrophyte Nymphea odorata covered the water surface. Potential denitrification was lowest in the fall, with significantly higher values where submerged plant cover was higher. While sediment nitrogen fixation was consistently below detection limits, periphyton nitrogen fixation, which was dominated by heterotrophs, was slightly higher in caged plots. Sediment nutrient fluxes exhibited some seasonality, with higher rates in spring than summer or fall. These results suggest that grazers have a significant impact on vascular plant community structure, leading to shifts in nitrogen cycling and a reduction of nitrogen fixation. Exclusion of grazers may be a management tool to protect wetland plants during the early stages of wetland development.

Library of Congress Subject Headings

Constructed wetlands--Ecology; Herbivores; Nitrogen cycle

Publication Date

8-8-2021

Document Type

Thesis

Student Type

Graduate

Degree Name

Environmental Science (MS)

Department, Program, or Center

Thomas H. Gosnell School of Life Sciences (COS)

Advisor

Anna Christina Tyler

Advisor/Committee Member

Carmody McCalley

Advisor/Committee Member

Elizabeth Hane

Campus

RIT – Main Campus

Plan Codes

ENVS-MS

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