Herbivore controls on macrophyte community structure and nitrogen retention in created wetlands

Session: Wetland Restoration in the Great Lakes Basin: Research and Innovation (2)

Evan Squier, Rochester Institute of Technology, [email protected]
Kimberly Lodge, Rochester Institute of Technology, [email protected]
Delanie Spangler, Rochester Institute of Technology, [email protected]
Christy Tyler, Rochester Institute of Technology, [email protected]
Carmody McCalley, Rochester Institute of Technology, [email protected]
Nathan Eddingsaas, Rochester Institute of Technology, [email protected]

Abstract

Wetlands are complex systems and the abiotic and biotic interactions that determine functionality are not fully understood, particularly in created wetlands. Herbivores may significantly decrease plant biomass and community structure, potentially altering nitrogen immobilization by plants, denitrification, nitrogen fixation and regeneration of inorganic nutrients in the sediments.  Caged and uncaged plots were established in three created wetlands in Western New York State, and the impact of grazer exclusion on vegetation community structure and nitrogen cycling processes assessed.  Herbivores, predominantly waterfowl, selectively removed emergent vegetation, leading to higher submerged macrophyte cover in uncaged plots in 2017. Submerged macrophyte cover increased in the 2018 season in both caged and uncaged plots. Below-ground biomass was slightly higher in the caged plots in two of the three study sites. High density of water lilies, not a preferred plant, at one site may explain higher below-ground biomass in the anomalous site. Potential denitrification rates were slightly higher in the uncaged plots at all study sites, and suggest a shift in net N removal by grazing activity. Herbivory is thus an important indirect control on nutrient cycling and biogeochemical processes in wetlands, and exclusion of grazers should be considered as a management technique in wetland creation.