# Effects of Grazer Exclusion on Carbon Cycling in Created Freshwater Wetlands  
[PERSON]  
[PERSON] Gosnell School of Life Sciences, Rochester Institute of Technology, Rochester, NY 14623-5603, USA; [PERSON]DRESS] (D.M.S. ); [EMAIL_ADDRESS] (A.C.T.) [PERSON]  
Correspondence: [EMAIL_ADDRESS] (C.K.) (D.M. natural and created wetlands, with an average shortcoming in soil C of 51.7% relative to natural wetlands within two decades of creation in the United States [17]. Globally, created wetlands require more than 20 years to reach C levels of natural wetlands [9], and estimates of time to reach comparable C levels in the United States range from 30 to 300 years [18], with variation among wetland types [17]. This highlights the need to identify wetland creation and management approaches that accelerate soil development and carbon uptake and storage. Herbivory has the potential to exacerbate plant and carbon cycling differences between created and natural wetlands. Hydrology plays a key role in this top-down dynamic in freshwater wetlands, with stable hydrologic regimes attracting waterfowl, in particular the Canada goose (_Branta canadensis_) and ducks (_Anas_ spp. ), to wetlands for nesting and feeding [19; 20; 21]. Created wetlands often feature deep standing water and young palatable vegetation, which offers desirable habitat for migratory waterfowl [22]. This, coupled with rising waterfowl populations [23], can cause created wetlands to be particularly vulnerable to intensive grazing [21]. Herbivory in wetlands can cause a top-down cascade that shifts ecosystem structure and function [24; 25]. Although primary functional traits of wetlands are determined by physico-chemical factors, especially hydrology and nutrient availability, interaction between bottom-up and top-down factors may ultimately control plant community composition and biomass [26; 27; 28; 29]. Excessive grazing by waterfowl in wetlands can cause a decrease in total plant cover [21; 30], and also in plant biomass [29; 31]. Preferential grazing, especially when heavy, may also shift plant community composition [21; 32; 33; 34]. Often waterfowl target younger, more palatable plants, leading to a shift in plant species composition [35; 36; 37] and changes in the quality and quantity of plant litter. When intensive grazing reduces plant cover or changes plant species composition, net primary productivity (NPP) and organic carbon brought into and stored in soil may decrease [38; 39; 40; 41]. In grasslands, grazing may also increase decomposition, by changing both litter quality and the soil environment [42]. In wetlands, plants also impact soil processes through oxygen transport into sediments [43; 44], and therefore intensive grazing of emergent plants could further alter belowground carbon cycling by reducing aerobic microsites. While the impact of waterfowl on plant cover, biomass and species composition has been studied in freshwater wetlands, the impact on CO\({}_{2}\) fluxes, net ecosystem exchange (NEE), and overall carbon storage is less well understood. One of the key limitations to many studies on herbivore impacts in wetlands is that experiments often last only one or two seasons, limiting the ability to observe long-term changes in carbon cycling and storage. The current study utilizes a long-term herbivore exclosure experiment and builds upon [PERSON] and [PERSON] [21], who found that during the first 2 years of grazer exclusion, plant cover increased by 55% and peak growing season plant diversity by 30% in a permanently flooded wetland, suggesting that, in some cases, grazer management could be used to establish desired plant communities during wetland creation. This result raised the question of whether shifts in plant communities following grazer exclusion also promote the development of C stocks in created wetlands.