# Effects of Grazer Exclusion on Carbon Cycling in Created Freshwater Wetlands
## 4 Discussion
latifolia_, which were virtually absent in open plots. In 2018, we also observed the emergence of _N. odorata_ in the open plots, suggesting that the removal of other palatable species allowed expansion of surface-covering lilies that may lead to further shifts in ecosystem structure. [PERSON] and [PERSON] [38] made similar observations in grasslands, reporting shifts in vegetation dominance consistent with grazer preferences, with a higher abundance of more palatable plants and higher diversity in ungrazed plots. In a review of the environmental impacts of expanding goose populations, a dominant grazer in our system, [PERSON] et al. [59] found that grazers not only reduce overall plant biomass, but also reduce plant diversity and modify the habitat. Growing season CO\({}_{2}\) fluxes in our system were comparable to other created/restored temperate emergent wetlands, with our estimated daily summer net CO\({}_{2}\) uptake for caged plots of \(-5.2\) g C m\({}^{-2}\) d\({}^{-1}\) (Figure 6), falling within the range of August CO\({}_{2}\) uptake rates (\(-8.5\) to \(-2.3\) g C m\({}^{-2}\) d\({}^{-1}\)) (California; [60]) and our hourly uptake rates of \(-0.7\) g C m\({}^{-2}\) h\({}^{-1}\) (caged) and \(-0.3\) g C m\({}^{-2}\) h\({}^{-1}\) (uncaged) bracketing growing season static chamber flux values of \(-0.45\)-\(0.55\) g C m\({}^{-2}\) h\({}^{-1}\) (Ohio; [61]). Changes in ecosystem CO\({}_{2}\) fluxes in response to grazing tracked patterns in aboveground biomass, with higher aboveground biomass correlated with higher rates of GPP and ER. Increases in growing season GPP in response to grazer exclusion was higher than that of ER, resulting in 25-100% higher summer net CO\({}_{2}\) uptake in caged plots. Higher temporal resolution of flux measurements would provide additional insights into the seasonality of grazer impacts on CO\({}_{2}\) fluxes and enable a more detailed assessment of shifts in carbon uptake in response to grazer exclusion. The relationship between CO\({}_{2}\) fluxes and plant cover confirms the strong influence of plant biomass on CO\({}_{2}\) uptake [62], suggesting that management that impacts the establishment and growth of vegetation communities can have large effects on carbon storage in these systems. Similar results were seen following grazer exclusion in alpine meadows [41] and high arctic wet meadows [40], where significantly lower carbon uptake in grazed plots was attributed to the substantial reduction in aboveground biomass. treatments, the fast decomposing species, _N. odorata_, contributed <0.3% of the aboveground biomass in caged plots (<1 g m\({}^{-2}\) in 2018) compared to 9% in uncaged plots at the end of the growing season (13 g m\({}^{-2}\) in 2018). In contrast, the slower decomposing _T. latifolia_ was only found in caged plots, with about 6% of the end of season biomass. While _L. oryzae_ides (40% of end of season biomass in caged plots only) was not used in our decomposition study, its high C:N (35.9 \(\pm\) 3.3) suggests persistence within the system. _T. latifolia_ and _L. oryzaeoides_ together contributed an additional 160 g m\({}^{-2}\) of relatively refractory material to caged plots in 2018. These species composition shifts, coupled with higher litter inputs associated with high aboveground biomass in caged plots will cascade over time to enhance the accumulation of soil carbon in the absence of grazers. Our results support findings that changes in decomposition in response to grazing can arise from both changes in plant communities and alterations in the soil environment [42]. Grazer exclusion promoted decomposition of the most labile species in our study (_N. odorata_), suggesting that changes in soil environment due to grazing has the largest impact on more labile plant litter.