P. A. Raymond

Northern wetlands and bogs are a large source of biogenic methane (CH 4 ) to the atmosphere and shape climate. There is then substantial interest in quantifying the effect sizes of controls on bog CH 4 emissions. Yet quantification is complicated because wetland emissions are, like the controls that regulate them, spatially and temporarily heterogeneous within individual wetland systems. To account for this heterogeneity, we established 55 measurement plots in a sampling design that had extensive spatial, and repeated temporal, coverage over one ombrotrophic bog. This coverage allowed us to robustly estimate the effect sizes of known environmental controls on CH 4 emissions such as temperature, water table depth (WTD), and plant functional composition. As expected, 89% of the cumulative measured flux came from 16% of the plots, with consistently high CH 4 emissions over two consecutive growing seasons. Soil temperature exhibited the strongest control on emissions, while WTD and vegetation composition had much smaller relative effects compared to temperature. Interestingly, at high temperatures, WTD was a strong determinant of whether a plot had high versus lower emissions. Despite temperature's large effect size, the controls we measured only explained ∼29% of the variance in CH 4 fluxes. Overall, our data confirm observations from other wetlands that CH 4 emissions are highly variable at local scales, and yet our data also reveal that effect sizes can be quantified robustly within this heterogeneity. Highly‐replicated, local designs may therefore be useful for generating data that can serve to help refine wetland CH 4 emissions uncertainties.