CO2 and CH4 Net Carbon Flux from a high-carbon peatland in Northern Minnesota: Plot scale observations of the Shrub, forb, Sphagnum and microbial community

Significant uncertainty exists regarding the fate of stored peatland carbon under future climate warming scenarios. Methods have been developed to track net flux of CO2 and CH4 from experimental warming plots at a scale appropriate to the in situ biological community. Surface flux measurements of CO2 and CH4 were made using and open-path analyzers over and area of 1.13 m2 within each of our 16 plots. A custom-designed chamber encloses the hummock-hollow topography and allows point in time measurements of the shrub, forb, Sphagnum and the complex microbial community complex. These observations are made with ambient light and imposed dark conditions to allow estimates of net community daytime and night respiratory processes. Sphagnum hollow temperatures, water table levels, hummock moisture levels, and recent PAR as a potential surrogate for labile C are all being evaluated as drivers of net CO2-C and CH4-C flux. Periodic observations from August 2011 through July 2013 show obvious seasonal trends with temperature being the obvious driving variable. During this ';wet' time period surface drying and lower water table depths have not been seen to be key drivers of net C flux. Midwinter conditions with a frozen peat surface produce zero CO2 and CH4 flux. Maximum net CO2 flux in mid summer shows daytime surface uptake values near -6 to -7 μmol m-2 s-1 and night loss rates of 6 to 7 μmol m-2 s-1. Maximum midsummer observed CH4 flux for this bog range from 0.4 to 0.5 μmol m-2 s-1. Integrating temperature dependent models of net flux across annual periods showed next CO2-C and net CH4-C flux to be 850 and 20 g C m-2 y-1, respectively. Sequential clipping of vegetation layers showed that the shrub (LAI = ~0.5 m2 m-2) and the forb/sedge layer (LAI = ~1 m2 m-2) dominated net carbon uptake during daytime periods while shading the Sphagnum layer (LAI >1 m2 m-2), but had limited impact on dark community respiration likely dominated by the subsurface microbial community. A comparison of current and historical data has shown our methods to be in good agreement and provides a basis for modeling C fluxes in this peatland. Continued monitoring will allow us to model the CO2/CH4 fluxes so we can better predict the carbon loss or storage in this peatland system under a range of warming and CO2 manipulations.