Belowground Functioning of a Forested Bog As a Sink or Source of Atmospheric Carbon.

To determine how climate change affects processes that determine wetland C uptake and CH4 and CO2 emissions, we are collaborating in a multi-disciplinary study of wetland responses to experimental warming and elevated atmospheric CO2 at the DOE Spruce and Peatland Responses Under Climatic and Environmental Change (SPRUCE) experiment. This study includes deep warming treatments applied to an ombrotrophic spruce bog in northern Minnesota during the 2014 growing season with whole-ecosystem warming and elevated CO₂ treatments beginning in spring 2015. To provide a historical context for recent and experiment-induced changes in the bog’s belowground C balance, we reconstructed historical C accumulation rates in peat using radiocarbon. This data, along with recent C flux measurements, show that the bog has been a been and continues to be a sink for atmospheric CO₂, but model predictions of how greenhouse gas balance of the bog will respond to future climate change are inconsistent. This uncertainty stems from the fact that wetlands soils release both CH4 and CO2 and it is unclear how C fluxes will be partitioned in the future (CH4 is 20 times more potent a greenhouse gas than CO2). Ecosystem observations of CH4 emissions lack mechanistic links reflecting the processes that govern CH4 efflux: microbial production, oxidation to CO2, and ebullition/diffusional transport. Understanding these processes, and their interactions, is critical to predict biosphere feedbacks to climate change.

To address this problem, we are identifying how key environmental factors change CH4 fluxes by: (1) Linking belowground C-sources and processes to atmospheric fluxes of CO2 and CH4 through natural abundance isotopic observations of 13C and 2H (IRMS) and 14C (AMS);  (2) Identifying key microorganisms influencing CH4 production and consumption using stable isotope probing (13C-Chip-SIP, NanoSIMS), and (3) Constraining ebullition rates with noble gas depth-profiles of subsurface pore water.