An Experimental Test of Nine Climate Change Scenarios on Trace Gas and Carbon Dynamics in a Minnesota Bog and Fen over Eight Years.

We constructed a large mesocosm facility in northern Minnesota to examine the effects of climate change on peatlands.  Twenty-seven intact peat monoliths (2.1 m², 60-cm depth) were removed each from a bog and intermediate fen and subjected to three infrared-loading treatments and three water-table treatments for eight years.  Ecosystem respiration as CO₂ flux increased with warmer soil temperatures, but this effect decreased substantially over several years, suggesting the exhaustion of a labile soil pool.  CH₄ fluxes were dependent on both water-table level and soil temperature, but the effect of water table was much greater in the fen mesocosms, suggesting an enhanced potential for methanotrophy in the fen.  The indirect effects of the water-table and warming treatments on CH₄ fluxes were as much through indirect effects on porewater chemistry as through the expected direct effects.

We integrated carbon responses as net carbon gain or loss for the various treatments.  Fen plots either had no change or were losing carbon, whereas the bogs gained carbon.  Wetter conditions enhanced carbon storage in the bogs and reduced carbon losses in the fens.  Rapid initial vertical peat accumulation in the wet bog treatments caused the water-table elevation to decrease in these plots over time, and this fed back into a large decrease in carbon storage rates.  These effects on carbon fluxes in the bog mesocosms were largely due to water-table effects on moss net primary production, whereas the effects in the fen appeared to be due to multiple factors.  Our results suggest large effects of climate change on carbon dynamics and trace gas emissions in peatlands, with important ecosystem feedbacks determining the trajectories of response.