The Effects of Infrared Loading and Water Table on Soil Energy Fluxes in Northern Peatlands
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Increased radiative forcing is an inevitable part of global climate change, yet little is known of its potential effects on the energy fluxes in natural ecosystems. To simulate the conditions of global warming, we exposed peat monoliths (depth, 0.6 m; surface area, 2.1 m2) from a bog and fen in northern Minnesota, USA, to three infrared (IR) loading (ambient, +45, and +90 W m-2) and three water table (-16, -20, and -29 cm in bog and -1, -10 and -18 cm in fen) treatments, each replicated in three mesocosm plots. Net radiation (Rn) and soil energy fluxes at the top, bottom, and sides of the mesocosms were measured in 1999, 5 years after the treatments had begun. Soil heat flux (G) increased proportionately with IR loading, comprising about 3%-8% of Rn. In the fen, the effect of IR loading on G was modulated by water table depth, whereas in the bog it was not. Energy dissipation from the mesocosms occurred mainly via vertical exchange with air, as well as with deeper soil layers through the bottom of the mesocosms, whereas lateral fluxes were 10-20-fold smaller and independent of IR loading and water table depth. The exchange with deeper soil layers was sensitive to water table depth, in contrast to G, which responded primarily to IR loading. The qualitative responses in the bog and fen were similar, but the fen displayed wider seasonal variation and greater extremes in soil energy fluxes. The differences of G in the bog and fen are attributed to differences in the reflectance in the long waveband as a function of vegetation type, whereas the differences in soil heat storage may also depend on different soil properties and different water table depth at comparable treatments. These data suggest that the ecosystem-dependent controls over soil energy fluxes may provide an important constraint on biotic response to climate change.
author list (cited authors)
Noormets, A., Chen, J., Bridgham, S. D., Weltzin, J. F., Pastor, J., Dewey, B., & LeMoine, J.
complete list of authors
Noormets, Asko||Chen, Jiquan||Bridgham, Scott D||Weltzin, Jake F||Pastor, John||Dewey, Brad||LeMoine, James