Influence of water table levels on CO2 emissions in a Colorado subalpine fen: an in situ microcosm study
Introduction
Peatlands accumulate carbon because mean annual primary production exceeds annual organic matter decomposition (Clymo, 1983). Peat accumulation in boreal and high mountain regions is a function of low decomposition rates rather than high net annual primary production (Malmer, 1986, Francez and Vasander, 1995), and only a small fraction of the carbon fixed by plants each year accumulates in the soil. More than 90% of the fixed carbon is re-released (Clymo, 1983), with up to 95% of the output being CO2 (Francez and Vasander, 1995, Waddington and Roulet, 2000). This small net carbon storage can be offset by increases in CO2 emissions, converting peatlands from sinks to sources of carbon to the atmosphere (Gorham, 1991, Francez and Vasander, 1995).
Air and soil temperature, water table level, and the quality of organic substrates are the main local controls of CO2 emissions from peatlands (Bridgham et al., 1995). Higher concentrations of labile organic matter can result in higher carbon mineralization rates while higher concentrations of recalcitrant organic matter decrease mineralization rates (Hogg et al., 1992, Updegraff et al., 1995). Warmer air and soil temperatures stimulate microbial activity resulting in higher CO2 emissions (Crill et al., 1988, Frolking and Crill, 1994, Silvola et al., 1996a). The temperature response of CO2 is modified by substrate quality, with higher substrate quality resulting in higher temperature responses (Valentine et al., 1994, Updegraff et al., 1995).
Water table levels can have important effects on CO2 emissions from peatlands, because saturated soils limit the diffusion of atmospheric oxygen into the peat, limiting microbial activity and decomposition rates (Clymo, 1983). Conversely, a water table decline increases oxygen diffusion into soils allowing aerobic decomposition, which increases CO2 emissions (Moore and Knowles, 1989, Bubier, 1995, Silvola et al., 1996a, Nykänen et al., 1998).
Rocky Mountain National Park has a number of water diversion ditches that pre-date the formation of the Park in 1915, and yet continue to alter water table levels in many wetlands (Cooper, 1990, Graf, 1997, Cooper et al., 1998, Woods, 2000, Chimner, 2000). We have found that the largest of these ditches, the Grand Ditch, has lowered water table levels in at least one fen, causing high organic matter decomposition rates as quantified by high CO2 emissions (Chimner, 2000). Although we have evidence to support the concept that lowered water tables can significantly alter carbon cycling in fens, it is unclear how much the water table must be lowered before changes occur. The sensitivity of fens to water level changes is critical to understand for evaluating the long-term effects of hydrologic changes due to water diversions, groundwater pumping or climate change. The objective of this study was to quantify in the field how changes in water table position influence CO2 emissions. Our approach involved manipulating water levels in microcosms installed for two-summers in a Colorado subalpine fen and measuring CO2 emissions.
Section snippets
Study site
This study was conducted in Moose fen, located at 2655 m elevation, on the western side of Rocky Mountain National Park, Colorado (Fig. 1). The fen is approximately 1 ha in size and the peat is 2.3 m thick at our study location. The fen is fed primarily by groundwater discharging from the toe of an adjacent mountain slope. Water table levels in this site have been above the soil surface for the 4 years that this site was analyzed (Cooper and Kennedy, unpublished data). Surface water has a pH of
Water table dynamics
Water table levels in the undisturbed fen (natural) and reference microcosms remained at or above the soil surface for the duration of the 2 year study period, averaging +3 and +2 cm, respectively, for 1998 and 1999 (Fig. 3). The natural water table levels measured for Moose Fen are typical for C. aquatilis dominated fens in the region (Chimner, 2000). The water addition treatment during 1998 increased water levels to between +5 and +8 cm above the soil surface (Fig. 3).
In 1998 the water level
Acknowledgements
Financial support for his project came from Rocky Mountain National Park, and the Society of Wetlands Scientists Student Grant. We thank Ken Czarnowski of Rocky Mountain National Park for his help and support. We thank Dan Reuss and Natural Resources Ecology Laboratory (NREL) Ft Collins, CO. for his generosity in letting us use the Infrared Gas Analyzer. We also thank Michel de Luz for field assistance and Jason Kaye, Sigrid Resh, Tom Stohlgren, Lee MacDonald, Eugene Kelly, and anonymous
References (37)
- et al.
Water-table changes and nutritional status affect trace gas emissions from laboratory columns of peatland soils
Soil Biology & Biochemistry
(1997) - et al.
Role of wetland plants in the diurnal control of CH4 and CO2 fluxes in peat
Soil Biology & Biochemistry
(1996) - et al.
Potential feedbacks of northern wetlands on climate change
BioScience
(1995) The relationship of vegetation to methane emission and hydrochemical gradients in northern peatlands
Journal of Ecology
(1995)- Chimner, R.A., 2000. Carbon dynamics of Southern Rocky Mountain fens. PhD Dissertation, Colorado State University, Ft...
Peat
- Cooper, D.J., 1990. Ecology of wetlands in Big Meadows, Rocky Mountain National Park, Colorado. US Fisheries Wildlife...
- et al.
Patterns of vegetation and water chemistry in peatlands of the west-central Wind River Range, Wyoming, USA
Canadian Journal of Botany
(1994) - et al.
Hydrologic restoration of a fen in Rocky Mountain National Park, Colorado, USA
Wetlands
(1998) - et al.
Methane flux from Minnesota peatlands
Global Biogeochemical Cycles
(1988)
Peat accumulation and peat decomposition after human disturbance in French and Finnish mires
Acta Oecolgica
Fluxes of CO2, CH4 and N2O from a Welsh peatland following simulation of water table draw-down: potential feedback to climatic change
Biogeochemistry
Climate controls on temporal variability of methane flux from a poor fen in southeastern New Hampshire: Measurements and modeling
Global Biogeochemical Cycles
Influence of water table on carbon dioxide, carbon monoxide, and methane fluxes from taiga bog microcosms
Global Biogeochemical Cycles
Northern peatlands: role in the carbon cycle and probable responses to climatic warming
Ecological Applications
Potential carbon losses from peat profiles: effects of temperature, drought cycles, and fire
Ecological Applications
The effect of clipping on methane emissions from Carex
Biogeochemistry
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