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TECHNICAL REPORTS

Quantifying Carbon Dioxide and Methane Emissions and Carbon Dynamics from Flooded Boreal Forest Soil

^a Dep. of Environment and Resource Studies, Univ. of Waterloo, Waterloo, ON Canada N2L 3G1
^b Dep. of Earth and Environmental Sciences, Univ. of Waterloo, Waterloo, ON Canada N2L 3G1

^* Corresponding author (moelberm{at}fes.uwaterloo.ca).

Received for publication January 16, 2008. The boreal forest is subject to natural and anthropogenic disturbances, but the production of greenhouse gases as a result of flooding for hydroelectric power generation has received little attention. It was hypothesized that flooded soil would result in greater CO₂ and CH₄ emissions and carbon (C) fractionation compared with non-flooded soil. To evaluate this hypothesis, soil C and nitrogen (N) dynamics, CO₂ and CH₄ mean production rates, and ¹³C fractionation in laboratory incubations at 14 and 21°C under non-flooded and flooded conditions and its effect on labile and recalcitrant C sources were determined. A ferro-humic Podzol was collected at three different sites at the Experimental Lakes Area, Canada, with a high (19,834 g C m^–2), medium (18,066 g C m^–2), and low (11,060 g C m^–2) soil organic C (SOC) stock. Soil organic C and total N stocks (g m^–2) and concentrations (g kg^–1) were significantly different (p < 0.05) among soil horizons within each of the three sites. Stable isotope analysis showed a significant enrichment in ¹³C and ¹⁵N with depth and an enrichment in ¹³C and ¹⁵N with decreasing SOC and N concentration. The mean CO₂ and CH₄ production rates were greatest in soil horizons with the highest SOC stock and were significantly higher at 21°C and in flooded treatments. The ¹³C of the evolved CO₂ (¹³C-CO₂) became significantly enriched with time during decomposition, and the greatest degree of fractionation occurred in the organic Litter, Fungal, and Humic forest soil horizons and in soil with a high SOC stock compared with the mineral horizon and soil with a lower SOC stock. The ¹³C-CO₂ was significantly depleted in flooded treatments compared with non-flooded treatments.

Abbreviations: CHR, charred layer • ELA, Experimental Lakes Area • GHG, greenhouse gases • JP-B, Jack pine-Betula • JP-L, Jack pine-Ledum • JP-P, Jack pine-Polytrichum • OE, organic matter enriched • SOC, soil organic carbon • SOM, soil organic matter