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

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 CO 2 and CH 4 emissions and carbon (C) fractionation compared with non‐flooded soil. To evaluate this hypothesis, soil C and nitrogen (N) dynamics, CO 2 and CH 4 mean production rates, and 13 C 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 δ 13 C and δ 15 N with depth and an enrichment in δ 13 C and δ 15 N with decreasing SOC and N concentration. The mean CO 2 and CH 4 production rates were greatest in soil horizons with the highest SOC stock and were significantly higher at 21°C and in flooded treatments. The δ 13 C of the evolved CO 2 (δ 13 C‐CO 2 ) 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 δ 13 C‐CO 2 was significantly depleted in flooded treatments compared with non‐flooded treatments.