Production of GHG from the Decomposition of in vitro Inundated Phytomass and Soil

Abstract

A set of experiments was designed to measure the production of carbon dioxide and methane during decomposition of inundated samples of representative vegetation and soil samples originating from the James Bay territory over a period of approximately one year. Controlled laboratory conditions were set for water temperature (4–22°C), pH (4.5–7.0) and dissolved oxygen concentration (< 2 mg·L−1 and > 2 mg·L−1). These conditions covered the range of conditions under which vegetation and soil are submitted during permanent flooding in newly created hydroelectric reservoirs. Representative phytomass samples consisted of spruce needles (Picea mariana sp.), alder leaves (Alnus sp.), lichen (Cladonia sp.), green moss (Pleurosium sp.) and herbaceous plants (mixed species). Representative forest soil samples consisted of lichen (Cladonia sp.) humus and green mosses (Pleurosium sp.) humus with Sphagnum moss (Sphagnum sp.) used as a representative ground component (phytomass) for wetlands. Production of carbon dioxide over time was observed from all samples under the given experimental conditions. The quantities of carbon dioxide produced from the vegetation samples were largest under oxic conditions at the higher temperature. The average cumulative quantities produced over 345 days ranged from 201 mg CO2·g−1 (dry weight) to 447 mg CO2·g−1 (dry weight) with the largest quantities produced from green moss. For the soil samples, the largest quantities of carbon dioxide produced occurred also at the higher temperature but were 15–40% larger under anoxic conditions. Under such conditions, the average cumulative quantities produced over 320 days from lichen humus and green moss humus were 72 g CO2·m−2 and 140 g CO2·m−2 respectively. Small quantities of methane were produced from the soil samples but only under the most favourable temperature and pH conditions and were higher under anoxic conditions. pH conditions and were higher under anoxic conditions. Under such conditions, the average cumulative quantities of methane produced over 320 days from lichen humus and green moss humus were 0.21 g CH4·m−2 and 0.56 g CH4·m−2 respectively. Production of methane from vegetation samples was significant only for the higher temperature under anoxic conditions. Under such conditions, the average cumulative quantities produced over 345 days were largest for green moss with a value of 1.72 mg CH4·g−1 (dry weight). Results have shown that, under the most favourable conditions for decomposition, the production of carbon dioxide and methane from inundated phytomass and humus soil samples was still very active after 345 and 320 days respectively. Rates of production of CO2 and CH4 calculated from the cumulative quantities released from the flooded vegetation and soil samples under the given experimental conditions represent a reference data set from which production of CO2 and CH4 emitted from reservoirs under field conditions can be estimated (Thérien and Morisson, Chap. 25).