In situCO₂profiles with complementary monitoring of O₂in a drained peat layer

Abstract

Peatlands can export large amounts of carbon in various forms, including surface gas emissions and the discharge of dissolved carbon under aerobic/anaerobic soil degradation. Therefore, an apparent imbalance can be expected between gaseous CO 2 production and O 2 consumption in unsaturated peat layers. The present study monitored profiles of soil CO 2 and O 2 in Bibai mire, Hokkaido, Japan, with the aim of examining the apparent imbalance between the two gases. The CO 2 abundance to the atmospheric level did not exceed the O 2 deficit because the CO 2 concentrations were 0.21, 0.75 and 2.92%, whereas the O 2 concentrations were 19.71, 18.05 and 9.51% at depths of 10, 20 and 30 cm, respectively. This shortage of CO 2 abundance implied that a remarkable amount of CO 2 dissolved into the liquid phase. The dissolved CO 2 mass on the basis of Henry's law ranged from 1.72 to 159.3 mmol m −2 (10 cm), and was 1.59-5.25-fold greater than the gaseous CO 2 mass. The mass balance analyses showed that the CO 2 production rate in the gaseous phase at a depth of 20 cm ranged from 6.52 to 23.11 mmol m −2 (10 cm) −1 day −1 , equivalent to 43% on average of the O 2 consumption rate. This CO 2 production rate contributed to less than 10% of the gaseous CO 2 produced in the unsaturated peat layer, which had a maximum thickness of 40 cm, implying the existence of a large CO 2 source in the peat layer, including in the saturated zone. The mass balance analyses also showed that the residence time of CO 2 in the gaseous phase alone was 0.351 day, whereas that in the whole peat soil matrix was 0.919 day at a depth of approximately 20 cm, suggesting that high water content serves as a tentative storage for gaseous CO 2 in peatlands.

Linking Soil O2, CO2, and CH4 Concentrations in a Wetland Soil: Implications for CO2 and CH4 Fluxes

“…The total subsurface O 2 flux (∼4 μmol O 2 m −2 s −1 ) was almost twice as high as the total surface CO 2 flux according to PROFILE simulations. This could be caused by a notable amount of CO 2 being dissolved in the liquid phase and transported out of the soil-ecosystem without being released to the atmosphere, in line with previous observations and high dissolved C export rates from wetlands which is an advective transport not represented in our profiles of transport coefficients . CH 4 concentrations increased from atmospheric levels above the water level to >100 μM with increasing depth.…”

Temporal Dynamics in Soil Oxygen and Greenhouse Gases in Two Humid Tropical Forests

“…Theory would predict a 1:1 M relationship of CO 2 production and O 2 consumption during organic C mineralization to CO 2 with O 2 as the dominant electron acceptor. This is not always observed in the field, however (Teh and others 2005;Iiyama and Hasegawa 2009), and was not observed here. The relationship could vary from the predicted 1:1 relationship because there are other processes in soils besides aerobic C mineralization that could result in CO 2 production (for example, heterotrophic denitrification, Fe reduction, methanotrophy, acetoclastic methanogenesis) or consumption (hydrogenotrophic methanogenesis) as well as geochemical reactions and root activity that can produce and consume O 2 or CO 2 in the soil.…”

Surface O2influx related to soil O2profiles in a drained tropical peatland

“…The profile of the O 2 concentration in the peat layer was also examined. Polyvinyl chloride (PVC) pipes containing the galvanic cell sensors described in Iiyama and Hasegawa (2009) were installed at points [4] and [5] in Fig. 1.…”