Inorganic carbon fluxes across the vadose zone of planted and unplanted soil mesocosms

Abstract

Abstract. The efflux of carbon dioxide (CO2) from soils influences atmospheric CO2 concentrations and thereby climate change. The partitioning of inorganic carbon fluxes in the vadose zone between emission to the atmosphere and to the groundwater was investigated. Carbon dioxide partial pressure in the soil gas (pCO2), alkalinity, soil moisture and temperature were measured over depth and time in unplanted and planted (barley) mesocosms. The dissolved inorganic carbon (DIC) percolation flux was calculated from the pCO2, alkalinity and the water flux at the mesocosm bottom. Carbon dioxide exchange between the soil surface and the atmosphere was measured at regular intervals. The soil diffusivity was determined from soil radon-222 (222Rn) emanation rates and soil air Rn concentration profiles, and was used in conjunction with measured pCO2 gradients to calculate the soil CO2 production. Carbon dioxide fluxes were modelled using the HP1 module of the Hydrus 1-D software. The average CO2 effluxes to the atmosphere from unplanted and planted mesocosm ecosystems during 78 days of experiment were 0.1 ± 0.07 and 4.9 ± 0.07 μmol carbon (C) m−2 s−1, respectively, and largely exceeded the corresponding DIC percolation fluxes of 0.01 ± 0.004 and 0.06 ± 0.03 μmol C m−2 s−1. Post-harvest soil respiration (Rs) was only 10% of the Rs during plant growth, while the post-harvest DIC percolation flux was more than one third of the flux during growth. The Rs was controlled by production and diffusivity of CO2 in the soil. The DIC percolation flux was largely controlled by the pCO2 and the drainage flux due to low solution pH. Plant biomass and soil pCO2 were high in the mesocosms as compared to a standard field situation. Our results indicate no change of the cropland C balance under elevated atmospheric CO2 in a warmer future climate, in which plant biomass and soil pCO2 are expected to increase.

Modeling Soil Processes: Review, Key Challenges, and New Perspectives

“…A number of numerical tools have been developed during the last decade accounting for these interactions, mainly based on principles of thermodynamic equilibrium (Steefel et al, 2014). The generic nature of these tools allows for implementing complex conceptual models for fate and transport (Jacques et al, 2008; Leterme et al, 2014; Thaysen et al, 2014), but these models generally lack kinetics, as well as the inclusion of physical nonequilibrium conditions. This includes nonequilibrium of water–air dynamics, as these interfaces control interactions and access to sorption sites, duration of interactions and local equilibrium assumption (LEA) validity, and biological activity.…”

“…Waste inputs range from feedlots dung and farm animals, irrigation by wastewater nonpoint pollution by atmospheric deposition, accidental spills to deliberate dumping of industrial byproducts in highly engineered waste landfills. A specific pathway is soil amendment to reduce metal leaching or to control CO 2 sequestration (Campbell et al, 2006; Abril et al, 2008; Thaysen et al, 2014). Supporting processes such as limiting water flow through waste zones, sorption of compounds, and biological degradation help to regulate contaminant release to the biosphere by dilution, dispersion, retardation, and decay (e.g., see “Water Cycling” or “Buffering and Filtering” sections).…”

Recent Developments and Applications of the HYDRUS Computer Software Packages

“…More recent HP1 applications include evaluations of (i) laboratory and field experiments involving the treatment of Hg‐contaminated soils with activated C (Bessinger and Marks, 2010; Leterme et al, 2014), (ii) CO 2 production and transport in bare and planted mesocosms (Thaysen et al, 2014a), (iii) the effects of lime and concrete waste on vadose zone C cycling (Thaysen et al, 2014b), (iv) chemical degradation of concrete during leaching with rain and different types of water (Jacques et al, 2010), and (v) the effects of chemical degradation on the hydraulic properties of concrete such as porosity, tortuosity, and the hydraulic conductivity (Jacques et al, 2013). Jacques et al (2012) additionally combined HP1 with the general optimization UCODE program (Poeter et al, 2005) to inversely optimize hydraulic, solute transport, and cation exchange parameters pertaining to column experiments subject to transient water flow and solute transport with cation exchange.…”

Effects of Lime and Concrete Waste on Vadose Zone Carbon Cycling

“…Mesocosms were planted with barley ( Hordeum vulgare L. cv. Anakin) and maintained and irrigated with a 50% strength Hoagland nutrient solution containing 8 mM NO 3 − and 0.5 mM NH 4 + , as described in Thaysen et al (2014b). The experiment was terminated 78 d after sowing.…”

“…The experiment was terminated 78 d after sowing. Two barley mesocosms from a previous experiment (Thaysen et al, 2014b) without any soil amendment served as controls.…”