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 (C) fluxes in the vadose zone between emission to the atmosphere and to the groundwater was investigated to reveal controlling underlying mechanisms. 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 modeled 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 C m−2 s−1, respectively, and grossly exceeded the corresponding DIC percolation fluxes of 0.01 ± 0.004 and 0.06 ± 0.03 μmol C m−2 s−1. Plant biomass was high in the mesocosms as compared to a standard field situation. 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. Modeling suggested that increasing soil alkalinity during plant growth was due to nutrient buffering during root nitrate uptake.

Reactive transport codes for subsurface environmental simulation

“…The versatility of HP1 was for example demonstrated for long-term transient flow and transport of major cations and heavy metals in a soil profile involving cation exchange processes [75], long-term U-migration in a soil profile following inorganic P-fertilization [76], inverse optimization of cation exchange parameters during transient flow [77], fate and transport of mercury in soils [78][79][80], chemical degradation of cement-based materials and alterations of transport parameters using a microstructural approach [73,81], and carbon fluxes in soil systems [82].…”

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.…”

Comparing soil carbon loss through respiration and leaching under extreme precipitation events in arid and semiarid grasslands

“…This approach is commonly used in process-related research (Hendry et al, 2001;Thaysen et al, 2014;Artiola and Walworth, 2009;Aslam et al, 2015) as it minimizes experimental errors and bias caused by unknown factors including soil heterogeneity and microbial community variations. It is also more favorable in terms of quantifying soil carbon leaching loss as it circumvents pore-water contamination by vacuum suction in the field.…”