The effect of water repellency on the short-term release of CO2 upon soil wetting

Abstract

The spike in carbon dioxide (CO2) observed after rewetting of dry soils, known as the 'Birch effect', can contribute substantially to total soil carbon (C) emissions, however, the exact mechanisms and timings underlying this sudden CO2 release remain unclear. The amount of applied water and duration of the previous dry period are considered the main factors affecting the magnitude of the CO2 peak, but the preceding change in soil wettability, triggered by low soil water content, could also be an important contributor.We investigated the effect of soil water repellency (SWR, assessed by water drop penetration time test) on the short-term release of CO2 upon wetting of dry soils with different water quantities. The experiments were conducted under laboratory conditions using homogeneous and autoclaved soil from two locations in South Wales (UK) in both wettable and extremely water-repellent states. The CO2 efflux was measured using chambers above and below the samples. Upon wetting, CO2 efflux was up to 10 times lower in water-repellent soils as a result of rapid percolation through preferential pathways, with only a small amount of water (up to 10%) retained in the soil. Total CO2 efflux was proportional to the water retained in the soil after infiltration, suggesting that the release of CO2 occurred only from limited pore-spaces of the soil. The quick CO2 release suggests that chemical or biochemical processes, rather than microbial respiration, is the main source of CO2 efflux in this study. Part of the CO2 released was transported to the bottom chamber, which under natural conditions could enhance the entrapment of gas in the subsoil. This study shows that alterations in 2 the water-filled pore-space as a result of SWR significantly reduced the CO2 efflux upon wetting and suggests that SWR could be a key factor when investigating and predicting C fluxes.

A Comparison of Linear Conventional and Nonlinear Microbial Models for Simulating Pulse Dynamics of Soil Heterotrophic Respiration in a Semi‐Arid Grassland

“…The moisture‐response function in conventional models affects the decomposition rates of different soil C pools and their response to environmental changes (Moyano et al., 2013), while in microbial models, the moisture‐response function is generally considered to modify the function of Michaelis‐Menten kinetics when microbial mechanisms are embedded in models (Abramoff et al., 2018; Wieder et al., 2013). Other factors can also affect the mechanistic relationship between the R H and soil moisture, such as soil properties in pore‐scale models (Moyano et al., 2012, 2013), microbial dormancy (Salazar et al., 2018), and soil water transfer processes (Manzoni et al., 2014, 2016; Sánchez‐García, Doerr, et al., 2020; Sánchez‐García, Oliveira, et al., 2020). Yan et al.…”

Influence of contamination with diesel oil on water sorptivity and hydrophobicity of sandy loam soil

“…Furthermore, deterioration of the water regime, which creates an anaerobic environment in the soil, influences the direction of organic matter transformation, causing a significant increase in soil hydrophobicity (Mielnik et al, 2021). Sánchez‐García, Doerr, and Urbanek (2020); Sánchez‐García, Oliveira, et al (2020) and Urbanek and Doerr (2017) showed that soil hydrophobicity can become a key factor affecting the release of CO 2 , especially during rainfall events. However, the interactions between water and hydrophobic particles derived from organic soil residues, which depend on the variability of environmental factors, such as temperature and soil biological activity, remain largely unrecognised (Mao et al, 2019; Seaton et al, 2019).…”

Climate change effects on soil carbon dynamics: CO2 flux from water-repellent and fire-affected soils

“…The specific objectives and a more detailed structure of this thesis are outlined at the end of Chapter 1. Chapters 2 and 3 are versions of peerreviewed publications (Sánchez-García et al, 2020a; and the material from Chapter 4 forms a third publication currently under second revision in a peer-reviewed journal (Sánchez-García et al, In submission). Chapters 2, 3 and 4 have been reformatted to incorporate the published articles and to ensure consistency throughout the thesis.…”