Journal cover Journal topic
Biogeosciences An interactive open-access journal of the European Geosciences Union
doi:10.5194/bg-2017-79
© Author(s) 2017. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
15 Mar 2017
Review status
This discussion paper is under review for the journal Biogeosciences (BG).
Spatially variable soil water repellency enhances soil respiration rates (CO2 efflux)
Emilia Urbanek and Stefan H. Doerr Department of Geography, College of Science, Swansea University, Swansea, SA2 8PP, UK
Abstract. Soil CO2 emissions are strongly dependent on water distribution in soil pores, which in turn can be affected by soil water repellency (SWR; hydrophobicity). SWR restricts infiltration and movement of water, affecting soil hydrology as well as biological and chemical processes. Effects of SWR on soil carbon dynamics and specifically on soil respiration (CO2 efflux) have been studied in a few laboratory experiments but they remain poorly understood. Existing studies suggest that soil respiration is reduced in water repellent soils, but the responses of soil CO2 efflux to varying water distribution created by SWR are not yet known.

Here we report on the first field-based study that tests whether soil water repellency indeed reduces soil respiration, based on in situ field measurements carried out over three consecutive years at a grassland and pine forest site under the humid temperate climate of the UK.

CO2 efflux was reduced on occasions when soil exhibited consistently high SWR and low soil moisture following long dry spells. However, the highest respiration rates occurred not when SWR was absent, but when SWR, and thus soil moisture, was spatially patchy, a pattern observed for the majority of the measurement period. This somewhat surprising phenomenon can be explained by SWR-induced preferential flow, directing water and nutrients to microorganisms decomposing organic matter concentrated in hot spots near preferential flow paths. Water repellent zones provide air-filled pathways through the soil, which facilitate soil-atmosphere O2 and CO2 exchanges. This study demonstrates that SWR have contrasting effects on CO2 fluxes and, when spatially-variable, can enhance CO2 efflux. Spatial variability in SWR and associated soil moisture distribution needs to be considered when evaluating the effects of SWR on soil carbon dynamics under current and predicted future climatic conditions.


Citation: Urbanek, E. and Doerr, S. H.: Spatially variable soil water repellency enhances soil respiration rates (CO2 efflux), Biogeosciences Discuss., doi:10.5194/bg-2017-79, in review, 2017.
Emilia Urbanek and Stefan H. Doerr
Emilia Urbanek and Stefan H. Doerr
Emilia Urbanek and Stefan H. Doerr

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Short summary
We studied CO2 emissions from soils that display distinctive water-repellent behaviour, limited wetting and water movement. We show that CO2 emissions are reduced when soil is consistently non-wettable usually during a long dry spells, but when water repellency and thus soil moisture is patchy CO2 emission rates are high. The presence of water repellency may therefore increase rather than reduce soil CO2 emissions, which may result in higher soil carbon losses than it was previously anticipated.
We studied CO2 emissions from soils that display distinctive water-repellent behaviour, limited...
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