Influence of soil–water content on CO₂ efflux within the elevation transect heavily impacted by erosion

Abstract

This study focused on the effects of organic carbon contents and soil hydraulic conditions on CO2 efflux. Samples were collected at 5 positions (summit, shoulder, backslope, footslope, and toeslope) of the elevation transect affected by erosion and the parent material (loess). Initially, air‐dried soil samples were placed on top of a clay tank, and the samples were wetted by capillary rise to soil saturation, and soil CO2 efflux was measured. Numerical inversions of the measured cumulative capillary rise and evaporation data using the HYDRUS‐1D program were applied to simulate the water regime in the columns and estimate the soil hydraulic parameters. In all cases, the net CO2 efflux (NCER) rapidly increased at the beginning of the wetting. NCER decreased with increasing soil–water content (summit, shoulder, backslope, and loess) or remained relatively stable (footslope and toeslope). The average soil–water content values at the maximal values of NCER (maxNCER) for the summit, shoulder, and footslope were similar. Lower average soil–water contents at maxNCER were simulated for the backslope, toeslope, and loess, which were attributed to the high contents of loess substrate in topsoil samples. The maxNCER measured on topsoils were closely related to the organic carbon contents (R = 0.94) and the maxNCER obtained on all samples correlated with the parameters αRES (R = 0.856) and nRES (R = −0.876) of the soil–water retention curves and saturated hydraulic conductivity (R = 0.856).

An empirical model for describing the influence of water content and concentration of sulfamethoxazole (antibiotic) in soil on the total net CO2 efflux

“…The range of the net CO2 efflux was similar (0-2 μmol s -1 m -2 ) for both soil sample (A1 and B1). The very high soil respiration in the beginning after rewetting and then decrease in soil respiration is called the respiration pulse or the Birch effect (Birch, 1958), which was also find in our previous study where undisturbed soil samples were wetted by a capillary rise from the bottom of the soil samples (Fér et al, 2018a). The similar results were obtained by Iovieno and Bååth (2008), who demonstrated almost no respiration on the air-dried soil samples and exponential decrease of soil respiration after rewetting to 60% of water holding capacity (WHC).…”

“…To avoid the influence of variable solar radiation (e.g., Fér et al, 2018a) and temperature (Schaufler et al, 2010;Yueste et al, 2007) on the measured values, the net CO2 and net H2O effluxes were measured in the dark and at 20°C in a growth chamber (KBF 240, Binder, Germany). The air humidity varied between 30 and 40%.…”

“…Next, the soil CO2 efflux data was analyzed with the R software (R Development Core Team, 2015) to eliminate error measurements. This procedure, which was in detailed described by Fér et al (2018a), includes the smoothing using the Savitzky-Golay filter to reduce the most urgent misleading records caused by the repeated disruption of the measurement conditions and the reconstruction of the potential unaffected course of the measurement by computing its continuum.…”

“…A CO2 efflux from the soil surface is influenced by many abiotic and biotic factors including soil temperature, soil water content, organic carbon content, composition and activity of microbial community, etc. (Balogh et al, 2011;Buchmann, 2000;Davidson and Janssens, 2006;Davidson et al, 1998;Fér et al, 2014Fér et al, , 2018aZhong et al, 2016). The microbial activity and consequently CO2 emission can be influenced by many amendments including contaminants that can occur in the soils environment.…”

Biohydrology—Walking on drylands and swimming through pores

“…Erosion at landscape scale causes a redistribution of topsoil and carbon that also affects soil structure along a slope. Fér et al () took intact specimens from along an eroded slope of loess soil to explore how its wetting from an air‐dry state affected CO 2 efflux. The unique aspect of this study is the combination of impacts of soil organic matter content with the soil hydraulic condition of eroded affected soils.…”