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

2021 ◽  
Author(s):  
◽  
Carmen Sánchez-García
Keyword(s):  
Climate Change ◽  
Soil Water ◽  
Co2 Flux ◽  
Water Repellency ◽  
Water Repellent ◽  
Soil Co2 ◽  
Soil Water Repellency ◽  
Soil Co2 Flux ◽  
Vegetation Fires ◽  
Birch Effect

Climate change is increasing the frequency and intensity of droughts and this is expected to enhance the development of soil water repellency: a very common property of both dry and fire-affected soils. In some regions climate change is also increasing the occurrence and severity of wildfires. Large pulses of CO2 flux from soil to the atmosphere caused by heavy rainfall events (i.e. the Birch effect) can contribute substantially to annual C emissions from soils. However, the effect of the first rainfall after a drought on water-repellent soils and the first post-fire rainfall event on soil CO2 flux remain poorly understood. To address these knowledge gaps this research focuses on: i) investigating the effects of soil water repellency on the CO2 pulse after wetting; ii) improving understanding of the effects of vegetation fires on post-fire soil CO2 flux; and iii) studying the role of ash produced naturally during vegetation fires in post-fire soil CO2 flux. The results from this research clearly indicate that water repellency is a key controller of the CO2 pulse following the wetting of dry and fire-affected soils. Both the amount of water and the increase in soil water content after wetting are used as indicators of the magnitude of the Birch effect, but this research suggests that their application in water-repellent soils should be re-evaluated. The findings presented here challenge the conceptual notion that the Birch effect is comprised of one large pulse of CO2 and highlights the need to incorporate high-frequency observations during the period following wetting to capture the entire CO2 response to wetting. The results from this thesis suggest that ash is a key player in post-fire C fluxes and should be considered in post-fire C investigations in order to make realistic predictions of the impacts of vegetation fires on C dynamics.

scholarly journals Spatially variable soil water repellency enhances soil respiration rates (CO<sub>2</sub> efflux)

2017 ◽  
Author(s):  
Emilia Urbanek ◽  
Stefan H. Doerr
Keyword(s):  
Soil Moisture ◽  
Soil Respiration ◽  
Soil Water ◽  
Water Distribution ◽  
Preferential Flow ◽  
Water Repellency ◽  
Water Repellent ◽  
Co2 Efflux ◽  
Soil Co2 ◽  
Soil Water Repellency

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.

Induced uneven spatial distribution of agrochemicals due to preferential flow in water repellent soils and its remediation by surfactant

2020 ◽  
Author(s):  
Felix Abayomi Ogunmokun ◽  
Rony Wallach
Keyword(s):  
Spatial Distribution ◽  
Soil Water ◽  
Soil Profile ◽  
Preferential Flow ◽  
Sandy Soils ◽  
Water Repellency ◽  
Treated Wastewater ◽  
Water Repellent ◽  
Soil Water Repellency ◽  
Mediterranean Countries

&lt;p&gt;Soil water repellency is a common feature of dry soils under permanent vegetation and drought conditions. Soil-water hydrology is markedly affected by soil-water repellency as it hinders infiltration, leading to enhanced surface runoff and soil erosion. Although this phenomenon was primarily ascribed to sandy soils, it has been observed in loam, clay, and peat soils in dry and humid regions. One detrimental effect of soil water repellency on plants is the reduction of soil water availability that stems from the non-uniform water retention and flow in preferential pathways (gravity-induced fingers) with relatively dry soil volume among these paths. It was recently discovered that prolonged irrigation with treated wastewater, a widely used alternative in Israel and other Mediterranean countries due to the limited freshwater, triggers soil water repellency which invariably resulted in preferential flow development in the field. Due to climate change events, the use of treated wastewater for irrigation as a means of freshwater conservation is expected to widen, including in countries that are not considered dry.&lt;/p&gt;&lt;p&gt;While a vast amount of research has been devoted to characterizing the preferential flow in water repellent soils, the effect of this flow regime on the spatial distribution of salt and fertilizers in the root zone was barely investigated. Results from a commercial citrus orchard irrigated with treated wastewater that includes the spatial and temporal distribution of preferential flow in the soil profile measured by ERT will be demonstrated. The associated spatial distribution of salinity, nitrate, phosphate, and SAR in the soil profile will be shown as well.&amp;#160; We investigated the efficacy of two nonionic surfactants application to remediate hydrophobic sandy soils both in the laboratory and field. The effect of the surfactant application to the water repellent soils in the orchards on the spatial distribution of soil moisture and the associated agrochemicals will be presented and discussed.&lt;/p&gt;

scholarly journals Eucalyptus reforestation induces soil water repellency

Soil Research ◽  
2015 ◽  
Vol 53 (2) ◽  
pp. 168 ◽  
Author(s):  
L. L. Walden ◽  
R. J. Harper ◽  
D. S. Mendham ◽  
D. J. Henry ◽  
J. B. Fontaine
Keyword(s):  
Soil Properties ◽  
Soil Water ◽  
Water Movement ◽  
Computer Modelling ◽  
Clay Content ◽  
Water Repellency ◽  
Water Repellent ◽  
Organic Carbon Content ◽  
Soil Water Repellency ◽  
Hydrophobic Compounds

There is an increasing interest in eucalypt reforestation for a range of purposes in Australia, including pulp-wood production, carbon mitigation and catchment water management. The impacts of this reforestation on soil water repellency have not been examined despite eucalypts often being associated with water repellency and water repellency having impacts on water movement across and within soils. To investigate the role of eucalypt reforestation on water repellency, and interactions with soil properties, we examined 31 sites across the south-west of Western Australia with paired plots differing only in present land use (pasture v. plantation). The incidence and severity of water repellency increased in the 5–8 years following reforestation with Eucalyptus globulus. Despite this difference in water repellency, there were no differences in soil characteristics, including soil organic carbon content or composition, between pasture and plantation soils, suggesting induction by small amounts of hydrophobic compounds from the trees. The incidence of soil water repellency was generally greater on sandy-surfaced (<10% clay content) soils; however, for these soils 72% of the pasture sites and 31% of the plantation were not water repellent, and this was independent of measured soil properties. Computer modelling revealed marked differences in the layering and packing of waxes on kaolinite and quartz surfaces, indicating the importance of interfacial interactions in the development of soil water repellency. The implications of increased water repellency for the management of eucalyptus plantations are considered.

Heating effects on water repellency in Australian eucalypt forest soils and their value in estimating wildfire soil temperatures

2004 ◽  
Vol 13 (2) ◽  
pp. 157 ◽  
Author(s):  
Stefan H. Doerr ◽  
William H. Blake ◽  
Richard A. Shakesby ◽  
Frank Stagnitti ◽  
Saskia H. Vuurens ◽  
...  
Keyword(s):  
Soil Temperature ◽  
Soil Water ◽  
Water Repellency ◽  
Water Repellent ◽  
Laboratory Studies ◽  
Soil Water Repellency ◽  
Eucalypt Forest ◽  
Heating Effects ◽  
Soil Temperatures ◽  
Eucalypt Forests

Wildfires can induce or enhance soil water repellency under a range of vegetation communities. According to mainly USA-based laboratory studies, repellency is eliminated at a maximum soil temperature (T) of 280–400°C. Knowledge of T reached during a wildfire is important in evaluating post-fire soil physical properties, fertility and seedbed status. T is, however, notoriously difficult to ascertain retrospectively and often based on indicative observations with a large potential error. Soils under fire-prone Australian eucalypt forests tend to be water repellent when dry or moderately moist even if long unburnt. This study aims to quantify the temperature of water repellency destruction for Australian topsoil material sampled under three sites with contrasting eucalypt cover (Eucalyptus sieberi, E. ovata and E. baxteri). Soil water repellency was present prior to heating in all samples, increased during heating, but was abruptly eliminated at a specific T between 260 and 340°C. Elimination temperature varied somewhat between samples, but was found to be dependent on heating duration, with longest duration resulting in lowest elimination temperature. Results suggest that post-fire water repellency may be used as an aid in hindcasting soil temperature reached during the passage of a fire within repellency-prone environments.

Petroleum residues as water-repellent substances in weathered nonwettable oil-contaminated soils

1999 ◽  
Vol 79 (2) ◽  
pp. 367-380 ◽  
Author(s):  
Julie L. Roy ◽  
William B. McGill ◽  
Marvin D. Rawluk
Keyword(s):  
Soil Water ◽  
Contaminated Soils ◽  
Impact Ionization ◽  
Water Repellency ◽  
Solvent Mixture ◽  
Water Repellent ◽  
Soil Water Repellency ◽  
Petroleum Origin ◽  
Soil Hydrophobicity ◽  
Gas Chromatography Mass Spectroscopy

Some soils develop severe water repellency several years or decades following oil contamination. We previously reported on the characteristics of three such soils. Here we report on the characteristics of putative water-repellent substances in them. We examined the effectiveness of various polar, nonpolar and amphiphilic solvents for removal of water-repellent substances in three nonwettable soils. Only the amphiphilic solvent mixture isopropanol/14.8 M ammonia (7:3, vol/vol) (IPA/NH4OH) completely eliminated soil water repellency in all three soils. We thus define putative water-repellent substances as those substances whose removal from soil by IPA/NH4OH removes water repellency. High-resolution CPMAS 13C-NMR spectroscopy and thermal desorption followed by conventional gas chromatography/mass spectroscopy with electron impact ionization (GC/EI/MS) and GC/MS with chemical ionization (GC/CI/MS) were used to characterize extracted putative water-repellent substances. We conclude that: (i) the identified representatives of these substances consist mostly of homologous series of long-chain and polycyclic aliphatic organic compounds; namely, n-fatty acids, n-alkanes, and cycloalkanes, and that (ii) they are of petroleum origin rather than plant or microbial origin. Key words: Soil hydrophobicity, petroleum hydrocarbons, soil water repellency, amphiphilic solvents, crude oil, nonwettable soil

A quick fix for modeling infiltration in water-repellent soils

2021 ◽  
Author(s):  
Ryan Stewart ◽  
Majdi R. Abou Najm ◽  
Simone Di Prima ◽  
Laurent Lassabatere
Keyword(s):  
Soil Water ◽  
Wide Spectrum ◽  
Correction Term ◽  
Water Repellency ◽  
Infiltration Rate ◽  
Water Repellent ◽  
Soil Water Repellency ◽  
Simple Method ◽  
Wide Range ◽  
Infiltration Models

&lt;p&gt;Water repellency occurs in soils under a wide spectrum of conditions. Soil water repellency can originate from the deposition of resinous materials and exudates from vegetation, vaporization and condensation of organic compounds during fires, or the presence of anthropogenic-derived chemicals like petroleum products, wastewater or other urban contaminants. Its effects on soils range from mild to severe, and it often leads to hydrophobic conditions that can significantly impact the infiltration response with effects extending to the watershed-scale. Those effects are often time-dependent, making it a challenge to simulate infiltration behaviors of water-repellent soils using standard infiltration models. Here, we introduce a single rate-constant parameter (&amp;#945;&lt;sub&gt;WR&lt;/sub&gt;) and propose a simple correction term (1-e&lt;sup&gt;-&amp;#945;WRt&lt;/sup&gt;) to modify models for infiltration rate. This term starts with a value of zero at the beginning of the infiltration experiment (t = 0) and asymptotically approaches 1 as time increases, thus simulating a decreasing effect of soil water repellency through time. The correction term can be added to any infiltration model (one- two- or three-dimensional) and will account for the water repellency effect. Results from 165 infiltration experiments from different ecosystems and wide range of water repellency effects validated the effectiveness of this simple method to characterize water repellency in infiltration models. Tested with the simple two-term infiltration equation developed by Philip, we obtained consistent and substantial error reductions, particularly for more repellent soils. Furthermore, results revealed that soils that were burned during a wildfire had smaller &amp;#945;&lt;sub&gt;WR&lt;/sub&gt;&amp;#160;values compared to unburned controls, thus indicating that the magnitude of &amp;#945;&lt;sub&gt;WR&lt;/sub&gt;&amp;#160;may have a physical basis.&lt;/p&gt;

The relationship of soil water repellency to aliphatic C and kaolin measured using DRIFT

Soil Research ◽  
2003 ◽  
Vol 41 (2) ◽  
pp. 251 ◽  
Author(s):  
I. McKissock ◽  
R. J. Gilkes ◽  
W. van Bronswijk
Keyword(s):  
Organic Matter ◽  
Soil Water ◽  
Soil Texture ◽  
Water Repellency ◽  
Water Repellent ◽  
Soil Water Repellency ◽  
Organic C ◽  
Aliphatic Carbon ◽  
Fourier Transform Spectra ◽  
Diffuse Reflectance Infrared

In general, water repellency by soil increases with the increase of total organic matter and decreases as the clay and silt contents of the soil increase. The prediction of water repellency from soil organic carbon (OC) content may be improved by examining the types of carbon associated with water repellency. This paper examines the hypothesis that measurement of aliphatic C can provide a better prediction of water repellency than measurement of total OC and also looks at the effects of soil texture on water repellency and the amount of aliphatic C in the soil. DRIFT (diffuse reflectance infrared fourier transform) spectra were measured on sandy soils from the West Midland Sandplains north of Perth in Western Australia. The areas of the aliphatic CH stretching signal (3000–2800/cm) and the OH stretching signal due to kaolin (3750–3570/cm) were used as relative measures of aliphatic carbon and kaolin contents. The relationships of aliphatic C and kaolin to water repellency have been examined and compared with the relationships of water repellency to total OC and clay contents of soil.Hydrophobic organic C as measured by DRIFT gave a better prediction of soil water repellency (r2 = 0.45) than did the total OC (r2 = 0.36). The specific hydrophobicity of organic matter (aliphatic C/OC ratio) increased as sand content increased. However, the direct influence of soil texture on water repellency was of more significance than its indirect influence on the amounts and forms of soil organic matter. A multivariate model including aliphatic C and clay + silt content was the best model for describing water repellency (r2 = 0.58). DRIFT is an effective, rapid method for screening soils for water repellent properties.For individual sand grains there was a weak positive relationship (r2 = 0.26) between the size of the aliphatic CH peak measured from surfaces of sand grains and the water repellency of the grains. A discontinuous aliphatic surface layer was present on the surface of individual sand grains.

Investigation into mechanisms leading to the development, spread and persistence of soil water repellency following contamination by crude oil

2000 ◽  
Vol 80 (4) ◽  
pp. 595-606 ◽  
Author(s):  
J. L. Roy ◽  
W. B. McGill
Keyword(s):  
Crude Oil ◽  
Soil Water ◽  
Oil Spill ◽  
Water Repellency ◽  
Vapour Phase ◽  
Water Repellent ◽  
Soil Sorption ◽  
Soil Water Repellency ◽  
Causative Agents ◽  
Crude Oil Spill

We investigated mechanisms by which soil water repellency may develop, spread and persist at old crude oil spill sites. We tested if its development may be due to soil sorption of vapour-phase petroleum compounds, its spread due to mechanical dispersal and mixing, and its persistence due to association of causative agents with humin and soil mineral surfaces. Development. Readily wettable soils acquired water repellency following 60 d of storage in the presence of oil-contaminated subsoil material. Change in soil wettability was attributed to soil sorption of vapour-phase petroleum compounds emanating from the contaminated material. We cite literature reports indicating that liquid-phase petroleum compounds can also cause soil water repellency. To that effect, we report how we tested and finally rejected the hypothesis that sorption of petroleum asphaltenes might be the sole cause of soil water repellency. Spread. We describe how mixing one mass unit of water-repellent soil with two to four mass units of wettable adjacent soil is sufficient to impart severe water repellency to soil mixes from three sites. Persistence. The water-repellent condition found at old crude oil spill sites is highly resistant to natural weathering and nondestructive extraction procedures. We show here that it also resists exhaustive extraction with 0.1 M NaOH and conclude that causative agents of soil water repellency are at least not solely associated with humic and fulvic acid fractions. Key words: Soil water repellency, asphaltenes, cultivation, humic acids, sorption, crude oil

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