Characteristics of soil water repellency after sand dune stabilization in the Tengger Desert

Soil water repellency （SWR） is one of the most important physical properties of soils found all over the world, and it may have significant effects on the eco-hydrological processes of land ecosystems. In this study, the Capillary Rise Method was used to measure the SWR in the artificial vegetation area in Shapotou, located in the southeast area of the Tengger Desert, Ningxia Prov- ince of western China. The variation of the soil water repellency among different minor topographies, different depths and differ- ent particle sizes was analyzed. The results of the study indicate that the SWR shows distinct changes with vegetation restoration, and it increases with an increase in the period of dune stabilization. In the same vegetation area, the SWR of soils in inter-dune depressions or windward slopes is slightly greater than that in crest or leeward slopes. The SWR of 0-3 cm topsoil is significantly greater than that in the 3-6 cm soil layer. The SWR decreases with an increase in grain size and the differences among the SWRs of different sieved soil fractions are found to be significant. There is also a significantly positive correlation between the SWR and the proportion of soils with grain sizes of 0-0.05, 0.05-0.01 and 0.01-0.15 mm, and a significantly negative correlation between the SWR and the propotion of soils with grain sizes exceeding 0.15 mm. The increase of SWR in revegetation areas may depend on the continuous depositing of atmospheric dust on the stabilized dune surface as well as the formation of biological soil crusts, especially on the formation of algal and lichen crusts. Enhanced SWR influences the effectiveness of water use of sand plants in- habiting the sand dunes.

Physical properties of soil in Pine elliottii and Eucalyptus cloeziana plantations in the Vhembe biosphere,Limpopo Province of South Africa

Plantation establishment using invasive alien plants is common in South Africa,but the effects of these plants on soil physical properties in the Vhembe biosphere is unknown.In this comparative study,soils underneath Pinus elliottii and Eucalyptus cloeziana were assessed for differences in physical properties compared to soils underneath adjacent natural sites in the Entabeni plantation in the Vhembe biosphere in Limpopo Province,South Africa.Soils were collected from topsoil over 3 months and quantified for gravimetric soil moisture,penetration resistance,soil infiltration,hydraulic conductivity and soil water repellency.For all 3 months,soils from both P.elliottii and E.cloeziana plantations were compact and had low penetration resistance compared to soils from adjacent natural sites.Soil infiltration and hydraulic conductivity were significantly(p\0.05)lower in soils from plantations compared to soils from adjacent natural sites,and more so from the E.cloeziana plantation than from P.elliottii.Soil water repellency was observed in soils from E.cloeziana only in May and June.Soils from the invasive alien tree plantation have decreased soil moisture,infiltration rate,hydraulic conductivity and are compact as well as repellent(only E.cloeziana),all poor soil physical properties.However,this decline in soil physical properties was not uniform between the two invasive alien plantation species;hence we cannot generalize about the effects of invasive alien plantation species on soil physical properties,and further research is required across different ecological regions.

Characteristics of Water Infiltration in Layered Water-Repellent Soils

Water-repellent(WR) soil greatly influences infiltration behavior. This research determined the impacts of WR levels of silt loam soil layer during infiltration. Three column scenarios were utilized, including homogeneous wettable silt loam or sand, silt loam over sand(silt loam/sand), and sand over silt loam(sand/silt loam). A 5-cm thick silt loam soil layer was placed either at the soil surface or 5 cm below the soil surface. The silt loam soil used had been treated to produce different WR levels, wettable, slightly WR, strongly WR, and severely WR. As the WR level increased from wettable to severely WR, the cumulative infiltration decreased. Traditional wetting front-related equations did not adequately describe the infiltration rate and time relationships for layered WR soils. The Kostiakov equation provided a good fit for the first infiltration stage. Average infiltration rates for wettable, slightly WR, strongly WR, and severely WR during the 2 nd infiltration stage were 0.126, 0.021, 0.002, and 0.001 mm min^(-1) for the silt loam/sand scenario,respectively, and 0.112, 0.003, 0.002, and 0.000 5 mm min^(-1) for the sand/silt loam scenario, respectively. Pseudo-saturation phenomena occurred when visually examining the wetting fronts and from the apparent changes in water content(?θ_(AP)) at the slightly WR,strongly WR, and severely WR levels for the silt loam/sand scenario. Much larger ?θAPvalues indicated the possible existence of finger flow. Delayed water penetration into the surface soil for the strongly WR level in the silt loam/sand scenario suggested negative water heads with infiltration times longer than 10 min. The silt loam/sand soil layers produced sharp transition zones of water content. The WR level of the silt loam soil layer had greater effects on infiltration than the layer position in the column.

Exploring the factors influencing the hydrological response of soil after low and high-severity fires with post-fire mulching in Mediterranean forests

Despite ample literature,the influence of the individual soil properties and covers on the hydrological response of burned soils of forests has not clearly identified.A clear understanding of the surface runoff and erosion rates altered by wildfires and prescribed fires is beneficial to identify the most suitable post-fire treatment This study has carried out a combined analysis of the hydrological response of soil and its driving factors in burned forests of Central-Eastern Spain.The pine stands of these forests were subjected to both prescribed fire and wildfire,and,in the latter case,to post-fire treatment with mulching.Moreover,simple multi-regression models are proposed to predict runoff and erosion in the experi-mental conditions.In the case of the prescribed burning,the fire had a limited impact on runoff and erosion compared to the unburned areas,due to the limited changes in soil parameters.In contrast,the wildfire increased many-fold the runoff and erosion rates,but the mulching reduced the hydrological response of the burned soils,particularly for the first two-three rainfalls after the fire.The increase in runoff and erosion after the wildfire was associated to the removal of the vegetation cover,soil water repellency,and ash left by fire;the changes in water infiltration played a minor role on runoff and erosion.The multi-regression models developed for the prescribed fire were accurate to predict the post-fire runoff coefficients.However,these models were less reliable for predictions of the mean erosion rates.The predictions of erosion after wildfire and mulching were excellent,while those of runoff were not satisfactory(except for the mean values).These results are useful to better understand the relations among the hydrological effects of fire on one side and the main soil properties and covers on the other side.Moreover,the proposed prediction models are useful to support the planning activities of forest managers and hydrologists towards a more effective conservation of forest soils.

Reclamation of oil-induced soil hydrophobicity in the hyper-arid Evrona Nature Reserve,southern Israel

Two oil spills occurred in the Evrona Nature Reserve(southern Israel),in 1975 and 2014.This oil contamination induced highly persistent soil hydrophobicity.The objective of this study was to investigate the decrease in oil-induced soil hydrophobicity under different environmental conditions and to assess the relationship between the hydrophobicity and hydrocarbon content.A laboratory incubation experiment was conducted over 1.5 years to monitor the soil hydrophobicity and total hydrocarbon concentration under different environmental conditions.We hypothesized that the addition of water(20% or 50% saturation),nutrients,and biosurfactants can accelerate the reduction in hydrophobicity and decomposition of hydrocarbons.Water drop penetration time and molarity of ethanol droplet tests were used to assess soil hydrophobicity.In parallel,alkane composition and total petroleum hydrocarbons were evaluated to indicate oil attenuation.The addition of water,nutrients,and biosurfactants resulted in a concomitant reduction in hydrophobicity and hydrocarbon concentration of varying degrees,exhibiting enhanced degradation and hydrophobicity reduction observed in treatments to which nutrients and biosurfactants were added.At the end of the incubation,however,soil hydrophobicity in all treatments remained severe,even though total petroleum hydrocarbon removal was fairly high and reached 40%–80%in the treatments to which water with or without nutrients and/or surfactants was added.