Development Of Soil Water Repellency Research Articles

Water Stress-Driven Changes in Bacterial Cell Surface Properties.

Increased drought intensity and frequency exposes soil bacteria to prolonged water stress. While numerous studies reported on behavioral and physiological mechanisms of bacterial adaptation to water stress, changes in bacterial cell surface properties during adaptation are not well researched. We studied adaptive changes in cell surface hydrophobicity (CSH) after exposure to osmotic (NaCl) and matric stress (polyethylene glycol 8000 [PEG 8000]) for six typical soil bacteria (Bacillus subtilis, Arthrobacter chlorophenolicus, Pseudomonas fluorescens, Novosphingobium aromaticivorans, Rhodococcus erythropolis, and Mycobacterium pallens) covering a wide range of cell surface properties. Additional physicochemical parameters (surface chemical composition, surface charge, cell size and stiffness) of B. subtilis and P. fluorescens were analyzed to understand their possible contribution to CSH development. Changes in CSH caused by osmotic and matric stress depend on strain and stress type. CSH of B. subtilis and P. fluorescens increased with stress intensity, R. erythropolis and M. pallens exhibited a generally high but constant contact angle, while the response of A. chlorophenolicus and N. aromaticivorans depended on growth conditions and stress type. Osmotically driven changes in CSH of B. subtilis and P. fluorescens are accompanied by increasing surface N/C ratio, suggesting an increase in protein concentration within the cell wall. Cell envelope proteins thus presumably control bacterial CSH in two ways: (i) by increases in the relative density of surface proteins due to efflux of cytoplasmic water and subsequent cell shrinkage, and (ii) by destabilization of cell wall proteins, resulting in conformational changes which render the surface more hydrophobic. IMPORTANCE Changes in precipitation frequency, intensity, and temporal distribution are projected to result in increased frequency and intensity of droughts and heavy rainfall events. Prolonged droughts can promote the development of soil water repellency (SWR); this impacts the infiltration and distribution of water in the soil profile, exposing soil microorganisms to water stress. Exposure to water stress has recently been reported to result in increased cell surface hydrophobicity. However, the mechanism of this development is poorly understood. This study investigates the changes in the physicochemical properties of bacterial cell surfaces under water stress as a possible mechanism of increased surface hydrophobicity. Our results improve understanding of the microbial response to water stress in terms of surface properties, the variations in stress response depending on cell wall composition, and its contribution to the development of SWR.

Time series of remote sensing and water deficit to predict the occurrence of soil water repellency in New Zealand pastures

Soil water repellency (SWR) is a natural phenomenon occurring in soils throughout the world, which impacts upon ecosystem services at multiple temporal and spatial scales (nano to ecosystem scale). In pastures, the development of SWR is primarily determined by the cycling of hydrophobic materials at the soil surface, and is controlled by climate, soil and water management, and soil properties. The complex interactions between these factors make it an intricate system to understand and model. Detailed spatiotemporal characterization of the surface moisture and biomass in pastoral ecosystems would allow for a better understanding of this phenomenon. Normalized Difference Vegetation Index (NDVI) and Synthetic Aperture Radar (SAR) backscatter are good predictors for surface biomass and soil moisture, respectively. Machine learning on remote sensing time series (TS) data shows promise to predict the occurrence of SWR in pastures. This study evaluates the ability of remote sensing TS data to predict the occurrence of SWR in New Zealand pastures, using three machine learning algorithms. Soil water repellency data were collected from 58 pastoral sites. Machine learning models were trained and cross-validated on a monthly aggregated remote sensing and water deficit TS data to predict SWR level. Prediction output from artificial neural networks (ANN), random forest (RF), and support vector machine (SVM) were compared using root mean squared error (RMSE). When using NDVI TS data from 58 site as predictors of SWR, SVM and RF (RMSE = 0.82 and 0.87, respectively) outperformed ANN (RMSE = 1.23). Random forest was used to map SWR magnitude over Hawke’s Bay region in the North Island of New Zealand, and the overall accuracy was equal to 86%. This study is the first investigation implicating remote sensing TS data to predict the occurrence of SWR at the regional scale. Mapping the potential SWR will aid in identifying critical zones of SWR, to attenuate its effect on pastures through adapted management.

Assessing the relations among the features of the land cover and of the soil on the soil-water interactions through a functional eco-hydrological indicator

Abstract Soil Water Repellency (SWR) is an important ecological property that has implications in the soil and water management and is a useful functional eco-hydrological indicator driven by several natural and human factors. In our research we assessed the relationships between SWR and soil properties, broaden the evidence of the influence of land cover on the development of SWR. We also evaluated the relation between SWR and erosion indicators (EI), and we checked the occurrence and severity of distilled water and aqueous ethanol solution repellency before and after the soil samples are compacted (that augmented the soil density in 10%). In the field, we collected superficial soil samples considering the local land cover features, and we assessed the EIs following a pre-established protocol. For evaluating the SWR we used the “drop penetration time” method. Our results show that the soils are mostly neutral (in terms of soil acidity), silt or sandy-textured and chiefly hydrophilic. The texture is an intrinsic soil attribute that primarily influences the relations between soil and water, and the affinity to water is significantly different among the land cover categories. Land cover change induces modifications in the soil surface, and the soil gets more hydrophilic. The EIs helped to evidence such changes caused by land cover changes. Compacted soils led them to be more hydrophilic, regardless of the reagent, being this finding still barely reported in the literature.

The effect of pH modification on wetting kinetics of a naturally water‐repellent coniferous forest soil

The interfacial dynamics of soil–water interactions are greatly affected by the hydrophobic properties of organic matter. The causes and underlying mechanisms responsible for the development of soil water repellency (SWR) are still under discussion. Various environmental factors control the appearance and degree of SWR. In addition to water content and temperature, the wetting of soil depends greatly on the physicochemical characteristics of soil surfaces, which in turn depend on pH. In this contribution, we propose a reaction mechanism for the change in SWR that is observed when soil pH is changed. Wetting kinetics were studied by time‐dependent sessile drop measurements (TISED) of the contact angle, the work of spreading and the diameter of the base of the drop as time elapsed under controlled relative humidity. Modification of pH strongly affected the wetting kinetics, suggesting maximum resistance to wetting at the control pH (3.6), with decreased resistance to wetting as pH was changed in either direction. The enhancement in wetting kinetics by the modification of soil pH can be attributed to the chemical modification in organic materials that coat the soil particles. This conclusion is based on the magnitude of activation energy associated with the spreading process. The combined effect of pH and temperature on the wetting kinetics, together with the compensation effect seen between the logarithmic pre‐exponential factor and activation energy, suggests acid–base catalysed hydrolysis–condensation reactions are the dominant processes responsible for the chemical nature of SWR.HighlightsHow does the modification of pH affect soil wetting mechanisms? The dynamic sessile drop method was used to measure the wetting activation energy. Modification of soil pH decreases resistance to wetting and increases activation energy of wetting. Acid or base catalysed hydrolysis reactions increase chemical sorption sites for water molecules in soil.

Eucalyptus reforestation induces soil water repellency

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.

Ongoing succession of biological soil crusts increases water repellency — a case study on Arenosols in Sekule, Slovakia

After soil surface disturbances biological soil crusts (BSC) cover rapidly the topmost soil millimeters. Depending on BSC age, development of soil water repellency, water infiltration and soil surface stability are influenced by this thin surface sealing. Within this study disturbed, early- mid- and late successional stages of BSC development were examined along a recovery transect. The results show an increase in water repellency and a decrease in water sorptivity and conductivity with ongoing BSC succession. Penetration resistance data shows very stable thin surface protection by cyanobacteria in early successional BSC that is non-repellent. Later successional stages show increased water repellency and lower water conductivity. We conclude that BSC development induces changes in surface structure and wettability. The soil surface wettability is strongly linked to the BSC community composition.

A Summary of Soil Hydrophobicity Trials in U.S. Golf Course Greens

Recommendations for golf course green construction have been for rootzone mixes with at least 90% sand while the remainder is typically peat or other organic material. This type of construction mix initially facilitates water movement through the profile but provides an environment conducive to soil hydrophobicity. Several factors such as sand texture, frequent wet to dry cycles, and accumulation of organic matter and thatch contribute to the development of soil water repellency in golf course greens. In research studies conducted over the past fifteen years in several locations across the United States, water drop penetration tests (WDPT) on golf greens have shown slightly and strongly water repellent soil is prevalently found at 0 and 1 cm depths. In the majority of locations, as the depth of profile increased, soil hydrophobicity decreased and was mostly non-existent at the 6 cm depth. These results suggest that despite soil texture and management practices, soil hydrophobicity in a managed turfgrass area is most severe in the thatch and mat area of the profile. While the knowledge of what contributes to water repellency is critical for alleviating symptoms associated with hydrophobic coatings, management practices may be more successful if the focus was on the depth of the repellency.

Fungi in century old managed soils could hold key to the development of soil water repellency

We examined the impact of fungi, using the biomarkers glomalin and ergosterol, on the influence of water repellency on 15 land management treatments, sourced from century old managed arable and grassland sites. We observed strong and significant positive correlations between each of the biomarkers and water repellency. Our results suggest a generic relation between fungi and water repellency.

Longevity of soil water repellency in a former wastewater disposal tree stand and potential amelioration

Previous studies have shown that long-term irrigation with wastewater can lead to the development of soil water repellency. Little is known about the longevity of this effect. Here we address this research gap by examining the effect of long-term (~ 20 years) use of low-quality wastewater for disposal purposes, followed by 6 years of ‘recovery’ with no irrigation, on the wettability of calcareous sandy soil (Xerofluvent) under a Populus alba tree stand used as a “green filter” in SE Spain. Water repellency (WR) and soil organic matter content (SOM) were determined for 120 air-dry samples from the plot and 80 control samples from adjacent and otherwise similar non-irrigated areas. To account for plot micro-topography 40 samples each were taken from ridges (R; 0–5 cm depth), furrows (F; 0–5 cm), and furrows at depth (FD; 5–10 cm). The controls included 40 samples each (0–5 cm depth) from unvegetated and unploughed soil, and from soil under the P. alba plantation. All control samples were non-repellent whereas at the irrigated plot, water repellency was present for 48, 95 and 93% of ridge, furrow and furrow-depth samples respectively. WR and SOM was strongly correlated within the whole sample population (R 2 = 0.623**) and within two sample groups (R: R 2 = 0.783**; FD: R 2 = 0.424**), but weakly within F samples (R 2 = 0.072 n.s.). The latter showed the highest frequency and persistence (WDPT) of WR, indicating that not only quantity of SOM is controlling WR. Exploratory kaolinite clay additions (0.5–8%) to samples substantially reduced WR even at the lowest concentration, indicating that this could be a promising amelioration treatment for the WR in the soils investigated here. We conclude that for the conditions studied here (i) long-term use with poor-quality wastewater for disposal had led to the development of soil WR, (ii) a 6-year period of ‘recovery’ (i.e. non-irrigation) was insufficient to eliminate the induced WR, and (iii) kaolinite addition could be a promising amelioration treatment for these sandy soils.

Granular wetting agents ameliorate water repellency in turfgrass of contrasting soil organic matter content

The effectiveness of four granular wetting agents to decrease water repellency in sandy soils of contrasting organic matter (OM) content and influences on kikuyugrass [Pennisetum clandestinum (Holst. Ex Chiov)] grown as turfgrass, were evaluated. A laboratory test assessed the wettability of two non-wetting soils (low OM, 4.7%; high OM, 17%) after treatment with granular soil wetting agents, with four being selected for field experimentation. A field experiment included two turfgrass ages (established from 20 week or 20 year old turfgrass in 2005; the latter included a 50 mm ‘mat’ layer and thus had high OM content in the surface soil), four granular soil wetting agents (plus a ‘nil’ as control), and five replicates. Surface soil (0–25 mm) water repellency, measured using the molarity of ethanol droplet test (MED), ranged from 0.4 M to 4.3 M during the irrigation season, and repellency was more severe in the soil with high OM (32%) content than low OM (8.6%) content. Soil wetting agents decreased the development of soil water repellency to varying extents, and maintained turfgrass quality; with improvement related to the amount of active ingredient applied. We recommend utilising an effective soil wetting agent, in combination with practices that limit the accumulation of soil OM, to decrease the severity and incidence of soil water repellency in turfgrass grown on sandy soils.

Evaluation of two soil conditioners for limiting post‐fire erosion as part of a soil conservation strategy

AbstractSoil conservation is a major concern for catchments affected by forest fires. The lack of vegetation cover and the development of soil water repellency increase the risk of topsoil erosion. This paper evaluates two soil conditioners (a wetting agent and a polyvinyl acetate) for limiting overland flow and erosion in inter‐rill areas. Unburned and burned soil samples were treated with one or both soil conditioners. The effects of these treatments on run‐off, water retention, erosion and plant growth were assessed using laboratory rainfall simulations. Polyvinyl acetate had little impact on water retention but was effective in reducing soil loss. The surfactant had little impact on water run‐off or soil loss but substantially improved water retention and plant biomass production. Application of soil conditioners on post‐fire areas could be a valuable technique in a soil conservation strategy. To maximize their benefits, soil conditioners could be applied with seeding using hydroseeding techniques and be limited to particular areas, such as paths and roadsides. Laboratory results indicate that field testing should also be carried out.

Sieving crusts and macrofaunal activity control soil water repellency in semiarid environments: Evidences from SE Spain

Quick overland flow peaks observed in runoff hydrographs from rainfall experiments carried out on mica schist soils in Rambla Honda (SE Spain) suggest development of soil water repellency (SWR). In order to spatially characterize its occurrence and severity and the factors controlling it, potential water repellency was measured in 120 soil samples using the WDPT test at laboratory conditions. Actual water repellency measurements were additionally performed at field conditions in order to increase our knowledge about the occurrence of this phenomenon. Samples were taken in bare soils ( n = 23), beneath plant clumps of Retama sphaerocarpa ( n = 23) and Anthyllis cytisoides ( n = 10) and from soils affected by rabbit latrines ( n = 9). Soil organic matter was also determined in 47 selected samples with a broad range of potential water repellency values. Results indicate that occurrence of SWR in Rambla Honda (potential water repellency values) varies in the three soil dimensions, areal and depth. The areal variation is due to the patchy pattern of organic matter and the variation with depth of the washed-in layer of sieving crusts developed in colluvial and alluvial soils after abandonment by agriculture. These layers act as physical barriers that restrict or impede the translocation of hydrophobic compounds to deeper layers. Such three-dimensional heterogeneity stresses the importance of the sampling scheme used for adequate SWR assessment. The severity of water repellency is generally reduced in this area because of the relatively scarce organic matter content and its spatial variability. A weak exponential relationship was found between the severity of potential water repellency and total organic carbon ( r 2 = 0.38; p-value < 0.01). Extreme values of actual and potential water repellency were found in rabbit latrines, stressing the importance of macrofauna in its development. Water repellency has an important impact on the local hydrology controlling runoff–runon between vegetated and bare patches, and possibly flash flooding during heavy rains in early autumn or after long dry periods. Review of a series of runoff hydrographs from previous rainfall simulations has distinguished four types of runoff patterns based on the occurrence of SWR.

Development of soil water repellency in the course of isothermal drying and upon pH changes in two urban soils

AbstractThe potential influence of pH on water repellency in soils has already been mentioned in some studies, but no clear correlation between these parameters has been found to date. In addition, although correlations of water content and water repellency have been found in numerous studies, the influence of drying and subsequent storage conditions on water repellency are still unclear. In this study, a series of samples showing water repellent and wettable conditions respectively at field moist states from two urban locations were compared regarding two main aspects: (i) the influence of artificial pH‐changes on their wetting behaviour and (ii) sample wettability changes during drying for different drying temperatures. The assumption made in a study by Hurraß and Schaumann (2006) on the same sample site, that differences in wettability of closely neighboured samples from one sample location can be interrelated with differences in pH, was confirmed. However, in contrast to the assumption that rising pH will improve the wettability and decreasing pH will intensify water repellency, we found a maximum in water repellency at a pH above the initial pH. The results from drying samples at different temperatures confirmed the dependence of water repellency development on the drying temperature. Additionally, we could confirm the conclusion from previous studies that the water content alone cannot explain the water content–WDPT (water drop penetration time) relationship. The results from drying and pH changes show that some location specific factors, like the number of pH active functional groups, may be relevant for sample wettability. As additional mechanism, which may be partly antagonistic to the influence of the water content, we assume temperature‐dependent conformational changes in SOM (Soil Organic Matter). It seems that aspects of these conformational changes may additionally be governed by pH in one of our two locations. Copyright © 2007 John Wiley &amp; Sons, Ltd.

Exponential increase of publications related to soil water repellency

Soil water repellency is much more wide-spread than formerly thought. During the last decades, it has been a topic of study for soil scientists and hydrologists in at least 21 States of the USA, in Canada, Australia, New Zealand, Mexico, Colombia, Chile, Congo, Nepal, India, Hong Kong, Taiwan, China, Ecuador, Venezuela, Brazil, Mali, Japan, Israel, Turkey, Egypt, South Africa, Germany, The Netherlands, Spain, Portugal, United Kingdom, Denmark, Sweden, Finland, Poland, Slovakia, Russia, France, Italy, and Greece. Although, water repellent soils already have been indicated at the end of the nineteenth century, they have been discovered and studied in most countries in the last decades. Water repellency is most common in sandy soils with grass cover and in nature reserves, but has also been observed in loam, heavy clay, peat, and volcanic ash soils. From 1940 to 1970 research was focussed on identifying vegetation types responsible for inducing water repellency and on developing techniques to quantify the degree of water repellency. Of special interest has been the effects of wildfire on the development of soil water repellency and its consequences for soil erosion. Due to increasing concern over the threat to surface and groundwater posed by the use of agrichemicals and organic fertilisers, studies on water repellent soils have also been focused on its typical flow behavior with runoff and the existence of preferential flow paths. Since the end of the 1950s, wetting agents and clay amendments have been studied to ameliorate water repellent soils. Since 1883, more than 1200 articles related to soil water repellency have been published in journals, reports, and theses. An exponential increase in number of publications started in 1960, resulting in an average of 200 publications per 5 years.

Occurrence of soil water repellency in arid and humid climates

Soil water repellency generally tends to increase during dry weather while it decreases or completely vanishes after heavy precipitation or during extended periods with high soil water contents. These observations lead to the hypothesis that soil water repellency is common in dry climates and rare in humid climates. The study objective is to test this hypothesis by examining the occurrence of soil water repellency in an arid and humid climate. The main conclusion of this study is that the effect of climate on soil water repellency is very limited. Field observations in the arid Middle Rio Grande Basin in New Mexico (USA) and the humid Piedras Blancas Watershed in Colombia show that the main impact of climate seems to be in which manner it affects the production of organic matter. An extremely dry climate will result in low organic matter production rates and, therefore, less potential for the development of soil water repellency. On the other hand, a very humid climate is favorable for organic matter production and, therefore, for the development of water repellency.

Water repellency in a New Zealand development sequence of yellow brown sands

A series of sands on the west coast of the lower North Island, New Zealand, were studied to investigate the effects of time, topography and vegetation cover upon the development of soil water repellency. Severe repellency was measured with the molarity of ethanol droplet (MED) index in the Waitarere and Motuiti dune phase sands, of age &lt;130 years and c. 500 years respectively. In each dune phase, the dune sands were more repellent than the lower lying soils of the sand plains. Low or zero MED values were measured in the 1600-6000 year old Foxton dune phase sands and 10 000-25 000 year old Koputaroa dune phase sandy loams under either pasture or native bush. There was no consistent relationship between bush or pasture cover and repellency severity in the Foxton and Koputaroa soils, however, the species composition of the pasture and bush differed. The Waitarere sand was the most repellent soil, despite a low organic carbon content. The carbon content profiles of most of the soils did not appear to be related to the respective MED profiles of repellency severity. The MED values of the surface layer from five dune sands were generally related inversely to the fulvic acid (FA) content and proportionally to the humic acid to fulvic acid ratio (HA/FA), which were measured in a previous study. The pH of the five soils ranged from 5.61 to 6.89, with no apparent relationship between pH and MED. A study of soil water content indicated that repellency reduced rainfall infiltration into the Waitarere and Motuiti sands and the Himatangi sand, found on elevated sand plains. The most severely repellent sands had the greater variability in soil water content after rainfall.