Water Repellent Sand Research Articles

Contrasting transport and fate of hydrophilic and hydrophobic bacteria in wettable and water-repellent porous media: Straining or attachment?

Bacterial transport and retention likely depend on bacterial and soil surface properties, especially hydrophobicity. We used a controlled experimental setup to explore hydrophilic Escherichia coli (E. coli) and hydrophobic Rhodococcus erythropolis (PTCC1767) (R. erythropolis) transport through dry (− 15,000 cm water potential) and water saturated (0 cm water potential) wettable and water-repellent sand columns. A pulse of bacteria (1 × 108 CFU mL–1) and bromide (10 mmol L–1) moved through the columns under saturated flow (0 cm) for four pore volumes. A second bacteria and bromide pulse was then poured on the column surfaces and leaching was extended six more pore volumes. In dry wettable sand attachment dominated E. coli retention, whereas R. erythropolis was dominated by straining. Once wetted, the dominant retention mechanisms flipped between these bacteria. Attachment by either bacteria decreased markedly in water-repellent sand, so straining was the main retention mechanism. We explain this from capillary potential energy, which enhanced straining under the formation of water films at very early times (i.e., imbibing) and film thinning at much later times (i.e., draining). The interaction between the hydrophobicity of bacteria and soil on transport, retention and release mechanisms needs greater consideration in predictions.

Seed row placement relative to the previous crop stubble row can harness systems benefits on water repellent sands

Context Innovations to improve crop establishment are critical to unlocking the full potential of early sown winter cereal cropping systems. Aims The aim of this set of experiments was to evaluate the systems benefits of near-row sowing treatments for surface soil water, crop establishment, crop competition with weeds, root disease infection and cereal crop yield on sandy soils in low-rainfall environments. Methods Six of the 10 site–years evaluated were on water repellent sands with the remainder on sand and loam. A second set of experiments on a water repellent sand evaluated if furrow applied amendments to increase soil fertility in the crop row might generate additional benefits to the near-row sowing effect. Key results Significant grain yield benefits from near-row placement (up to 30%) were measured in 2 site years and these were associated with crop establishment gains, improved access to furrow soil water storage and weed seed reductions, which occurred in 3 site years. In a water repellent sand, near-row placement combined with extra nutrition input generated an additional grain yield benefit (+0.4 t/ha), as did a one-off 22 cm deep furrow tilling treatment designed to bring deeper soil moisture into the seed zone (+0.4 t/ha). Conclusions Near-row placement of crop seeds can provide systems benefits in water repellent sands. The conversion of these benefits to yield benefits occurred in 30% of site-years tested on repellent sand. Implications Further innovation is required to ensure that these seeder-based innovations generate predictable responses and scaled up evaluation is necessary to fully understand the systems and landscape level benefits of improved crop establishment in soils that often suffer low and uneven crop establishment numbers.

Fungal-induced water repellency in sand

Water infiltration into granular soils and the associated pore water pressure increase and reduction in shear strength can trigger landslides, instability of vertical cuts and failure of retaining walls. Water-repellent soils can reduce infiltration to maintain soil suction. Recent research has demonstrated the creation of synthetic water-repellent soils using chemical methods. This paper investigates a biological treatment for creating water-repellent sand by way of the growth of the fungus Pleurotus ostreatus. Water repellency was assessed using: (a) the water drop penetration test; (b) the molarity of ethanol drop test; and (c) the modified sessile drop method with contact angle (θ) determination by way of image analysis. Fungal-induced water repellency was found to be ‘extreme’ (θ > 110°) up to 4 weeks and ‘severe’ (θ > 105°) up to 12 weeks, even with no further supply of moisture or nutrients. A water-repellent layer was formed and maintained in saturated conditions, which is difficult to achieve using chemical methods.

Surfactant Chemistry Effects on Organic Matter Removal from Water Repellent Sand

Core Ideas Confirmed for the first time that certain wetting agents can remove organic coatings that cause soil hydrophobicity. A novel laboratory experiment was performed to precisely quantify this effect. Possible mechanisms regarding the removal of organic coatings following application of certain wetting agents were discussed. Soil surfactants, which represent a wide range of wetting agent chemistries, have been used as the primary tool for mitigating drought issues caused by soil water repellency (SWR). However, the residual effects of soil surfactants are often short‐lived, requiring repeated applications. Alternatively, certain groups of wetting agents may remove hydrophobic organic matter for extended control of SWR. This laboratory study investigated the effects of selected wetting agent chemistries, including products of alkyl block polymer (ABP), nonionic surfactant + acidifiers (NIS), and polyoxyalkylene polymer (PoAP), for removing organic matter and reducing SWR. Naturally‐occurring hydrophobic sand was packed into sand columns and subjected to wetting agent application. The treated columns were then washed three times with deionized water, and the volume of the leachates from each wash event was determined. Sand treated by PoAP showed enhanced water‐holding capacity, although the effect diminished after the second wash. In comparison, ABP resulted in 2.3‐fold greater output of combined dissolved organic carbon (DOC) and particulate organic carbon (POC) in the leachates than PoAP, and made the hydrophobic sand completely wettable. Alternatively, NIS showed similar effects compared with the control. Although PoAP reduced SWR to a minimum level, it was sorbed strongly to the sand, which resulted in 27% greater solid phase organic carbon (SOC) in treated sand, compared with the untreated control. However, the exact mechanisms underlying surfactant effects on DOC and POC are unclear and the long‐term effects of surfactants following repeated application in the field are yet to be determined.

Modeling Escherichia coli and Rhodococcus erythropolis transport through wettable and water repellent porous media.

Water protection and bioremediation strategies in the vadose zone require understanding the factors controlling bacterial transport for different hydraulic conditions. Breakthrough experiments were made in two different flow conditions: i) an initial bacteria pulse under ponded infiltration into dry sand (-15,000 cm); ii) a second bacteria pulse into the same columns during subsequent infiltration in constant water content and steady-state flow. Escherichia coli (E. coli) and Rhodococcus erythropolis (R. erythropolis) were used to represent hydrophilic and hydrophobic bacteria, respectively. Equilibrium and attachment/detachment models were tested to fit bromide (Br-) and bacteria transport data using HYDRUS-1D. Derjaguin-Landau-Verwey-Overbeek (DLVO) and extended DVLO (XDLVO) interaction energy profiles were calculated to predict bacteria sorption at particles. Adsorption of bacteria at air-water interfaces was estimated by a hydrophobic force approach. Results suggested greater retention of bacteria in water repellent sand compared with wettable sand. Inverse parameter optimization suggested that physico-chemical attachment of both E. coli and R. erythropolis was thousands of times lower in wettable than repellant sand and straining was 10-fold lower in E. coli for wettable vs repellant sand compared to the exact opposite by orders of magnitude with R. erythropolis. HYDRUS did not provide a clear priority of importance of solid-water or air-water interfaces in bacteria retention. Optimized model parameters did not show a clear relation to the (X)DLVO adsorption energies. This illustrated the ambivalence of (X)DLVO to predict bacterial attachment at solid soil particles of different wetting properties. Simultaneous analysis of mass recovery, numerical modeling, and interaction energy profiles thus suggested irreversible straining due to bacteria sizing as dominant compared to attachment to liquid-solid or liquid-air interfaces. Further studies are needed to distinguish straining mechanisms (i.e. pore structure or film straining) in different hydraulic conditions.

Flume tests in wettable and water repellent sands: insights into the initiation of wildfire-related debris flows

Flume tests in wettable and water repellent sands: insights into the initiation of wildfire-related debris flows

Processes in model slopes made of mixtures of wettable and water repellent sand: Implications for the initiation of debris flows in dry slopes

Debris flows in slopes initially dry, such as post-wildfire debris flows, are initiated by surface runoff and sediment bulking due to reduced infiltration. Soil water repellency, extreme dry soils, and loose, cohesionless materials influence their initiation. The exact link between these features, the resulting infiltration processes and the initiation mechanism of a debris flow remains unclear. Here, we examine the relation between soil particle wettability and slope processes in physical models. Flume experiments were conducted in 10% increments of mass ratios of wettable to water repellent sand, subjected to artificial rainfall with monitoring of soil water content, pore water pressure, sediment and water discharge and failure mode. To date, wettability was considered only for the water repellent end, because it reduces infiltration, enhancing surface runoff. This study demonstrates that slight wettability changes, in the full wettable to water repellent range, impact a variety of slope processes. The two extremes, fully wettable and water repellent gave opposite responses, retrogressive slides for infiltration-initiated in wettable sand and erosion by surface runoff in water repellent sand. The transition was dominated by surface runoff and preferential flow, yielding a combination of erosion and slides. From the tests, a continuous capping effect generated by water repellency was a necessary condition for erosion and sand bulking i.e., the generation of runoff-initiated debris flows. The sensitivity of the model slope response to artificial rainfall was particularly acute at high ratios of wettable to water repellent sand. For mixtures above a critical ratio of wettable to water repellent sand, the measurements with an index test revealed a fully wettable material despite differences in the infiltration, saturation and pore water pressure built-up trends. Implications for post-wildfire debris flows and debris flows in slopes initially dry in general are discussed.

Experimental Investigation of Evaporation and Drainage in Wettable and Water-Repellent Sands

This study presents experimental results on evaporation and drainage in both wettable and water-repellent sands whose surface wettability was artificially modified by silanization. The 2D optical and 3D X-ray computed tomographic imaging was performed during evaporation and the water retention during cyclic drainage and infiltration was measured to assess effects of wettability and initial wetting conditions. The evaporation gradually induces its front at the early stage advance regardless of the wettability and sand types, while its rate becomes higher in water-repellent Ottawa sand than the wettable one. Jumunjin sand which has a smaller particle size and irregular particle shape than Ottawa sand exhibits a similar evaporation rate independent of wettability. Water-repellent sand can facilitate the evaporation when both wettable and water-repellent sands are naturally in contact with each other. The 3D X-ray imaging reveals that the hydraulically connected water films in wettable sands facilitate the propagation of the evaporation front into the soil such that the drying front deeply advances into the soil. For cyclic drainage-infiltration testing, the evolution of water retention is similar in both wettable and water-repellent sands when both are initially wet. However, when conditions are initially dry, water-repellent sands exhibit low residual saturation values. The experimental observations made from this study propose that the surface wettability may not be a sole factor while the degree of water-repellency, type of sands, and initial wetting condition are predominant when assessing evaporation and drainage behaviors.

Wetting Agent Influence on Water Infiltration into Hydrophobic Sand: II. Physical Properties

Wetting agents are commonly used to remedy localized dry spot (LDS) caused by soil water repellency on golf course putting greens. Information gleaned from field experiments assessing wetting agent effects on infiltration can be difficult to interpret due to temporal and spatial variations. To avoid this challenge, a laboratory study was conducted to evaluate the influence of six commercial wetting agents at four concentrations (500, 1000, 3000, and 5000 mg L−1) on surfactant physical properties and to establish relationships between physical properties and water infiltration into a water‐repellent U.S. Golf Association (USGA)‐grade sand. As wetting agent concentration increased, notable decreases in surface tension (γ), liquid‐solid contact angle (θ), and liquid entry pressure head (hp) were measured. These decreases were negatively correlated with the hydraulic conductivity (K) of water‐repellent sands treated with wetting agents. Improved infiltration as a function of wetting agent concentration was explained by reduced hydrophobicity following wetting agent application. Cascade Plus and LescoFlo Ultra at concentrations of ≥3000 and 1000 mg L−1, respectively, transformed the water‐repellent sand to a wettable media, as evidenced by negative hp values. A multiple regression model (R2 = 0.82) found that K of wetting agent treated soil can be explicated by variables γ, hp, and wetting agent concentration. Our results showed that all tested wetting agents improved water infiltration, but the effectiveness was compound dependent. Therefore, it is essential to select appropriate wetting agents and application rates when seeking to improve water infiltration into hydrophobic sands.

Hydraulic Modeling and in situ Electrical Resistivity Tomography to Analyze Ponded Infiltration into a Water Repellent Sand

Water repellency (WR) might affect the spatial and temporal dynamics of a wetting front during infiltration and redistribution in a way that is difficult to predict with standard approaches. Therefore, the objectives of this study were to simulate the wetting plume geometry with a three‐dimensional numerical model and to test whether electrical resistivity tomography (ERT) is able to illustrate the geometry under highly dynamic conditions. At our study site under agricultural use (Gleyic Podzol, groundwater affected), persistent WR in the subsoil to the 120‐cm depth was responsible for a conical plume geometry observed after ponded tracer application with Brilliant Blue (BB) and bromide. The process was invasively observed with hydraulic sensors. At the same time, ERT was used to monitor a second ponded infiltration event under equal boundary conditions at the same site. Numerical simulation of the process showed that hysteresis in the water retention curve is needed to describe the specific infiltration plume geometry correctly. The main wetting function was derived from scaling the main drying curve with measured contact angle data. A comparison of wetting front arrival times among the hydraulic model, sensors, and independent ERT observations indicates an overall good agreement and shows the usefulness of ERT measurements under highly dynamic in situ conditions. Our results confirm the need to include strong hysteresis effects scaled with independent contact angle data when simulating infiltration dynamics in a water repellent soil to avoid an underestimation of the wetting front arrival.

Pore scale consideration in unstable gravity driven finger flow

To explain the dynamic behavior of the matric potential at the wetting front of gravity driven fingers, we take into account the pressure across the interface that is not continuous and depends on the radius of the meniscus, which is a function of pore size and the dynamic contact angle θd. θd depends on a number of factors including velocity of the water and can be found by the Hoffman‐Jiang equation that was modified for gravity effects. By assuming that water at the wetting front imbibes one pore at a time, realistic velocities are obtained that can explain the capillary pressures observed in unstable flow experiments in wettable and water repellent sands.

Ameliorating water repellency under turfgrass of contrasting soil organic matter content: Effect of wetting agent formulation and application frequency

Abstract Water conservation strategies are being developed in regions of the world expected to experience decreases in water resources due to changing climates. Strategies advocated for improving water-use efficiency may increase the incidence of soil water repellency in sandy-textured soils. We evaluated the effect of soil wetting agent formulation, and application frequency, on water repellency in sandy soil with two contrasting organic matter (OM) contents under kikuyugrass [Pennisetum clandestinum (Holst. Ex Chiov)], and irrigated at 60% replacement of net evaporation in a climate subject to hot, dry summers. The randomized plot design included two turfgrass ages [established from 20 week (7.7% OM) or 20 year old (30% OM) turfgrass in 2005, the latter included a 50 mm ‘mat’ layer], two soil wetting agent formulations (granular or liquid); two application frequencies (one or two applications per irrigation season); and plots of both turfgrass ages that did not receive any wetting agent (nil control). Both wetting agent formulations contained the same active ingredient (propylene oxide–ethylene oxide block polymer), and all wetting agent treatments received the same rate (69 L active ingredient ha−1). Water repellency in the surface soil (0–5 mm), measured using the molarity of ethanol droplet test (MED), ranged from 1.09 M to 4.32 M during the irrigation season, and was more severe in the soil with high OM (average MED, 3.3 M) than low OM content (average MED, 2.7 M). Applying one application of either granular or liquid soil wetting agent at the commencement of the irrigation season decreased the severity of soil water repellency by up to 30% in the high OM soil and by up to 60% in the low OM soil during the summer, and without the need for a second application. The decline in soil water repellency in response to soil wetting agent application was not matched by an increase in soil VWC in summer, and turfgrass quality was considered acceptable throughout the study. The soil wetting agents were less effective at treating water repellent sand containing a significant amount of OM than sand with low OM content.

Surfactants Increase Uniformity of Soil Water Content and Reduce Water Repellency on Sand-Based Golf Putting Greens

Abstract Water repellency and related localized dry spots are common problems on sand-based root zones often used for golf putting greens. The objective of this study was to quantify the effect of three commonly used surfactants applied to a sand-based root zone on turfgrass visual quality and drought symptoms, soil water content and uniformity, and soil water repellency. In 2007 and 2008, a study was conducted in Wisconsin on a creeping bentgrass golf putting green with a water-repellent sand soil. Prolonged periods of drought occurred in both years. Treatments included three surfactants and two controls, one irrigated at 30% of potential evapotranspiration (ETp) and a second irrigated at 100% of ETp. The surfactant treatments were irrigated at 30% of ETp. Soil moisture was measured weekly in each plot on a 5 × 5 30-cm grid pattern, along with visual estimates of area exhibiting drought symptoms and turfgrass visual quality. Soil water repellency was measured before and at the conclusion of each growing season. In 2007, the surfactant treatments maintained visual quality lower than the well-irrigated control treatment but greater than the reduced-irrigation control treatment. In 2008, substantial drought symptoms appeared on all surfactant treatments, which recovered faster than the reduced-irrigation control treatment. Soil water contents of surfactant treatments were similar to each other and the reduced-irrigation control on most testing dates. During periods of drought, surfactant-treated soils had the greatest uniformity of moisture content and lowest water repellency at the end of each growing season. These results indicate that use of these surfactants can reduce water use while improving visual quality compared with untreated areas, prevent localized dry-spot development, and increase moisture uniformity in sand-based golf putting green root zones.

Claying and deep ripping can increase crop yields and profits on water repellent sands with marginal fertility in southern Western Australia

Sandplain soils on the south coast of Western Australia have multiple limitations to crop production that include water repellence, low water and nutrient retention, subsoil acidity, and high soil strength. Crops on sandplain soils achieve, on average, almost 85% of their rainfall-limited yield potential; however, where there are multiple limitations the corresponding value is often <50% in any given year. Previous research has shown the value of applying clay-rich subsoil (‘claying’) to ameliorate water repellent soils and improve nutrient retention. Other studies have shown that deep ripping is effective in reducing compaction in sandplain soils. This paper quantifies the effects of 5 subsoil clay rates (0, 50, 100, 200, and 300 t/ha), with and without deep ripping to 0.5m, on soil properties, crop growth, and profitability in a replicated field experiment. Crop yields were increased by 0.3–0.6 t/ha as result of added clay. The clay content of the surface soil required to alleviate water repellence and achieve the highest yield increases was 3–6% in soils with ~1% organic carbon. Longer term effects of claying included increased soil organic carbon by 0.2%, pH by 0.6 units, potassium by 47 mg/kg, soil strength by 250 kPa, and cation exchange capacity by 1.3 cmolc/kg to a depth of 0.1 m. However, changes in plant-available water (mm/m) were inconsistent between the clay treatments. Deep ripping to 0.5 m increased crop yields by 0.1–0.5 t/ha. These crop yield responses were still evident 3 years after the ripping treatment had been applied. Soil strength measurements indicate that re-compaction of the ripped treatments had occurred to a depth of 0.2 m in the second year following ripping. Crop responses to claying and deep ripping were additive. Claying and deep ripping, while almost doubling yields, achieved only 50–70% of the rainfall-limited yield potential on these marginally fertile soils. The highest clay rates (>3–6%) had cumulative discounted cash returns $AU100–200/ha higher than the unclayed ‘control’ treatment and $300/ha higher than the lowest clay rates. For most of the clay treatments, deep ripping increased discounted returns between 2005 and 2007 by $80–120/ha.

Using spectral reflectance to document water stress in bermudagrass grown on water repellent sandy soils

AbstractTo conserve natural water resources, athletic fields may be mandated to follow phase water restrictions. In order to optimize irrigation reduction, early plant responses to water stress need to be identified to avoid loss in turfgrass performance and the requirement of additional irrigation to overcome water stress. Current irrigation scheduling based on using potential evapotranspiration (ET) and water stress indices are not suitable for all growing conditions, especially in the water repellent sand soils of South Florida. This experiment was conducted to use spectral reflectance as a means to document normal and progressive water stress in ‘Tifgreen’ bermudagrass (Cynodon dactylon (L.) Pers. X Cynodon transvaalensis Burtt Davy) grown on a native water repellent sand soil. Three consecutive trials were conducted, in which bermudagrass was subjected to either no irrigation until severe visual wilt (non‐irrigated) or irrigated daily (irrigated) over a dry down period. Visual assessment of turf quality and localized dry spot occurrence verified that bermudagrass receiving daily irrigation was not water‐limited and bermudagrass receiving no irrigation was experiencing increased water stress over time. An experimentally active near‐IR/red sensor was used to monitor changes in plant architecture as a means to determine early water stress. Monitoring near‐IR/red ratios determined mid‐day depression when water demand is at the highest as well as overnight rehydration in both bermudagrasses. At the end of the dry down period, pooled trial morning near‐IR/red ratios‐afternoon near‐IR/red ratios from non‐irrigated bermudagrass was significantly greater than irrigated bermudagrass (P = 0·0035), documenting severe water stress from the non‐irrigated bermudagrass. Spectral reflectance allows real‐time, site‐specific bermudagrass water stress evaluation before it is visually identifiable. Using spectral reflectance as an early warning detection tool can be used for better irrigation decisions including pre‐emptive irrigation to avoid water stress, compared to models based on predetermined ET and water stress indices. Copyright © 2007 John Wiley & Sons, Ltd.

Delving of sandy surfaced soils reduces frost damage in wheat crops

Delving is a farming practice involving the mixing of a deep clayey subsoil layer with a sandy topsoil. One of the many effects of this practice is to reduce soil albedo and increase water-holding capacity of the topsoil, thus increasing the potential for storage and release of heat and potential attenuation of the effects of radiative frost. At Keith, a frost-prone location of South Australia, we investigated the effect of management practices with putative capacity to reduce frost damage, with emphasis on delving. Three field experiments were established on Brown Sodosols with a water-repellent sand topsoil. In relation to crops in untreated control soil, delving increased wheat yield from 1.9 to 3.1 t/ha in 2003, and from 0.5 to 1.5 t/ha in 2004. This large delving effect contrasted with the minor effects of other treatments including soil rolling, sowing rate, row spacing, and cultivar mixture. Lack of significant interactions between treatments indicated a robust response to delving across a range of management practices. Topsoil and canopy-height minimum temperatures were consistently higher in the delved treatment. The average difference in canopy-height minimum temperature between delved and control treatments was 0.3–0.4°C, with a maximum of 1.6°C in 2003 and 1.2°C in 2004. A single, robust relationship between yield and frost damage fitted the data pooled across treatments and seasons. This, together with the temperature differential between treatments, and significant relationships between minimum canopy-height temperature around flowering and frost damage supported the conclusion that a substantial part of the yield gain attributable to delving was related to reduced frost damage.

Transport and Retention Mechanisms of Colloids in Partially Saturated Porous Media

The transport, retention, and release of hydrophobic and hydrophilic polystyrene latex microsphere colloids were examined in 0.5-cm-thick, 26-cm-long slab chambers filled with either regular (hydrophilic) or weakly water-repellent sand. The water-repellent sand consisted of a mixture of 0.4% strongly water-repellent grains with unmodified regular sand for the remainder. The concentration of colloids in the outflow water was measured at the same time as the pore-scale distribution of colloids was recorded in still and video images. Although the type of sand affected the flow pattern in the top of the chamber, it did not affect the breakthrough for the same type of colloids. More hydrophilic colloids were eluted in the drainage water than hydrophobic colloids. Images showed that there was a greater retention of the hydrophobic colloids due to strongly attractive hydrophobic interaction forces between colloids and subsequent filtering of colloidal aggregates in the narrow passages between grains. Once filtered, these aggregates then served as preferred sites for attachment of other hydrophobic colloids. The hydrophilic colloids were retained primarily in a thin film of water at the edge of the menisci, the air–water–solid (AWS) interface. Centrifugal motion within the pendular rings observed in the videos contributed to movement of the colloids toward the AWS interface, where colloids were retained due to both low laminar flow velocities near the grain surface and straining in the thin water film at the edge of the meniscus. Except near the solid interface, sorption at the air–water (AW) interface was not observed and appeared unimportant to the retention of colloids. The findings form an essential link between colloid retention and transport processes at the interfacial, pore, and Darcy scales.

Analysis of the endophytic actinobacterial population in the roots of wheat (Triticum aestivum L.) by terminal restriction fragment length polymorphism and sequencing of 16S rRNA clones.

The endophytic actinobacterial population in the roots of wheat grown in three different soils obtained from the southeast part of South Australia was investigated by terminal restriction fragment length polymorphism (T-RFLP) analysis of the amplified 16S rRNA genes. A new, validated approach was applied to the T-RFLP analysis in order to estimate, to the genus level, the actinobacterial population that was identified. Actinobacterium-biased primers were used together with three restriction enzymes to obtain terminal restriction fragments (TRFs). The TRFs were matched to bacterial genera by the T-RFLP Analysis Program, and the data were analyzed to validate and semiquantify the genera present within the plant roots. The highest diversity and level of endophytic colonization were found in the roots of wheat grown in a dark loam from Swedes Flat, and the lowest were found in water-repellent sand from Western Flat. This molecular approach detected a greater diversity of actinobacteria than did previous culture-dependent methods, with the predominant genera being Mycobacterium (21.02%) in Swedes Flat, Streptomyces (14.35%) in Red Loam, and Kitasatospora (15.02%) in Western Flat. This study indicates that the soil that supported a higher number of indigenous organisms resulted in wheat roots with higher actinobacterial diversity and levels of colonization within the plant tissue. Sequencing of 16S rRNA clones, obtained using the same actinobacterium-biased PCR primers that were used in the T-RFLP analysis, confirmed the presence of the actinobacterial diversity and identified a number of Mycobacterium and Streptomyces species.

Characteristics of Sludges Produced by Destabilization of CCA Preservative Solutions

Summary Chromated copper arsenate (CCA) working solution is partially destabilized over time as a result of hexavalent chromium (CrVI) reduction by wood extractives and reactive additives such as water repellents and polyethylene glycol (PEG) wood softening agents. Hot water extracts of several softwood and hardwood species were used to prepare 2% CCA type C solutions. The softwoods included sapwood and heartwood of red pine (Pinus resinosa Ait.), jack pine (Pinus banksiana Lamb.), black spruce (Picea mariana Mill.), balsam fir (Abies balsamea (L.) Mill.) and sapwood of southern yellow pine (Pinus spp.). Hard wood samples were mixed sapwood and heartwood of red maple (Acer rubrum L.), basswood (Tilia americana L.), yellow poplar (Liriodendron tulipifera L.) and red oak (Quercus rubra L.). In a similar way, 2% CCA solutions were prepared containing 4% PEG and 1% paraffin wax formulated water repellent. The pH and hexavalent chromium content of the CCA solutions were monitored over time until sludge formation was observed. The obtained sludges were separated and analyzed by Fourier Transform Infrared Spectroscopy (FT-IR) in the mid-infrared range and by atomic absorption spectroscopy (AAS) for chromium, copper and arsenic contents. The results of FT-IR and AAS analyses of the sludges indicate that the products of sludging are of comparable chemical nature regardless of the agent responsible for the destabilization of CCA solutions. Arsenic and chromium are the major and copper the minor constituent of the sludges produced by destabilization of CCA solutions examined here.

New Colloid Silicate Solutions for Restoration and Conservation of Stone Facades

The kinetics of water absorption by samples taken from facades of buildings (marbled footinglimestone, bricks, plaster), both in initial state, those treated with solutions of classical water repellentsand new hydrophilic and hydrophobic colloid silicates, was studied, and the state of the initial materialwas assessed. Recommendations on how to stabilize stone and protect it from the destructive influence of the humid atmosphere are given.