Soil In Close Proximity Research Articles

Dynamic soil hydraulic resistance regulates stomata.

The onset of stomatal closure reduces transpiration during drought. In seed plants, drought causes declines in plant water status which increases leaf endogenous abscisic acid (ABA) levels required for stomatal closure. There are multiple possible points of increased belowground resistance in the soil-plant atmospheric continuum that could decrease leaf water potential enough to trigger ABA production and the subsequent decreases in transpiration. We investigate the dynamic patterns of leaf ABA levels, plant hydraulic conductance and the point of failure in the soil-plant conductance in the highly embolism-resistant species Callitris tuberculata using continuous dendrometer measurements of leaf water potential during drought. We show that decreases in transpiration and ABA biosynthesis begin before any permanent decreases in predawn water potential, collapse in soil-plant hydraulic pathway and xylem embolism spread. We find that a dynamic but recoverable increases in hydraulic resistance in the soil in close proximity to the roots is the most likely driver of declines in midday leaf water potential needed for ABA biosynthesis and the onset of decreases in transpiration.

Scleromatobacter humisilvae gen. nov., sp. nov., a novel bacterium isolated from oak forest soil.

A novel bacterial strain, designated BS-T2-15T, isolated from forest soil in close proximity to decaying oak wood, was characterized using a polyphasic taxonomic approach. Phylogenetic analyses based on 16S rRNA gene sequences as well as phylogenomic analyses based on coding sequences of 340 concatenated core proteins indicated that strain BS-T2-15T forms a distinct and robust lineage in the Rubrivivax-Roseateles -Leptothrix-Azohydromonas -Aquincola-Ideonella branch of the order Burkholderiales. The amino acid identity and the percentage of conserved proteins between the genome of strain BS-T2-15T and genomes of closely related type strains ranged from 64.27 to 66.57% and from 40.89 to 49.27 %, respectively, providing genomic evidence that strain BS-T2-15T represents a new genus. Its cells are Gram-stain-negative, aerobic, motile by a polar flagellum, rod-shaped and form incrusted white to ivory colonies. Optimal growth is observed at 20-22 °C, pH 6 and 0% NaCl. The predominant fatty acids of strain BS-T2-15T are C16 : 1 ω7c, C16 : 0 and C14 : 0 2-OH. Its polar lipid profile consists of a mixture of phosphatidylethanolamine, diphosphatidylglycerol and phosphatidylglycerol and its main respiratory quinone is ubiquinone 8. The estimated size of its genome is 6.28 Mb with a DNA G+C content of 69.56 mol%. Therefore, on the basis of phenotypic and genotypic properties, the new strain BS-T2-15T represents a novel genus and species for which the name Scleromatobacter humisilvae gen. nov., sp. nov., is proposed. The type strain is BS-T2-15T (DSM 113115T=UBOCC-M-3373T).

Vibration transfer from slab tracks on piled foundations

Railway tracks on soft soil are often supported by a piled foundation to increase track stiffness and reduce track deformation and settlement. In this paper, we consider the case of a slab track on a piled foundation and a floating slab track on a piled foundation, and compare their vibration transfer to the free field with the case of a slab track and a floating slab track. The case of a floating slab track on a piled foundation is inspired by the design of a new light railway line on very soft soil in close proximity of research labs with vibration sensitive equipment. We predict the track-soil mobility using state-of-the-art two-and-a-half-dimensional (2.5D) and periodic finite element models with perfectly matched layers, taking dynamic track-soil interaction into account. A comparison of the four track structures shows that the track-soil mobility is highest for the slab track in most of the frequency range between 1 and 80Hz. For the floating slab track, the vibration transfer is reduced by 10 to 15dB between 50 and 80Hz due to the insertion of a flexible material below the slab. Around the slab resonance frequency (20Hz), the free field response is 1 to 3dB higher compared to the slab track. For the slab track on a piled foundation, the track-soil mobility is approximately 10dB lower at frequencies below 10Hz compared to the slab track due to the higher static stiffness of the track, and close to 8dB lower at higher frequencies. The reduction at low frequencies is mainly due to the piles beneath the track, while their contribution to vibration reduction at high frequencies is rather limited. By combining a floating slab track with a piled foundation, an additional reduction of approximately 12dB compared to the slab track on a piled foundation is achieved. Hence, the total vibration reduction compared to the slab track is close to 20dB. However, the free field mobility at low frequencies increases for the floating slab track on a piled foundation compared to the slab track on a piled foundation.

A decharming metamorphosis: The larval and adult morphology of the common spadefoot toad, Pelobates fuscus

Anurans are a highly diverse amphibian order with a biphasic lifestyle. The larva, better known as tadpole, and the adult frog of one species typically occupy different habitats and exploit different resources. Therefore, both are subject of largely independent selection and are able to evolve stage-specific adaptations. Among others, the musculoskeletal features of the larval and adult head of anurans and the description of their specific traits are important to gain a deeper understanding of the evolution and the phylogeny of this highly diverse group. Here we present an overview of the larval and adult cranial morphology of the common spadefoot toad Pelobates fuscus. We provide a detailed description of the cranial musculoskeletal structures based on micro-computed tomography and following 3D reconstruction of two long-term stored specimens of P. fuscus and refer to striking adaptations of this species. P. fuscus inhabits a wide spectrum of habitats including mixed forests, steppes, fields and sandy areas with soft soils in close proximity to permanent water bodies. Adults have a semi-fossorial lifestyle and they are able to dig themselves in using their hindlimbs whereas the tadpoles are the largest of all European anurans. Derived larval features are the presence of an adrostral cartilage within the lower jaw, the presence of three portions of the M. subarcualis rectus I, the presence of the M. diaphragmatopraecordialis and a bipartite suprarostral cartilage. The presence of an enlarged prehallux and the co-ossification of the frontoparietal, as well as a pterygoid that borders the orbit ventrally and rostrally are striking adult features and adaptation to the semi-fossorial lifestyle. With the described morphological features, we want to underline their importance for several adaptations which may have facilitated and stimulated the evolution of anurans and provide baseline data for further investigations.

Distribution and extent of heavy metal(loid) contamination in agricultural soils as affected by industrial activity

In Korea, rapid industrialization has often caused severe soil and water pollution near industrial complexes. Particularly, heavy metal(loid) contamination of agricultural lands could induce serious long-term problems for crop safety and productivity, requiring continual safety assessment. This study investigated heavy metal(loid) contamination of agricultural lands near fifteen industrial complexes. At each of industrial sites in Gyeongsangbuk-do, topsoils and subsoils were collected at two different distances from each site (0–500 m and 500–1000 m). For comparison, at each site, non-polluted soils were also collected more than 1000 m away from each industrial complex. With the exception of one sample, heavy metal(loid) concentration of all soils were lower than the Korean guidelines for soil contamination. However, the difference between the heavy metal(loid) concentrations of Cu, Pb and Zn in topsoil and subsoil increased the closer the samples were the industrial complexes, which implied that these elements were being generated by industrial activities and were freshly loaded on to near surface soils. While the heavy metal(loid) concentration in the studied sites did not exceed the Korean guideline, the geoaccumulation index of each soil indicated that the degree of Cd, Cu, and Pb contamination was heavily or extremely serious in more than twenty of the examined soils. The elevation of specific metals associated with industrial activity in soils in close proximity to industrial sites is of some concern and should be taken into consideration for the future management of agricultural soils around such complexes as well as the industrial complex operation itself.

Characterization and microbial mitigation of fugitive methane emissions from oil and gas wells: Example from Indiana, USA

Hydrocarbon gas emissions from active, inactive, and improperly sealed or abandoned oil/gas wells significantly contribute to anthropogenically emitted greenhouse gases, predominantly in the form of methane (CH4). We explored the extent of hydrocarbon gas emissions from 20 active, inactive, plugged and abandoned oil/gas wells in Indiana (USA), where it is estimated that there are more than 80,000 well sites throughout the state. After this initial survey, using a static flux tent, we quantified fugitive CH4 emissions from an active gas well to approximately 2 L h−1. To evaluate the potential for microbial mitigation of hydrocarbon emissions to the atmosphere, we conducted laboratory microcosm experiments to quantify the CH4 oxidizing potential of soils collected from sites with varying distances to the leaking gas well. Soils in close proximity to the well (0.5 m) efficiently consumed nearly all (97%) of the added CH4, while only 14% of added CH4 was consumed by soils that were more distant from the well (20 m). These results suggest that fugitive CH4 emissions enrich methanotrophic bacteria in soils immediately adjacent to the well. Consistent with this view, we found that prolonged exposure of soils to elevated concentrations of CH4 enhanced the methanotrophic activity. Together, these findings prompted us to design a “methanotrophic soil mound” to assess the feasibility of mitigating point sources of CH4 by harnessing the natural methanotrophic capacity of soil microbial communities. We found that a methanotrophic soil mound from a landfill could sustainably mitigate the CH4 emission from the artificial source, providing a promising low-cost solution to ameliorate fugitive CH4 emissions from abandoned oil and gas wells to the atmosphere. The effectiveness of microbe-based remediation is limited in cold climates and arid environments.

Impact Assessment of Gas Flaring on Soil Bacterial Community Structure and Physicochemical Property in Nigeria

Gas flaring is the wasteful emission of hydrocarbon gases into the atmosphere; it is routinely used to dispose flammable gas that either is assumed unusable or uneconomical to recover. The burning of the wasteful gas has been shown to have significant environmental consequences. Therefore, this study was designed to determine the impact of gas flaring on soil bacterial spectrum and its physicochemical property. Soil microbiological quality was investigated using culture techniques while physicochemical property of the soil was analyzed using standard analytical procedures. Results obtained showed that pH and Av. phosphorus decreased from 5.80 and 8.86mg/kg in control soil to 5.40 and 6.50mg/kg in flared soil respectively. Electrical conductivity and total organic carbon increased from 100μS/cm and 0.20% in control soil to 160μS/cm and 0.63% in flared soil respectively. Total nitrogen slightly increased from 0.01% in control soil to 0.02% in flared soil. Soil textural class was sandy-clay-loam for both control and flared soils. Mean counts of bacteria increased from 4x10 3 cfu/g in SD50m to 2.0x10 4 cfu/g in SD100m, 3.1x10 4 cfu/g in SD200m, 4.5x10 4 in SD300m to 4.8x10 5 cfu/g in control soil. All the bacterial species were isolated from control and SD300m soils except Acinetobacter and Microbacteriun species which did not occur in SD300m soil. Six (6) organisms: Bacillus, Corynebacterium , Pseudomonas , Paenibacillus, Pusillimonas and Salinicoccus species were isolated from SD50m soil. The number of bacterial genera isolated increased to eleven (11) in SD100m soil with Cronobacter , Enterobacter , Escherichia coli , Kluyvera , and Microbacterium species added to those of SD50m soil. Fifteen (15) organisms occurred in SD200m soil as Acinetobacter , Arthrobacter , Brevibacterium , Klebsiella , Rathayibacter and Staphylococcus species were added. This study revealed that gas flaring decreased bacterial population in soil in close proximity to the flare point; the effect being reduced as the sampling distance from the flare point increased. Some physicochemical parameters decreased in flared soils and others increased when compared with control soils. Gas flaring selectively inhibited soil bacteria with more species occurring in soils farther away from the flare and soil closest to the flare point having less numbers of bacteria. In conclusion, gas flaring had negative impact on soil bacteria and varied effect on physicochemical properties of the soil; in this way soil fertility could have been hampered. Oil and gas companies as well as government agency need to adopt measures that would curb unnecessary gas flaring in Nigeria by putting the flared gas into economic use.

The toxicity of the methylimidazolium ionic liquids, with a focus on M8OI and hepatic effects

Ionic liquids are a diverse range of charged chemicals with low volatility and often liquids at ambient temperatures. This characteristic has in part lead to them being considered environmentally-friendly replacements for existing volatile solvents. However, methylimidazolium ionic liquids are slow to break down in the environment and a recent study at Newcastle detected 1 octyl 3 methylimidazolium (M8OI) – an 8 carbon variant methylimidazolium ionic liquid - in soils in close proximity to a landfill site. The current M8OI toxicity database in cultured mammalian cells, in experimental animal studies and in model indicators of environmental impact are reviewed. Selected analytical data from the Newcastle study suggest the soils in close proximity to the landfill site, an urban soil lacking overt contamination, had variable levels of M8OI. The potential for M8OI - or a structurally related ionic liquid – to trigger primary biliary cholangitis (PBC), an autoimmune liver disease thought to be triggered by an unknown agent(s) in the environment, is reviewed.

A new species of Scolecoseps (Reptilia: Scincidae) from coastal north-eastern Mozambique

ABSTRACTSeven specimens of Scolecoseps Loveridge, 1920 from the vicinity of Palma on the north coast of Mozambique are compared morphologically with other known material of this genus. The new material can be distinguished morphologically from all other Scolecoseps by the presence and position of certain head scales, particularly a supraciliary and four small suboculars, a small mental and high subcaudal counts. It is described as a new species, Scolecoseps broadleyi sp. nov. The new species is found in coastal savannah habitat under leaf litter of Berlinia orientalis trees, in sandy soils in close proximity to large wetlands. Its currently known distribution is south of the range of Scolecoseps litipoensis Broadley, 1995 and north of that of Scolecoseps boulengeri Loveridge, 1920. We provide a review of the available literature for the genus Scolecoseps and highlight the necessity for additional research on these poorly known fossorial skinks.ZooBank— Scolecoseps broadleyi: urn:lsid:zoobank.org:act:C4E3723C-F982-4CFA-900B-0B23A9AD5B84

Temporal and spatial variation of polychlorinated biphenyls (PCBs) contamination in environmental compartments of highly polluted area in Central Russia

This study highlights the fact that serious contamination from polychlorinated biphenyls (PCBs) still exists in Serpukhov City (Russia). The research help to determine the temporal (16- and 24-year periods) and spatial PCBs distribution in the environmental compartments of the studied region. Samples of soil, sediments, water and plants were analysed in order to establish their contamination levels. The most recent data on the Serpukhov City's soil contamination showed that the PCBs concentrations varies from 0.0009 to 1169 mg/kg depending on the sampling point and the distance from the pollution source. The temporal trends of the contamination distribution with the soil depth showed contamination migration in the upper soil layers of the highly polluted site. The high level of water pollution (11.5 μg/L) in the proximity to the contamination source and the sediments contamination (0.098–119 mg/kg) were determined, as well as the water migration pathways of the PCBs that were prevalent in the studied region. The PCB congener group (by the level of chlorination) analysis showed that heptachlorinated biphenyls were only found in the soils in close proximity to the contamination place, while biphenyls with Cl ≤ 6 were found in the soil samples downstream of the condenser plant and with Cl ≤ 5 in the soil samples upstream of the plant. The plant uptake of PCBs, even on the extremely contaminated site, was shown. In turn, this research present new knowledge necessary for the development of a contaminated territory remediation strategy.

Landscape Scale and Microhabitat of the Endangered New Mexico Meadow Jumping Mouse in the White Mountains, Arizona

Abstract The New Mexico meadow jumping mouse Zapus hudsonius luteus was listed as endangered under the U.S. Endangered Species Act in 2014, with critical habitat designated in 2016. Despite these recent conservation actions, there is a paucity of published information regarding its habitat associations. The taxon is a riparian obligate that occurs along both low-elevation rivers and high-elevation headwater streams in several disjunct areas of the American Southwest. Habitat information from one region might not apply to others. The distribution and habitat preferences of the New Mexico meadow jumping mouse in the White Mountains in eastern Arizona are poorly known. Objectives of this study were to 1) identify and resurvey historical locations in the White Mountains, 2) survey for new populations in areas with potentially suitable habitat in the White Mountains, and 3) use quantitative data to evaluate habitat associations at the landscape and microhabitat scales and to compare habitat at sites where I captured or did not capture the New Mexico meadow jumping mouse. I found 123 historical records of the New Mexico meadow jumping mouse from 21 locations in the White Mountains, indicating a formerly broad distribution. I conducted field surveys and collected habitat data at 35 sites (14 historical, 21 new) and caught 37 (39 total captures) New Mexico meadow jumping mice at 12 sites, including 6 of 12 historical locations surveyed. The overall capture rate was 0.36%, with an average capture rate at sites where it was present of 1.28% (range = 0.25–2.5%). All historical sites where I caught the New Mexico meadow jumping mouse were in the drainage of the Black River. The six new sites included the first records for Nutrioso Creek and Corduroy Creek and confirmed persistence of the taxon in the East Fork Little Colorado River, San Francisco River, and Blue River watersheds. Habitat used by the New Mexico meadow jumping mouse in the White Mountains was similar to that reported for other montane populations, characterized by tall, dense herbaceous vegetation composed primarily of forbs and sedges on saturated soil in close proximity to flowing water. However, there was significantly more cover provided by alders Alnus spp. at capture sites at both the stream reach and microhabitat scales. All sites where I captured the New Mexico meadow jumping mouse had no authorized livestock grazing, and the taxon was more likely to occur at sites where there were no signs of unauthorized livestock grazing. Further, there was a significant positive relationship between alder cover and time since an area was excluded from livestock grazing. The widespread exclusion of livestock from riparian areas in the White Mountains may have contributed to the higher rate of population persistence of the New Mexico meadow jumping mice in the White Mountains compared with the Jemez and Sacramento mountains, New Mexico. Although the overall persistence rate in the White Mountains (47%) was higher than other populations, the population is at risk of further losses due to small, isolated occupied areas and ongoing threats.

Heavy metal and metalloid mobilisation and rates of contamination of water, soil and bottom sediments in the Chiprovtsi mining district, Northwestern Bulgaria

Geochemical studies of seasonally collected mine, stream and drinking waters, bottom sediments (mine and stream) and soil samples from all mining sections were carried out in order to assess the rates of pollution in the immediate proximity to underground mining facilities and related waste rock dumps. The determined concentrations of studied elements in water (As, Pb, Cu, Zn and Sb) show spatial distribution corresponding to ore mineralisation in different sections. Arsenic concentrations show gradual decrease in west-east direction, whereas Pb concentrations peak in the central and eastern sections. Arsenic and, to a lesser extent, Pb proved to be major pollutants in mine and surface waters, as well as in bottom sediments and soils. Detailed geochemical study of soils revealed strong spatial relation with host rocks and ore mineralogy. Comparisons with state guidelines for harmful elements revealed that alluvial and meadow soils in close proximity to waste dumps contain As, Pb, Cu, Zn and Cd above maximum permissible levels. It was also found that, compared to other Bulgarian and world alluvial (fluvisol) soils and the upper continental crust, the soils in Chiprovtsi mining district are enriched in Te, Re, W, Pd, Au, Ag, Mo, Ti, Mn, Co, Se, Sb, Bi and Cs. Since the processes of weathering and oxidation of mine waste remaining in the area continue naturally, the pollution with As and Pb will presumably carry on with decreasing effect.

Egg survival is reduced by grave-soil microbes in the carrion beetle, Nicrophorus vespilloides.

BackgroundNicrophorus vespilloides eggs are deposited into the soil in close proximity to the decomposing vertebrate carcasses that these insects use as an obligate resource to rear their offspring. Eggs in this environment potentially face significant risks from the bacteria that proliferate in the grave-soil environment following nutrient influx from the decomposing carcass. Our aims in this paper are twofold: first, to examine the fitness effects of grave-soil bacteria to eggs, and second, to quantify egg immunocompetence as a defence against these bacteria.ResultsOur results provide strong evidence that grave-soil microbes significantly reduce the survival of Nicrophorus eggs. Females provided with microbe rich carcasses to rear broods laid fewer eggs that were less likely to hatch than females given uncontaminated carcasses. Furthermore, we show that egg hatch success is significantly reduced by bacterial exposure. Using a split-brood design, which controlled for intrinsic differences in eggs produced by different females, we found that eggs washed free of surface-associated bacteria show increased survival compared to unwashed eggs. By contrast, eggs exposed to the entomopathogen Serratia marcescens show decreased survival compared to unexposed eggs. We next tested the immune competence of eggs under challenge from bacterial infection, and found that eggs lacked endogenous production of antimicrobial peptides, despite well-developed responses in larvae. Finally, we found that despite lacking immunity, N. vespilloides eggs produce an extraembryonic serosa, indicating that the serosa has lost its immune inducing capacity in this species.ConclusionsThe dependency on ephemeral resources might strongly select for fast developing animals. Our results suggest that Nicrophorus carrion beetles, and other species developing on ephemeral resources, face a fundamental trade-off between egg immunity and development time.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-014-0208-x) contains supplementary material, which is available to authorized users.

Evaluation of heavy metal and total petroleum hydrocarbon contamination of roadside surface soil

The present study was conducted along three major highways namely State Highway (SH49), National Highway (NH66 and 45A) connecting Puducherry (India) for assessing heavy metals and total petroleum hydrocarbon contamination from surface soils in close proximity at a depth of 0–15 cm into automobile repair workshops and agricultural fields located beside the highways. Contamination levels of copper, lead, zinc, manganese, cadmium and chromium were assessed in the surface sediments soil on the basis of geoaccumulation index, contamination factors and spatial variability. The results revealed that sampling sites in the proximity to automobile workshops were moderately to considerably pollution impacted as compared to soil from agricultural fields along highways suggesting a direct influence of anthropogenic activities on levels of contamination. The concentration of heavy metals in the surface soil of automobile workshops close to NH66 ranged between 143.07 and 319.28 mg kg−1 copper; 68.72–396.41 mg kg−1 lead; 162.42–284.91 mg kg−1 zinc; 212.72–401.33 mg kg−1 manganese; 0.12–15.41 mg kg−1 chromium; and 0.73–1.06 mg kg−1 cadmium in dry soil. However, in agricultural fields, the concentrations varied between 33.68 and 66.62 mg kg−1 copper; 27.22–73.66 mg kg−1 lead; 26.24–75.59 mg kg−1 zinc; 137.88–242.07 mg kg−1 manganese; 0–0.21 mg kg−1 chromium; and 1.04–1.58 mg kg−1 cadmium. Total petroleum hydrocarbon concentration near automobile workshops ranged between 90.72 and 121.79 mg kg−1 in contrast to 44.94–83.4 mg kg−1 in agricultural fields. Total petroleum hydrocarbon concentration indicated strong positive correlation with zinc (r = 0.811), copper (r = 0.761); lead (r = 0.642), Mn (r = 0.571), chromium (r = 0.530) and strong negative correlation with cadmium (r = −0.765) at 0.05 significance level. Pearson correlation indicated a strong association of total petroleum hydrocarbon with copper, lead and zinc suggesting that the metal contaminants from roadside surface soil had emanated from a common source.

Modeling Riparian Zones Utilizing DEMS and Flood Height Data

Riparian ecotones are unique, diverse networks of vegetation and soils in close proximity to streams, rivers, and lakes. Previous approaches to riparian boundary delineation utilized fixed width buffers, but using a fixed width riparian buffer only takes the watercourse into consideration; it does not consider the surrounding landscape. By hydrologically defining a riparian ecotone to occur at the 50-year flood height and incorporating digital elevation data, the spatial modeling capabilities of ArcMap ® GIS are utilized to map riparian zones accurately. This approach better characterizes the watercourse and its associated floodplain. Riparian zones delineated using 10 versus 30 meter DEMs and stream course information from the National Hydrography Dataset differ significantly. Within our study areas, 30 meter DEMs are not adequate to map elevation changes for accurate riparian area delineation. The result is a robust GIS based model in an ArcMap ® Toolbox format to delineate a variable-width riparian boundary.

Genetic diversity and salt tolerance of Sinorhizobium populations from two Tunisian soils

Leguminous plants are promising pioneer-species for colonization of marginal areas and soils undergoing desertification. They derive part of their colonization abilities from their symbiotic interaction with nitrogen-fixing bacteria known as rhizobia. In this work, we analyzed total and culturable rhizobium communities from two Tunisian soils in close proximity to each other: one non-salty and cultivated and the other uncultivated and salty. The taxonomic diversity of the Rhizobiaceae family, evaluated by terminal restriction fragment length polymorphism (T-RFLP) on total soil DNA, revealed a high diversity of ribotypes and soil-based differentiation of the communities. We then used PCR-RFLP of the intergenic space and salt tolerance to characterize the genetic and phenotypic polymorphism of 150 Sinorhizobium isolates trapped on Medicago truncatula. In the salty soil, two different species, Sinorhizobium meliloti and Sinorhizobium medicae, were trapped; by contrast, only isolates of S. meliloti were trapped from the agricultural soil. Moreover, isolates from the salty soil were more tolerant to NaCl, and strains growing up to 1 M NaCl were found. No relationships between genotypic profiles and salt tolerance phenotypes were found.

Modelling suspended sediment lead concentrations in contaminated peatland catchments using digital terrain analysis

Upland peat soils in close proximity to urban and industrial areas can be contaminated with high concentrations of atmospherically deposited lead. The peat soils of the Peak District (UK) are characterised by extensive eroding gullies. Fine-resolution digital topographic data were used to map the extent and depth of these gullies. Peat samples from eroding gully walls and suspended sediments were collected and analysed for lead content. Variability in lead concentrations of gully wall material and suspended sediments can be explained by differences in mean upslope gully depth. The lead content of suspended sediment exported from catchments characterised by shallow peat gullies is higher than that exported from catchments with deep peat gullies. The empirical relationship between sediment-associated lead concentration and mean upslope gully depth was combined with the gully depth mapping to produce a predictive spatial model of suspended sediment lead concentrations across the Peak District. This model may be particularly useful for catchment managers who are currently involved in the restoration of eroding peat soils in the Peak District uplands.

Reducing the cost of subsidence damage despite global warming

Much of the housing stock in the UK is built on shrinkable clay soils, particularly in the south‐east of the country. When the moisture content of the clay soils is reduced the clay shrinks causing downward movement. This extraction of moisture from the clay may occur in a number of ways, but the main causes are either prolonged periods of dry weather (a combination of high average temperatures and low average rainfall) or tree roots extracting the moisture from the soil in close proximity to a property. The most extreme cases occur when a combination of the two causes is evident. Over the past few years the UK has seen some of the driest periods of weather on record which has meant that clay soils have not been able to replenish their seasonal moisture loss during the winter months. This has caused an increase in the number of cracks appearing in properties and a rise in the number of subsidence claims made against insurance companies. If climatologists are right about global warming, then subsidence damage has become an endemic hazard of home ownership. Prolonged periods of dry weather will continue to cause serious and very expensive damage to the country’s housing stock. The annual subsidence bill of £300 million can only be reduced by improving education and communication within the construction industry and encouraging house owners to look after their investments more carefully. This paper attempts to identify how the cost of subsidence damage can be reduced despite the changes in climate conditions.

USE OF TENSIOMETER RESPONSE TIME TO DETERMINE THE HYDRAULIC CONDUCTIVITY OF UNSATURATED SOIL

The response time of tensiometers is controlled by the soil hydraulic conductivity when the flow resistance of the porous cup is sufficiently small. Therefore, we can determine the hydraulic conductivity of unsaturated soils from the response of a tensiometer to an artificially-induced perturbation of pressure. We evaluated a practical procedure to determine the conductivity by numerical simulations and by laboratory and field tests. The data can be analyzed by a simple graphical technique based on the linear "slug test" equation because nonlinear dependence of hydraulic conductivity on matric potential head is not significant when the head perturbation is small (<0.5 m). Using readily available equipment, a field tensiometer response test generally takes less than 1 h. Tests can be repeated over time to determine the in situ relationship between hydraulic conductivity and matric potential. The estimated conductivity is sensitive to the disturbance of the soil in close proximity to the porous cup. To improve the reliability of response tests, new methods need to be developed to install tensiometers with minimum soil disturbance. Despite the problem of soil disturbance, the tensiometer response test is an attractive method in clay-rich soils where other field methods are not easily applicable.

Effect of organic carbon on the uptake of benzene vapor by soil

Abstract Batch experiments were conducted to determine the uptake of benzene vapor by soils with difierent organic carbon content (foc), under benzene vapor concentration equal to that of vapor pressure. The time required to reach equilibrium increased with increasing foc and the sorbed equilibrium concentrations (qobs) were 0.44±0.2, 7.1±0.6, 12.3±0.8, 14.8±1.2, and 25.2±1.8 mg g‐1 for sand and soils with foc of 0.39%, 1.54%, 2.09%, and 4.15%, respectively. Vapor uptake due to mono‐layer surface coverage (qm) was less than 4% of qobs. The difference qobg‐qm normalized with respect to foc was several orders of magnitude higher than 20.2 mg g‐l reported for benzene vapor partitioning into soil humic acid, indicating that benzene uptake at saturated vapor pressure was mostly due to condensation rather than partitioning or monolayer sorption. These data would be applicable to soil in close proximity to liquid benzene, such as a spill or a leak.