Soil Core Samples Research Articles

Effects of soil and water conservation practices on soil physicochemical\xa0properties in Gumara watershed, Upper Blue Nile Basin, Ethiopia

BackgroundSoil erosion is among the foremost causes of declining soil resources in Ethiopia, which in turn affect agricultural productivity. To limit this problem, for the last two decades in Gumara watershed, soil and water conservation measures have been practiced through free labor community mass-mobilization. However, their effect on soil fertility has not been evaluated. This study investigated the impact of implemented soil and water conservation measures on fertility improvement in the Gumara watershed. Both composite and core soil samples were taken from upstream, midstream, and downstream adjacent conserved and non-conserved cultivated and grazing plots. Selected soil fertility indicators were analyzed using standard laboratory procedures.ResultsSoil and water conservation practices have resulted in a statistically significantly higher mean values of total nitrogen, exchangeable Na+ and Mg2+ at p < 0.01, and of soil organic carbon and organic matter at p < 0.05 in the watershed. The clay content, soil reaction, cation exchange capacity, and exchangeable K+ showed non-significant, but higher mean values in conserved plots. Furthermore, the effects of conservation practices on soil properties were found more effective in cultivated land uses as compared to that of grazing land uses. This is because conservation treatments had significant effects on organic carbon, total nitrogen, exchangeable Na+ and Mg2+ in cultivated land uses but only on exchangeable Na+ in grazing land uses. The interaction effect of treatments and land uses did not reach a statistically significant result for any of the soil properties considered in this study.ConclusionConservation measures have important implications for improving soil fertility in the Gumara watershed. Therefore, proper guidance and follow-up, use of agro-forestry and grass strips, and maintenance are required for the watershed’s sustainability and good soil conditions.

Association between land cover and &lt;i&gt;Culicoides&lt;/i&gt; (Diptera: Ceratopogonidae) breeding sites on four Danish cattle farms

Bitingmidges of the genus Culicoides are vectors of bluetongue virus. Their larval habitats are poorly known in Northern Europe. Three classes of the CORINE land cover index, found within 300 m of four farms in Denmark, were used to stratify sampling sites for a total of 360 soil core samples from 30 sampling points. Soil samples were set up in emergence chambers for hatching adult Culicoides. Two species of Culicoides (C. punctatus and C. pulicaris) emerged from nine of 12 soil samples froma wet, grazed field with manure. Seventy-two other samples from similar land cover on the three other farms were negative. Seven sampling points from pastures were incorrectly classified by CORINE. The remaining 23 sampling points were classified correctly. The visually observed land use was not sufficiently detailed to adequately predict Culicoides breeding sites in this study. The CORINE index failed to identify pastures in which Culicoides breeding sites were found.

In-situ multi-sensor characterization of soil cores along an erosion-deposition gradient

Soil landscape research is faced with wide-ranging questions of soil erosion, precision farming, and agricultural risk management. Digital Soil Morphometrics is a powerful tool to provide respective answers or recommendations but requires soil data from the pedon-to-field scale with high horizontal and vertical resolutions, including the subsoil. We present an efficient sampling and measurement method for easily obtainable soil driving cores with low-destructive preparation. Elemental contents and soil organic and mineral matter composition were measured rapidly and in large numbers using a multi-sensor approach, i.e., visible and near-infrared (Vis-NIR), diffuse reflectance infrared Fourier transform (DRIFT), and X-ray fluorescence (XRF) spectroscopy. The suitability of the approach with respect to three-dimensional soil landscape models was tested using soils along a slope representing different stages of erosion and deposition in a hummocky landscape under arable land use (Calcaric Regosols, Calcic Luvisols, Luvic Stagnosols, Gleyic-Colluvic Regosols). The combination of soil core sampling, pedological description, and three spectroscopic techniques enabled rapid determination and interpretation of horizontal and vertical spatial distributions of soil organic carbon (SOC), soil organic and mineral matter composition, as well as CaCO3, Fe, and Mn contents. Depth profiles for SOC, CaCO3, and Fe contents were suitable indicators for site-specific degrees of erosion and matter transport processes at the pedon-to-field scale. Fe and Mn profiles helped identifying zones of reductive and oxic domains in subsoils (gleyzation). Further methodical developments should implement plant-availability of nutrients, characterization of Fe-oxides, and calibration of the spectroscopic techniques to field-moist samples.

Conservation Agriculture Enhances Soil Fauna Richness and Abundance in Low Input Systems: Examples From Kenya

Conservation agriculture (CA) is believed to improve soil nutrient status, soil structure, control soil erosion, and also enhance soil biodiversity. Despite the widespread interest in CA, empirical evidence of the benefits of CA on soil biodiversity is limited, especially in low-input systems of sub-Saharan Africa (SSA). Consequently, the magnitude and effect by CA on soil fauna remains unquantified. The aim of this study was to evaluate the effect of CA and associated management practices on soil fauna richness and abundance. We hypothesized that CA (zero tillage + organic inputs as surface residue) and mixed cropping would positively influence soil fauna richness and abundance. We compared CA with conventional till (CT; with or without residues) in sole maize and maize-bean cropping systems. Soil macrofauna and mesofauna were sampled across the treatments in medium-term (6 yrs) trials in Embu, Central Kenya, and Kakamega (6 yrs) and a long-term trial in Nyabeda (15 yrs) using soil monoliths and core samplers, respectively. In agreement with our hypothesis, higher macrofauna taxonomic richness and mesofauna was recorded in CA than in CT without residues. This study demonstrated that: 1) medium to long-term addition of organic residues enhances soil fauna richness and abundance, 2) CA increases soil fauna taxonomic richness and abundance compared with CT, and 3) CA under maize-bean intercropping, rotation and sole maize cropping systems promote soil fauna richness and abundance compared with sole legume (common beans). We conclude that adoption of CA is important in enhancing richness of soil fauna. Given the numerous challenges faced by smallholder farmers of SSA in the adoption of CA, who in most cases rarely practice all the three CA principles simultaneously, we propose a further study that will determine the effects and interactions between each of the CA components on soil fauna richness and abundance.

Комплексные организационные и методические подходы к выводу из эксплуатации хранилищ РАО

Purpose: Development of comprehensive organizational and methodical approaches to decommissioning of shallow radwaste (RW) repositories.&#x0D; Material and methods: The following researches were conducted during assessment of radiation and hygiene situation:&#x0D; - assessing the state of physical barriers of repositories (tanks) of solid and liquid RW;&#x0D; - assessing radiation situation at the repository site before and after remediation;&#x0D; - measuring specific activity of 90Sr and 137Cs in ground and subsurface water, core sample, soils, building structures.&#x0D; Methods: on foot gamma survey; gamma-ray spectrometric measurement of radionuclides in environmental samples using a stationary spectrometer; radiochemical extraction of radionuclides and their radiometry.&#x0D; Results: The surveys were performed in 2014–2016. They delivered data on gamma dose rate at the RW repository site, specific activity of 90Sr and 137Cs in ground and subsurface water, core sample, soils, building structures.&#x0D; The surveys showed that content of 90Sr in subsurface water varied from 0.25 to 0.4 Bq/kg, while content of 137Cs was below the detection threshold (0.01 Bq per sample). It was founded that distribution of 90Sr and 137Cs in soil (core sample) forming the top layer of the area is highly uneven. In some cases specific activity of soil exceeded 1000 Bq/kg (C-23 well at the depth of 2.75 m and C-24 well at the depth of 5 m). In all other cases specific activity of the core sample did not exceed 10 Bq/kg, and specific activity of soil was up to 50 Bq/kg which is over background values. The ambient dose equivalent rate at the site varied from 0.1 to 0.3 µSv/h.&#x0D; After remediation activities content of radionuclides in soil and subsurface water was at the levels of background values.&#x0D; More than 6700 measurements were performed (more than 2400 measurements of the ambient dose equivalent rate, more than 4100 measurements of beta-contamination of work surfaces and equipment, and more than 200 measurements of specific and volumetric activity of environmental samples). &#x0D; Conclusions: This work allowed to substantiate technical solutions, procedure of RW accounting and control, using of shelters and mobile systems for radiation safety of the personnel and environmental protection.&#x0D; It was demonstrated that average external radiation doses for the workers involved in decommissioning activities did not exceed 0.7 mSv (variation from 0.16 to 1.7 mSv), while internal radiation doses varied from 0.35 to 3.3 µSv. &#x0D; Density of beta-contamination of the site did not exceed 38 beta-particles/(cm2∙min) which corresponds to background values. The ambient dose equivalent rate of the site was within 0.09-0.15 µSv/h after the work has been done.

First records of Opetiopalpus sabulosus Motschulsky, 1840 (Coleoptera, Cleridae) for the European Alps

The genusOpetiopalpusfrom the family of checkered beetles (Coleoptera: Cleridae) is represented by 28 species worldwide, with 11 species found in the Palearctic and only four sparsely in Europe prior to 1998. One species,OpetiopalpussabulosusMotschulsky, 1840, was recently found in Eastern Europe (i.e. Ukraine, Bulgaria, and Moldavia), with the most recent record in 2015 in Eastern Romania; no data are available for Central Europe. During a comprehensive sampling survey in 2016 in the dry inner-Alpine Vinschgau Valley (South Tyrol, Italy), one individual ofO.sabulosuswas recorded from soil core samples on an extensively managed steppe-like dry pasture at 2000 m a.s.l. This was the first record ofO.sabulosusfor the European Alps and Central Europe. Further intensive samplings were conducted in 2017 and 2018, in which one additional specimen at a dry pasture at 2500 m confirms the presence of this checkered beetle.Opetiopalpussabulosusseems to have a cryptic lifestyle and therefore a low detection probability. The locations from where the species was recorded, all steppe-like dry grasslands that are part of the LTSER area “Val Mazia/Matschertal” within the LTER-Italia network, are characterized by low precipitation (730 mm at 2000 m a.s.l.) and traditional low input management (grazing cattle, sheep, and horses). BesideO.sabulosus, other rare and new species for South Tyrol and Italy were found at the sampling area. Therefore, our records underline the high biodiversity and the high nature conservational value of these steppe-like dry grasslands and the importance of long-term research to monitor such species.

Vertical distribution of 129I and radiocesium in forest soil collected near the Fukushima Daiichi Nuclear Power Plant boundary

Three soil core samples were collected from a forest located about 1.1 km south of the Fukushima Daiichi Nuclear Power Plant (FDNPP) boundary in 2017, and the vertical profiles of 129I from the FDNPP accident were determined by the combination of TMAH (tetramethyl ammonium hydroxide) extraction and ICP-MS/MS analysis. The humus layer above the soil layer was heavily contaminated with 134Cs (1983–5985 Bq g−1) and 137Cs (1947–5902 Bq g−1) (decay-corrected to March 11, 2011). The 129I activity concentrations decreased sharply with the soil depth, from 1894 to 34.1, from 9384 to 78.9, and from 2536 to 51.3 mBq kg−1, for the three sites. Downward migration of 129I was slightly faster than the one of 134Cs. In addition, the cumulative 129I inventories were observed to be 43.4 ± 1.0, 71.7 ± 1.8, and 56.5 ± 1.8 Bq m−2, respectively. Subsequently, the cumulative 131I inventories were estimated to be 1.76 ± 0.06, 2.90 ± 0.11, and 2.28 ± 0.10 GBq m−2 (decay-corrected to March 11, 2011), respectively. Finally, the total atmospheric deposition of 129I on the land of Japan due to the FDNPP accident was estimated to be around 1.09–1.71 kg (7.11–11.2 GBq).

Quantitative and qualitative evaluation of the impact of the G2 enhancer, bead sizes and lysing tubes on the bacterial community composition during DNA extraction from recalcitrant soil core samples based on community sequencing and qPCR.

Soil DNA extraction encounters numerous challenges that can affect both yield and purity of the recovered DNA. Clay particles lead to reduced DNA extraction efficiency, and PCR inhibitors from the soil matrix can negatively affect downstream analyses when applying DNA sequencing. Further, these effects impede molecular analysis of bacterial community compositions in lower biomass samples, as often observed in deeper soil layers. Many studies avoid these complications by using indirect DNA extraction with prior separation of the cells from the matrix, but such methods introduce other biases that influence the resulting microbial community composition. To address these issues, a direct DNA extraction method was applied in combination with the use of a commercial product, the G2 DNA/RNA Enhancer, marketed as being capable of improving the amount of DNA recovered after the lysis step. The results showed that application of G2 increased DNA yields from the studied clayey soils from layers from 1.00 to 2.20 m. Importantly, the use of G2 did not introduce bias, as it did not result in any significant differences in the biodiversity of the bacterial community measured in terms of alpha and beta diversity and taxonomical composition. Finally, this study considered a set of customised lysing tubes for evaluating possible influences on the DNA yield. Tubes customization included different bead sizes and amounts, along with lysing tubes coming from two suppliers. Results showed that the lysing tubes with mixed beads allowed greater DNA recovery compared to the use of either 0.1 or 1.4 mm beads, irrespective of the tube supplier. These outcomes may help to improve commercial products in DNA/RNA extraction kits, besides raising awareness about the optimal choice of additives, offering opportunities for acquiring a better understanding of topics such as vertical microbial characterisation and environmental DNA recovery in low biomass samples.

Investigation of temperature effects and performance evaluation of a newly developed capacitance probe

Capacitance probes are soil water monitoring device that have the advantages of high accuracy, low cost and ease of automation of data acquisition. This study was carried out to investigate the effect of temperature and to evaluate soil water measurement capability of a newly developed capacitance probes (HydraSCOUT). Undisturbed soil core samples were de-aired and saturated in a vacuum chamber at a suction pressure of −70 kPa. At saturation, the probes were inserted into the soil core, thereafter it was left to drain. The results shows that the response of the sensors of the capacitance probes at constant water content to temperature can be classified into 3 different stages: Constant stage (between 15 °C and 38 °C), with no temperature effect on the readings; Falling stage (between 3 °C and ≤15 °C), where the readings declined with temperature; Erratic stage (2 °C to ≤3 °C), where the readings had no pattern. Volumetric water contents were plotted against the sensors readings to develop calibration equations. Results indicated that calibration functions developed for the soils were linear (Clay loam) and polynomial (Sandy loam). Volumetric water content was well predicted with the soil specific equation for clay loam (RMSE of 0.001 m3 m−3 and D-index of 0.99) and Sandy loam (RMSE of 0.001 m3 m−3 and D-index of 0.99) soil textural classes. It was recommended that the soil specific laboratory calibration equations developed during this study should be used especially, for the Sandy loam soil type, in a situation where many probes are in use.

Improving In-Situ Estimation of Soil Profile Properties Using a Multi-Sensor Probe.

Optical diffuse reflectance spectroscopy (DRS) has been used for estimating soil physical and chemical properties in the laboratory. In-situ DRS measurements offer the potential for rapid, reliable, non-destructive, and low cost measurement of soil properties in the field. In this study, conducted on two central Missouri fields in 2016, a commercial soil profile instrument, the Veris P4000, acquired visible and near-infrared (VNIR) spectra (343–2222 nm), apparent electrical conductivity (ECa), cone index (CI) penetrometer readings, and depth data, simultaneously to a 1 m depth using a vertical probe. Simultaneously, soil core samples were obtained and soil properties were measured in the laboratory. Soil properties were estimated using VNIR spectra alone and in combination with depth, ECa, and CI (DECS). Estimated soil properties included soil organic carbon (SOC), total nitrogen (TN), moisture, soil texture (clay, silt, and sand), cation exchange capacity (CEC), calcium (Ca), magnesium (Mg), potassium (K), and pH. Multiple preprocessing techniques and calibration methods were applied to the spectral data and evaluated. Calibration methods included partial least squares regression (PLSR), neural networks, regression trees, and random forests. For most soil properties, the best model performance was obtained with the combination of preprocessing with a Gaussian smoothing filter and analysis by PLSR. In addition, DECS improved estimation of silt, sand, CEC, Ca, and Mg over VNIR spectra alone; however, the improvement was more than 5% only for Ca. Finally, differences in estimation accuracy were observed between the two fields despite them having similar soils, with one field demonstrating better results for all soil properties except silt. Overall, this study demonstrates the potential for in-situ estimation of profile soil properties using a multi-sensor approach, and provides suggestions regarding the best combination of sensors, preprocessing, and modeling techniques for in-situ estimation of profile soil properties.

Technical advances in measuring greenhouse gas emissions from thawing permafrost soils in the laboratory

Understanding permafrost soils’ response to global warming is critical for understanding changing global ecosystems. In the present study, we developed a dynamic system for measuring gas emissions from permafrost soils at different soil temperatures and checked the validity of this methodology using 10 permafrost and active layer soil core samples collected under frozen conditions from northern Alaska in winter. We observed that more time (several hours to half a day) was required to control the temperature of permafrost soils than normal soils, particularly during freeze-thaw cycles. Gas emissions were quite variable between samples. However, CO2 emissions were positively related to temperature in all samples, as were CO emissions, particularly for the permafrost samples. CH4 emissions were not detected in any sample, possibly because of atmospheric air as the carrier gas, and H2 was detected in only two samples. Conversely, NO emissions were detected in nearly all samples and were highly correlated with soil nitrogen content, while N2O emissions were detected in only one sample with very low NO emissions. Our findings demonstrate that this novel system could be a powerful tool for understanding gas emission dynamics in permafrost soils.

Calibration of capacitance sensor for Andosol under field and laboratory conditions in the temperate monsoon climate

Capacitance sensors (CS) were developed to continuously measure soil water content using the dielectric properties of soils. Although CS are calibrated in soils of various types, the default calibrated functions may not work for all conditions as in the case of this soil that has high organic matter content, hence, soil-specific calibrations are sometimes required to achieve reasonable accuracy. This study (1) evaluated the suitability of the default calibrated functions of a Decagon 5 T M CS for Andosol (Kuroboku), and (2) derived soil-specific calibration functions to Andosol. A field monitoring experiment was conducted at Sakaecho (western suburb of Tokyo) from August 2016 to July 2017, where volumetric soil water content (θv) was measured in bare field and repacked soils using both gravimetric method with oven drying and CS installed at 5 cm depth. The values of θv monitored using soil cores sampled from the field under natural condition and CS revealed large errors under both field and laboratory conditions when the default factory supplied calibration function (FSC) was used. The deviations depicted significant (P < 0.001) underestimations of the observed θv measured in soil cores by 0.117 - 0.199 and -0.004 - 0.131 cm3 cm−3 for field and laboratory conditions, respectively. Accordingly, soil-specific calibration functions were developed by correlating the dielectric permittivity of the soil with θv measured from the soil core samples. The θv recalculated based on the site-specific calibration function under field condition best fitted to the observed θv. Calibration of CS improved the θv measurement error from 15% with FSC to ≤ ±2%. Whereas the improvement with laboratory calibration was from ±15% with FSC to ±4% when the function was implemented to the field measured data, hence, it still underestimated the observed field θv. The deviation between the field and laboratory procedures was attributed to the deformation of the well-aggregated soil structure and its consequent changes in hydraulic properties due to crushing when a 2-mm sieve was used for sample preparation. Quasi-field calibration of the 5 T M CS under natural condition is highly recommended for real-time monitoring of θv in Andosol. In cases when field calibration is impractical, laboratory calibration further verified with field data could also offer a reliable method for calibration of the 5 T M CS for Andosols.

Measuring Rotation and Manure Effects in an Iowa Farm Soil Health Assessment

Core Ideas Farms with known management histories contribute to soil health research. Rotation‐based systems may increase soil organic carbon when combined with appropriate tillage. Inherent soil properties must be considered in soil health assessments. Rotation effects were more noticeable than manure effects on soil health groupings. Data from on‐farm sites with known management histories are needed to quantify soil biological, chemical, and physical properties influencing carbon stocks and soil health. Surface (0–15 cm) and deep core (0–122 cm) soil samples were collected from fields under two rotations in Boone County, IA. The first was a 5‐yr corn [Zea mays (L.)], soybean [Glycine max (L.) Merr.], corn, oat [Avena sativa (L.)], and alfalfa [Medicago sativa (L.)] rotation to which 0, 18, or 36 Mg ha−1 of a manure/biosolids mixture was applied prior to planting corn. The second was an 8‐yr rotation with 6 yr of mixed grass and legume pasture followed by corn and an oat crop within which the pasture mixture was reestablished. Soil samples were collected evenly across the predominant soil map units (SMUs). Bulk density (BD), soil organic C (SOC), water‐stable aggregates (WSA), microbial biomass carbon (MBC), pH, Mehlich‐3 and diethylenetriaminepentaacetic acid (DTPA) extractable nutrients, electrical conductivity (EC), and nitrogen (total‐, NH4–, and NO3–N) were measured. Surface SOC data were consistent with Soil Survey values for the various SMUs. Crop rotation effects were more noticeable than manure/biosolid application rate effects. Data from this study were combined with previously published SOC data in Iowa. Results suggest extended rotation systems or those with cover crops may increase SOC 8 ± 4 g kg−1 compared to corn–soybean rotations (33 vs. 25 g kg−1). This study provides on‐farm reference values for soil health assessment tools and draws attention to the importance of inherent soil properties for these assessments.

Nestedness in Arbuscular Mycorrhizal Fungal Communities in a Volcanic Ecosystem: Selection of Disturbance-tolerant Fungi along an Elevation Gradient.

Arbuscular mycorrhizal (AM) fungi play a significant role in the establishment and resilience of vegetation in harsh environments, such as volcanic slopes, in which soil is frequently disturbed by ash falling and erosion. We characterized AM fungal communities associated with a pioneer grass in a volcanic slope based on the disturbance tolerance of the fungi, addressing the hypothesis that soil disturbance is a major ecological filter for AM fungi in volcanic ecosystems and, thus, fungi that are more tolerant to soil disturbance are selected at higher elevations (i.e. nearer to the crater). Paired soil-core samples were collected from the rhizosphere of Miscanthus sinensis between the vegetation limit and forest limit on a volcanic slope and used in a trap culture with M. sinensis seedlings, in which one of the paired samples was sieved to destroy hyphal networks (disturbance treatment), while the other was not (intact treatment). Seedlings were grown in a greenhouse for two months, and the roots were subjected to molecular analysis of fungal communities. AM fungal diversity decreased with increasing elevations, in which nested structure was observed. Community dissimilarity between the disturbed and intact communities decreased with increasing elevations, suggesting that communities at higher elevations were more robust against soil disturbance. These results suggest that AM fungi that are more tolerant to soil disturbance are more widely distributed across the ecosystem, that is, they are generalists. The wide distribution of disturbance-tolerant fungi may have significant implications for the rapid resilience of vegetation after disturbance in the ecosystem.

ЭКСПЕРИМЕНТАЛЬНОЕ ИССЛЕДОВАНИЕ ВЛИЯНИЯ ФОРМЫ УДАРНОГО ИМПУЛЬСА НА ПРОЦЕСС ПОГРУЖЕНИЯ ПОЛЫХ СТЕРЖНЕВЫХ ЭЛЕМЕНТОВ В ГРУНТЫ

The work has experimental nature and it is aimed to development of vibro-percussion method of pipe-cover sinking during trenchless constructions of underground utilities. The maid idea of the research is the determination of regularities of filling inner tube hollow by soil at different forms of percussive pulse. Theoretical dependences of impact of percussion energy structure (form of percussion pulse) on efficiency of hollow rod element advance in the solid at different stages of insertion. Dimensionless parameter – filling coefficient is used for quantitative evaluation of filling rate by soil. Influence of pipe diameter on incrementation of length of soil core-sample for different percussive machines with the same percussive energy is shown. Stand and method of field test operation at various soil condition and interpretation of obtained data and its comparison with previous results obtained by the authors of the work and foreign researchers are represented.

ПРЕДПОСЫЛКИ СОЗДАНИЯ ГРУНТОПРОХОДЧИКА НЕПРЕРЫВНОГО ДЕЙСТВИЯ

Features of combined method of hole forming with particular compaction and excavation of soil are considered. Scheme with continuous cycle of drifting and transportation of soil core-sample at pipe line by flow of worked air is proposed. The possibility of using pneumohummer with elastic valve in system of air distribution as drive for soil drifter is studied. Behavior of change of its energetic indicators when there is backpressure at exhaust chamber is clarified.

Sodium transport and attenuation in soil cover materials for oil sands mine reclamation

Reclamation soil covers are used in oil sands mine closure to support vegetative growth over tailings. Geochemical processes within these covers may impact solute transport during upward migration of oil sands process-affected water (OSPW) from the underlying tailings. In this study, we examined the geochemical processes controlling Na transport and attenuation within the peat and clay-till cover soils at Sandhill Fen in northern Alberta, Canada. We analyzed soil core samples collected along transects of this 54-ha pilot-scale oil sands mine reclamation wetland. The geochemical (Na, Ca, Mg, K, Cl, SO4, HCO3) and isotopic (δ2H, δ18O) compositions of extracted pore water were analyzed statistically to identify OSPW and fresh surface water within the cover. Depth-dependent trends in pore water sodium concentrations were not apparent, suggesting that the soil cover had been fully flushed by a mixture of OSPW and fresh surface water used to flood the fen. Relative concentrations of Na, Ca and Mg were used to define the extent of cation exchange within the clay cover. Complementary laboratory column experiments showed that cation exchange removed up to 50% of dissolved Na as the first pore volume of simulated OSPW passed through the peat and till. However, Na attenuation by these materials declined rapidly and was limited after 4 (peat) to 7 (till) pore volumes of OSPW flushing. Reactive transport modeling confirmed that cation exchange was the dominant control on Na attenuation and corresponding Ca and Mg release within the till and peat columns. Mineral precipitation-dissolution reactions also influenced dissolved Ca and Mg concentrations and, therefore, indirectly impacted Na attenuation. Overall, this study helps constrain the geochemical processes controlling Na transport and attenuation in oil sands reclamation soil covers exposed to OSPW, and indicates that the attenuation of Na from OSPW by these covers is short-lived.

Assessment of soil contamination caused by underground fuel leakage from selected gas stations in Riyadh, Saudi Arabia

ABSTRACTSpills and leakage from underground fuel storage tanks (UFSTs) can potentially contaminate soil and groundwater and pose harmful effects to public health and the environment. This study evaluated the feasibility of using volatile organic compounds (VOCs), total petroleum hydrocarbons (TPHs), electrical conductivity (EC), and pH to examine the contamination caused by leaking UFSTs. Screening water assessments for VOCs and general water quality parameters were conducted on the premises of 53 gas stations in Riyadh, Saudi Arabia, to identify potentially contaminated sites, and 25 ground bores were drilled for the quantification of TPH concentrations, EC, and pH values in 407 soil samples. The experimental approach followed in this study included geochemical analyses based on borehole drilling at five targeted gas stations, analyses of water samples from underground storage reservoirs, and analyses of soil core samples obtained from different depths to determine the degree of TPH contamination. Thirty-five VOCs were identified in the water samples collected from gas stations. Methylene chloride, tribromomethane, toluene, chlorobenzene, dibromochloromethane, and benzene were frequently encountered in most of the water samples. Some of these samples exceeded the World Health Organization and Saudi Arabian guidelines for acceptable levels of pH, total dissolved solids, chloride, nitrate, sulfate, calcium, and total hardness. The measured TPH levels were clearly indicative of subsoil contamination and subsequent accumulation in soil over time, particularly at depths of 1–6 m; there was not a noticeable dependence or impact on pH.

Evidence for the Role of Subterranean Termites (Reticulitermes spp.) in Temperate Forest Soil Nutrient Cycling

Termites are ecosystem engineers in tropical systems, constructing visible biogenic structures (mounds) that influence soil characteristics, decomposition, nutrient cycling, vegetative growth, and biodiversity. Subterranean termites (Reticulitermes spp.) likely influence nutrient cycling within their endemic range in the temperate Holarctic through the translocation of elements from wood to soil by lining their below-ground biogenic structures with frass (feces). We designed a study to ‘follow the frass’ by comparing concentrations of 18 elements (Al, B, Ba, C, Ca, Co, Cr, Cu, Fe, K, Mg, Mn, N, Na, P, Si, Sr, and Zn) in substrates—food before and after digestion (wood and frass), as well as soil with and without direct termite manipulation (shelter tubes and soil core samples)—associated with 18 subterranean termite colonies. Fourteen elements were more concentrated in frass than wood, and only Cr and Fe were lower in frass. The shelter tube-to-soil contrasts indicate that termites decrease levels of Al, Ba, Co, and Cr while increasing C and Ca in soil. Therefore, Reticulitermes likely modulate element flows by returning organic C and base cations to weathered, acidic Ultisols of southeastern US forests. Research on the ecological role of subterranean termites outside of the built environment is showing the scale of impact these cryptic superorganism ecosystem engineers can have on temperate forest functions.

Effect of Harvesting and Non-Harvested Forest Management on Carbon Stocks

Forest management is an important strategy which can significantly contribute to climate change mitigation through appropriate care of forest resources. This study was carried out to evaluate two systems of carbon stock accumulation; a harvested forest verses a non-harvested forest. Both the above-ground and below-ground cabon stocks were assessed. Biomass of standing trees, poles and ground vegetation was measured for carbon determination in defined areas using an allometric relationship. Soil (core and composite) samples were collected from 0 –20, 20 – 40 cm and below 40 cm depths, assessed for density, carbon concentration, and profiles C-stocks were estimated. ANOVA and t-tests were performed to compare the effects of forest management on total carbon stocks. The results showed that the total above ground timber carbon (AGTC) was higher in non-harvested forest (220±154 t/ha–1) than in harvested forest (128.6±86.1 t/ha-1). The overall mean carbon stock was higher in the non-harvested forest (357±179) than in the harvested forest (257.4±93.1), which was statistically significant (p=0.031, &gt;0.05). However, the soil organic carbon (SOC) pool was observed to be higher in the harvested forest (101.5±36.1) than in non-harvested forest (89.6±26.5).