Glacial Till Soil Research Articles

Simulated Cropping Season Effects on N Mineralization from Accumulated No-Till Crop Residues

The adoption of no-till management practices has increased in the United States over the last decade. In the state of North Dakota, approximately 5.7 million hectares of cropland is managed under no-till or conservation tillage management practices. Even though conservation tillage is known for building soil health, increasing soil organic matter, capturing soil moisture, and reducing wind and water erosion, it also presents a unique best management practice since an increased mass of crop residue remains on the soil surface. Producers are concerned about whether plant needs are being met by nitrogen fertilizer that is currently being applied based on current North Dakota recommendations for long-term no-till systems. A Forman clay loam soil (fine-loamy, mixed, superactive, frigid Calcic Argiudolls) was used in this study, as it represented glacial till soils of the region. We examined whether N mineralization from surface-applied crop residue would result in similar or different results when compared to crop residue mixed into the soil. Soil freeze-thaw contribution to soil N mineralization was also evaluated. Six residue treatments with different C/N ratios including corn (Zea mays L.), soybean (Glycine max L.), forage radish (Raphanus sativus L.), winter pea (Pisum sativum L.), spring wheat (Triticum aestivum L.), and winter wheat (Triticum aestivum L.) were used. Five 10–14-week cycles with a three-week freeze period between each cycle at 0 ºC were evaluated for NO3-N production. Crop residues with a narrow C/N ratio contributed to greater instances of N mineralization during each incubation cycle, and the accumulation of crop residues with a wide C/N ratio over each incubation cycle following the first incubation did not offset the immobilization trends observed in the first incubation. A change in N mineralized in the untreated control soil during the last two incubation cycles may have been caused by freeze-thaw effects or a shift in microbial population due to a lack of fresh C inputs.

Long-Term Ecosystem Nutrient Pool Status for Aspen Forest Harvest Simulations on Glacial Till and Sandy Outwash Soils

Sandy outwash and glacial till soils compose large amounts of public forestland due to historically poor agricultural yields. The outwash soils have low fertility, poor nutrient retention and are restricted from whole-tree harvesting (WTH) in some states, whereas the glacial till has medium nutrient retention and fertility, and is unrestricted from WTH. To assess the long-term sustainability of harvesting, a nutrient budget was constructed from field measurements, the National Cooperative Soil Survey (NCSS) database, and literature values for stem-only harvesting (SOH) and WTH at a 45-year rotation length and 11 rotations were simulated. The budgets showed that SOH and WTH recovery years, or the time necessary for the inputs to match outputs through leaching and one harvest, exceeded common rotation lengths for both soil types under all weathering scenarios, and the average WTH reduced the total available rotations by one harvest. The large variation in soil nutrient pools and harvest removals complicated the ability to identify the difference between SOH and WTH early in the model, but differences became apparent with sequential harvests. The recovery years were 2–20 times the 45-year rotation length under all weathering rates. Taken together, models in this study bridge the gap between short- and long-term studies and bring into question the sustainability of WTH and SOH practices on nutrient-poor soils.

A Laboratory Study on the Shear Strength Behavior of Two Till Deposits from Northern Germany

This paper presents the findings of a laboratory study of the shear strength and yielding behavior of two glacial till soil deposits from the area of Heiligenhafen, northern Germany. The tests were conducted on reconstituted forms of the soils using a triaxial cell capable of controlling the temperature of the specimens. The experimental program included a series of multi-stage consolidated drained (CD) compression triaxial tests at temperature ranges between 20 and 60 °C. For the temperature range considered in this study, a mild reduction in the effective friction angle of the two till soils of less than 1° was observed due to an increase in temperature from 20 to 60 °C. All the results were carefully assessed in view of the intrinsic soil behavior and fabric, and existing trends are highlighted. The findings of this study provide valuable insights into the shearing properties of till deposits, and can contribute to the enhancement of existing soil constitutive models as well as the development of new models that are particularly suited to the behavior of glacial tills under elevated temperatures.

Undrained shear strength of glacial till soils and its determining factors

This article presents results of the test conducted on the undrained shear strength of till clayey soils of Eastern Lithuania, which are characterized by rigid and very stiff consistency and low plasticity. According to the classification of soils presented in LST EN ISO 14688–2:2018 Geotechnical Investigation and Testing – Identification and Classification of Soil − Part 2: Principles for a Classification, the tested soils are classified as sandy low plasticity clays. The undrained shear strength was tested using the triaxial compression (unconsolidated undrained) method. The test results showed that peculiarities of the particle size distribution had a crucial impact on the undrained strength of these soils, i.e. on the correlation of clay and fine silt fractions with the rest of soil components.

PISA design model for monopiles for offshore wind turbines: application to a marine sand

This paper describes a one-dimensional (1D) computational model for the analysis and design of laterally loaded monopile foundations for offshore wind turbine applications. The model represents the monopile as an embedded beam and specially formulated functions, referred to as soil reaction curves, are employed to represent the various components of soil reaction that are assumed to act on the pile. This design model was an outcome of a recently completed joint industry research project – known as PISA – on the development of new procedures for the design of monopile foundations for offshore wind applications. The overall framework of the model, and an application to a stiff glacial clay till soil, is described in a companion paper by Byrne and co-workers; the current paper describes an alternative formulation that has been developed for soil reaction curves that are applicable to monopiles installed at offshore homogeneous sand sites, for drained loading. The 1D model is calibrated using data from a set of three-dimensional finite-element analyses, conducted over a calibration space comprising pile geometries, loading configurations and soil relative densities that span typical design values. The performance of the model is demonstrated by the analysis of example design cases. The current form of the model is applicable to homogeneous soil and monotonic loading, although extensions to soil layering and cyclic loading are possible.

Catchment export of base cations: improved mineral dissolution kinetics influence the role of water transit time

Abstract. Soil mineral weathering is one of the major sources of base cations (BC), which play a dual role in forest ecosystems: they function as plant nutrients and buffer against the acidification of catchment runoff. On a long-term basis, soil weathering rates determine the highest sustainable forest productivity that does not cause acidification. It is believed that the hydrologic residence time plays a key role in determining the weathering rates at the landscape scale. The PROFILE weathering model has been used for almost 30 years to calculate weathering rates in the rooting zone of forest soils. However, the mineral dissolution equations in PROFILE are not adapted for the saturated zone, and employing these equations at the catchment scale results in a significant overprediction of base cation release rates to surface waters. In this study, we use a revised set of PROFILE equations which, among other features, include retardation due to silica concentrations. Relationships between the water transit time (WTT) and soil water concentrations were derived for each base cation, by simulating the soil water chemistry along a one-dimensional flow path, using the mineralogy from a glacial till soil. We show how the revised PROFILE equations are able to reproduce patterns in BC and silica concentrations as well as BC ratios (Ca2+/BC, Mg2+/BC and Na+/BC) that are observed in the soil water profiles and catchment runoff. In contrast to the original set of PROFILE equations, the revised set of equations could reproduce the fact that increasing WTT led to a decreasing Na+/BC ratio and increasing Ca2+/BC and Mg2+/BC ratios. Furthermore, the total release of base cations from a hillslope was calculated using a mixing model, where water with different WTTs was mixed according to an externally modeled WTT distribution. The revised set of equations gave a 50 % lower base cation release (0.23 eq m−2 yr−1) than the original PROFILE equations and are in better agreement with mass balance calculations of weathering rates. Thus, the results from this study demonstrate that the revised mineral dissolution equations for PROFILE are a major step forward in modeling weathering rates at the catchment scale.

Investigating Surficial Geologic Controls on Soil Properties, Inorganic Nutrient Uptake, and Northern Hardwood Growth in Western Massachusetts, USA

The influence of glacial geologic materials on soil properties, tree nutrient acquisition, and tree growth rates in New England is not well-constrained. Here, our research investigates the effect of two dominant surficial deposits, glacial till and glaciofluvial deposits, on soils and northern hardwood trees in western Massachusetts. We investigated sixteen paired glaciofluvial and glacial till sites located on the perimeters of glacial lake Hitchcock sediments, which drained 12,400 years ago. At each site, a 12.2-m-radius circular plot was selected, a soil pit was excavated, and all trees within the plot were sampled for foliage and cored with an increment borer. Our analyses found glaciofluvial soils to have significantly higher pH, clay fraction, and water field capacity than glacial till soils. Glaciofluvial soils also had less rock fragments and lower sand content than glacial till soils. We observed significantly higher pseudo-total K, Ca, Mg, and Mn concentrations in glacial till soils, but found similar foliar concentrations for five of the six tree species. Tree cores showed Black Birch, Red Maple, and Red Oak grew 1.3 to 2.1 times faster on glaciofluvial soils. Our study found that glaciofluvial soils, which exhibit greater water retention, less rocks, more fine particles, and higher soil pH than glacial till soils, promote faster growth of Black Birch, Red Maple, and Red Oak. However, the growth of American Beech, White Oak, and Eastern Hemlock was not impacted by surficial deposits, implying adaptation to nutrient limitations, coarser rocky soils, and potential water stress. Thus, the growth of some common tree species is affected by geologic materials, but others are not affected.

Lodgepole pine tree-ring growth, Δ13C and the inverse texture effect across a soil chronosequence in glacial till

Our goal was to better understand tree growth and photosynthetic responses to variations in plant available water and elucidate the role of the inverse texture effect in snow dominated montane forests. We measured tree ring carbon isotope composition and annual growth over a 31-year record for lodgepole pine (Pinus contorta Douglas ex Loudon) growing on three different-aged glacial till surfaces in Wyoming, USA. Soils of different ages developed on till surfaces from three separate glaciation events were significantly different in clay content and distribution with depth; maximum clay content at depth ranged from 19 to 20% on the two youngest till surfaces, but was as high as 36% on the oldest till surface. Ring growth was lowest at the youngest till sites, and only on these coarse-textured soils was growth positively correlated with annual maximum snow water equivalent (SWEmax). Δ13C was highest for trees at these young till sites, suggesting that hydraulic conductivity and stomatal conductance is comparatively high during growth periods on these coarse-textured soils. Taken together, we found that age of glacial till and related soil texture differences strongly influenced tree-ring growth and Δ13C response of lodgepole pine to interannual variation in precipitation and drought severity, but responses did not support an inverse texture effect in these semi-arid forest systems.

Evolution of soil organic carbon in a carbonaceous glacial till as an effect of crop and fertility management over 50 years in a field experiment

Changes in soil organic carbon (SOC) content depending on different factors are extensively investigated when the soil is in steady-state equilibrium between formation and decomposition of soil organic matter. However, studies of SOC formation and dynamics in initally organic matter free soil are rare. Evolution of soil organic carbon was studied in a field experiment established in 1964 on a carbonaceous glacial till soil with very low initial SOC content (1.28 g kg−1). The effects on SOC content changes of bare fallow, barley and different perennial fodder crops such as grasses, clover-grass mixture, galega, hybrid lucerne and a turfgrass mixture, with or without mineral N and PK fertilisation and manure, were studied. There were 19 treatments in total and most had unchanged plant cover composition throughout the experiment. During 1964–2014, SOC stock increased in all treatments, by 0.11 Mg ha−1 y−1 in bare fallow and by at most 0.50 Mg ha−1 y−1 in the treatment with hybrid lucerne and manure. Average SOC sequestration rate was 0.35 ± 0.11 Mg ha−1 y−1. SOC changes were highly correlated with estimated C inputs and were therefore higher in treatments with perennials than with an annual barley crop. C retention efficiency for total crop-derived C inputs and for organic amendments was 6.1% and 22%, respectively. Water-soluble C measured in 2014 increased linearly with SOC, indicating that the quality of recently formed SOC was not strongly affected by the treatments. However, water-soluble C as a fraction of SOC was significantly lower in treatments with legumes than in treatments with bare fallow or a barley or grass crop. These results demonstrate that the quantity and quality of C inputs were both main drivers for observed changes in SOC. However, C retention efficiency of C inputs was relatively low. This may be related to soil texture with high sand proportion, suggesting that SOC sequestration rates in light-textured soils may be lower than expected even in case of low initial SOC content.

Predicting Soil Organic Carbon and Total Nitrogen at the Farm Scale Using Quantitative Color Sensor Measurements

Sensor technology can be a reliable and inexpensive means of gathering soils data for soil health assessment at the farm scale. This study demonstrates the use of color system readings from the Nix ProTM color sensor (Nix Sensor Ltd., Hamilton, ON, Canada) to predict soil organic carbon (SOC) as well as total nitrogen (TN) in variable, glacial till soils at the 147 ha Cornell University Willsboro Research Farm, located in Upstate New York, USA. Regression analysis was conducted using the natural log of SOC (lnSOC) and the natural log of TN (lnTN) as dependent variables, and sample depth and color data were used as predictors for 155 air dried soil samples. Analysis was conducted for combined samples, Alfisols, and Entisols as separate sample sets and separate models were developed using depth and color variables, and color variables only. Depth and L* were significant predictors of lnSOC and lnTN for all sample sets. The color variable b* was not a significant predictor of lnSOC for any soil sample set, but it was for lnTN for all sample sets. The lnSOC prediction model for Alfisols, which included depth, had the highest R2 value (0.81, p-value < 0.001). The lnSOC model for Entisols, which contained only color variables, had the lowest R2 (0.62, p-value < 0.001). The results suggest that the Nix ProTM color sensor is an effective tool for the rapid assessment of SOC and TN content for these soils. With the accuracy and low cost of this sensor technology, it will be possible to greatly increase the spatial and temporal density of SOC and TN estimates, which is critical for soil management.

Multi‐year simulation and model calibration of soil moisture and temperature profiles in till soil

SummaryIn Nordic regions water infiltration into soil is controlled by soil moisture content and frozen soil conditions, which are regulated by soil temperature. For long‐term model predictions of the effects of climate change, models need to be tested with long‐term data to assess model sensitivity to parameter uncertainties under both typical and exceptional conditions. Ten‐year (2002–2011) daily soil moisture and temperature data at different depths in glacial till soils in central Finland were used to assess the sensitivity of a coupled heat and water transfer model, COUP, to model parameters. The model was most sensitive to the parameters controlling snow accumulation and melt, the thermal conductivity of frozen soil and soil water retention characteristics. Observed time series for soil temperature and moisture at different depths were matched reasonably well by model simulations, although the model performance with respect to moisture dynamics in the topsoil was relatively poor. The model was not able to simulate accurately exceptional winter conditions, such as mid‐winter snowmelt events. This study showed that the main characteristics of long‐term variation in soil temperature for till‐derived soil in a cold climate can be resolved by a coupled water and heat transport model. Better characterization of infiltration in cold climates would require measurement of water fluxes, and soil frost occurrence and penetration.Highlights Ten‐year soil temperature and moisture observations are predicted with coupled heat and water model. Snow processes and soil thermal and water retention properties proved critical in our simulations. Exceptional winter conditions pose a challenge in parameterization of the model. Studies measuring water fluxes and soil frost occurrence are needed for advances in modelling.

Estimating Carbon and Nitrogen Pools in a Forest Soil: Influence of Soil Bulk Density Methods and Rock Content

Core Ideas Three bulk density methods used in a rocky soil gave different total bulk density values, but not fine bulk density. Bulk density sampling method had little effect on C and N pool estimates in the surface 20 cm of soil, but did so deeper in the soil. Small‐diameter cores probably underestimated total soil bulk density and C and N pools at deeper soil depths. Rocks present on the soil surface cause an overestimation of soil C and N pools. Soils with high rock content are common in many US forests, and contain large amounts of stored C. Accurate measurements of soil bulk density and rock content are critical for calculating and assessing changes in both C and nutrient pool size, but bulk density sampling methods have limitations and sources of variability. Therefore, we evaluated the use of small‐diameter soil cores (SD), irregular soil volume excavation (IR), and a nuclear density gauge (ND) to measure bulk density and rock content, and estimate C and N pools in three 10‐cm increments to a 30‐cm depth in a glacial till soil in northern Wisconsin. Total and fine bulk densities were lower when measured with SD cores than with larger soil volume IR and ND methods. No differences in C pools among bulk density sampling methods were found in the 10‐cm increments, but when combined to 30 cm, the C pool estimate with IR (81.6 Mg ha–1) was significantly higher than those of ND (75.3 Mg ha–1) and SD (73.4 Mg ha–1). No significant differences in N pools were detected in the 10‐cm increments, but the 0‐ to 30‐cm N pool estimates by IR (5.65 Mg ha–1) and ND (5 Mg ha–1) were higher than that of SD (4.22 Mg ha–1). Surface rocks could lower soil C and N pools by 20% or more. Overall, the bulk density method had little effect on soil C and N pool estimates in the surface 20 cm of this soil but did when sampled to 30 cm soil depth.

Hydraulic conductivity of a glacial clay till liner

The study of water flow through soils is an important aspect of soil mechanics. Past experience with glacial clay till deposits investigated in central and southern Saskatchewan has demonstrated that in situ saturated hydraulic conductivities vary from about 10−6 to 10−9 cm/s. In some applications and regulatory references, an accepted practice in the past is to assume that the field hydraulic conductivity value for a soil liner will be one order of magnitude (i.e. ten times) greater than the confirmed laboratory hydraulic conductivity value for a remoulded sample composed of the same soil. In fact, experience has shown that measured as-built field hydraulic conductivity values for a soil liner can be several orders of magnitude greater than the laboratory value if the liners are poorly constructed and, therefore, would not be compliant with regulatory criteria. The reliability of artificially applying any correction factor to a laboratory value to obtain an assumed field value is, therefore, questionable. This paper describes field and laboratory investigations that were conducted to characterize the general properties and the hydraulic conductivity of a glacial clay till soil liner. For this example case study, laboratory measurements of the hydraulic conductivity for remoulded soil samples were undertaken using a flexible wall permeameter (FWP). Air-entry permeameter (AEP) tests were performed on a soil test pad prior to construction and then on the completed soil liner immediately after construction to measure the as-built hydraulic conductivity. Both the FWP and AEP tests resulted in comparable hydraulic conductivity values that were in the order of 10−8–10−9 cm/s. A preceding and preliminary empirical approach was also found to be reasonable for purposes of determining soil suitability and estimating the “achievable” hydraulic conductivity value. The preliminary estimate was determined to be conservatively greater than the values determined by both the FWP and AEP test methods.

Effect of stump size and timing of stump harvesting on ground disturbance and root breakage diameter

Stump wood is a possible alternative to fossil fuel. Its harvesting, however, disturbs the ground and this has not yet been quantified at stump level. Such disturbance is likely to be dependent on stump size, type of soil and timing of stump harvesting. Therefore, we measured ground disturbance and root breakage diameter at two Norway spruce sites with sandy glacial till soil. The sites were harvested with a fork type head, 6 and 18 months after clear cutting. Measurements were made within 2 weeks of harvest. No difference was found between the two sites. The mean area of disturbed ground was 6.06 (std 3.14) m per stump and increased exponentially with stump size. A regression function modelling the relationship was constructed. Unexpectedly, many fine roots where extracted in the harvest. The arithmetic and basal area weighted mean root breakage diameter was 4.6 (std 2.2) and 29.5 (std 17.9) mm, respectively. There seems to be a limited increase in root breakage diameter with increased stump size. The small root breakage diameter is associated with reduced fuel quality and greater nutrient removal. It appears that much of the ground disturbance is associated with the creation of ruts rather than stump harvestper se. Stump harvesting disturbs a larger percentage of the area of a harvested site than mounding. Postponing stump harvest by one year did not decrease the ground disturbance or increase the root breakage diameter. To achieve less disturbance and larger root breakage diameter, probably new stump harvesting technology is required.2

Extending the Kenney–Lau method to dam core soils of glacial till

The Kenney–Lau method, which is used to assess the internal stability of granular soils, is stretched in engineering practice to include soils with fines. This strays beyond the method’s intended range and may introduce potential uncertainty in terms of validity. Herein, results are presented from the assessment of grain size curves from core construction data belonging to a large number of existing dams with core material composed of widely graded glacial till soils. Some have experienced internal erosion events, and others have not, and based on the benchmark of historic performance data of these dams, the validity of the Kenney–Lau method in terms of glacial tills is investigated. Only dams in the same filter coarseness range are studied in order to reduce the influence of the filter. By contrasting dams with documented internal erosion history against the application results of the method, it indicates that the Kenney–Lau method can be extended with caution to include glacial till cores if within the proposed fines content and finer fraction ranges.

Utilization of Coal/Biomass Fly Ash and Glacial Till Soil as a Flow-Through Reactive Barrier for the Treatment of Acid Mine Drainage

Utilization of Coal/Biomass Fly Ash and Glacial Till Soil as a Flow-Through Reactive Barrier for the Treatment of Acid Mine Drainage

Mapping of Total Carbon and Clay Contents in Glacial Till Soil Using On-the-Go Near-Infrared Reflectance Spectroscopy and Partial Least Squares Regression

Characterizing spatial variability of soil attributes, using traditional soil sampling and laboratory analysis, is cost prohibitive. The potential benefit of managing soils on a site-specific basis is well established. High variations in glacial till soil render detailed soil mapping difficult with limited number of soil samples. To overcome this problem, this paper demonstrates the feasibility of soil carbon and clay mapping using the newly developed on-the-go near-infrared reflectance spectroscopy (NIRS). Compared with the geostatistics method, the partial least squares regression (PLSR), with NIRS measurements, could yield a more detailed map for both soil carbon and clay. Further, by using independent validation dataset, the accuracy of predicting could be improved significantly for soil clay content and only slightly for soil carbon content. Owing to the complexity of field conditions, more work on data processing and calibration modeling might be necessary for using on-the-go NIRS measurements.

Phosphorus forms and related soil chemistry in preferential flowpaths and the soil matrix of a forested podzolic till soil profile

Preferential flow affects subsurface flow and solute transport processes in forested glacial till soils. Preferential flowpaths (PFPs) have been detected in forest soils, with higher microbial biomass, organic carbon content and increased nitrogen cycling compared with the soil matrix. However, the role of preferential flow in phosphorus (P) cycling in forest soils is still unknown. This study characterised the P forms of a forested podzolic till soil profile in Southern Finnish Lapland using P extraction and ignition procedures, fractionation and solution 31P nuclear magnetic resonance (NMR) spectroscopy. PFPs were identified by introducing the dye tracer Acid Blue 9 at the surface of a 1.25m2 study plot. The soil profile was vertically sliced and samples were collected from the unstained soil matrix and the dye-stained PFPs of each horizon of the podzol. Amorphous metal sesquioxides, naturally bound P (Pox), total P (Pt), inorganic P (Pin), organic P (Po), different inorganic P fractions (soluble P, Al–P, Fe–P, Ca–P, occluded P) and organic and inorganic P forms (31P-NMR spectroscopy) were analysed in the samples.The concentrations of different forms of P and amorphous metal sesquioxides varied between the different PFPs and the soil matrix within the podzol soil horizons. The PFPs in soils on stone surfaces contained less amorphous metal sesquioxides, Pox and Pt than the other flow regions. The PFPs related to coarse grains and roots contained equivalent or higher Pox and Pt concentrations than the soil matrix. Inorganic P was present as orthophosphates and pyrophosphates, and was mainly bound with Al and Ca oxides in PFPs, but also with Fe oxides in the soil matrix. PFPs contained more occluded P than the soil matrix, especially on stone surfaces. The results indicate increased mobilisation and P losses in PFPs on stone surfaces due to enhanced mineral weathering, root uptake and leaching of P adsorbed by the sesquioxides. The results of the 31P NMR study also showed higher proportions of pyrophosphate, orthophosphate diesters and monoesters other than phytic acid in the PFPs on stone surfaces than in the other flow regions, indicating higher amounts of labile forms of inorganic and organic P on stone surfaces than in other flow regions. To conclude, PFPs seem to have a twofold role in P dynamics: P can leach through PFPs on stone surfaces and accumulate on PFPs related to coarse grains and roots.

Effect of soil composition on electrokinetically enhanced persulfate oxidation of polychlorobiphenyls

In situ oxidation processes for the remediation of organic contaminants in soils have gained much interest in last decade. They are rapid, aggressive and easy to apply, but their application in low permeability soils is limited due to the ineffective delivery of oxidants in such soils. In this study, electrokinetically enhanced persulfate delivery and oxidation is investigated in two diverse low permeability soils: artificially contaminated kaolin and glacial till soil. These two soils were used to investigate the effects of soil type on persulfate oxidation of tetrachlorobiphenyl (PCB 44), a representative polychlorobiphenyl (PCB). Laboratory batch tests were conducted using the soils spiked with PCB 44 at an initial concentration of 50mg/kg to determine the optimal conditions for effective oxidation. This study also investigated the activation of persulfate by elevated temperature (45°C) and high pH (at anode) as a means to maximize PCB degradation. The activation of persulfate improved the oxidation of PCB in kaolin, but the effect in the glacial till was insignificant. The final pH values of the kaolin were around 1, while they were around 7 for glacial till because of the high buffering capacity of glacial till. Low pH conditions are also shown to activate persulfate, leading to higher PCB oxidation. The degradation of PCB 44 was significantly higher for the kaolin than the glacial till. In kaolin, the highest level of PCB oxidation, 77.9%, was achieved with temperature activated persulfate in 7 days. However, in the glacial till the highest PCB oxidation was 14.4% with 30% Na-persulfate concentration without any activation. The high buffering capacity, non-homogeneous mineral content and high organic content of glacial till may have contributed to the low persulfate oxidation of PCB.

Rapid, non-destructive carbon analysis of forest soils using neutron-induced gamma-ray spectroscopy

Forest soils are pivotal to understanding global carbon (C) cycling and evaluating policies for mitigating global change. However, they are very difficult to monitor because of the heterogeneity of soil characteristics, the difficulty of representative sampling, and the slow time scale of response to environmental change. Here we demonstrate that use of gamma-ray spectroscopy facilitates in situ non-destructive analysis of C and other elements in forest soils. In this approach the element-specific gamma-rays are induced by fast and thermal neutrons interacting with the nuclei of the elements present in the soil. Background gamma-rays emanating from naturally occurring radionuclides in the forest are recorded as well. We applied this approach in a mature northern hardwood forest on glacial till soils at the Bartlett Experimental Forest in New Hampshire, USA. The inelastic neutron scattering (INS) system yielded strong signals in gamma-ray counts/h, from C and other elements present in the soil matrix that included silicon, oxygen, hydrogen, iron, aluminum, manganese and potassium. The INS sensitivity for carbon was 20.656 counts h −1 kg −1 C m −2 based on current net C gamma-ray counts and the data for the O horizon and mineral soil to a depth of 30 cm obtained from a nearby quantitative soil pit (7.35 kg C m −2). We estimate the minimum detectable change to be ∼0.34 kg C m −2, which is ∼5% of the current soil C content, and the minimum detectable limit to be ∼0.23 kg C m −2. Eight % reproducibility from 11 measurements was limited, in part, by the large variability in the system counting geometry due to the uneven forest microtopography. The INS approach has the potential to revolutionize belowground monitoring of C and other elements, because the possibility of detecting a 5% change in forest soils has not been possible with destructive sampling methods.