Low Organic Soils Research Articles

The microstructure and the behaviour of low organic clayey soils in Sri Lanka

Numerous studies focus on investigating organic soils with high organic content. However, only a limited amount of literature discusses the properties and behaviour of low organic content soils. Sri Lankan organic soil is an excellent example of a low organic content soil, demonstrating different behaviour from highly organic fibrous soil. Scanning electron microscope (SEM) images of Sri Lankan organic soil were studied to determine the reasons for these observed variations. Sri Lankan organic soils were observed to consist of highly decomposed organic matter in an amorphous state with higher proportions of mineral matter. The microstructure characteristics observed through SEM images mostly explained the variation of properties and behaviour of the Sri Lankan organic soil in contrast to highly organic fibrous soil. Correlations were also derived between properties of Sri Lankan organic soil and compared with similar relationships derived from other geological conditions. While some correlations derived in this study closely follow the relationships for other organic soils with similar microstructure characteristics, the acidity of the deposit resulted in different behaviour of a few correlations. This study improves the current knowledge of the effect of microstructure characteristics on the properties and behaviour of Sri Lankan low-organic clayey soils, which otherwise primarily depend on theories for highly organic peaty soils. Furthermore, the correlations derived and validated for low organic soils can be utilized in any organic clay deposit with similar microstructure characteristics.

Biochar considerably increases the easily available water and nutrient content in low-organic soils amended with compost and manure

The soil hydraulic properties of two low-organic soils (Fluvisol; Regosol) were investigated following their amendment with biochar alone or in combination with manure, compost and co-composted biochar. Self-irrigating boxes containing the soil and amendment combinations were purposed with a battery of soil moisture sensors as well as soil porewater sampling devices. Static sampling determined bulk density, porosity and derived soil water retention curves. The aim of this study was to identify the most advantageous amendment combinations to enhance soil water retention whilst simultaneously avoiding excessive nutrient leaching arising, primarily, from manure application.Biochar significantly decreased bulk density and increased total porosity when compared to compost in the Fluvisol, whereas manure affected the greatest changes in the Regosol. All of the tested amendments adjusted the shape or extent of the soil water retention curves, but biochar addition resulted in the greatest increase (⁓50%) in easily available water content (for plants) in both soils, when compared to the control. Saturated hydraulic conductivity was, however, not changed by any of the amendments which reflects a lack of influence on infiltration. An enhancement in nutrient retention occurred in some of the soil amendment configurations, such as for co-composted biochar at 2% dosage and 5% manure-biochar mixture, as revealed by porewater analysis.In summary, the application of biochar with and without additional compost and manure can enhance soil water retention in low-organic soils whilst maintaining or enhancing nutrient retention. Such finding supports the application of mixed organic amendments to low-organic (and therefore drought-prone) arable soils.

Cold Adapted Nitrosospira sp.: A Potential Crucial Contributor of Ammonia Oxidation in Cryosols of Permafrost-Affected Landscapes in Northeast Siberia.

Permafrost-affected landscape soils are rich in organic matter and contain a high fraction of organic nitrogen, but much of this organic matter remains inaccessible due to nitrogen limitation. Microbial nitrification is a key process in the nitrogen cycle, controlling the availability of dissolved inorganic nitrogen (DIN) such as ammonium and nitrate. In this study, we investigate the microbial diversity of canonical nitrifiers and their potential nitrifying activity in the active layer of different Arctic cryosols in the Lena River Delta in North-East Siberia. These cryosols are located on Samoylov Island, which has two geomorphological landscapes with mineral soils in the modern floodplain and organic-rich soils in the low-centered polygonal tundra of the Holocene river terrace. Microcosm incubations show that the highest potential ammonia oxidation rates are found in low organic soils, and the rates depend on organic matter content and quality, vegetation cover, and water content. As shown by 16S rRNA amplicon sequencing, nitrifiers represented 0.6% to 6.2% of the total microbial community. More than 50% of the nitrifiers belonged to the genus Nitrosospira. Based on PCR amoA analysis, ammonia-oxidizing bacteria (AOB) were found in nearly all soil types, whereas ammonia-oxidizing archaea (AOA) were only detected in low-organic soils. In cultivation-based approaches, mainly Nitrosospira-like AOB were enriched and characterized as psychrotolerant, with temperature optima slightly above 20 °C. This study suggests a ubiquitous distribution of ammonia-oxidizing microorganisms (bacteria and archaea) in permafrost-affected landscapes of Siberia with cold-adapted AOB, especially of the genus Nitrosospira, as potentially crucial ammonia oxidizers in the cryosols.

Arsenic mobility in weathered gold mine tailings under a low-organic soil cover

Historical gold mining operations in Nova Scotia, Canada, resulted in numerous deposits of publicly accessible, arsenic (As)-rich mine waste that has weathered in situ for 75–150 years, resulting in a wide range of As-bearing secondary minerals. The geochemical heterogeneity of this mine waste creates a challenge for identifying a single remediation approach that will limit As mobility. A 30-cm-thick, low-organic content soil cover was evaluated in a laboratory leaching experiment where, to simulate natural conditions, the equivalent of 2 years of synthetic rainwater was leached through each column and two dry seasons were incorporated into the leaching protocol. Each column was a stratigraphic representation of the four major tailings types found at the historical Montague and Goldenville gold mine districts: hardpan tailings, oxic tailings, wetland tailings, and high Ca tailings. Hardpan tailings released acidic, As-rich waters (max 12 mg/L) under the soil cover but this acidity was buffered by surrounding oxic tailings. Leachate from the oxic tailings was circumneutral, with average As concentrations between 4.4 and 9.7 mg/L throughout the experiment. The presence of carbonates in the high Ca tailings resulted in near-neutral to weakly alkaline leachate pH values and average As concentrations between 2.1 and 6.1 mg/L. Oxidation of sulfides in the wetland tailings led to acidic leachate over time and a decrease in As concentrations to values that were generally less than 1 mg/L. This study shows that the use of a low-organic content soil cover does not create reducing conditions that would destabilize oxidized, As-bearing secondary phases in these tailings. However, oxygen penetration through the cover during dry seasons would continue to release As to tailings pore waters via sulfide oxidation reactions.

Stabilizing Very High Moisture Content Fine Grained Soils with Calcium Sulfoaluminate Cements

Abstract This paper focuses on rapidly stabilizing very high moisture soils via calcium sulfoaluminate (CSA) cements. Producing a short-term construction material and/or handling contaminated sediments are the two primary anticipated applications. Literature review showed CSA cements have promise for an application of this nature, but that this subject has largely been unexplored. Behaviors of CSA cements were compared with ordinary portland cements (OPCs) where multiple soil types at a range of cement dosages and moisture contents were tested. There were distinct conditions where OPC outperformed CSA and vice versa. With the exception of very rare and isolated instances, there appears to be no advantage to using CSA cement below 10 % dosage. Moisture contents of 133 % or higher and high cement dosages (e.g., 15 to 20 %) in conjunction with a relatively low organic soil with a moderate liquid limit (e.g., 45 to 65) appears to be a good application for CSA cements.

Comparative ecotoxicity of chlorantraniliprole to non-target soil invertebrates

The insecticide chlorantraniliprole (CAP) is gaining importance in agricultural practice, but data on its possible negative effects on non-target organisms is severely deficient. This study therefore determined CAP toxicity to non-target soil invertebrates playing a crucial role in ecosystem functioning, including springtails (Folsomia candida), isopods (Porcellio scaber), enchytraeids (Enchytraeus crypticus) and oribatid mites (Oppia nitens). In sublethal toxicity tests in Lufa 2.2 soil, chronic exposure to CAP concentrations up to 1000 mg/kgdw did not affect the survival and reproduction of E. crypticus and O. nitens nor the survival, body weight and consumption of P. scaber. In contrast, the survival and reproduction of F. candida was severely affected, with an EC50 for effects on reproduction of 0.14 mg CAP/kgdw. The toxicity of CAP to the reproduction of F. candida was tested in four different soils following OECD guideline 232, and additionally in an avoidance test according to ISO guideline 17512-2. A significantly lower toxicity in soils rich in organic matter was observed, compared to low organic soils. Observations in the avoidance test with F. candida suggest that CAP acted in a prompt way, by affecting collembolan locomotor abilities thus preventing them from escaping contaminated soil. This study shows that CAP may especially pose a risk to non-target soil arthropods closely related to insects, while other soil invertebrates seem rather insensitive.

Shifts of tundra bacterial and archaeal communities along a permafrost thaw gradient in Alaska.

Understanding the response of permafrost microbial communities to climate warming is crucial for evaluating ecosystem feedbacks to global change. This study investigated soil bacterial and archaeal communities by Illumina MiSeq sequencing of 16S rRNA gene amplicons across a permafrost thaw gradient at different depths in Alaska with thaw progression for over three decades. Over 4.6million passing 16S rRNA gene sequences were obtained from a total of 97 samples, corresponding to 61 known classes and 470 genera. Soil depth and the associated soil physical-chemical properties had predominant impacts on the diversity and composition of the microbial communities. Both richness and evenness of the microbial communities decreased with soil depth. Acidobacteria, Verrucomicrobia, Alpha- and Gamma-Proteobacteria dominated the microbial communities in the upper horizon, whereas abundances of Bacteroidetes, Delta-Proteobacteria and Firmicutes increased towards deeper soils. Effects of thaw progression were absent in microbial communities in the near-surface organic soil, probably due to greater temperature variation. Thaw progression decreased the abundances of the majority of the associated taxa in the lower organic soil, but increased the abundances of those in the mineral soil, including groups potentially involved in recalcitrant C degradation (Actinomycetales, Chitinophaga, etc.). The changes in microbial communities may be related to altered soil C sources by thaw progression. Collectively, this study revealed different impacts of thaw in the organic and mineral horizons and suggests the importance of studying both the upper and deeper soils while evaluating microbial responses to permafrost thaw.

Stabilization of Artificial Organic Soil at Room Temperature Using Blended Lime Zeolite

Organic content in soil is believed to inhibit formation of reaction products in lime stabilization which resulted in low gain of strength when dealing with organic soils. Zeolite, a kind of pozzolan with high CEC capacity is proposed to be use in this study in order to improve lime stabilization of organic soil. The effectiveness of blended lime zeolite in stabilization of organic soils was investigated by using two types of artificial organic soils with predetermined organic contents. Artificial organic soils were formed by mixing inorganic soil (commercial kaolin) with organic matter (commercial humic acid) at specific ratio. Initial consumption of lime for organic soils was determined in order to determine the minimum percentage of stabilizer required for each soil. Potential influencing factors that might affect the strength such as organic contents, contents of stabilizer, and curing periods were studied. The findings of the study showed that high organic contents and low lime contents resulted in lower gain of strength. However, it is found that slight replacement of lime with zeolite works well with low organic soil at long curing period which resulted in highest strength among all the mixes. Overall, longer curing periods will increase the strength of the soil in the order of 56 days > 28 days > 7 days. Nevertheless, the percentage of strength increment over curing periods is linear with the lime contents, which proved that lime is required for pozzolanic reaction.

A Field Study of the Fates of Arsenal and Escort Applied on the Cumberland Plateau in Tennessee

Problem statement: The low organic soils of the Cumberland Plateau, as well as the karst geology of the region, may promote increased transport of herbicides outside of application sites. We have studied the fates of imazapyr and metsulfuron-methyl applied to a privately owned tract on the Cumberland Plateau in Tennessee and compared the field results with herbicide fate predicted by the computer model GLEAMS. Approach: The fate of the two herbicides, applied for pine release at a site on the Cumberland Plateau, was monitored over a sixteen month period. Concentrations in soil water were monitored using vacuum soil lysimeters. Grab samples were taken of water in ephemeral streams draining the clearcut area and of a perennial stream which receives water from the study area. Uncut streamside management zones of about 50 m bordered the streams. The field results were compared with those obtained using the GLEAMS computer model. Results: Concentrations of both herbicides in soil water dropped significantly within the first two months after application, imazapyr to less than 50 µg L-1 and metsulfuron-methyl to less than 3 µg L-1 and decreased more gradually in the following months. The maximum concentrations observed in soil water were 252 µg L-1 (imazapyr) and 13 µg L-1 (metsulfuron-methyl). Except on two dates occurring 5 months after application, the herbicides were not detected in the stream samples. GLEAMS predicted that very little herbicide should have been lost from the site in runoff or erosion sediment. The model predicted greater retention of the herbicides by the soil than was found through the field measurements. Conclusion/Recommendation: The rapid transport of imazapyr and metsulfuron we observed indicates that further study is justified at other locations on the Cumberland Plateau. Streamside management zones effectively prohibited contamination of receiving streams by herbicides at the study site.

A Field Study of the Fates of Arsenal and Escort Applied on the Cumberland Plateau in Tennessee

Problem statement: The low organic soils of the Cumberland Plateau, as well as the karst geology of the region, may promote increased transport of herbicides outside of application sites. We have studied the fates of imazapyr and metsulfuron-methyl applied to a privately owned tract on the Cumberland Plateau in Tennessee and compared the field results with herbicide fate predicted by the computer model GLEAMS. Approach: The fate of the two herbicides, applied for pine release at a site on the Cumberland Plateau, was monitored over a sixteen month period. Concentrations in soil water were monitored using vacuum soil lysimeters. Grab samples were taken of water in ephemeral streams draining the clearcut area and of a perennial stream which receives water from the study area. Uncut streamside management zones of about 50 m bordered the streams. The field results were compared with those obtained using the GLEAMS computer model. Results: Concentrations of both herbicides in soil water dropped significantly within the first two months after application, imazapyr to less than 50 µg L −1 and metsulfuron-methyl to less than 3 µg L −1 and decreased more gradually in the following months. The maximum concentrations observed in soil water were 252 µg L −1 (imazapyr) and 13 µg L −1 (metsulfuron-methyl). Except on two dates occurring 5 months after application, the herbicides were not detected in the stream samples. GLEAMS predicted that very little herbicide should have been lost from the site in runoff or erosion sediment. The model predicted greater retention of the herbicides by the soil than was found through the field measurements. Conclusion/Recommendation: The rapid transport of imazapyr and metsulfuron we observed indicates that further study is justified at other locations on the Cumberland Plateau. Streamside management zones effectively prohibited contamination of receiving streams by herbicides at the study site.

Percutaneous Absorption of 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) from Soil

Eight dermal absorption experiments (two in vivo; six in vitro) and one intravenous experiment were conducted using 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) either neat (high dose at ∼250 μg/cm2 and low dose at 10 ng/cm2) or sorbed on a low organic soil (LOS) or high organic soil (HOS) at 1 ppm (10 ng TCDD/10 mg soil/cm2). After 96 h the percent of applied dose absorbed (PADA) for the neat low dose was 78% in vivo (rat) and 76% in vitro (rat). PADA for the equivalent TCDD dose sorbed on LOS were 16.3% (rat in vivo), 7.7% (rat in vitro) and 2.4% (human in vitro). The PADA for TCDD sorbed on HOS (1 ppm) was 1.0% (rat in vitro). Generally, rat skin was observed to be three to four times more permeable to TCDD than human skin. At steady state, the dermal flux of TCDD in neat form, sorbed on LOS at 1 ppm, and sorbed on HOS at 1 ppm (all in vitro, rat) was 120, 0.007, and 0.0007 ng/cm2/h, respectively (ratio = 1.7 × 105:10:1). Making adjustments to account for differences between in vitro and in vivo results and adjusting for application to monolayer loads, the 24-h TCDD absorption for human skin is estimated as 1.9% from LOS (1 ppm) and 0.24% from HOS (1 ppm).

Site‐Specific Sorption Values for Mixtures of Volatile and Semivolatile Organic Compounds in Sandy Soils

AbstractThe purpose of this work was to determine site‐specific partition coefficients, Kd values, for the sorption and desorption of a mixture of 11 volatile and semivolatile organic compounds (VOC and SVOC) in subsurface, low organic soils (average site ƒOC = 0.00019) and ground water from the Toms River superfund site in southern New Jersey. Although literature Kd values are available for some of these compounds, many of the previously published values were measured with single compounds instead of a mixture of compounds. Kd values were determined via column desorption studies using soils with preexisting contamination and uncontaminated site ground water via retardation factors and via batch sorption studies with contaminated ground water and uncontaminated soils. Partition coefficients estimated from the batch and column studies were usually not different across VOC/SVOC and were usually not related to solubility characteristics of the target compounds. Kd values derived from the column experiments were usually an order of magnitude smaller than those estimated from the batch studies. Estimates of Kd values through log KOW or water solubility relationships were usually greater than the experimentally derived Kd values, especially for those compounds with log KOW values greater than 3. Predicted Kd values from the partition models were similar to calculated values for the less hydrophobic compounds (Log KOW < 3). In addition, Kd values determined from batch and column studies were usually smaller than literature values. These comparisons suggest that determining site‐specific partition coefficients is necessary for hydrophobic compounds in soils or sediments that have low organic carbon contents.

Change in Gasoline Constituent Mass Transfer during Soil Venting

The mass transfer of gasoline constituents [benzene, toluene, ethylbenzene, xylenes (BTEX), and naphthalene] to air during laboratory-simulated soil vapor extraction (referred to here as soil venting) was determined. Soil venting was conducted on laboratory-packed columns brought to residual water then residual gasoline saturations. The columns contained either a sandy, low organic soil (0.10% organic carbon), a sandy organic soil (1.65% organic carbon), or glass beads. Gasoline-air partitioning at the start of soil venting was experimentally determined to be adequately described by Raoult’s law for many gasoline constituents of interest. The application of the local equilibrium assumption used to describe the mass transfer of gasoline constituents from the residual gasoline to air during soil venting was investigated using: (1) Experimental techniques such as reduction of air flow rate; flow-interruption and discrete sampling of soil following soil venting; and (2) a local-equilibrium-based model employing Raoult’s law to describe gasoline-air partitioning. The local equilibrium assumption was shown to be valid for describing the mass transfer of various gasoline constituents until such time when the constituent was nearly depleted from the non-aqueous-phase liquid gasoline (NAPL). Mass transfer of constituents became rate-limiting when the constituent was depleted from the residual gasoline. The effect of soil organic matter content was only slightly apparent at this time, as evidenced by the higher benzene and toluene air concentrations in the effluent of columns containing the sandy organic soil.

Changes in the bacterial community after application of oily sludge to soil

The changes in the bacterial flora after application of oily sludge and fertilizer to two different soils, both sandy, but one somewhat richer in organic material, have been studied. Application of oily sludge and fertilizer to the soils had no influence on direct counts. The CFUs increased in the low-organic soil when sludge was applied, but did not change in the richer soil by the same treatment. When both sludge and fertilizer were applied together, strong increases in CFUs were found in both soils. Application of fertilizer together with sludge excluded sporeforming rods and actinomycetes from the poorer soil and strongly stimulated pleomorphic rods+ cocci and non-sporeforming regular rods. The same treatment of the richer soil resulted in an enhancement of CFUs of all tested groups.