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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Investigating the influence of lithologic heterogeneity on gas hydrate formation and methane recycling at the base of the gas hydrate stability zone in channelized systems

In marine environments, gas hydrate preferentially accumulates in coarse-grained sediments. At the meso- to micro-scale, however, hydrate distribution in these coarse-grained units is often heterogeneous. We employ a methane hydrate reservoir simulator coupling heat and mass transfer as well as capillary effects to investigate how capillary controls on methane solubility affect gas and hydrate accumulations in reservoirs characterized by graded bedding and alternating sequences of coarse-grained sands and fine-grained silt and clay. Simulations bury a channelized reservoir unit encased in homogeneous, fine-grained material characterized by small pores (150 nm) and low permeability (~1 md in the absence of hydrate). Pore sizes within each reservoir bed between vary between coarse sand and fine silt. Sands have a median pore size of 35 microns and a lognormal pore size distribution. We also investigate how the amount of labile organic carbon (LOC) affects hydrate growth due to microbial methanogenesis within the sediments. In a diffusion-dominated system, methane movies into reservoir layers along spatial gradients in dissolved methane concentration. Hydrate grows in such a way as to minimize these concentration gradients by accumulating slower in finer-grained reservoir layers and faster in coarser-grained layers. Channelized, fining-upwards sediment bodies accumulate hydrate first along their outer surfaces and thence inward from top to bottom. If LOC is present in thin beds within the channel, higher saturations of hydrate will be distributed more homogeneously throughout the unit. When buried beneath the GHSZ, gas recycling can occur only if enough hydrate is present to form a connected gas phase upon dissociation. Simulations indicate that this is difficult to achieve for diffusion-dominated systems, especially those with thick GHSZs and/or small amounts of LOC. However, capillary-driven fracturing behavior may be more prevalent in settings with thick GHSZs.

Daigle, Hugh↗
DOE OSTI2019

Comparison of {sup 238}U, {sup 210}Po and {sup 210}Pb Speciation in Six Different Types of Soils

Speciation of {sup 238}U, {sup 210}Po and {sup 210}Pb in six different types of Syrian soil (Entisols, Inceptisol, Aridisol, Mollisols, Vertisols and Rock outcrops) was studied using a four-step sequential extraction procedure. The binding nature of {sup 238}U, {sup 210}Po and {sup 210}Pb was correlated with soil properties including soil particles, pH, EC, OM, sand, silt and clay. The results showed that the exchangeable and carbonate fractions of {sup 238}U did not exceed 10%. In addition, the {sup 238}U, {sup 210}Po and {sup 210}Pb fractions bonded to organic matter increased as the soil clay content decreased. The highest {sup 210}Po fraction was found to be bonded to soil Fe/Al/Mn-oxides for Entisols soils (56%) and silica for Aridisol soils (53%). Soil clay content showed a linear correlation with {sup 210}Po concentrations in soils ranging from 0.34 to 0.91. The results are considered useful in assessing the risks resulting from soils contaminated by naturally occurring radioactive material from the phosphate and oil industry.

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2011

Reconciling Apparent Variability in Effects of Biochar Amendment on Soil Enzyme Activities by Assay Optimization

Applying biochar to soils as an ameliorative substance and mechanism for C sequestration has received a great deal of interest in light of the sustained fertility observed in the Terra Preta soils of Brazil. The effects of synthetic biochars on biochemical processes needs to be better understood in order to determine if this is a reasonable practice in managed systems. The biochar studied was formed from the fast-pyrolysis of a switchgrass feedstock. Four soil enzymes were studied: β-glucosidase, β-N-acetylglucosaminidase, lipase, and leucine aminopeptidase. Both colorimetric and fluorescent assays were used for β-glucosidase and β-N-acetylglucosaminidase. Seven days after biochar was added to microcosms of a Palouse silt loam, the fluorescence-based assays indicated increased activities of the four enzymes, compared to non-amended soil. To clarify the mechanisms of the observed effects,in the absence of soil, purified enzymes or substrates were briefly exposed to biochar and then assayed. Except for β-N-acetylglucosaminidase, the exposure of substrate to biochar reduced the apparent activity of the remaining three enzymes in vitro, suggesting that sorption reactions between the substrate and biochar either removed the substrate from the assays or impeded the enzyme binding. The activity of purified β-N-acetylglucosaminidase increased significantly following biochar exposure, suggesting a chemical stimulation of enzyme functioning. We conclude that biochar added to soil acts as a substrate that can stimulate the soil microbial biomass and its activity. Our in vitro study suggests that biochar is not biochemically inert. Biochar amendments are likely to have effects that are currently difficult to predict, and that could impact overall soil function.

09 BIOMASS FUELS↗
DOE OSTI2011

Assessment of the methane oxidation capacity of compacted soils intended for use as landfill cover materials

The microbial oxidation of methane in engineered cover soils is considered a potent option for the mitigation of emissions from old landfills or sites containing wastes of low methane generation rates. A laboratory column study was conducted in order to derive design criteria that enable construction of an effective methane oxidising cover from the range of soils that are available to the landfill operator. Therefore, the methane oxidation capacity of different soils was assessed under simulated landfill conditions. Five sandy potential landfill top cover materials with varying contents of silt and clay were investigated with respect to methane oxidation and corresponding soil gas composition over a period of four months. The soils were compacted to 95% of their specific proctor density, resulting in bulk densities of 1.4-1.7 g cm{sup -3}, reflecting considerably unfavourable conditions for methane oxidation due to reduced air-filled porosity. The soil water content was adjusted to field capacity, resulting in water contents ranging from 16.2 to 48.5 vol.%. The investigated inlet fluxes ranged from 25 to about 100 g CH{sub 4} m{sup -2} d{sup -1}, covering the methane load proposed to allow for complete oxidation in landfill covers under Western European climate conditions and hence being suggested as a criterion for release from aftercare. The vertical distribution of gas concentrations, methane flux balances as well as stable carbon isotope studies allowed for clear process identifications. Higher inlet fluxes led to a reduction of the aerated zone, an increase in the absolute methane oxidation rate and a decline of the relative proportion of oxidized methane. For each material, a specific maximum oxidation rate was determined, which varied between 20 and 95 g CH{sub 4} m{sup -2} d{sup -1} and which was positively correlated to the air-filled porosity of the soil. Methane oxidation efficiencies and gas profile data imply a strong link between oxidation capacity and diffusive ingress of atmospheric air. For one material with elevated levels of fine particles and high organic matter content, methane production impeded the quantification of methane oxidation potentials. Regarding the design of landfill cover layers it was concluded that the magnitude of the expected methane load, the texture and expected compaction of the cover material are key variables that need to be known. Based on these, a column study can serve as an appropriate testing system to determine the methane oxidation capacity of a soil intended as landfill cover material.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2015

Fate and transport of contaminants at soils sites - 15512

As part of the Soils Activity of the Environmental Management Operations at the NNSA, Nevada Field Office, radionuclide-contaminated Soils sites will undergo regulatory closure in accordance with the 1996 Nevada Federal Facilities Agreement and Consent Order. One closure alternative that has been evaluated for each Soils site has been -closure-in-place- with fencing and posting, along with administrative controls. However, potential disturbance agents for radionuclide-contaminated soils left in place are possible erosion and transport by wind and water. Previous work with radionuclide-contaminated soils has indicated that the highest activity levels of Pu tend to be found in the fine sands, silts, or clays, which are the most likely particle sizes to be transported by wind re-suspension, and by runoff flow events. Monitoring and sampling stations have been deployed at specific Soils sites to collect meteorological data, airborne particulate filter samples, and both suspended and bed-load sediment transport samples during and after runoff flow events, as needed. The primary objective of the air monitoring and sampling stations is to evaluate whether there is wind transport of radionuclide-contaminated soils from Soils sites. The primary objective of the precipitation and runoff flow data collection, as well as both suspended and bed-load sediment sampling, is to determine during which rainfall events (i.e., precipitation return interval, duration, and intensity) radionuclide-contaminated soils are likely to be transported. The NNSS continues to demonstrate compliance with US DOE Order 458.1 for the Radiation Protection of the Public and the Environment, as reported in annual environmental reports. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2018

Uranium Distribution Coefficient (Kd) Determination and Use in Assessing Transport, Fate, and Risk at Jefferson Proving Ground, I - 18593

Jefferson Proving Ground (JPG), located near Madison, Indiana is a 55,000-acre site with firing ranges for test firing of conventional munitions and depleted uranium penetrators. The penetrators were fired from three positions, but the majority (89 percent) was fired from a single location. Impacts from the penetrators along this firing line created an impact trench roughly 5 meters (m) to 8 m wide, 1,200 m long, and 1 m deep. Periodic surface sweeps were conducted to recover test fired penetrators, but roughly 73,500 kilograms (kg) of depleted uranium (DU) still remain at JPG. Co-located and intermingled with the penetrators are unexploded ordnance (UXO), making complete recovery and site restoration both risky and costly. Understanding the transport and fate of the depleted uranium at JPG was critical to assessing the potential radiological risks posed to human health and the environment from the penetrators and associated impacted soils on site. JPG is underlain by loess (wind-blown silt), glacial till, and carbonate bedrock, and transected by surface water (Big Creek, Middle Fork Creek, and smaller tributaries). The Army determined site-specific values of the uranium distribution coefficient (Kd) for each of the underlying units. The Army evaluated uranium transport and fate in column, groundwater, and surface water models. The Army used the Residual Radiation (RESRAD)- OFFSITE code to complete the uranium risk assessment for a period of 1,000 years. Results from the site-specific Kd tests are presented in this paper along with its use and results in assessing transport, fate, and potential risks associated with exposure to the penetrators remaining at JPG. The authors supported the decommissioning activities discussed in this paper under the direction of and with funding from the U.S. Army, specifically the U.S. Army Installation Management Command (IMCOM, Robert N. Cherry), U.S. Army Environmental Command (AEC, Joan F. Jackson), and U.S. Army Corps of Engineers (USACE, Andrew [Brooks] Evens). (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2019

Erosion Control Measures at Oak Ridge Reservation Landfills Oak Ridge, Tennessee - 19190

URS-CH2M Oak Ridge LLC (UCOR) manages the cleanup of the 2,200-acre East Tennessee Technology Park (ETTP) for its client, the U.S. Department of Energy (DOE), in Oak Ridge, Tennessee. The ETTP was contaminated with radioactive, hazardous and industrial wastes generated by more than 40 years of national defense and energy missions. In disposing of low-level radioactive and other wastes from demolition activities, the UCOR approach relies on the availability of onsite facilities to streamline disposal, reduce costs and enhance cleanup schedules while confining shipments and related hazards onsite. The sanitary/industrial waste facility, known as the Oak Ridge Reservation Landfill Facility (ORRLF) is a solid waste operation that receives and disposes of sanitary/industrial, construction/demolition and classified, special waste; and spoil materials types of waste generated at the U.S. Department of Energy (DOE) Oak Ridge facilities. ETTP is the primary generator; however, the landfill accepts waste from Y-12 National Security Complex (Y-12), Oak Ridge National Laboratory and other DOE prime contractors in the Oak Ridge area. ORRLF's mission is to receive nonhazardous, non-radioactive, and non-Resource Conservation and Recovery Act of 1976 (RCRA)-regulated solid wastes. Approved operations include receiving, compacting, and covering wastes; leachate management, site drainage; erosion control and prevention, inspections, maintenance and recording keeping. The Oak Ridge Reservation has three separate State of Tennessee-permitted active landfills (Landfill IV, Landfill V, and Landfill VII) that meet different disposal needs -- classified industrial waste, industrial waste that includes office trash and cafeteria waste, and construction and demolition debris,. As with a typical landfill, strategic waste placement and covering involves moving a lot of soil, usually resulting in large areas of exposed land. After increased sediment was noted in streams following heavy rains, a concerted erosion prevention and sediment control effort began in 2017. While not uncommon for landfills, the ORRLF staff knew they could do better in controlling sediment. In response, the ORRLF staff developed an approach of aggressive revegetation, ditch improvements and other erosion controls. Staff developed a list of all the areas that needed the most attention and requested resources. UCOR management arranged funding for needed improvements. The oldest of the three landfills is Industrial Landfill IV, which opened in 1989 and has an expected remaining 60 years of life. Therefore, how the landfills are maintained/managed today directly affects the compliance posture, the capacity, and the infrastructure in the future. A systematic, aggressive and multi-pronged approach was taken to address the major concerns first, then continue with longer-term, and/or lower priority projects. Buy-in was obtained from both craft and supervision, resulting in approaches like 'Ditch of the Month'. In addition, management support at the highest levels has provided resources and recognition that further fuels progress. After working on the site for the past year, what used to be exposed brown hills looks more like a golf course now. Now that the grass is established and other erosion controls are in place, the amount of sediment leaving the site has been reduced, and the appearance of the landfills is improved. Vegetation dissipates the kinetic energy from rain droplets while the root system helps hold the soil in place, and wire-reinforced silt fences and straw wattles have greatly improved erosion control. Improved ditches reduce the runoff velocities allowing sediments to fall out of suspension in the stormwater before they reach the receiving waters, and structures are in place to let finer sediment settle in ponds rather than going downstream. In addition, the project has added more stone to roadways to minimize tracking dirt down the road as an average of 20 to 40 trucks per day enter and leave the site. Ongoing landfill erosion and sediment control must be funded and maintained continually. The lack of attention to either resource will negatively affect the condition of the landfill fairly quickly. Constant compliance commitment is necessary to ensure protection to the environment, the operator/workers and the public. Operations must include sediment control, pond maintenance and clean out, road maintenance and construction, erosion prevention, seeps repair, leachate management, landfill expansion, mowing and grounds upkeep and much more. Knowledgeable/experience staff is also crucial. Knowing how to build lifts, create leachate drainage windows, respond to high rains events, compact waste will impact operations today and future operations into the closure / post closure periods. (author)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2015

Predicting the permeability of sediments entering subduction zones

Abstract Using end‐member permeabilities defined by a worldwide compilation of sediment permeabilities at convergent margins, we compare permeability predictions using a geometric mean and a two‐component effective medium theory (EMT). Our implementation of EMT includes a threshold fraction of the high‐permeability component that determines whether flow occurs dominantly in the high‐ or low‐permeability component. We find that this threshold fraction in most cases is equal to the silt + sand‐sized fraction of the sediment. This suggests that sediments undergoing primary consolidation tend to exhibit flow equally distributed between the high‐ and low‐permeability components. We show that the EMT method predicts permeability better than the weighted geometric mean of the end‐member values for clay fractions <0.6. This work provides insight into the microstructural controls on permeability in subducting sediments and valuable guidance for locations which lack site‐specific permeability results but have available grain‐size information.

Daigle, Hugh↗
DOE OSTI2016

Evaluating the long-term hydrology of an evapotranspiration-capillary barrier with a 1000 year design life

A surface barrier (or cover) is a commonly used technology for subsurface remediation. A key function of the barrier is to reduce or eliminate the movement of meteoric precipitation into the underlying waste zone, where it could mobilize and transport contaminants. Surface barriers are expected to perform for centuries to millennia, yet there are very few examples of performance for periods longer than a decade. The Prototype Hanford Barrier was constructed in 1994 over an existing waste site to demonstrate its long-term performance for a design period of 1000 years. This barrier is a field-scale evapotranspiration-capillary (ETC) barrier. In this design, the storage layer consists of 2-m-thick silt loam. The 19-year monitoring results show that the store-and-release mechanism for the ETC barrier worked efficiently as the storage layer was recharged in the winter season (November to March) and the stored water was released to the atmosphere in the summer season (April to October) via soil evaporation and plant transpiration. The capillary break functioned normally in improving the storage capacity and minimizing drainage. The maximum drainage observed through the ET barrier at any of the monitoring stations was only 0.178 mm yr -1 (under an enhanced precipitation condition), which is less than the design criterion. A very small amount (2.0 mm yr -1 on average) of runoff was observed during the 19-year monitoring period. The observed storage capacity of the storage layer was considerably (39%) larger than the estimated value based on the method of equilibrium of water pressure. After a controlled fire in 2008, the newly grown vegetation (primarily shallow-rooted grasses) could still release the stored water and summer precipitation to the atmosphere via transpiration. The findings are useful for predicting water storage and ET under different precipitation conditions and for the design of future barriers.

58 GEOSCIENCES↗
DOE OSTI2017

Substantial soil organic carbon retention along floodplains of mountain streams

Small, snowmelt–dominated mountain streams have the potential to store substantial organic carbon in floodplain sediment because of high inputs of particulate organic matter, relatively lower temperatures compared with lowland regions, and potential for increased moisture conditions. This work (i) quantifies mean soil organic carbon (OC) content along 24 study reaches in the Colorado Rocky Mountains using 660 soil samples, (ii) identifies potential controls of OC content based on soil properties and spatial position with respect to the channel, and (iii) and examines soil properties and OC across various floodplain geomorphic features in the study area. Stepwise multiple linear regression (adjusted r 2 = 0.48, p < 0.001) indicates that percentage of silt and clay, sample depth, percent sand, distance from the channel, and relative elevation from the channel are significant predictors of OC content in the study area. Principle component analysis indicates limited separation between geomorphic floodplain features based on predictors of OC content. A lack of significant differences among floodplain features suggests that the systematic random sampling employed in this study can capture the variability of OC across floodplains in the study area. Mean floodplain OC (6.3 ± 0.3%) is more variable but on average greater than values in uplands (1.5 ± 0.08% to 2.2 ± 0.14%) of the Colorado Front Range and higher than published values from floodplains in other regions, particularly those of larger rivers.

58 GEOSCIENCES↗
DOE OSTI2018

Depressurization-Induced Fines Migration in Sediments Containing Methane Hydrate: X-Ray Computed Tomography Imaging Experiments

Depressurization of hydrate-bearing sediments (HBS) can cause the movement of fine particles, and in turn, such fines migration affects fluid flow and mechanical behavior of sediments, ultimately affecting long-term hydrocarbon production and wellbore stability. In this work, we investigate how and to what extent depressurization of HBS causes fines migration using X-ray computed tomography (CT) imaging. Methane hydrate was synthesized in sediments with 10% fines content (FC), composed of sands with silt and/or clay, and the hydrate-bearing samples were stepwisely depressurized while acquiring CT images. The CT images were analyzed to quantify the spatial changes in FC in the host sediment and thus to capture the fines migration during depressurization. It was found that the FC changes began occurring from the hydrate dissociation regions. This confirms that the multiphase flow caused by depressurization accompanies fines migration. Depressurization of HBS with a hydrate saturation of ~20–40% caused FC reduction from ~10% to ~6–9%, and the extent of fines migration differed with the particle sizes of the host sands and the types of fines. It was found that fines migration was more pronounced with coarse sands and with silty fines. Such observed level of FC reduction is estimated to increase sediment permeability by several factors based on the Kozeny-type permeability model. In conclusion, our results support the notion that the extent of fines migration and its effect on fluid flow behavior need to be assessed in consideration of physical properties of host sediment and fine particles to identify optimum depressurization strategies.

42 ENGINEERING↗
DOE OSTI2017

Chemistry, Mineralogy, and Grain Properties at Namib and High Dunes, Bagnold Dune Field, Gale Crater, Mars: A Synthesis of Curiosity Rover Observations: Bagnold Dune Sands Composition

The Mars Science Laboratory Curiosity rover performed coordinated measurements to examine the textures and compositions of aeolian sands in the active Bagnold dune field. The Bagnold sands are rounded to subrounded, very fine- to medium- sized (~45-500 µm) with ≥6 distinct grain colors. In contrast to sands examined by Curiosity in a dust-covered, inactive bedform called Rocknest and soils at other landing sites, Bagnold sands are darker, less red, better sorted, have fewer silt-sized or smaller grains, and show no evidence for cohesion. Nonetheless, Bagnold mineralogy and Rocknest mineralogy are similar with plagioclase, olivine, and pyroxenes in similar proportions comprising >90% of crystalline phases, along with a substantial amorphous component (35% ± 15%). Yet, Bagnold and Rocknest bulk chemistry differ. Bagnold sands are Si-enriched relative to other soils at Gale crater, and H 2 O, S, and Cl are lower relative to all previously measured martian soils and most Gale crater rocks. Mg, Ni, Fe, and Mn are enriched in the coarse-sieved fraction of Bagnold sands, corroborated by VNIR spectra that suggest enrichment of olivine. Together, patterns in major element chemistry and volatile release data indicate two distinctive volatile reservoirs in martian soils: (1) amorphous components in the sand-sized fraction (represented by Bagnold) that are Si-enriched, hydroxylated alteration products and/or impact or volcanic glasses; and (2) amorphous components in the fine fraction (<40 µm; represented by Rocknest and other bright soils) that are Fe-, S-, and Cl-enriched with low Si and adsorbed and structural H 2 O.

58 GEOSCIENCES↗
DOE OSTI2022

Permeability-Engineered Compartmentalization Enables In Vitro Reconstitution of Sustained Synthetic Biology Systems

In nature, biological compartments such as cells rely on dynamically controlled permeability for matter exchange and complex cellular activities. Likewise, the ability to engineer compartment permeability is crucial for in vitro systems to gain sustainability, robustness, and complexity. However, rendering in vitro compartments such a capability is challenging. Here, a facile strategy is presented to build permeability-configurable compartments, and marked advantages of such compartmentalization are shown in reconstituting sustained synthetic biology systems in vitro. Through microfluidics, the strategy produces micrometer-sized layered microgels whose shell layer serves as a sieving structure for biomolecules and particles. In this configuration, the transport of DNAs, proteins, and bacteriophages across the compartments can be controlled an guided by a physical model. Through permeability engineering, a compartmentalized cell-free protein synthesis system sustains multicycle protein production; ≈100 000 compartments are repeatedly used in a five-cycle synthesis, featuring a yield of 2.2 mg mL -1 . Further, the engineered bacteria-enclosing compartments possess near-perfect phage resistance and enhanced environmental fitness. In a complex river silt environment, compartmentalized whole-cell biosensors show maintained activity throughout the 32 h pollutant monitoring. It is anticipated that permeability-engineered compartmentalization should pave the way for practical synthetic biology applications such as green bioproduction, environmental sensing, and bacteria-based therapeutics.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2020

Irrigation, carbon amelioration, nitrogen, and stover removal effects on continuous corn

Corn (Zea mays L.) residue or stover is harvested as supplemental feed for livestock and is a potential feedstock for cellulosic biofuels. Limited information is available on corn stover removal effects on grain yield under different irrigation rates, nitrogen (N) fertilizer rates, and practices to maintain soil carbon (C) and minimize soil erosion. Here, we evaluated potential interactions between irrigation rate (full or limited), C amelioration practices (cover crop, surface-applied manure, or no amelioration practice), fertilizer N management (125 or 200 kg N ha –1 ), and stover removal (residue removal or no residue removal), on no-till continuous corn grain yield located on a silt loam soil in south-central Nebraska (2011–2018). Stover removal increased (P = .0017) grain yield by 1.02 Mg ha –1 and grain N uptake compared with no stover removal. Manure increased corn grain yield by 899 kg ha –1 compared to either the control or cover crop with stover removal while C amelioration practices did not affect grain yield under stover retention. Grain N concentration was higher (P < .0001) with stover removal (13.2 g kg –1 ) than residue retained (12.7 g kg –1 ). Partial factor productivity (grain yield/N rate) was highest for manure treatments with residue removal. The farmgate N balance (N applied – N removed) from stover removal was negative, yet grain yield was not affected after eight growing seasons. Grain yield increased with stover removal and manure application resulting in a cost-effective C amelioration practice whereas incorporating a winter cover crop resulted in similar grain yield as the control.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2022

Impact of the Three Gorges Dam on riverbed scour and siltation of the middle reaches of the Yangtze River

Abstract This study investigated the influence of the Three Gorges Dam (TGD) on the evolution of nearby channels in the Yangtze River (Changjiang River) system in order to better understand the environmental impact of large‐scale reservoir operations. From 2003 to 2017, the amounts of runoff and sediment transport in the Yangtze River were reduced by 3.3–14.5% and 67.8–92.7%, respectively, relative to 1955–2002 before the TGD was operational. Topographic measurements of the middle reaches (Yichang to Hukou) of the Yangtze River were analyzed from 1975 to 2017, during which time the cumulative erosion of the flood channel was 22.78 × 10 8 m 3 , and the dry channel accounted for 90.3% of the erosion. Following commissioning of the TGD, the scouring intensity of the sandy gravel section near the dam initially increased then decreased, whereas the scouring intensity of sandy sections away from the dam continued to increase. Beaches on convex banks of curved sections were scoured, and deep channels on concave banks became silted. In braided sections, the braids tended to shrink, and the diversion ratio of the main branch during dry seasons reduced, resulting in frequent branch alternation. Compared to changes in the downstream river channels of other large reservoirs worldwide, scouring from the TGD is extensive. The findings of this study are significant for river channel regulation and waterway planning in the Yangtze River and worldwide.

Yang, Yunping↗
DOE OSTI2019

Bound and mobile soil water isotope ratios are affected by soil texture and mineralogy, whereas extraction method influences their measurement

Questions persist about interpreting isotope ratios of bound and mobile soil water pools, particularly relative to clay content and extraction conditions. Interactions between pools and resulting extracted water isotope composition are presumably related to soil texture, yet few studies have manipulated the bound pool to understand its influence on soil water processes. Using a series of drying and spiking experiments, we effectively labelled bound and mobile water pools in soils with varying clay content. Soils were first vacuum dried to remove residual water, which was then replaced with heavy isotope-enriched water prior to oven drying and spiking with heavy isotope-depleted water. Water was extracted via centrifugation or cryogenic vacuum distillation (at four temperatures) and analysed for oxygen and hydrogen isotope ratios via isotope ratio mass spectrometry. Water from centrifuged samples fell along a mixing line between the two added waters but was more enriched in heavy isotopes than the depleted label, demonstrating that despite oven drying, a residual pool remains and mixes with the mobile water. Soils with higher clay + silt content appeared to have a larger bound pool. Water from vacuum distillation samples have a significant temperature effect, with high temperature extractions yielding progressively more heavy isotope-enriched values, suggesting that Rayleigh fractionation occurred at low temperatures in the vacuum line. By distinctly labelling bound and mobile soil water pools, we detected interactions between the two that were dependent on soil texture. Although neither extraction method appeared to completely extract the combined bound and mobile (total water) pool, centrifugation and high temperature cryogenic vacuum distillations were comparable for both δ 2 H and δ 18 O of soil water isotope ratios.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2022

Design and demonstration of a low‐field magnetic resonance imaging rhizotron for in‐field imaging of energy sorghum roots

Abstract Root phenotyping provides critical information to plant breeders for developing varieties with improved drought tolerance, greater root biomass, and greater nutrient use efficiency. Phenotyping roots in the natural environment is important for understanding the effect of the soil environment on root genotypic expressions. The goal of this work was to design and test a field‐scale mobile low‐field magnetic resonance imaging (LF‐MRI) Rhizotron that produces actionable root phenotyping data. We demonstrated this novel technology for root visualization and quantification using a LF‐MRI Rhizotron operating at 47 mT with two soil types. The LF‐MRI Rhizotron weights 453 kg, with a height of 90 cm, a diameter of 28 cm and an imaging field of view of 28 cm × 28 cm. The unit was operated in a Belk clay (Entic Hapluderts) and Weswood silt loam (Udifluventic Halustepts) generating 2‐D and 3‐D image data sets. The 2‐D image data had a collection time of 16.5 min per image at an image resolution of 2.2 mm per pixel. The 3‐D data had a collection time of 13 h per image with a 2.2 × 2.2 × 2.2 mm voxel resolution. Low‐field magnetic resonance imaging worked well for visualizing roots in moderate to high clay soils, demonstrating the potential for this technology; however, the broad application of this platform is hampered due to the prohibitively long scanning time to obtain 3‐D images. By increasing the field strength, and therefore the signal‐to‐noise ratio, faster scan times can enable a more useful system for root phenotyping.

Bagnall, G. Cody↗