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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Surface and Active Layer Water Chemistry, Teller Road Mile Marker 27, Seward Peninsula, Alaska, 2016-2018

This dataset provides the results of spatial surveys of aqueous geochemistry conducted at Teller Road Site, Seward Peninsula, Alaska. Surface water and soil pore water samples were collected from multiple depth within the active layer at designated Intensive Stations 2 through 9 at the Teller Road MM 27 Site (TL_MM27). Reported analytes include dissolved methane and carbon dioxide, dissolved organic and inorganic carbon, major inorganic anions, and major and minor cations. Samples and measurements were collected from 2016-2018. Specifically, samples were collected in September of 2016, August and September of 2017, and August of 2018. Most of the samples were collected from piezometers installed at various depths within the active layer (70 cm max). A few are surface water grab samples. Data are provided in a single comma separated (.xlsx / .csv) file. One supplemental file is also included. It provides the results of a limited set of analyses (dissolved methane and carbon dioxide and Fe(II)) on surface and soil pore water samples collected at Teller (TL_MM27) and Council (CN_MM71) locations in September 2019. The metadata and data are draft with outstanding clarifications and additions to come. The Next-Generation Ecosystem Experiments: Arctic (NGEE Arctic), was a 10-year research effort (2012-2022) to reduce uncertainty in Earth System Models by developing a predictive understanding of carbon-rich Arctic ecosystems and feedbacks to climate. NGEE Arctic was supported by the Department of Energy?s Office of Biological and Environmental Research. The NGEE Arctic project had two field research sites: 1) located within the Arctic polygonal tundra coastal region on the Barrow Environmental Observatory (BEO) and the North Slope near Utqiagvik (Barrow), Alaska and 2) multiple areas on the discontinuous permafrost region of the Seward Peninsula north of Nome, Alaska. Through observations, experiments, and synthesis with existing datasets, NGEE Arctic provided an enhanced knowledge base for multi-scale modeling and contributed to improved process representation at global pan-Arctic scales within the Department of Energy?s Earth system Model (the Energy Exascale Earth System Model, or E3SM), and specifically within the E3SM Land Model component (ELM).

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2020

A Flux Detection Probe to Quantify Dynamic Groundwater-Surface Water Exchange in the Hyporheic Zone

A new probe was designed to quantify groundwater-surface water exchange in the hyporheic zone under dynamic stage condition. Current methods focus on either vertical pore water velocity or Darcy flux measurements. Both parameters must be understood to evaluate residence time and mass flux of constituents. Furthermore, most instruments are not well suited for monitoring instantaneous velocity or flux under dynamic exchange conditions. For this reason, the flux detection probe (FDP) was designed that employs electrogeophysical measurements to estimate in situ sediment porosity, which can be used to convert pore water velocity to Darcy flux. Dynamic pore water velocity is obtained by monitoring fluid conductivity and temperature along the FDP probe. Pressure sensors deployed at the top and bottom of the probe provide the additional information necessary to estimate vertical permeability. This study focuses on the use of a geophysical method to estimate pore water velocity, porosity, and permeability within a controlled soil column where simulated river water displaces simulated groundwater. The difference between probe derived and theoretical pore water velocity using natural tracers such as electrical conductivity and temperature was -4.9 and 3.9% for downward flow and 1.1 and 12.8% for upward flow, respectively. The difference in porosity calculated from mass and volume packed in the soil column and probe measure porosity ranged between -3.2% and 1.5%. Also, the calculated hydraulic conductivity differed from probe derived values by -8.9%.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1991

Method for determining stable isotope ratios of dissolved organic carbon in interstitial and other natural marine waters

A procedure is described for the analysis of the stable carbon isotopic composition of dissolved organic carbon (DOC) in natural waters from marine and higher-salinity environments. Rapid (less than 5 min) and complete oxidation of DOC is achieved using a modification of previous photochemical oxidation techniques. The CO2 evolved from DOC oxidation can be collected in less than 10 min for isotopic analysis. The procedure is at present suitable for oxidation and collection of 1-5 micromoles of carbon and has an associated blank of 0.1-0.2 micromole of carbon. Complete photochemical oxidation of DOC standards was demonstrated by quantitative recovery of CO2 as measured manometrically. Isotopic analyses of standards by photochemical and high-temperature sealed-tube combustion methods agreed to within 0.3%. Photochemical oxidation of DOC in a representative sediment pore-water sample was also quantitative, as shown by the excellent agreement between the photochemical and sealed-tube methods. The delta 13C values obtained for pore-water DOC using the two methods of oxidation were identical, suggesting that the modified photochemical method is adequate for the isotopically non-fractionated oxidation of pore-water DOC. The procedure was evaluated through an analysis of DOC in pond and pore waters from a hypersaline microbial mat environment. Concentrations of DOC in the water column over the mat displayed a diel pattern, but the isotopic composition of this DOC remained relatively constant (average delta 13C = -12.4%). Pore-water DOC exhibited a distinct concentration maximum in the mat surface layer, and delta 13C of pore-water DOC was nearly 8% lighter at 1.5-2.0-cm depth than in the mat surface layer (0-0.5-cm depth). These results demonstrate the effectiveness of the method in elucidating differences in DOC concentration and delta 13C over biogeochemically relevant spatial and temporal scales. Carbon isotopic analysis of DOC in natural waters, especially pore waters, should be a useful probe of biogeochemical processes in recent environments.

NASA Discipline Exobiology↗
DOE OSTI2023

High methane concentrations in tidal salt marsh soils: Where does the methane go?

Abstract Tidal salt marshes produce and emit CH 4 . Therefore, it is critical to understand the biogeochemical controls that regulate CH 4 spatial and temporal dynamics in wetlands. The prevailing paradigm assumes that acetoclastic methanogenesis is the dominant pathway for CH 4 production, and higher salinity concentrations inhibit CH 4 production in salt marshes. Recent evidence shows that CH 4 is produced within salt marshes via methylotrophic methanogenesis, a process not inhibited by sulfate reduction. To further explore this conundrum, we performed measurements of soil–atmosphere CH 4 and CO 2 fluxes coupled with depth profiles of soil CH 4 and CO 2 pore water gas concentrations, stable and radioisotopes, pore water chemistry, and microbial community composition to assess CH 4 production and fate within a temperate tidal salt marsh. We found unexpectedly high CH 4 concentrations up to 145,000 μmol mol −1 positively correlated with S 2− (salinity range: 6.6–14.5 ppt). Despite large CH 4 production within the soil, soil–atmosphere CH 4 fluxes were low but with higher emissions and extreme variability during plant senescence (84.3 ± 684.4 nmol m −2 s −1 ). CH 4 and CO 2 within the soil pore water were produced from young carbon, with most Δ 14 C‐CH 4 and Δ 14 C‐CO 2 values at or above modern. We found evidence that CH 4 within soils was produced by methylotrophic and hydrogenotrophic methanogenesis. Several pathways exist after CH 4 is produced, including diffusion into the atmosphere, CH 4 oxidation, and lateral export to adjacent tidal creeks; the latter being the most likely dominant flux. Our findings demonstrate that CH 4 production and fluxes are biogeochemically heterogeneous, with multiple processes and pathways that can co‐occur and vary in importance over the year. This study highlights the potential for high CH 4 production, the need to understand the underlying biogeochemical controls, and the challenges of evaluating CH 4 budgets and blue carbon in salt marshes.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2021

Colloidal metal transport in soils developing on historic coal mine spoil

Chemical weathering of pyrite via oxidative dissolution is well-known for generating Fe(III)-bearing colloids at acid mine drainage (AMD) sites; however, the potential for physical weathering of pyrite-bearing materials and subsequent release and transport of colloidal pyrite and associated trace metals has not been studied. Here, we monitored the colloidal metal transport in soil developing on abandoned coal mine spoil with a history of AMD generation to systematically study the contribution of colloids to base and trace metal transport and determine the elemental and mineralogical composition of colloids. Additionally, we collected soil pore water using lysimeters with a pore size of approximately 1.3 μm and centrifugation was used to separate the colloids from aqueous fractions. Metal concentrations of Na, Ca, Mg, K, Si, Al, Mn, Fe, Cu, and Zn were analyzed. Our results show only 14% of the total Al and Cu were present in colloidal fractions whereas 23%, 43%, and 54% of Fe, Mn, and Zn were transported in the colloidal phase, respectively. In contrast, all base metals were primarily present in the aqueous concentration with a small fraction (<10%) present in the colloidal phase. The colloidal fractions of the base metals were inferred to be associated with the concentration of clay colloids. The release of colloids exhibited possible sensitivity toward weather conditions such as alternating high temperatures and rainfall during summer (May–July) compared to fall (August–November). The morphology, elemental, and mineral composition of colloids were determined by a scanning electron microscopy equipped with energy dispersive spectroscopy (SEM-EDS) and X-ray diffraction (XRD). Colloids were dominated by phyllosilicates (biotite, muscovite, and kaolinite) with minor quartz and feldspars. Other minerals phases identified in colloidal fractions were hematite, goethite, arsenopyrite, and chalcopyrite. Colloids consisting of Fe, S, and O with structures resembling framboidal pyrite were identified, which is consistent with the non-silicates minerals identified by XRD. Our study suggests that the physical weathering of pyrite in the mine spoil can generate colloidal pyrite, which is mobilized and transported by soil pore water. Our results also indicate that these pyritic colloids are associated with toxic trace metals including Cu, Mn, and Zn. Colloid mobilization is also impacted by changes in temperature and precipitation, where clay mobilization afer rain events is favored. Further, sudden spikes in aqueous and/or colloidal concentrations may be the result of local heterogeneity within soils developing on mine spoil, indicating that further field-based work is necessary to better characterize pore-scale processes that control aqueous and colloid transport at similar sites to have a better understanding of potential contaminant transport from mine spoil systems.

58 GEOSCIENCES↗
DOE OSTI2024

Characterization of Nitrate, Nitrite, Ammonia, and Tritium in D0220 Cores

This report describes characterization of nitrogen species (nitrate, nitrite, ammonia) in aqueous and solid phases in cores taken in borehole D0220 (well 299-E25-245) under crib 216-A-37-1 at the Hanford Site in 2022 to evaluate (a) the types of nitrogen species currently in the vadose zone and (b) the migration of nitrogen species in the vadose zone. Ammonia and tritium from PUREX decladding condensate were sporadically discharged to the crib from 1977 to 1989. During discharge operations, the estimated travel time through the vadose zone to groundwater was 2.5 to 9 months. By 2003, a characterization borehole (C4106) showed residual pore water with elevated tritium and nitrate in the first 100 ft of the vadose zone, which is likely from the crib. However, there was significantly more nitrate present at the shallowest depth (15 to 22 ft), which may indicate a different source for nitrate, such as adsorbed ammonia slowly being oxidized or nitrogen species precipitates slowly dissolving. In this study, more extensive nitrogen species characterization was done on D0220 cores (drilled in 2022) at 40- and 262-ft depths, which included (a) aqueous nitrate, nitrite, and tritium; (b) adsorbed ammonia; (c) nitrogen in carbonates (or other minerals dissolved in acidic acid); (d) nitrogen in iron oxides (or other minerals dissolved in oxalic acid); and (e) nitrogen in hard-to-extract minerals (minerals dissolved in nitric acid). High pore water nitrate (226 to 331 mg/L) at 40-ft depth measured in D0220 (2022) compared to 60 mg/L at 40-ft depth in C4106 (2003) may indicate nitrate is migrating deeper. Tritium concentrations (pore water 132,000 to 148,000 pCi/L) measured in D0220 at 40-ft depth in 2022 were considerably higher than in C4106 at 40-ft depth (160 pCi/L). Additional nitrogen species mass was present in adsorbed and precipitated phases in D0220 cores. Low adsorbed ammonia was measured at 40.1- and 261.7-ft depths. Low concentrations of carbonate associated nitrogen and iron oxide-associated nitrogen were present at 40.1 and 40.6 ft depths. Nitrogen species in solid phase extractions indicate nitrogen precipitates or aqueous nitrate or ammonia trapped in sediment microfractures that are coated by precipitates. Overall, the nitrogen species and tritium characterization at two depths in D0220 showed that additional nitrogen species were present in the vadose zone. In addition, elevated pore water nitrate in D0220 at 40 ft depth from 2022 may indicate vertical migration compared to C4106 nitrate profile from 2003. Analysis of additional depths in D0220 and spatial variability of the nitrate plume along the length of the crib (from surface electrical resistivity) would be extremely useful for this comparison.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2022

High nitrate variability on an Alaskan permafrost hillslope dominated by alder shrubs

Abstract. In Arctic ecosystems, increasing temperatures are driving the expansion of nitrogen (N) fixing shrubs across tundra landscapes. The implications of this expansion to the biogeochemistry of Arctic ecosystems are of critical importance and more work is needed to better understand the form, availability, and transportation potential of N from these shrubs across a variety of Arctic landscapes. To gain insights into the processes controlling N within a permafrost hillslope system, the spatiotemporal variability of nitrate (NO3-) and its environmental controls were investigated at an alder (Alnus viridis spp. fruticosa) dominated permafrost tundra landscape in the Seward Peninsula, Alaska, USA. Soil pore water was collected from locations within alder shrubland growing along a well-drained hillslope and was compared to soil pore water collected from locations outside (upslope, downslope, and between) the alder shrubland. Soil pore water collected within alder shrubland had an average NO3-N (nitrogen from nitrate) concentration of 4.27±8.02 mg L−1 and differed significantly from locations outside alder shrubland (0.23±0.83 mg L−1; p<0.05). Temporal variation in NO3-N within and downslope of alder shrubland co-occurred with precipitation events where NO3- that accumulated in the soil was likely flushed downslope during rainfall. These findings have important implications for nutrient availability and mobility in N-limited permafrost systems that are experiencing shrub expansion in response to a warming Arctic.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2024

Data for publication: "A fresh take: Seasonal changes in terrestrial freshwater inputs impact salt marsh hydrology and vegetation dynamics"

This data repository contains data associated with the manuscript "A fresh take: Seasonal changes in terrestrial freshwater inputs impact salt marsh hydrology and vegetation dynamics". This study was conducted at the Elkhorn Slough National Estuarine Research Reserve in Watsonville, California from October 2019 - June 2022. We sought to understand the role of shallow freshwater inputs from adjacent uplands on salt marsh hydrologic behavior and vegetation productivity. This dataset contains CSV files of the following: daily salt marsh subsurface water level and pore water conductivity, monthly vegetation survey measurements, soil core data. Estuary surface water level, conductivity, and local precipitation were downloaded from the National Estuarine Research Reserve System (Centralized Data Management Office) at https://cdmo.baruch.sc.edu/.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS2014

Estimating Major Ion and Nutrient Concentrations in Mangrove Estuaries in Everglades National Park Using Leaf and Satellite Reflectance

Coastal mangrove ecosystems are under duress worldwide because of urban development, sea-level rise, and climate change, processes that are capable of changing the salinity and nutrient concentration of the water utilized by the mangroves. This study correlates long-term water chemistry in mangrove environments, located in Everglades National Park,with mangrove spectral reflectance measurements made at both the leaf and canopy scales. Spectral reflectance measurements were collected using a handheld spectrometer for leaf-level measurements and Landsat 5TMdata for regional coverage. Leaf-level reflectance data were collected from three mangrove species (i.e., red, black and white mangroves) across two regions; a tall mangrove (approximately 18m) and dwarf mangrove (1- 2 m) region. The reflectance data were then used to calculate a wide variety of biophysical reflectance indices (e.g., NDVI, EVI, SAVI) to determine signs of stress. Discrete, quarterly water samples from the surface water, groundwater, and pore water (20 and 85 cm depths) and daily autonomous surface water samples were collected at each site and analyzed for major anions (Cl(−) and SO(2(-)/4)), cations (Na(+), K(+), Mg(sup 2(+)), and Ca(sup 2(+)), total nitrogen (TN) and total phosphorus (TP).Mangrove sites that exhibited the highest salinity and ionic concentrations in the surface and subsurface water also had the lowest near-infrared reflectance at both the leaf and satellite levels. Seasonal reflectance responses were measured in the near-infrared (NIR) wavelengths at both the leaf and canopy scales and were strongly correlated with nutrient and ionic concentrations in the surface and subsurface water, even though there was no significant separability between the three mangrove species. Study sites that experienced the greatest variability in surface and subsurface water ionic concentrations also exhibited the greatest fluctuations in NIR spectral reflectance. Landsat 5TM images were able to detect tall and dwarf mangroves by the differences in spectral indices (e.g., NDVI, NDWI, and EVI) because of the variability in the background conditions amongst the environments. In addition, Landsat 5TM images spanning 16 years (1993- 2009) were successfully used to estimate the seasonal variability in ionic concentrations in the surface water across the Florida Coastal mangrove ecotone. This study has shown that water chemistry can be estimated indirectly by measuring the change in spectral response at the leaf- or satellite-scale. Furthermore, the results of this research may be extrapolated to similar coastal mangrove systems throughout the Caribbean and world-wide wherever red, black, and white mangroves occur.

Mangroves↗
NASA NTRS2024

Hydrocarbon Burn Facility, SWMU 007 Per- and Polyfluoroalkyl Substances (PFAS) Assessment Report Addendum

This document discusses the Per-and Polyfluoroalkyl Substances (PFAS) assessment activities performed from May through August 2023 at the Hydrocarbon Burn Facility (HBF) located at Kennedy Space Center (KSC), Florida. HBF was used for firefighting training between 1966 and 1994. Aqueous film-forming foams (AFFFs) that contained PFAS were used as suppressants for fighting petroleum fuel fires during training. PFAS sampling was first completed at HBF in 2015. This PFAS Assessment Report Addendum (ARA) is a continuation of sampling efforts, with an overall objective to further delineate PFAS concentrations in groundwater to the pGCTLs and the United States Environmental Protection Agency (EPA) Tapwater Regional Screening Levels (RSLs) dated November 2023 and better understand groundwater to surface water interaction at the Site. The field activities presented in this PFAS ARA were conducted between May and August 2023 and included the collection of 132 direct push groundwater samples and the collection of five colocated surface water, sediment, and pore water samples from locations south/southeast of HBF in August 2023. Exceedances of the pGCTLs and Tapwater RSLs were observed in the direct push groundwater results; however, groundwater has been delineated to the pGCTLs. Exceedances of the Florida provisional Surface Water Screening Levels (pSWSLs) were observed in surface water and porewater, and concentrations of PFAS in these media confirm PFAS migration within surface channels to the south of the HBF site area. Maximum sediment concentrations, which correlate with the maximum surface water and porewater concentrations, demonstrate that PFAS impacted surface water is the source of sediment impacts. Overall, elevated concentrations of PFAS are centered on the HBF site area that trend north and south along the surface water filled swales and along the edge of Banana River. Based on analytical results, not all surface water features in this area exhibit evidence of transport. PFAS migration/transport appears to be more dominant in surface water features during the wet season. Discharges to the Banana River primarily occur where surface water facilitates transport. In contrast, groundwater transport is more effective during the dry season. During precipitation events in either the dry season or the wet season, there appears to be migration from the intermediate groundwater zone to the shallow zone into the surface water features. Additional sampling and data collection is recommended to support further refinement of PFAS groundwater delineation, a remedial alternative evaluation, and the fate and transport model.

Jennifer Buel↗
NASA NTRS2013

Bulk Moisture and Salinity Sensor

Measurement and feedback control of nutrient solutions in plant root zones is critical to the development of healthy plants in both terrestrial and reduced-gravity environments. In addition to the water content, the amount of fertilizer in the nutrient solution is important to plant health. This typically requires a separate set of sensors to accomplish. A combination bulk moisture and salinity sensor has been designed, built, and tested with different nutrient solutions in several substrates. The substrates include glass beads, a clay-like substrate, and a nutrient-enriched substrate with the presence of plant roots. By measuring two key parameters, the sensor is able to monitor both the volumetric water content and salinity of the nutrient solution in bulk media. Many commercially available moisture sensors are point sensors, making localized measurements over a small volume at the point of insertion. Consequently, they are more prone to suffer from interferences with air bubbles, contact area of media, and root growth. This makes it difficult to get an accurate representation of true moisture content and distribution in the bulk media. Additionally, a network of point sensors is required, increasing the cabling, data acquisition, and calibration requirements. measure the dielectric properties of a material in the annular space of the vessel. Because the pore water in the media often has high salinity, a method to measure the media moisture content and salinity simultaneously was devised. Characterization of the frequency response for capacitance and conductance across the electrodes was completed for 2-mm glass bead media, 1- to 2-mm Turface (a clay like media), and 1- to 2-mm fertilized Turface with the presence of root mass. These measurements were then used to find empirical relationships among capacitance (C), the dissipation factor (D), the volumetric water content, and the pore water salinity.

Nurge, Mark↗
DOE OSTI2026

Assessment of the hydromechanical higher-order MPM for the simulation of geotechnical problems

The Material Point Method (MPM) has been increasingly used to simulate large strain deformations. Linear interpolation functions are commonly used to perform the spatial integration. It is well-known that the discontinuities in the interpolation function derivatives induce shock-like artifacts known as ‘cell-crossing’ error. These errors compound with volumetric locking errors when used with hydromechanical formulations for porous media, where different velocity fields are used for each phase. The capabilities of higher-order MPM frameworks have not been explored for real-scale geotechnical problems. As such, this paper aims to assess, validate, and further discuss a higher-order B-spline MPM (BS-MPM) framework. First, the BS-MPM framework is verified against the large-strain oedometer consolidation problem. Second, the framework is validated against a real-scale slope failure experiment triggered by pore water pressure recharge. Landslide features that are captured using the higher-order framework are specifically highlighted, and results (e.g., pore water pressure and deformation) are validated with field measurements. A generally convergent numerical solution is observed when using cubic interpolation functions. Third, a footing penetration problem is simulated using the multi-patch BS-MPM. Trends are examined with respect to penetration velocity and variation in hydraulic conductivity. The BS-MPM framework ultimately presents a stabilized numerical solution that captures plausible hydromechanical interaction trends important in geotechnical engineering applications.

36 MATERIALS SCIENCE↗
NASA NTRS1992

Acetate concentrations and oxidation in salt marsh sediments

Acetate concentrations and rates of acetate oxidation and sulfate reduction were measured in S. alterniflora sediments in New Hampshire and Massachusetts. Pore water extracted from cores by squeezing or centrifugation contained in greater than 0.1 mM acetate and, in some instances, greater than 1.0 mM. Pore water sampled nondestructively contained much less acetate, often less than 0.01 mM. Acetate was associated with roots, and concentrations varied with changes in plant physiology. Acetate turnover was very low whether whole core or slurry incubations were used. Radiotracers injected directly into soils yielded rates of sulfate reduction and acetate oxidation not significantly different from core incubation techniques. Regardless of incubation method, acetate oxidation did not account for a substantial percentage of sulfate reduction. These results differ markedly from data for unvegetated coastal sediments where acetate levels are low, oxidation rate constants are high, and acetate oxication rates greatly exceed rates of sulfate reduction. The discrepancy between rates of acetate oxidation and sulfate reduction in these marsh soils may be due either to the utilization of substrates other than acetate by sulfate reducers or artifacts associated with measurements of organic utilization by rhizosphere bacteria. Care must be taken when interpreting data from salt marsh sediments since the release of material from roots during coring may affect the concentrations of certain compounds as well as influencing results obtained when sediment incubations are employed.

Source record↗
DOE OSTI2023

Investigation of the Effect of Injected CO 2 on the Morrow B Sandstone through Laboratory Batch Reaction Experiments: Implications for CO 2 Sequestration in the Farnsworth Unit, Northern Texas, USA

About one million tons of CO 2 have been injected into the Farnsworth unit to date. The target reservoir for CO 2 injection is the Morrow B Sandstone, which is primarily made of quartz with lesser amounts of albite, calcite, chlorite, and clay minerals. The impact of CO 2 injection on the mineralogy, porosity, and pore water composition of the Morrow B Sandstone is a major concern. Although numerical modeling studies suggest that porosity changes will be minimal, significant alterations to mineralogy and pore water composition are expected. Given the implications for CO 2 storage effectiveness and risk assessment, it is crucial to verify the accuracy of theoretical model predictions through laboratory experiments. To this end, batch reaction experiments were conducted to model conditions near an injection well in the Morrow B Sandstone and at locations further away, where the CO 2 has been diluted by formation water. The laboratory experiments involved submerging thin sections of both coarse- and fine-grained facies of the Morrow B Sandstone in formation water samples with varying levels of CO 2 . The experiments were conducted at the reservoir temperature of 75 °C. Two experimental runs were conducted, one lasting for 61 days and the other for 72 days. The initial fluid composition used in the second run was the same as in the first. The mineralogy changes in the thin sections were analyzed using SEM and the Tescan Integrated Mineral Analyzer (TIMA), while changes in the composition of the formation water were determined using ICP-AES. During each experiment, a thin layer of white fine-grained particles consisting mainly of dolomite and silica formed on the surface of the thin sections, leading to significant reductions in Ca, Mg, and Sr in the formation water. This outcome is consistent with numerical model predictions that dolomite would be the primary mineral that would react with injected CO 2 and that silica would be oversaturated in the formation water. Changes in mineral abundance in the thin sections themselves were much less systematic than in the theoretical modeling experiments, perhaps reflecting heterogeneities in the mineral grain size surface area to volume ratios and mineral distributions in the thin sections not considered in the numerical models.

58 GEOSCIENCES↗
DOE OSTI2022

Fast redox switches lead to rapid transformation of goethite in humid tropical soils: A Mössbauer spectroscopy study

Abstract Humid tropical forest soils experience frequent rainfall, which limits oxygen diffusion and creates redox heterogeneity in upland soils. In this study we gauged the effect of short‐term anoxic conditions on Fe mineralogy of relatively Fe‐ and C‐rich surface soils (C/Fe mole ratio ∼5) from a humid tropical forest in Puerto Rico. Soils subjected to 4‐d oxic/anoxic oscillation were characterized by selective chemical extractions, Mössbauer spectroscopy (MBS), and X‐ray diffraction. Chemical extraction data suggested that rapidly switching redox conditions had subtle effects on bulk Fe mineralogy. Mössbauer, on the other hand, indicated that (a) the soil Fe is a mixture of goethites of varying characteristics with minor contributions from ferrihydrite (<5%) and Fe(III)‐organic matter (OM) phases (∼10%), and (b) anoxic conditions rapidly transformed all forms of goethite to relatively stable Fe oxides. Such fast changes in goethite features could be due to rapid depletion and sorption of bio‐released structural Al or sorbed OM onto residual soil components. The rapid temporal changes in MBS parameters and corresponding pore water nominal oxidation state of C values suggest that Fe‐C transformations in these upland tropical soils are complex and intricately coupled. A comprehensive understanding of the fate of Fe, Al, and OM (Fe‐organic moieties) during redox switches and concurrent changes in pore water chemistry is critical for development of robust transport models in humid tropical soils, which are subject to episodic low‐redox events.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2022

Sources and Variability of Nitrate on an Alaskan Hillslope Dominated by Alder Shrubs, Kougarok, Alaska, 2017 and 2018

Data provided include results of analyses of soil pore-water, soil moisture, and leaf litter samples collected at a Kougarok Hillslope site dominated by alder shrubs (KG_MM64) in the Seward Peninsula, Alaska during July and September 2017 and 2018. Samples were from surface soils in close proximity to 5 alder patches, collected upslope, within, and downslope of the alder patches. Pore water was analyzed for a comprehensive set of anions, cations, elemental analyses, and oxygen and nitrogen isotopes. Soil samples were collected for soil moisture determination. Leaf litter extracts were analyzed for carbon and nitrogen content and carbon and nitrogen isotopes. This dataset contains 3 *.csv files and 1 *.pdf file. The Next-Generation Ecosystem Experiments: Arctic (NGEE Arctic), was a research effort to reduce uncertainty in Earth System Models by developing a predictive understanding of carbon-rich Arctic ecosystems and feedbacks to climate. NGEE Arctic was supported by the Department of Energy's Office of Biological and Environmental Research. The NGEE Arctic project had two field research sites: 1) located within the Arctic polygonal tundra coastal region on the Barrow Environmental Observatory (BEO) and the North Slope near Utqiagvik (Barrow), Alaska and 2) multiple areas on the discontinuous permafrost region of the Seward Peninsula north of Nome, Alaska. Through observations, experiments, and synthesis with existing datasets, NGEE Arctic provided an enhanced knowledge base for multi-scale modeling and contributed to improved process representation at global pan-Arctic scales within the Department of Energy's Earth system Model (the Energy Exascale Earth System Model, or E3SM), and specifically within the E3SM Land Model component (ELM).

54 ENVIRONMENTAL SCIENCES↗