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DOE OSTI2026

Data for Impacts of Legacy and Contemporary Nitrogen Inputs on N2O and CO2 Emissions in Miscanthus and Maize Cultivated Soils

Nutrient inputs influence the sustainability of bioenergy crop production through contemporary (shortly after addition) and legacy effects (persisting over years) on microbial nitrogen (N) and carbon cycling, which contribute to greenhouse gas emissions. However, the relative importance of contemporary and legacy effects and how that could vary by crop functional types is poorly understood. Considering its rhizomatous roots and perennial growth, we hypothesized that Miscanthus × giganteu s ( M × g ) would be more sensitive to legacy N fertilization and the historical context of its environment than an annual crop like maize. To test this hypothesis, we examined the effects of legacy and contemporary N inputs on nitrous oxide (N2O) and carbon dioxide (CO2) emissions, as well as key N cycling genes in soils where M × g and maize were grown. A 150-day soil incubation experiment was conducted using soils from a long-term M × g and maize fertility experiment with three historic N fertilization rates (0, 112, and 336 kg N ha−1 year−1) and a contemporary amendment (60 mg N kg−1) with negative control (0 mg N kg−1). We observed significant increases in cumulative N2O emissions in M × g soils relative to maize soils, particularly at higher legacy fertilization rates, while contemporary N had no significant effect. Bacterial amoA gene abundance, which plays a significant role in nitrification in nutrient-rich soils, also increased with higher legacy fertilization rates in M × g soils but was unaffected by the contemporary N. In maize soils, legacy and contemporary N did not significantly affect N2O emissions, but cumulative CO2 emissions and amoA gene abundance significantly increased. The abundances of norB genes were not significantly influenced by either legacy fertilization or contemporary N amendments in either soil. Our findings demonstrate the greater importance of fertilization history over contemporary N in mediating soil N2O emissions, particularly for perennial bioenergy crops.

Carbon↗

DOE OSTI2024

Constraints and Drivers of Dissolved Fluxes of Pyrogenic Carbon in Soil and Freshwater Systems: A Global Review and Meta‐Analysis

Abstract Pyrogenic carbon (PyC) is a significant component of the global soil carbon pool due to its longer environmental persistence than other soil organic matter components. Despite PyC's persistence in soil, recent work has indicated that it is susceptible to loss processes such as mineralization and leaching, with the significance and magnitude of these largely unknown at the hillslope and watershed scales. We present a review of the work concerning dissolved PyC transport in soil and freshwater. Our analysis found that the primary environmental controls on dissolved PyC (dPyC) transport are the formation conditions and quality of the PyC itself, with longer and higher temperature charring conditions leading to less transport of dPyC. While correlations between dPyC and dissolved organic carbon in rivers and other pools are frequently reported, the slope of these correlations was pool‐dependent (i.e., soil‐water, precipitation, lakes, streams, rivers), suggesting site‐specific environmental controls. However, the lack of consistency in analytical techniques and sample preparation remains a major challenge to quantifying environmental controls on dPyC fluxes. We propose that future research should focus on the following: (a) consistency in methodological approaches, (b) more quantitative measures of dPyC in pools and fluxes from soils to streams, (c) turnover times of dPyC in soils and aquatic systems, and (d) improved understanding of how mechanisms controlling the fate of dPyC in dynamic post‐fire landscapes interact. With more refined quantitative information about the controls on dPyC transport at the hillslope and landscape scale, we can increase the accuracy and utility of global carbon models.

58 GEOSCIENCES↗

DOE OSTI2025

Carbon-carbon interactions in warm dense titanium carbide

Encouraged by experimental reports of diamond precipitation in carbon-containing materials under warm dense matter conditions and in shock compression experiments, we examine the behavior of carbon in TiC using density functional theory-molecular dynamics simulations. Two polymorphs of TiC are considered, the ambient-pressure B1 ($Fm$$\overline{3}$$m$) structure in which C-C interactions are prevented by geometric constraints, and a high-pressure Cmcm structure in which C atoms condense into zigzag chains. Chemistry-inspired bonding analyses confirm the covalently bound nature of these chains and further illuminate important interatomic interactions in both structures. Upon melting of B1 TiC, new short-range C-C interactions develop in the liquid, while the pre-existing C-C interactions in Cmcm TiC persist in the liquid. Here, the resulting carbon networks in the melt provide a promising environment for eventual diamond nucleation.

Ab initio molecular dynamics↗

NASA NTRS2023

Tree Growth Enhancement Drives a Persistent Biomass Gain in Unmanaged Temperate Forests

While enhanced tree growth over the last decades has been reported in forests across the globe, it remains unclear whether it drives persistent biomass increases of forest stands, particularly in mature forests. Enhanced tree growth and stand-level biomass are often linked with a simultaneous increase in density-driven mortality and a reduction in tree longevity. Identifying empirical evidence regarding the balance between these processes is challenging due to the confounding effects of stand history, management, and environmental changes. Here, we investigate the link between growth and biomass via the negative relationship between average tree size and stand density (tree number per area). We find increasing stand density for a given mean tree size in unmanaged closed-canopy forests in Switzerland over the past six decades and a positive relationship between tree growth and stand density across forest plots—qualitatively consistent with our simulations using a mechanistic, cohort-resolving ecosystem model (BiomeE). Model simulations show that, in the absence of other disturbances, enhanced tree growth persistently increases biomass stocks despite simultaneous decreases in carbon residence time and tree longevity. However, the magnitude of simulated biomass changes for a given growth enhancement critically depends on the shape of the mortality functions. Our analyses reconcile reports of growth-induced reductions of tree longevity with model predictions of persistent biomass increases, and with our finding of trends toward denser forests in response to growth—also in mature stands.

biomass stocks↗

NASA NTRS2013

Evaluation of Contrail Reduction Strategies Based on Environmental and Operational Costs

This paper evaluates a set of contrail reduction strategies based on environmental and operational costs. A linear climate model was first used to convert climate effects of carbon dioxide emissions and aircraft contrails to changes in Absolute Global Temperature Potential, a metric that measures the mean surface temperature change due to aircraft emissions and persistent contrail formations. The concept of social cost of carbon and the carbon auction price from recent California's cap-and-trade system were then used to relate the carbon dioxide emissions and contrail formations to an environmental cost index. The strategy for contrail reduction is based on minimizing contrail formations by altering the aircraft's cruising altitude. The strategy uses a user-defined factor to trade off between contrail reduction and additional fuel burn and carbon dioxide emissions. A higher value of tradeoff factor results in more contrail reduction but also more fuel burn and carbon emissions. The strategy is considered favorable when the net environmental cost benefit exceeds the operational cost. The results show how the net environmental benefit varies with different decision-making time-horizon and different carbon cost. The cost models provide a guidance to select the trade-off factor that will result in the most net environmental benefit.

social cost of carbon↗

NASA NTRS2020

Unexpected Source and Transport of Iron from the Deep Peru Margin

Iron is the most important micronutrient in the ocean, but the nature and magnitude of its sources and sinks to the ocean are poorly constrained. Here we assess our understanding of the sources and sinks of iron in margin environments by synthesizing observations from the U.S. GEOTRACES GP16 Eastern Tropical Pacific Zonal Transect (EPZT) cruise near the Peru margin. GP16 observations showed elevated dissolved iron (dFe) concentrations along the margin, but a larger westward plume of dFe at slope depths (1000-3000 m) in oxygenated waters, rather than at shelf depths (100-300 m) in oxygen deficient waters. We examine the potential explanations for this unexpected observation. Multiple tracers from GP16 suggest that sediment resuspension was important at slope depths, which would lead to enhanced benthic flux of dFe above what was previously measured. The difference in the apparent persistence and penetration of shelf vs slope plumes of dFe into the interior of the ocean likely results from faster removal rates of the shelf dFe compared to slope dFe. DFe sourced from the shelf was almost entirely in the dFe(II) form, whereas dFe sourced from the slope was almost entirely in the dFe(III) form. Although benthic dFe(II) diffuses into oxygen deficient overlying waters, there is still oxidation of dFe(II), which precipitates to particulate Fe(III). In contrast, the slope plume appears to persist in a stabilized dFe(III) form. We hypothesize that sediment porewaters with moderate organic carbon delivery to sediments and shallow oxygen penetration are especially good sources of persistent dFe to the water column.

iron↗

DOE OSTI2025

Glaciers in California’s Sierra Nevada are likely disappearing for the first time in the Holocene

Mountain glaciers are sensitive climate indicators. Glaciers in the western United States are projected to disappear by 2100 CE, but whether they were previously absent in the current interglacial (past 11,700 years) remains debated. Here, we present evidence that two of the largest glaciers in California’s Sierra Nevada near Yosemite National Park persisted throughout the Holocene. Cosmogenic in situ carbon-14 and beryllium-10 exposure dating in newly exposed proglacial bedrock indicates continuous Holocene cover, likely by ice. At a nearby smaller glacier, bedrock exposure-burial ages suggest glacier expansion at ~7 thousand years ago, earlier than previously recognized. Moraine exposure ages at these sites and the Sierra Nevada’s largest glacier are distributed across the past several thousand years, suggesting that glaciers were near their preindustrial extent for much of the late Holocene. These findings imply that a glacier-free Sierra Nevada is unprecedented since before the Holocene. Future alpine glacial environments in California are thereby likely a no-analog scenario within the current interglacial.

Jones, Andrew G. [University of Wisconsin, Madison↗

DOE OSTI2026

Alginate–Amorphous Calcium Carbonate Hydrogels for Controlled Therapeutic Release

Alginate hydrogels are widely explored as biocompatible matrices for transdermal delivery of therapeutic compounds but burst release and mechanical stability remain persistent challenges in drug delivery systems. This experimental study investigated alginate–amorphous calcium carbonate (ACC) hydrogel composites designed to regulate release of model anti-inflammatory compound, ibuprofen. Hydrogels containing 1.6–2.0 wt% sodium alginate were crosslinked with CaCl₂ and combined with ACC through two incorporation pathways: (i) separate addition of ACC and ibuprofen or (ii) co-precipitation of ACC onto ibuprofen prior to hydrogel incorporation. Hydrogels without ACC served as Control. Biocomposite structure and properties were characterized and release profiles quantified using Korsmeyer–Peppas (KP) model.Burst release was curbed as crosslinking time increased, highlighting importance of network density in diffusion control. Co-precipitating ACC with ibuprofen prior to incorporating into the hydrogel suppressed burst release and sustained release for > ~72 h. Rheological measurements indicate ACC reinforces hydrogel network, increasing storage modulus while maintaining hydration and flexibility. KP model indicates release is diffusion-controlled, with deviations reflecting contributions from diffusion barriers and morphologic/structural changes near the ACC coated ibuprofen. ACC within alginate hydrogels provides a strategy for tuning drug release while preserving mechanical properties relevant to transdermal applications.

36 MATERIALS SCIENCE↗

DOE OSTI2024

Corrosion-Resistant Non-Carbon Electrocatalyst Supports for PEFCS

Insufficient durability of commercial catalysts is a persistent issue for PEFC applications.1 Herein, Pt on Nb-doped-TiO 2 is reported as a highly durable electrocatalyst on which the direct 4-electron reduction of oxygen to water is more facile compared to Pt/C. All performance metrics are reported comparing Pt/Nb-TiO2 with a 15% Pt loading, against a commercial Pt/C catalyst (46.5% Pt loading, Tanaka, K. K.). Nb-doped-TiO 2 with high surface area and high electronic conductivity was synthesized using the supercritical fluid method. Initially, the durability of the catalyst was characterized using accelerated stability tests (ASTs) involving 10,000 high potential cycles (DOE/FCCJ protocol) and the Pt/Nb-TiO 2 was found to retain 78% of its initial electrochemically active surface area (ECSA) compared to the 57.6 % retained by Pt/C. These observations were in excellent agreement with previous reports that the Pt particle size of Pt/C grew from 2nm to 8nm during the AST protocol along with severe corrosion and amorphization of the carbon surface.2, 3 TEM and XPS studies of the Pt-Nb-doped-TiO 2 catalyst showed that the Pt particle size grew from 3nm to 6nm and the Nb(IV) and Ti(III) in the support were oxidized to Nb(V) and Ti(IV) after the durability test. Thus, the improvement in Pt/Nb-TiO 2 ECSA retention was attributed to the lower extent of particle growth and lack of oxidative support loss upon oxidation as compared to Pt/C. The oxygen reduction reaction (ORR) performance was characterized by linear polarization using a rotating disk electrode (RDE). The electrochemical surface areas of Pt/Nb-TiO 2 and Pt/C were found to be 48m2·g -1 and 83m2·g -1 respectively, and the mass activity for the ORR at 0.9V vs. RHE were found to be 150 mA·mg-1Pt and 124 mA·mg-1Pt respectively. The improved mass activity on Pt/Nb-TiO 2 was attributed to strong metal support interaction (SMSI) between the Nb-TiO 2 support and the Pt catalyst based on the 625 meV decrease in the binding energy of the Pt4f x-ray photo-electron spectroscopy (XPS) peaks of Pt/Nb-TiO 2 compared to Pt/C. To quantify the impact of the SMSI, a kinetic model was applied to calculate the elementary reaction rate constants for the various steps of the ORR on both catalysts. The reaction rate constant (k1) for the direct 4-electron transfer pathway to produce H 2 O was significantly larger in Pt/Nb-TiO 2 as compared to Pt/C. Thus, the reduction in the electron binding energy as observed in the XPS was found to aid the facile filling of the higher energy 2p orbitals of O 2 thereby leading to improved 4-electron transfer kinetics and improved overall activity.

08 HYDROGEN↗

DOE OSTI2024

Impacts of Legacy and Contemporary Nitrogen Inputs on N 2 O and CO 2 Emissions in Miscanthus and Maize Cultivated Soils

ABSTRACT Nutrient inputs influence the sustainability of bioenergy crop production through contemporary (shortly after addition) and legacy effects (persisting over years) on microbial nitrogen (N) and carbon cycling, which contribute to greenhouse gas emissions. However, the relative importance of contemporary and legacy effects and how that could vary by crop functional types is poorly understood. Considering its rhizomatous roots and perennial growth, we hypothesized that Miscanthus × giganteus (M×g) would be more sensitive to legacy N fertilization and the historical context of its environment than an annual crop like maize. To test this hypothesis, we examined the effects of legacy and contemporary N inputs on nitrous oxide (N 2 O) and carbon dioxide (CO 2 ) emissions, as well as key N cycling genes in soils where M×g and maize were grown. A 150‐day soil incubation experiment was conducted using soils from a long‐term M×g and maize fertility experiment with three historic N fertilization rates (0, 112, and 336 kg N ha −1 year −1 ) and a contemporary amendment (60 mg N kg −1 ) with negative control (0 mg N kg −1 ). We observed significant increases in cumulative N 2 O emissions in Mxg soils relative to maize soils, particularly at higher legacy fertilization rates, while contemporary N had no significant effect. Bacterial amo A gene abundance, which plays a significant role in nitrification in nutrient‐rich soils, also increased with higher legacy fertilization rates in M×g soils but was unaffected by the contemporary N. In maize soils, legacy and contemporary N did not significantly affect N 2 O emissions, but cumulative CO 2 emissions and amo A gene abundance significantly increased. The abundances of nor B genes were not significantly influenced by either legacy fertilization or contemporary N amendments in either soil. Our findings demonstrate the greater importance of fertilization history over contemporary N in mediating soil N 2 O emissions, particularly for perennial bioenergy crops.

09 BIOMASS FUELS↗

DOE OSTI2024

germs-lab/PAPER_miscanthus_soil_response

Nutrient inputs influence the sustainability of bioenergy crop production through contemporary (shortly after addition) and legacy effects (persisting over years) on microbial nitrogen (N) and carbon cycling, which contribute to greenhouse gas emissions. However, the relative importance of contemporary and legacy effects and how that could vary by crop functional types is poorly understood. Considering its rhizomatous roots and perennial growth, we hypothesized that Miscanthus × giganteus (M×g) would be more sensitive to legacy N fertilization and the historical context of its environment than an annual crop like maize. To test this hypothesis, we examined the effects of legacy and contemporary N inputs on nitrous oxide (N2O) and carbon dioxide (CO2) emissions, as well as key N cycling genes in soils where M×g and maize were grown. A 150-day soil incubation experiment was conducted using soils from a long-term M×g and maize fertility experiment with three historic N fertilization rates (0, 112, and 336 kg N ha−1 year−1) and a contemporary amendment (60 mg N kg−1) with negative control (0 mg N kg−1). We observed significant increases in cumulative N2O emissions in Mxg soils relative to maize soils, particularly at higher legacy fertilization rates, while contemporary N had no significant effect. Bacterial amoA gene abundance, which plays a significant role in nitrification in nutrient-rich soils, also increased with higher legacy fertilization rates in M×g soils but was unaffected by the contemporary N. In maize soils, legacy and contemporary N did not significantly affect N2O emissions, but cumulative CO2 emissions and amoA gene abundance significantly increased. The abundances of norB genes were not significantly influenced by either legacy fertilization or contemporary N amendments in either soil. Our findings demonstrate the greater importance of fertilization history over contemporary N in mediating soil N2O emissions, particularly for perennial bioenergy crops.

Lee, Jaejin↗

DOE OSTI2024

Design of biphenylene-derived tunable dirac materials

The exploration of carbon allotropes has unveiled a series of two-dimensional (2D) materials with unique electronic and mechanical properties, yet the need for stable structures with tailored electronic properties persists. Here, in this study, we introduce a new class of 2D carbon allotropes derived from the biphenylene network (BPN), incorporating acetylenic linkages to tune their structural and electronic characteristics. Through density functional theory calculations, we identified ten novel BPN-derived structures that exhibit both energetic and dynamic stability, confirmed by cohesive energy and phonon spectrum analyses. Among them, BPN-02 and BPN04 are metallic, featuring critically-tilted type-III Dirac cones under ~ 5 % biaxial strain, while BPN-22 is a semiconductor with a band gap of 0.95 eV and exhibits highly anisotropic carrier mobility. Additionally, these structures demonstrate significant anisotropy in their elastic properties, further distinguishing them from other 2D carbon materials like graphene. Our findings suggest that these novel BPN-based structures have strong potential for next-generation electronic and optoelectronic applications, providing new avenues for the design and synthesis of advanced carbon materials.

2D carbon allotropes↗

DOE OSTI2026

Ultra-Low Amounts of Transition Metals in Carbon-Based Catalysts Improve Their Alkaline OER Performance: A Systematic Study

The pursuit of green hydrogen production highlights a persistent gap in electrocatalyst research: while academic efforts prioritize cost-efficiency via activity enhancement, industrial viability demands greater emphasis on electrochemical stability. Carbon-based electrocatalysts, particularly those incorporating transition metals, have shown promise in alkaline oxygen evolution (OER) due to their high activity, cost-efficiency, and resource-efficiency. However, these catalysts suffer from insufficient stability under oxidizing conditions compared to pure transition metal catalysts due to erosion of the carbon support resulting from carbon corrosion, among other degradation mechanisms. In this systematic study, the influence of ultra-low amounts (<1 wt %) of iron, cobalt, nickel, and their most common combinations on the stability of a hydrothermally derived, N-doped carbon support and the overall catalyst performance during alkaline OER is systematically explored. By identifying critical stability descriptors and correlating them with synthesis conditions and catalyst properties, primary and secondary corrosion pathways are unraveled. Subsequently, through careful adjustment of carbonization temperature and composition of incorporated transition metals, overall catalyst corrosion can be suppressed immensely. Especially, the inclusion of Ni and Fe is paramount for the formation of stable catalyst materials under laboratory conditions (10 mA/cm 2 in 0.1 M KOH), which is surprisingly unconstrained by the degree of graphitization of the carbon support. Mixing this electrochemically stable material with a graphitic carbon powder results in an excellent stability of over 400 h at 100 mA/cm 2 in 1 M KOH, implying great potential for the future improvement of carbon-based electrodes under oxidizing conditions toward industrial application.

N-doped carbon↗

DOE OSTI2025

Observations and modeling reveal that heatwaves reduce photosynthesis, plant carbon reserves, and net carbon uptake

Heatwaves threaten ecosystem carbon balances, yet the mechanisms driving short-term carbon flux responses remain poorly understood. Here, integrating high-frequency eddy covariance (EC) data from 140 global flux tower sites (872 site-years) with detailed process-based modeling, we examine ecosystem responses during and immediately after heatwaves. We show that heatwaves caused a −40% (range [−29%, −128%]) reduction in net ecosystem productivity (NEP) compared to pre-heatwave values, with this reduction persisting over the following two weeks (−38% range [+3%, −154%]). We attributed NEP decreases to photosynthesis decreases more than to ecosystem respiration (RE) increases. Forest sites had greater NEP decreases during heatwaves than non-forest sites, but remained carbon sinks afterwards, indicating resilience. Our modeling analysis of extreme heatwaves at selected EC sites shows that decreased photosynthesis, increased maintenance respiration, and decreased plant non-structural carbon reserves during heatwaves drive carbon cycle changes that persist for weeks. Consistent with phenocam observations, we modeled a reduction in leaf area index caused by reduced non-structural carbon reserves, leading to early leaf senescence and longer-term impacts. Ongoing increases in heatwaves are therefore likely to reduce NEP across a range of ecosystems, exacerbating carbon cycle feedback.

carbon cycle↗

NASA NTRS2003

Strangelove Ocean and Deposition of Unusual Shallow-Water Carbonates After the End-Permian Mass Extinction

The severe mass extinction of marine and terrestrial organisms at the end of the Permian Period (approx. 251 Ma) was accompanied by a rapid negative excursion of approx. 3 to 4 per mil in the carbon-isotope ratio of the global surface oceans and atmosphere that persisted for some 500,000 into the Early Triassic. Simulations with an ocean-atmosphere/carbon-cycle model suggest that the isotope excursion can be explained by collapse of ocean primary productivity (a Strangelove Ocean) and changes in the delivery and cycling of carbon in the ocean and on land. Model results also suggest that perturbations of the global carbon cycle resulting from the extinctions led to short-term fluctuations in atmospheric pCO2 and ocean carbonate deposition, and to a long-term (>1 Ma) decrease in sedimentary burial of organic carbon in the Triassic. Deposition of calcium carbonate is a major sink of river-derived ocean alkalinity and for CO2 from the ocean/atmosphere system. The end of the Permian was marked by extinction of most calcium carbonate secreting organisms. Therefore, the reduction of carbonate accumulation made the oceans vulnerable to a build-up of alkalinity and related fluctuations in atmospheric CO2. Our model results suggest that an increase in ocean carbonate-ion concentration should cause increased carbonate accumulation rates in shallow-water settings. After the end-Permian extinctions, early Triassic shallow-water sediments show an abundance of abiogenic and microbial carbonates that removed CaCO3 from the ocean and may have prevented a full 'ocean-alkalinity crisis' from developing.

Rampino, Michael R.↗

DOE OSTI2025

Lipids represent a dynamic, yet stable pool of microbially-derived soil carbon

There is an emerging consensus that microorganisms are a primary source of persistent, slow-cycling soil organic matter (SOM), however which microbial residues contribute to SOM and what controls their accumulation remains unresolved. Lipids are a commonly overlooked biomolecular pool that could contribute significantly to stable SOM. While current estimates for phospholipid degradation in soils are rapid, lipids are structurally heterogeneous molecules that could turnover at different rates. Through a year-long soil incubation and compound-specific, stable isotope probing (SIP)-lipidomics, we were able to rigorously track the persistence of lipid compounds in silty and sandy switchgrass bioenergy crop soils. Here, we assessed the influence of lipid structure on soil lipid accrual and degradation as moderated by soil texture, since mineral association is presumed to be the primary mechanism for lipid persistence. After rapid incorporation of 13 C glucose into microbial biomass, we found 13 C label was retained broadly across chemically diverse lipid classes, even after one year. 13 C-labeled lipid profiles varied significantly with soil texture; however, we found no difference between sandy and silty soils in lipid retention, suggesting soil texture may only play a minor role in modulating lipid persistence. Only two lipid subclasses were found to be persistent (i.e., retention of 13 C label without significant degradation or production): phosphatidylinositol lipids and hydroxyceramide lipids, both of which are negatively charged, possibly facilitating stabilization by mineral complexation. However, several other subclasses displayed substantial ongoing production. In particular, the accumulation of triacylglycerol lipids across soil textures suggests that storage lipids may be an important component of SOC, highlighting a potential target for management strategies to promote C retention by lipid accrual. Overall, the retention for over a year of 13 C label in microbial intact lipid biomarkers reveals the importance of efficient biomass production and turnover when considering microbial C contributions to SOM.

compound-specific↗

DOE OSTI2026

Interactions between molecular-scale biogeochemical processes and hyporheic exchange for understanding coupled Fe-S-C cycling in iron-rich riparian wetlands (Final Technical Report)

Riparian wetlands are dynamic interfaces that exert strong control over water quality, contaminant mobility, and greenhouse gas emissions. These systems are characterized by hyporheic exchange between oxic surface water and anoxic groundwater, which generates steep redox gradients and promotes spatially and temporally variable microbial activity. Despite growing recognition of tightly coupled iron (Fe), sulfur (S), and carbon (C) cycling in these environments, the mechanisms governing these interactions—particularly under low-sulfate freshwater conditions—remain poorly constrained. This project developed a mechanistic understanding of how hydrologic variability and microbial processes interact to control Fe–S–C cycling in iron-rich riparian wetlands. Using a multi-scale and multi-method approach integrating field observations, geochemical and spectroscopic analyses, metagenomics, and reactive transport modeling, we demonstrate that “cryptic” sulfur cycling—rapid sulfur transformations involving intermediate-valence species—plays a dominant and previously underrecognized role in freshwater wetlands. These processes persist despite low sulfate concentrations and significantly influence iron reduction, carbon mineralization, and methane dynamics. The results show that cryptic sulfur cycling enhances dissolved Fe 2+ production, regulates methane concentrations, and is strongly controlled by climate-driven hydrologic fluxes. By linking hydroclimate, subsurface flow, and biogeochemical reactions, this work provides a predictive framework for understanding how wetland systems respond to environmental change, with direct implications for water quality and carbon cycling.

54 ENVIRONMENTAL SCIENCES↗

NASA NTRS2019

Integrating Remote Sensing Observations with NASA's GEOS-5 Modeling Framework in Support of Retrospective Analyses and Seasonal Prediction of Biosphere-Atmosphere CO2 Flux

The absorption of nearly half of all anthropogenic carbon dioxide (CO2) emissions by terrestrial and marine ecosystems has played a critical role in mitigating climate change. However, a persistent lack of understanding of these uptake processes impedes attribution, and thereby introduces large uncertainties into projections of the trajectory of carbon and climate in coming decades. A better understanding and quantification of the seasonal and interannual variability of carbon flux between the atmosphere and ocean and terrestrial biospheres is critically needed to improve predictions from Earth system models. We propose to bring together a diverse suite of remote sensing observations, mechanistic models, and NASA's Goddard Earth Observing System, version 5 (GEOS-5) model to address two objective 1) quantify the processes controlling the temporal variability of biosphere-atmosphere CO2 flux on seasonal and interannual timescales from 1989 to 2018 and 2) evaluating the predictability of the components of carbon flux on seasonal timescales. Because GEOS-5 has been developed to incorporate a variety of Earth system observations and includes a complete and physically consistent depiction of the atmosphere, land, and ocean carbon cycles, it represents a unique and ideal synthesis framework for this effort. By expanding the realism of processes that could be included in GEOS-5 seasonal forecasts, this effort supports NASA's goals toward an integrated Earth system modeling and prediction framework.We propose to integrate a number of observations into the GEOS-5 modeling system to refine retrospective estimates of both terrestrial and marine carbon flux and to test hypotheses regarding the effects of climate drivers on terrestrial carbon flux. This will include assimilating several satellite ocean color products in the NASA Ocean Biogeochemistry Model (NOBM) to improve the representation of ocean biology. We will also utilize remote sensing datasets to increase the temporal resolution of global land-use change estimates and fire emissions to better constrain the temporal variability of the terrestrial carbon cycle. This information will be incorporated into two NASA terrestrial biosphere models Catchment-CN, a dynamic vegetation model that is integrated within GEOS-5 and the Ecosystem Demography (ED) model, a core modeling resource supporting the Global Ecosystem Dynamics Investigation (GEDI) mission to map biomass. Fluxes will be evaluated through 1) comparison to top-down flux estimates inferred from surface CO2 observations and 2) comparison against available aircraft and satellite observations.By combining predictions of net ecosystem exchange and air-sea CO2 flux from land and ocean models with statistical predictions of land use change, fire, and fossil fuel emissions, we propose to create the first dynamical CO2 forecast on seasonal timescales. Because of the experimental nature of this endeavor, an important project objective will be to evaluate the limits to the predictability of different carbon cycle processes over lead times of 1-12 months using different satellite and surface data streams.

Ott, Lesley↗