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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,783 records · Page 99
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Carbon dioxide Angiography-Guided Renal-Related Interventions in Patients with Takayasu Arteritis and Renal Insufficiency

BackgroundUse of iodinated contrast agents for angiography in patients with renal insufficiency risks further deterioration of renal function and its adverse sequelae.ObjectiveTo study the effectiveness and safety of carbon dioxide (CO{sub 2}) angiography in guiding percutaneous renal-related interventions in patients with Takayasu arteritis and renal insufficiency.MethodsData on CO{sub 2} angiography-guided interventions were obtained from a 23-year database of 692 Takayasu arteritis patients who underwent percutaneous interventions and were analyzed retrospectively. Follow-up data were also obtained. The CO{sub 2} angiography system used was developed in-house and was pressure-driven.ResultsSeven patients (6 female, age 16–59 years, baseline serum creatinine 1.62–4.55 mg/dl, estimated glomerular filtration rate 12.2–36.9 ml/min/1.73 m{sup 2}) underwent CO{sub 2} angiography-guided interventions: five underwent angioplasty or stenting to treat six stenotic/occluded renal arteries, one underwent extensive endovascular repair for spontaneous focal abdominal aortic dissection with false lumen aneurysm and aorto-iliac true lumen narrowing, and one underwent balloon dilatation of previously deployed aortic stents used to treat aortic occlusion at two levels. Follow-up (median 5 years, range 2 months–16 years) was obtained in all patients. All the procedures were successful and resulted in relief of symptoms, better blood pressure control, improvement in left ventricular systolic function and recovery or stabilization of renal function. There were no early or late complications related to CO{sub 2} angiography. Three renal lesions that had restenosis at follow-up were managed successfully by repeat intervention.ConclusionCO{sub 2} angiography-guided renal-related interventions are effective and safe in patients with Takayasu arteritis and renal insufficiency; they significantly improve the care of such patients.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2019

Reason of Discontinuation After Transarterial Chemoembolization Influences Survival in Patients with Hepatocellular Carcinoma

Background: Transarterial chemoembolization (TACE) for intermediate-stage hepatocellular carcinoma (HCC) is often repeated until unTACEable progression (UTP) occurs. There is little data on the various reasons for stopping TACE and its consequences for subsequent treatment and survival. Aim: To assess the impact of the various reasons of UTP on survival and consequences for subsequent treatments. Methods: Consecutive HCC patients who underwent TACE between 2003 and 2016 were analyzed retrospectively for the reason of TACE discontinuation. UTP was defined according to the EASL guidelines, considering radiological pattern of progression, liver function and performance status (PS). Overall and post-progression survival (OS, PPS) for different reasons of TACE discontinuation were compared. The correlation between time to untreatable progression by chemoembolization (TTUPc) and OS was analyzed. Results: One hundred and sixty-six patients (BCLC-A 40%, BCLC-B 54%, BCLC-C: 7%) were included, undergoing a median of 2 TACE procedures with a median OS of 22.1 months (95% CI 17.4–26.7). UTP occurred in 116 patients (70%) after a median TTUPc of 11.6 months (95% CI 7.8–15.4). There was a strong positive correlation (ρ = 0.816, p < 0.001) between TTUPc and OS. The main reason of UTP was radiological progression (61%), which was mostly intrahepatic (75%). Hepatic decompensation and worsening of PS were independent predictors of OS and PPS. Conclusion: The majority of HCC patients treated with TACE have UTP due to intrahepatic tumor progression with preserved liver function and PS, making them potential candidates for subsequent liver-directed or systemic treatment. TTUPc may be a valuable surrogate endpoint for OS in patients treated with TACE. Level of Evidence: Level II, prognosis study.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2019

Radioablation by Image-Guided (HDR) Brachytherapy and Transarterial Chemoembolization in Hepatocellular Carcinoma: A Randomized Phase II Trial

Background and Aims: The aim of this single-center, open-label phase II study was to assess the efficacy of image-guided high-dose-rate (HDR) brachytherapy (iBT) compared with conventional transarterial embolization (cTACE) in unresectable hepatocellular carcinoma. Methods: Seventy-seven patients were treated after randomization to iBT or cTACE, as single or repeated interventions. Crossover was allowed if clinically indicated. The primary endpoint was time to untreatable progression (TTUP). Eligibility criteria included a Child–Pugh score of ≤ 8 points, absence of portal vein thrombosis (PVT) at the affected liver lobe, and ≤ 4 lesions. Survival was analyzed by using the Cox proportional hazard model with stratification for Barcelona Clinic Liver Cancer (BCLC) stages. Results: Twenty patients were classified as BCLC-A (iBT/cTACE 8/12), 35 as BCLC-B (16/19), and 22 as BCLC-C (13/9). The 1-, 2-, and 3-year TTUP probabilities for iBT compared with cTACE were 67.5% versus 55.2%, 56.0% versus 27.4%, and 29.5% versus 11.0%, respectively, with an adjusted hazard ratio (HR) of 0.49 (95% confidence interval 0.27–0.89; p = 0.019). The 1-, 2-, and 3-year TTPs for iBT versus cTACE were 56.0% versus 28.2%, 23.9% versus 6.3%, and 15.9% versus 6.3%, respectively, with an adjusted HR of 0.49 (0.29–0.85; p = 0.011). The 1-, 2-, and 3-year OS rates were 78.4% versus 67.7%, 62.0% versus 47.3%, and 36.7% versus 27.0%, respectively, with an adjusted HR of 0.62 (0.33–1.16; p = 0.136). Conclusions: This explorative phase II trial showed a superior outcome of iBT compared with cTACE in hepatocellular carcinoma and supports proceeding to a phase III trial.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2019

Lymphangiography and Lymphatic Embolization for the Management of Pelvic Lymphocele After Radical Prostatectomy in Prostatic Cancer

Purpose: To retrospectively evaluate the short-term outcomes of lymphangiography and lymphatic embolization in the treatment of pelvic lymphocele after radical prostatectomy in patients with prostate cancer. Materials and Methods: The data of nine, consecutive patients who underwent lymphangiography and lymphatic embolization for pelvic lymphocele after radical prostatectomy with pelvic lymph node dissection (PLND) between January 2016 and May 2018, were retrospectively reviewed. Lymphangiography was performed through inguinal lymph nodes in order to identify the lymphatic leakage. When a leakage was found, lymphatic embolization was performed using a directly punctured fine needle at the closest upstream lymph node or lymphopseudoaneurysm and with N-butyl cyanoacrylate glue. Results: Lymphangiography demonstrated extravasation and/or lymphopseudoaneurysm in all of these patients. A total of 13 sessions of lymphangiography and lymphatic embolization were performed. The median number of lymphangiography and lymphatic embolizations required to achieve clinical success was one (range, 1–3). Three patients underwent repeated embolization with successful results. The technical and clinical success rates were 100%, respectively. The median time to resolution was 7 days (range, 2–19 days). There was no recurrence and no procedure-related complications during the follow-up period (mean, 26 weeks; range, 8–77 weeks) in all patients. Conclusions: Lymphangiography and lymphatic embolization are safe and effective for the management of pelvic lymphoceles after radical prostatectomy with PLND.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2019

Percutaneous Treatment of Giant Cystic Echinococcosis in Liver: Catheterization Technique in Patients with CE1 and CE3a

Purpose: This study aimed to evaluate the efficacy, safety, and follow-up results of the percutaneous treatment of cystic echinococcosis (CE) patients with giant hepatic cysts (at least one diameter > 10 cm). Methods: Between January 2013 and 2018, 31 CE patients with 34 giant cysts classified as CE1 or CE3a (Gharbi type 1 or 2) according to the World Health Organization criteria and treated with the catheterization technique were analyzed retrospectively. Results: Thirty-four giant hepatic cysts were treated using the catheterization technique. Technical success was 100%. One procedure was sufficient for 27 of these cysts, while six patients underwent a second procedure due to recurrence, recollection or complications; one did not accept a repeat procedure and decided to refer to surgery due to pain. Ten (29%) major complications developed. The overall clinical success was 97%. The mean follow-up period was 20 months (5–61 months), and the total reduction in the cyst volume was 92%. Conclusion: The catheterization technique is effective in treating giant CE with acceptable complication rates. Level of Evidence: Level 4, Clinical Investigation.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2019

Safety and Feasibility of Helical I-125 Seed Implants Combined with Transcatheter Arterial Chemoembolization in Hepatocellular Carcinomas with Main Portal Vein Tumor Thrombus

Purpose: To investigate the feasibility and safety of a helical iodine-125 (I-125) seed implant combined with transcatheter arterial chemoembolization (TACE) for the treatment of hepatocellular carcinoma (HCC) with main portal vein tumor thrombus (MPVTT). Methods: From December 2016 to February 2018, 26 cases of HCC with MPVTT patients were enrolled in this prospective study. Helical I-125 seed implants were placed into the portal vein through the percutaneous transhepatic route. Subsequently, TACE was performed. Follow-up with enhanced CT was performed every 6–8 weeks and TACE was repeated if the residual or recurrent tumor was found. Treatment response was measured with the modified response evaluation criteria in solid tumors. Complication rates and overall survival were also evaluated. Results: Implantation and TACE were successful in all patients. There were no grade ≥ 3 complications observed in the patients. The objective response rates (ORR) and disease control rates (DCR) of MPVTT at 3 months after implantation were 42.3% and 84.6%, respectively, whereas ORR and DCR of the liver lesions were 34.6% and 46.2%, respectively. The median overall survival was 10.7 months (95% CI 6.2–15.2 months). Conclusion: Helical I-125 seed implants can be safely placed into the human main portal vein. Helical I-125 seed implants combined with TACE for HCC with MPVTT are safe and feasible.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2019

Propofol Compared to Midazolam Sedation and to General Anesthesia for Percutaneous Microwave Ablation in Patients with Hepatic Malignancies: A Single-Center Comparative Analysis of Three Historical Cohorts

Purpose: In percutaneous ablation procedures, periprocedural pain, unrest and respiratory concerns can be detrimental to achieve a safe and efficacious ablation and impair treatment outcome. This study aimed to compare the association between anesthetic technique and local disease control in patients undergoing percutaneous microwave ablation (MWA) of colorectal liver metastases (CRLM) and hepatocellular carcinoma (HCC). Materials and Methods: This IRB-exempted single-center comparative, retrospective analysis of three cohorts analyzed 90 patients treated for hepatic malignancies from January 2013 until September 2018. The local tumor progression-free survival (LTPFS), safety and periprocedural pain perception were assessed using univariate and multivariate Cox proportional hazard regression analyses to correct for potential confounders. Results: In 114 procedures (22 general anesthesia; 32 midazolam; 60 propofol), 171 liver tumors (136 CRLM; 35 HCC) were treated with percutaneous MWA. Propofol and general anesthesia were superior to midazolam/fentanyl sedation regarding LTPFS (4/94 [4.3%] vs. 19/42 [45.2%] vs. 2/35 [5.7%]; P < 0.001, respectively). Local tumor progression rate was 14.6% (25/171). Eighteen tumors (72.0%) were retreated by ablation. Of them, 14 (78%) were previously treated with midazolam. Propofol versus midazolam (P < 0.001), general anesthesia versus midazolam (P = 0.016), direct postprocedural visual analog pain score above 5 (P = 0.050) and more than one tumor per procedure (P = 0.045) were predictors for LTPFS. Multivariate analysis revealed that propofol versus midazolam (HR 7.94 [95% CI 0.04–0.39; P < 0.001]) and general anesthesia versus midazolam (HR 6.33 [95% CI 0.04–0.69; P = 0.014]) were associated with LTPFS. Pain during and directly after treatment was significantly worse in patients who received midazolam sedation (P < 0.001). Conclusions: Compared to propofol and general anesthesia, midazolam/fentanyl sedation was associated with an increased periprocedural perception of pain and lower local tumor progression-free survival. To reduce the number of repeat procedures required to eradicate hepatic malignancies, general anesthesia and propofol sedation should be favored over midazolam.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2019

Drug-Coated Balloon Angioplasty of Infrapopliteal Lesions in Patients with Critical Limb Ischaemia: 1-Year Results of the APOLLO Trial

Purpose: This study intended to assess effectiveness and safety of the drug-coated balloon (DCB) angioplasty of infrapopliteal atherosclerotic lesions in patients with critical limb ischaemia (CLI) in a real-world setting. Methods: Consecutive patients with critical limb ischaemia who underwent infrapopliteal drug-coated balloon angioplasty with the ELUTAX SV DCB were enrolled into the prospective, multicentre, single-arm observational registry. Primary outcome was clinical improvement at 6 and 12 months. Secondary outcomes were change in quality of life, primary patency, freedom from repeat revascularisation, and amputation-free survival at 6 and 12 months. Results: A total of 164 patients (74.7 ± 9.2 years) with CLI were included at nine German sites between November 2015 and September 2017. The majority (79.9%) of patients had diabetes mellitus, 57.3% had renal insufficiency, and 35.3% had coronary artery disease. Mean lesion length was 71.2 ± 76.5 mm. The Rutherford category improved by 3.0 ± 2.0 (p < 0.0001) within 12 months, resulting in a clinical improvement by at least one Rutherford category in 80.2% of the patients. Walking impairment questionnaire score, European Quality of Life index, and patient-reported pain improved significantly from baseline to 6 and 12 months. Primary patency was 68.5%, freedom from target lesion revascularisation 90.6%, and amputation-free survival 83.5% at 12 months. Conclusion: Infrapopliteal drug-coated balloon angioplasty with the ELUTAX SV DCB in patients with critical limb ischaemia was efficacious and safe over the medium term. The study is registered with Clinical.Trials.gov (Identifier: NCT02539940).

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2019

Transapical Coil Embolization of a Postsurgical Ascending Thoracic Aortic Pseudoaneurysm

Ascending aortic pseudoaneurysms are a rare but potentially life-threatening complication of aortic root or cardiac surgery. Surgical repair is established as first-line treatment; however, patient comorbidities, technical considerations, and anatomic limitations often preclude patients from repeat surgery, thus necessitating alternative approaches. Here, we present a case of coil embolization of an ascending aortic pseudoaneurysm via a transapical approach in a particularly complex scenario where percutaneous and peripheral access was technically unfeasible.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2019

Calculating the Symmetry Number of Flexible Sphere Clusters

We present a theoretical and computational framework to compute the symmetry number of a flexible sphere cluster in R 3 , using a definition of symmetry that arises naturally when calculating the equilibrium probability of a cluster of spheres in the sticky-sphere limit. We define the sticky symmetry group of the cluster as the set of permutations and inversions of the spheres which preserve adjacency and can be realized by continuous deformations of the cluster that do not change the set of contacts or cause particles to overlap. The symmetry number is the size of the sticky symmetry group. We introduce a numerical algorithm to compute the sticky symmetry group and symmetry number, and show it works well on several test cases. Furthermore, we show that once the sticky symmetry group has been calculated for indistinguishable spheres, the symmetry group for partially distinguishable spheres (those with nonidentical interactions) can be efficiently obtained without repeating the laborious parts of the computations. Finally, we use our algorithm to calculate the partition functions of every possible connected cluster of six identical sticky spheres, generating data that may be used to design interactions between spheres so they self-assemble into a desired structure.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2017

Experimental study of shock-accelerated inclined heavy gas cylinder

An experimental study examines shock acceleration with an initially diffuse cylindrical column of sulfur hexafluoride surrounded by air and inclined with respect to the shock front. Three-dimensional vorticity deposition produces flow patterns whose evolution is captured with planar laser-induced fluorescence in two planes. Both planes are thus parallel to the direction of the shock propagation. The first plane is vertical and passes through the axis of the column. The second visualization plane is normal to the first plane and passes through the centerline of the shock tube. Vortex formation in the vertical and centerline planes is initially characterized by different rates and morphologies due to differences in initial vorticity deposition. In the vertical plane, the vortex structure manifests a periodicity that varies with Mach number. The dominant wavelength in the vertical plane can be related to the geometry and compressibility of the initial conditions. At later times, the vortex interaction produces a complex and irregular three-dimensional pattern suggesting transition to turbulence. We present highly repeatable experimental data for Mach numbers 1.13, 1.4, 1.7, and 2.0 at column incline angles of 0, 20, and 30 degrees for about 50 nominal cylinder diameters (30 cm) of downstream travel.

42 ENGINEERING↗
DOE OSTI2020

A new spatially distributed added value index for regional climate models: the EURO-CORDEX and the CORDEX-CORE highest resolution ensembles

The added value of using regional climate models (RCMs) to downscale data from general circulation models (GCMs) has often been questioned and researched. Although several studies have used different methods to identify (and in some cases quantify) the added value, there is still a need to find a general metric that quantifies the added value of any variable. This paper builds on past studies to propose a new metric of added value in the simulation of present-day climate which measures the difference in the probability density functions (PDFs) at each grid-cell between a model and an observation source, and then compares the results of the RCM and GCM in order to spatially compute the added value index. The same method is also adapted to quantify the climate change downscaling signal in a way that is consistent with the present-day metric. These new metrics are tested on the daily precipitation output from the EURO-CORDEX and CORDEX-CORE projection ensembles and reveal an overall positive added value of RCMs, especially at the tail-end of the distribution. Higher added value is obtained in areas of complex topography and coast-lines, as well as in tropical regions. Areas with large added value in present-day climate are consistent with areas of significant climate change downscaling signal in the RCP 8.5 far future simulations, and when the analysis is repeated at a low-resolution. The use of different resolution observations shows that the added value tends to decrease when models are compared to low-resolution observation datasets.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2023

Mallat Scattering Transformation based surrogate for Magnetohydrodynamics

Abstract A Machine and Deep Learning (MLDL) methodology is developed and applied to give a high fidelity, fast surrogate for 2D resistive MagnetoHydroDynamic (MHD) simulations of Magnetic Liner Inertial Fusion (MagLIF) implosions. The resistive MHD code is used to generate an ensemble of implosions with different liner aspect ratios, initial gas preheat temperatures (that is, different adiabats), and different liner perturbations. The liner density and magnetic field as functions of x , y , and z were generated. The Mallat Scattering Transformation (MST) is taken of the logarithm of both fields and a Principal Components Analysis (PCA) is done on the logarithm of the MST of both fields. The fields are projected onto the PCA vectors and a small number of these PCA vector components are kept. Singular Value Decompositions of the cross correlation of the input parameters to the output logarithm of the MST of the fields, and of the cross correlation of the SVD vector components to the PCA vector components are done. This allows the identification of the PCA vectors vis-a-vis the input parameters. Finally, a Multi Layer Perceptron (MLP) neural network with ReLU activation and a simple three layer encoder/decoder architecture is trained on this dataset to predict the PCA vector components of the fields as a function of time. Details of the implosion, stagnation, and the disassembly are well captured. Examination of the PCA vectors and a permutation importance analysis of the MLP show definitive evidence of an inverse turbulent cascade into a dipole emergent behavior. The orientation of the dipole is set by the initial liner perturbation. The analysis is repeated with a version of the MST which includes phase, called Wavelet Phase Harmonics (WPH). While WPH do not give the physical insight of the MST, they can and are inverted to give field configurations as a function of time, including field-to-field correlations.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2024

Beyond the Surface: Non-Invasive Low-Field NMR Analysis of Microbially-Induced Calcium Carbonate Precipitation in Shale Fractures

Microbially-induced calcium carbonate precipitation (MICP) is a biological process in which microbially-produced urease enzymes convert urea and calcium into solid calcium carbonate (CaCO 3 ) deposits. MICP has been demonstrated to reduce permeability in shale fractures under elevated pressures, raising the possibility of applying this technology to enhance shale reservoir storage safety. For this and other applications to become a reality, non-invasive tools are needed to determine how effectively MICP seals shale fractures at subsurface temperatures. In this study, two different MICP strategies were tested on 2.54 cm diameter and 5.08 cm long shale cores with a single fracture at 60 °C. Flow-through, pulsed-flow MICP-treatment was repeatedly applied to Marcellus shale fractures with and without sand (“proppant”) until reaching approximately four orders of magnitude reduction in apparent permeability, while a single application of polymer-based “immersion” MICP-treatment was applied to an Eagle Ford shale fracture with proppant. Low-field nuclear magnetic resonance (LF-NMR) and X-Ray computed microtomography (micro-CT) techniques were used to assess the degree of biomineralization. With the flow-through approach, these tools revealed that while CaCO 3 precipitation occurred throughout the fracture, there was preferential precipitation around proppant. Without proppant, the same approach led to premature sealing at the inlet side of the core. In contrast, immersion MICP-treatment sealed off the fracture edges and showed less mineral precipitation overall. This study highlights the use of LF-NMR relaxometry in characterizing fracture sealing and can help guide NMR logging tools in subsurface remediation efforts.

MICP↗
DOE OSTI2022

Tuning working potential of silicon-phosphorus anode via microstructure control for high-energy lithium-ion batteries

The primary research on anode materials of lithium-ion batteries have been focused on increasing the specific capacity, while the working potential that is also closely related to the practical energy density of batteries has been paid much less attention. In this paper, starting from micrometer-sized silicon and black phosphorus, we have reported a high-energy silicon-phosphorus/carbon anode (denoted as mSPC) via a high-energy ball milling process, which demonstrates an average discharge working potential of 0.3 volts versus lithium, together with a high reversible capacity of > 2000 mAh/g, high initial coulombic efficiency of 84%, excellent cycle stability, and superior rate capability up to 15 A/g. Furthermore, in situ focused-ion-beam scanning electron microscopy reveals that the volume change of the mSPC anode during repeated (de) lithiation is effectively alleviated. In contrast, starting from nanometer-sized silicon, the resulted anode (denoted as nSPC) not only presents a lower reversible capacity (~1200 mAh/g), but also exhibits a higher charge/discharge working potential, leading to reduced energy density. Our results indicate the importance of composition/structure control in tailoring the working potential and specific capacity of alloying-type anodes towards high-energy lithium-ion batteries.

25 ENERGY STORAGE↗
DOE OSTI2017

Human virus and microbial indicator occurrence in public-supply groundwater systems: meta-analysis of 12 international studies

Groundwater quality is often evaluated using microbial indicators. This study examines data from 12 international groundwater studies (conducted 1992–2013) of 718 public drinking-water systems located in a range of hydrogeological settings. Focus was on testing the value of indicator organisms for identifying virus-contaminated wells. One or more indicators and viruses were present in 37 and 15% of 2,273 samples and 44 and 27% of 746 wells, respectively. Escherichia coli ( E. coli ) and somatic coliphage are 7– 9 times more likely to be associated with culturable viruspositive samples when the indicator is present versus when it is absent, while F-specific and somatic coliphages are 8–9 times more likely to be associated with culturable viruspositive wells. However, single indicators are only marginally associated with viruses detected by molecular methods, and all microbial indicators have low sensitivity and positive predictive values for virus occurrence, whether by culturable or molecular assays, i.e., indicators are often absent when viruses are present and the indicators have a high false-positive rate. Wells were divided into three susceptibility subsets based on presence of (1) total coliform bacteria or (2) multiple indicators, or (3) location of wells in karst, fractured bedrock, or gravel/cobble settings. Better associations of some indicators with viruses were observed for (1) and (3). Findings indicate the best indicators are E. coli or somatic coliphage, although both indicators may underestimate virus occurrence. Repeat sampling for indicators improves evaluation of the potential for viral contamination in a well.

58 GEOSCIENCES↗
DOE OSTI2016

Chamber measurements of high CO 2 emissions from a rainforest stream receiving old C-rich regional groundwater

Carbon emissions from fluvial systems are a key component of local and regional carbon cycles. We used floating chambers to investigate the CO 2 flux from stream water to air (f CO 2 ) in the Arboleda, a stream in the lowland rainforest of Costa Rica, fed partly by old regional groundwater high in dissolved inorganic carbon (DIC). Drifting and static chambers showed f CO 2 averaging 35.5 and 72.7 μmol C m –2 s –1 , respectively, bracketing the previously-published f CO 2 value of 56 μmol C m –2 s –1 obtained using tracer methods in this stream. These values are much higher than most f CO 2 data in the literature and reflect a large flux of deep crustal (non-biogenic) CO 2 out of the Arboleda, a flux that does not represent a component of ecosystem respiration. Static chambers appeared to overestimate f CO 2 by creating artificial turbulence, while drifting chambers may have underestimated f CO 2 by under-sampling areas of potentially high gas exchange (e.g., riffles around coarse woody debris obstructions). Both static and drifting chambers revealed high spatial heterogeneity in f CO 2 at the scale of 5–30 m reaches. Some observed temporal trends were localized, e.g., among three reaches with repeated measurements through the wet and dry seasons, (1) only the reach located between the other two showed significantly lower f CO 2 during the dry season, and (2) the highest and lowest f CO 2 were consistently observed in the reaches farthest upstream and downstream, respectively. As a result, streams like the Arboleda receiving significant inputs of high-DIC regional groundwater merit additional study as hotspots for C emissions from terrestrial ecosystems.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2024

The Median Isn’t the Message: soil nutrient hot spots have a disproportionate influence on biogeochemical structure across years, seasons, and depths

Abstract Soil nutrient distribution is heterogeneous in space and time, potentially altering nutrient acquisition by trees and microorganisms. Ecologists have distinguished “hot spots” (HSs) as areas with enhanced and sustained rates of nutrient fluxes relative to the surrounding soil matrix. We evaluated the spatial and temporal patterns in nutrient flux HSs in two mixed-conifer forest soils by repeatedly sampling the soil solution at the same spatial locations (horizontally and vertically) over multiple seasons and years using ion exchange resins incubated in situ. The climate of these forests is Mediterranean, with intense fall rains occurring following summers with little precipitation, and highly variable winter snowfall. Hot spots formed most often for NO 3 − and Na + . Although nutrient HSs often occurred in the same spatial location multiple times, HSs persisted more often for PO 4 3− NH 4 + , and NO 3 − , and were more transient for Ca 2+ , Mg 2+ , and Na + . Sampling year (annual precipitation ranged from 558 to 1223 mm) impacted the occurrence of HSs for most nutrients, but season was only significant for PO 4 3− , NH 4 + , NO 3 − , and Na + , with HSs forming more often after fall rains than after spring snowmelt. The frequency of HSs significantly decreased with soil depth for all nutrients, forming most commonly immediately below the surficial organic horizon. Although HSs accounted for less than 17% of the sampling volume, they were responsible for 56–88% of PO 4 3− , NH 4 + , and NO 3 − resin fluxes. Our results suggest that macronutrient HSs have a disproportional contribution to soil biogeochemical structure, with implications for vegetation nutrient acquisition strategies and biogeochemical models. Graphical abstract

54 ENVIRONMENTAL SCIENCES↗