Flux Measurements Research Articles

Mix-method toolbox for monitoring greenhouse gas production and microbiome responses to soil amendments

In this study, we adopt an interdisciplinary approach, integrating agronomic field experiments with soil chemistry, molecular biology techniques, and statistics to investigate the impact of organic residue amendments, such as vinasse (a by-product of sugarcane ethanol production), on soil microbiome and greenhouse gas (GHG) production. The research investigates the effects of distinct disturbances, including organic residue application alone or combined with inorganic N fertilizer on the environment. The methods assess soil microbiome dynamics (composition and function), GHG emissions, and plant productivity. Detailed steps for field experimental setup, soil sampling, soil chemical analyses, determination of bacterial and fungal community diversity, quantification of genes related to nitrification and denitrification pathways, measurement and analysis of gas fluxes (N2O, CH4, and CO2), and determination of plant productivity are provided. The outcomes of the methods are detailed in our publications (Lourenço et al., 2018a; Lourenço et al., 2018b; Lourenço et al., 2019; Lourenço et al., 2020). Additionally, the statistical methods and scripts used for analyzing large datasets are outlined. The aim is to assist researchers by addressing common challenges in large-scale field experiments, offering practical recommendations to avoid common pitfalls, and proposing potential analyses, thereby encouraging collaboration among diverse research groups.•Interdisciplinary methods and scientific questions allow for exploring broader interconnected environmental problems.•The proposed method can serve as a model and protocol for evaluating the impact of soil amendments on soil microbiome, GHG emissions, and plant productivity, promoting more sustainable management practices.•Time-series data can offer detailed insights into specific ecosystems, particularly concerning soil microbiota (taxonomy and functions).

Ocean surface radiation measurement best practices

Ocean surface radiation measurement best practices have been developed as a first step to support the interoperability of radiation measurements across multiple ocean platforms and between land and ocean networks. This document describes the consensus by a working group of radiation measurement experts from land, ocean, and aircraft communities. The scope was limited to broadband shortwave (solar) and longwave (terrestrial infrared) surface irradiance measurements for quantification of the surface radiation budget. Best practices for spectral measurements for biological purposes like photosynthetically active radiation and ocean color are only mentioned briefly to motivate future interactions between the physical surface flux and biological radiation measurement communities. Topics discussed in these best practices include instrument selection, handling of sensors and installation, data quality monitoring, data processing, and calibration. It is recognized that platform and resource limitations may prohibit incorporating all best practices into all measurements and that spatial coverage is also an important motivator for expanding current networks. Thus, one of the key recommendations is to perform interoperability experiments that can help quantify the uncertainty of different practices and lay the groundwork for a multi-tiered global network with a mix of high-accuracy reference stations and lower-cost platforms and practices that can fill in spatial gaps.

Quantifying the fluxes of carbon loss from an undrained tropical peatland ecosystem in Indonesia

Conservation of undrained tropical peatland ecosystems is critical for climate change mitigation as they store a tremendous amount of soil carbon that is preserved under anoxic water-logged conditions. Unfortunately, there are too few measurements of carbon fluxes from these ecosystems to estimate the climate change mitigation potential from such conservation efforts. Here, we measured carbon dioxide (CO2) and methane (CH4) fluxes as well as fluvial organic carbon export over the peat swamp forest within an undrained tropical peatland landscape in East Kalimantan, Indonesia. Our measurements throughout one year (Oct 2022–Sep 2023) showed that despite its water-logged condition, peat and water overlying the swamp forest on average emits 11.02 ± 0.49 MgCO2 ha−1 yr−1 of CO2 and 0.58 ± 0.04 MgCO2e ha−1 yr−1 of CH4. Further, the fluvial organic carbon export contributes to additional carbon loss of 1.68 ± 0.06 MgCO2e ha−1 yr−1. Our results help improve the accuracy of carbon accounting from undrained tropical peatlands, where we estimated a total carbon loss of 13.28 ± 0.50 MgCO2e ha−1 yr−1. Nevertheless, the total carbon loss reported from our sites is about half than what is reported from the drained peatland landscapes in the region and resulted in a larger onsite carbon sink potential estimate compared to other undrained peat swamp forests. Together, these findings indicate that conserving the remaining undrained peatland ecosystems in Indonesia from drainage and degradation is a promising natural climate solution strategy that avoids significant carbon emissions.

Massive crustal carbon mobilization and emission driven by India underthrusting Asia

The active Himalayan-Tibetan orogen, where India underthrusts into Asia, is an important geological source of carbon dioxide (CO2) emission into Earth’s atmosphere. However, the extent to which Indian underthrusting could stimulate the mobilization of deeply-sourced carbon and its subsequent emission remains unknown. Here, we use a combination of field observations coupled with in-situ CO2 flux measurements and helium and carbon isotopic data, to study the controls on CO2 origins and fluxes in a 400-kilometre-long rift transecting northern Himalaya and southern Tibet. High diffuse CO2 fluxes sustained by pure crustal fluids are confined to rift segments in the northern Himalaya, while toward southern Tibet, CO2 fluxes become lower but mantle fluid inputs are identified. Such rift-related CO2 degassing profile suggests metamorphic decarbonation and release of carbon-bearing fluids enhanced by the underthrusting Indian lower crust, agreeing well with Himalayan metamorphism and orogen-parallel lithospheric extension. Deep CO2 fluxes from extensional tectonics in northern Himalaya and southern Tibet, primarily of crustal origins, are comparable to mantle CO2 fluxes from global mid-ocean ridges. Our findings demonstrate that geophysical and geo-tectonic responses to continental underthrusting could facilitate massive crustal carbon mobilization and emission, making active collisional orogens globally important carbon sources.

Disaggregating the Carbon Exchange of Degrading Permafrost Peatlands Using Bayesian Deep Learning

AbstractExtensive regions in the permafrost zone are projected to become climatically unsuitable to sustain permafrost peatlands over the next century, suggesting transformations in these landscapes that can leave large amounts of permafrost carbon vulnerable to post‐thaw decomposition. We present 3 years of eddy covariance measurements of CH4 and CO2 fluxes from the degrading permafrost peatland Iškoras in Northern Norway, which we disaggregate into separate fluxes of palsa, pond, and fen areas using information provided by the dynamic flux footprint in a novel ensemble‐based Bayesian deep neural network framework. The 3‐year mean CO2‐equivalent flux is estimated to be 106 gCO2 m−2 yr−1 for palsas, 1,780 gCO2 m−2 yr−1 for ponds, and −31 gCO2 m−2 yr−1 for fens, indicating that possible palsa degradation to thermokarst ponds would strengthen the local greenhouse gas forcing by a factor of about 17, while transformation into fens would slightly reduce the current local greenhouse gas forcing.

Absolute measurement of vacuum ultraviolet fluxes from inductively coupled plasmas via metal surface photoemission currents

Quantifying vacuum-ultraviolet (VUV) fluxes typically requires vacuum-compatible spectrometers and is often associated with significant cost and effort. A simple technique for the absolute measurement of local VUV fluxes from plasmas using the photoemission from a set of coated metal plates, is described. The radiant power from a 13.56 MHz hydrogen plasma operating at 40–87 mTorr and with an radio frequency (RF) input power from 100 to 120 W was investigated by irradiating a set of 2 cm diameter Au, Ag and Cu plates. The variation in photoemission currents was compared with the photoelectric yield curves to estimate the absolute flux incident on the surfaces in the 113–190 nm range. The measured fluxes were found to have an uncertainty of 5%–30% when compared with the VUV spectrometer measurements. The VUV output power was found to have a maximum at a pressure of 70–80 mTorr and to increase with RF power. In all cases, the VUV output power was measured to be approximately 12%–16% of the RF input power to the matching network, in good agreement with spectroscopy results.

Reducing Soil-Emitted Nitrous Acid as a Feasible Strategy for Tackling Ozone Pollution.

Severe ozone (O3) pollution has been a major air quality issue and affects environmental sustainability in China. Conventional mitigation strategies focusing on reducing volatile organic compounds and nitrogen oxides (NOx) remain complex and challenging. Here, through field flux measurements and laboratory simulations, we observe substantial nitrous acid (HONO) emissions (FHONO) enhanced by nitrogen fertilizer application at an agricultural site. The observed FHONO significantly improves model performance in predicting atmospheric HONO and leads to regional O3 increases by 37%. We also demonstrate the significant potential of nitrification inhibitors in reducing emissions of reactive nitrogen, including HONO and NOx, by as much as 90%, as well as greenhouse gases like nitrous oxide by up to 60%. Our findings introduce a feasible concept for mitigating O3 pollution: reducing soil HONO emissions. Hence, this study has important implications for policy decisions related to the control of O3 pollution and climate change.

Trapped flux in a small crystal of CaKFe4As4 at ambient pressure and in a diamond anvil pressure cell

In an extension of our previous work, (Bud’ko et al 2023 Supercond. Sci. Technol. 36 115001) the measurements of temperature dependent magnetization associated with trapped magnetic flux in a small single crystal of CaKFe4As4, using zero—field—cooled and field—cooled protocols were performed, on the same crystal, at ambient pressure without a pressure cell and at 2.2 GPa in a commercial diamond anvil cell (DAC), showing comparable results. The data show that with a proper care and understanding, trapped flux measurements in superconductors indeed can be performed on samples in DACs under pressure, as was done on superhydrides (Minkov et al 2023 Nat. Phys. 19 1293).

Three-Dimensional Cell Culture Models to Investigate the Epithelial Barrier in Eosinophilic Esophagitis.

The squamous epithelium of the esophagus is directly exposed to the environment, continuously facing foreign antigens, including food antigens and microbes. Maintaining the integrity of the epithelial barrier is critical for preventing infections and avoiding inflammation caused by harmless food-derived antigens. This article provides simplified protocols for generating human esophageal organoids and air-liquid interface cultures from patient biopsies to study the epithelial compartment of the esophagus in the context of tissue homeostasis and disease. These protocols have been significant scientific milestones in the last decade, describing three-dimensional organ-like structures from patient-derived primary cells, organoids, and air-liquid interface cultures. They offer the possibility to investigate the function of specific cytokines, growth factors, and signaling pathways in the esophageal epithelium within a three-dimensional framework while maintaining the phenotypic and genetic properties of the donor. Organoids provide information on tissue microarchitecture by assessing the transcriptome and proteome after cytokine stimulation. In contrast, air-liquid interface cultures allow the assessment of the epithelial barrier integrity through transepithelial resistance (TEER) or macromolecule flux measurements. Combining these organoids and air-liquid interface cultures is a powerful tool to advance research in impaired esophageal epithelial barrier conditions.

An enormous increase in atmospheric positron flux during a summer thunderstorm on Mount Aragats

On July 11, 2023, we observed a remarkable 500% increase in positron flux, coinciding with a significant Thunderstorm Ground Enhancement (TGE). The enhanced flux of electrons and gamma rays was attributed to relativistic runaway electron avalanches (RREAs) generated within the dipole formed between the main negatively charged layer in the middle of the thundercloud and the Lower Positively Charged Region (LPCR) at the bottom of the thundercloud. Concurrently, a substantial enhancement in the 511 keV gamma-ray flux resulting from electron-positron annihilation was recorded. This surge is intricately linked to the LPCR within the thundercloud. The emergence of the LPCR induces a polarity change in the atmospheric electric field (AEF) below the LPCR (fourth dipole), leading to the deceleration of electrons and the acceleration of positrons.Particle flux measurements were conducted using scintillation and NaI(TL) spectrometers. To mitigate the contamination of natural gamma radiation and refine the 511 keV flux measurements, the ORTEC spectrometer was shielded with a 4 cm thick lead filter. CORSIKA simulations corroborate the observed positron flux enhancement.Highlighting the synergy between high-energy physics in the atmosphere and astroparticle physics, we introduce a new scenario to elucidate the enigmatic large flux of galactic positrons measured by the Alpha Magnetic Spectrometer (AMS) aboard the International Space Station (ISS).

Examining a hadronic γ-ray scenario for the radiative shell and molecular clouds of the old GeV supernova remnant G298.6−0.0

Abstract Based on the 13.7 yr Fermi-LAT data, Yeung, Bamba, and Sano (2023, PASJ, 75, 384) claimed detection of two γ-ray sources (namely Src-NE and Src-NW) associated with the supernova remnant (SNR) G298.6−0.0, and interpreted it as an old GeV SNR interacting with molecular clouds (MCs). In this follow-up study, we refine the flux measurements below 2 GeV with Fermi-LAT event types of better angular reconstruction. Then, we report our γ-ray spectral fittings and cosmic-ray phenomenology in a hadronic scenario, considering both the shell and MC regions of SNR G298.6−0.0. We confirm that the γ-ray spectra of both Src-NE and Src-NW exhibit spectral breaks, at $1.50_{-0.50}^{+0.60}$ and $0.68_{-0.11}^{+0.32}\:$GeV, respectively. Src-NW has a harder broad-band photon index than Src-NE, suggesting an appreciable difference between the physical separations of their respective emission sites from SNR G298.6−0.0. The cosmic-ray spectrum responsible for Src-NE starts with a minimum energy $E_\mathrm{CR,min}=1.38_{-0.16}^{+0.47}\:$GeV, and has a proton index $\Gamma _\mathrm{CR}=2.57_{-0.21}^{+0.18}$ below the exponential cutoff energy $E_\mathrm{CR,max}=240_{-150}^{+240}\:$GeV. Accordingly, we argue that Src-NE is dominated by the SNR shell, while only a minor portion of lower-energy emission is contributed by the MCs interacting with the SNR. The cosmic-ray population for Src-NW starts at a higher energy such that the ECR, min ratio of Src-NW to Src-NE is ≳2. The high ECR, min, as well as the high cosmic-ray energy density required (∼26 eV cm−3), supports the interpretation that Src-NW is predominantly the γ-ray emission from the farther MCs being bombarded by protons that had earlier escaped from SNR G298.6−0.0. By comparing the high-energy features of G298.6−0.0 with those of analogical SNRs, especially SNR W 28 and SNR W 44, we further constrain the age of SNR G298.6−0.0 to be 10–30 kyr, under the assumption of a purely hadronic scenario.

Investigations of Massive Filaments and Star Formation (INFANT). I. Core Identification and Core Mass Function

Filamentary structures are ubiquitously found in high-mass star-forming clouds. To investigate the relationship between filaments and star formation, we carry out the INFANT (Investigations of Massive Filaments and Sar Formation) survey, a multiscale, multiwavelength survey of massive filamentary clouds with Atacama Large Millimeter/submillimeter Array (ALMA) band 3/band 6 and Very Large Array K band. In this first paper, we present the ALMA band 6 continuum observations toward a sample of eight high-mass star-forming filaments. We covered each target with an approximately rectangular mosaic field of view with two 12 m array configurations, achieving an angular resolution of ∼0.″6 (2700 au at 4.5 kpc) and a continuum rms of ∼0.1 mJy beam−1 (∼0.06 M ⊙ in gas mass assuming 15 K). We identify cores using the getsf and astrodendro and find the former is more robust in terms of both identification and measuring flux densities. We identify in total 183 dense cores (15–36 cores in each cloud) and classify their star formation states via outflow and warm gas tracers. The protostellar cores are statistically more massive than the prestellar cores, possibly indicating further accretion onto cores after the formation of protostars. For the high-mass end ( Mcore > 1.5 M ⊙) of the core mass function (CMF) we derive a power-law index of −1.15 ± 0.12 for the whole sample and −1.70 ± 0.25 for the prestellar population. We also find a steepening trend in CMF with cloud evolution (−0.89 ± 0.15 for the young group versus. −1.44 ± 0.25 for the evolved group) and discuss its implications for cluster formation.

Methodological advancement in deriving primary productivity and ecosystem respiration fluxes across different biomes

In this paper, we introduce a methodology that can improve the estimations of Gross Primary Productivity (GPP) and ecosystem Respiration (Reco) processes at a regional scale. This method is based on a satellite data-driven approach which is suitable for regions like India where there exists a serious shortage of ground-based observations of biospheric carbon fluxes (e.g., Eddy Covariance (EC) flux measurements). We relied on the Moderate Resolution Imaging Spectroradiometer (MODIS) reflectance for capturing vegetation dynamics in the Light-Use Efficiency (LUE)-based vegetation model. Further, we utilised recently available satellite-based Solar-Induced Fluorescence (SIF) and other variables such as Soil Moisture (SM) and Soil Temperature (ST) to refine the predictions of GPP and Reco. The methodology involves establishing a relationship between SIF and GPP for different vegetation classes over India. The SIF-GPP relationship established across the biomes was then used to correct the GPP fluxes simulated by the LUE-based model. Similarly, the ecosystem respiration estimations by the model have undergone refinement by incorporating ST and SM information. This innovative method shows remarkable potential to improve biospheric CO2 uptake and release, especially for in situ data-constrained regions like India.• SIF-based information is introduced to a light-use efficiency-based vegetation model.• SIF-GPP relationship is established for major biomes across India.• SM and ST information is incorporated into the Reco simulations in the model.

Carbon Stocks and Fluxes From a Boreal Conifer Swamp: Filling a Knowledge Gap for Understanding the Boreal C Cycle

AbstractThe carbon (C) dynamics of boreal coniferous swamps are a largely understudied component of wetland carbon cycling. We investigated the above‐ and below‐ground carbon stocks and growing season carbon dioxide (CO2) and methane (CH4) fluxes from a representative boreal coniferous swamp in northern Alberta, Canada in 2022. Tree inventories, understory vegetation biomass and peat cores were collected across three sub‐sites within the broader swamp, with gas flux collars placed in the dominant plant communities present. Alongside the C flux measurements, environmental variables such as water table depth, soil temperature and growing season understory green leaf phenology were measured. Our results show that these boreal coniferous swamps store large volumes of organic C in their biomass and soil (134 kg C m−2), comparable with other wetland and forest types, although 95% of the total C stock at our site was within the soil organic carbon. We also found that understory CO2 and CH4 fluxes indicated that the ground layer of the site is a source of greenhouse gases (GHGs) to the atmosphere across the growing season. However, we did not measure litterfall input, tree GHG fluxes or net primary productivity of the overstory, therefore we are not able to say whether the site is an overall source of C to the atmosphere. This study provides a much‐needed insight into the C dynamics of these under‐valued wetland ecosystems, and we highlight the need for a coordinated effort across boreal regions to try to improve inventories of C stocks and fluxes.

Testing the LSST Difference Image Analysis Pipeline Using Synthetic Source Injection Analysis

We evaluate the performance of the Legacy Survey of Space and Time Science Pipelines Difference Image Analysis (DIA) on simulated images. By adding synthetic sources to galaxies on images, we trace the recovery of injected synthetic sources to evaluate the pipeline on images from the Dark Energy Science Collaboration Data Challenge 2. The pipeline performs well, with efficiency and flux accuracy consistent with the signal-to-noise ratio of the input images. We explore different spatial degrees of freedom for the Alard–Lupton polynomial-Gaussian image subtraction kernel and analyze for trade-offs in efficiency versus artifact rate. Increasing the kernel spatial degrees of freedom reduces the artifact rate without loss of efficiency. The flux measurements with different kernel spatial degrees of freedom are consistent. We also here provide a set of DIA flags that substantially filter out artifacts from the DIA source table. We explore the morphology and possible origins of the observed remaining subtraction artifacts and suggest that given the complexity of these artifact origins, a convolution kernel with a set of flexible bases with spatial variation may be needed to yield further improvements.

CEERS: Diversity of Lyα Emitters during the Epoch of Reionization

We analyze rest-frame ultraviolet to optical spectra of three z ≃ 7.47–7.75 galaxies whose Lyα emission lines were previously detected with Keck/MOSFIRE observations, using the JWST/NIRSpec observations from the Cosmic Evolution Early Release Science survey. From NIRSpec data, we confirm the systemic redshifts of these Lyα emitters, and emission-line ratio diagnostics indicate these galaxies were highly ionized and metal-poor. We investigate Lyα line properties, including the line flux, velocity offset, and spatial extent. For the one galaxy where we have both NIRSpec and MOSFIRE measurements, we find a significant offset in their flux measurements (∼1.3–5× greater in MOSFIRE) and a marginal difference in the velocity shifts. The simplest interpretation is that the Lyα emission is extended and not entirely encompassed by the NIRSpec slit. The cross-dispersion profiles in NIRSpec reveal that Lyα in one galaxy is significantly more extended than the nonresonant emission lines. We also compute the expected sizes of ionized bubbles that can be generated by the Lyα sources and discuss viable scenarios for the creation of sizable ionized bubbles (>1 physical Mpc). The source with the highest-ionization condition is possibly capable of ionizing its own bubble, while the other two do not appear to be capable of ionizing such a large region, but require additional sources of ionizing photons. Therefore, the fact that we detect Lyα from these galaxies suggests diverse scenarios for the escape of Lyα during the epoch of reionization. High-spectral-resolution spectra with JWST/NIRSpec will be extremely useful for constraining the physics of patchy reionization.

Measurement of residual flux density in the single-phase transformer by applying DC voltage

The inrush current causes many adverse effects on electrical equipment. One of the reasons for inrush current is residual flux. When a no-load transformer is energized and the closing angle is inappropriate, the residual flux accelerates the core saturation, resulting in high-amplitude inrush current. It is necessary to measure the amplitude and direction of residual flux to reduce its harm. This paper proposes a novel strategy for measuring the residual flux of transformers based on externally applied DC voltages. Firstly, a relationship between residual flux and response current is established based on field-circuit coupling analysis. Then, the core-type transformer and shell-type transformer are modeled by the finite element method, and the fitted model for calculating residual flux is obtained. Finally, experiments are carried out on a square core and a 10 kV, 250 kVA single-phase transformer. The feasibility and accuracy of the proposed strategy are verified by the measurement results.

JWST/MIRI Detection of Suprathermal OH Rotational Emissions: Probing the Dissociation of the Water by Lyα Photons near the Protostar HOPS 370

Using the MIRI medium-resolution spectrometer on JWST, we have detected pure rotational, suprathermal OH emissions from the vicinity of the intermediate-mass protostar HOPS 370 (OMC2/FIR3). These emissions are observed from shocked knots in a jet/outflow and originate in states of rotational quantum number as high as 46 that possess excitation energies as large as E U /k = 4.65 × 104 K. The relative strengths of the observed OH lines provide a powerful diagnostic of the ultraviolet radiation field in a heavily extinguished region (A V ∼ 10–20) where direct UV observations are impossible. To high precision, the OH line strengths are consistent with a picture in which the suprathermal OH states are populated following the photodissociation of water in its B˜−X band by ultraviolet radiation produced by fast (∼80 km s−1) shocks along the jet. The observed dominance of emission from symmetric ( A′ ) OH states over that from antisymmetric (A″) states provides a distinctive signature of this particular population mechanism. Moreover, the variation of intensity with rotational quantum number suggests specifically that Lyα radiation is responsible for the photodissociation of water, an alternative model with photodissociation by a 104 K blackbody being disfavored at a high level of significance. Using measurements of the Brα flux to estimate the Lyα production rate, we find that ∼4% of the Lyα photons are absorbed by water. Combined with direct measurements of water emissions in the ν 2 = 1 − 0 band, the OH observations promise to provide key constraints on future models for the diffusion of Lyα photons in the vicinity of a shock front.

Modeling Heat and Water Exchanges between the Atmosphere and an 85-km2 Dimictic Subarctic Reservoir Using the 1D Canadian Small Lake Model

Abstract Accurately modeling the interactions between inland water bodies and the atmosphere in meteorological and climate models is crucial, given the marked differences with surrounding landmasses. Modeling surface heat fluxes remains a challenge because direct observations available for validation are rare, especially at high latitudes. This study presents a detailed evaluation of the Canadian Small Lake Model (CSLM), a one-dimensional mixed-layer dynamic lake model, in reproducing the surface energy budget and the thermal stratification of a subarctic reservoir in eastern Canada. The analysis is supported by multiyear direct observations of turbulent heat fluxes collected on and around the 85-km2 Romaine-2 hydropower reservoir (50.7°N, 63.2°W) by two flux towers: one operating year-round on the shore and one on a raft during ice-free conditions. The CSLM, which simulates the thermal regime of the water body including ice formation and snow physics, is run in offline mode and forced by local weather observations from 25 June 2018 to 8 June 2021. Comparisons between observations and simulations confirm that CSLM can reasonably reproduce the turbulent heat fluxes and the temperature behavior of the reservoir, despite the one-dimensional nature of the model that cannot account for energy inputs and outputs associated with reservoir operations. The best performance is achieved during the first few months after the ice break-up (mean error = −0.3 and −2.7 W m−2 for latent and sensible heat fluxes, respectively). The model overreacts to strong wind events, leading to subsequent poor estimates of water temperature and eventually to an early freeze-up. The model overestimated the measured annual evaporation corrected for the lack of energy balance closure by 5% and 16% in 2019 and 2020. Significance Statement Freshwater bodies impact the regional climate through energy and water exchanges with the atmosphere. It is challenging to model surface energy fluxes over a northern lake due to the succession of stratification and mixing periods over a year. This study focuses on the interactions between the atmosphere of an irregular shaped northern hydropower reservoir. Direct measurements of turbulent fluxes using an eddy covariance system allowed the model assessment. Turbulent fluxes were successfully predicted during the open water period. Comparison between observed and modeled time series showed a good agreement; however, the model overreacted to high wind episodes. Biases mostly occur during freeze-up and breakup, stressing the importance of a good representation of the ice cover processes.

Winter harvesting reduces methane emissions and enhances blue carbon potential in coastal phragmites wetlands

Enhancing the ability of coastal blue carbon to accumulate and store carbon and reduce net greenhouse gas emissions is an essential component of a comprehensive approach for tackling climate change. The annual winter harvesting of Phragmites is common worldwide. However, the effects of harvesting on methane (CH4) emissions and its potential as an effective blue carbon management strategy have rarely been reported. In this study, the effects of winter Phragmites harvesting on the CH4 and carbon dioxide (CO2) fluxes and the underlying mechanisms in coastal Phragmites wetlands were investigated by comparing the eddy covariance flux measurements for three coastal wetlands with different harvesting and tidal flow conditions. The results show that harvesting can greatly reduce the CH4 emissions and the radiative forcing of CH4 and CO2 fluxes in coastal Phragmites wetlands, suggesting that winter Phragmites harvesting has great potential as a nature-based strategy to mitigate global warming. The monthly mean CH4 fluxes were predominantly driven by air temperature, gross primary productivity, and latent heat fluxes, which are related to vegetation phenology. Additionally, variations in the salinity and water levels exerted strong regulation effects on CH4 emissions, highlighting the important role of proper tidal flow restoration and resalinization in enhancing blue carbon sequestration potential. Compared with the natural, tidally unrestricted wetlands, the CH4 fluxes in the impounded wetland were less strongly correlated with hydrometeorological variables, implying the increased difficulties of predicting CH4 variations in impounded ecosystem. This study facilitates the improved understanding of carbon exchange in coastal Phragmites wetlands with harvesting or impoundment, and provides new insights into effective blue carbon management strategies beyond tidal wetland restoration for mitigating the effects of climate change.