David Bastviken

Convenient in situ methods are key for detecting, quantifying, and mitigating gas emissions. Uncrewed aerial vehicles (UAVs), comprising drones equipped with lightweight integrated instruments, offer a promising platform for mapping greenhouse gas (GHG) emissions. However, flux area attribution can be challenging, and the low-weight gas analyzers or sensors required for drones may exhibit drift over time that degrades detection limits and increases measurement uncertainty. We have developed a UAS (uncrewed aerial system) based approach with all instrumentation onboard, mapping gases, here focusing on simultaneous measurements of the GHGs methane (CH₄), carbon dioxide (CO₂), nitrous oxide (N₂O), and ethane (C₂H₆). The key innovations are the combination of onboard multi-gas measurements, in-flight drift correction using onboard reference air, and integration of controlled tracer gas (C₂H₆) release to constrain the area attribution of detected fluxes. We explore four different flight patterns (box, two-wall, long wall, and 2D-mapping), each suited to different measurement scenarios, and demonstrate their application in diverse environments, including a rewetted peatland, the littoral zone of a lake, manure wells, and a barn housing dairy cows. Our results show the importance of in-flight drift correction or drift control, and that this can reduce baseline-related uncertainty of UAS-based mass balance approaches, which can be key for improving detection limits and estimation of GHG fluxes in a wide range of environments and settings. Furthermore, combining tracer gas emissions with drone flights aids in separation of sources in the area of interest, verification that targeted emissions are intercepted by the sampling walls, and determination of the upper integration height needed to capture source-related transport.

Convenient in situ methods are key for detecting, quantifying, and mitigating gas emissions. Uncrewed aerial vehicles (UAVs), comprising drones equipped with lightweight integrated instruments, offer a promising platform for mapping greenhouse gas (GHG) emissions. However, flux area attribution can be challenging, and the low-weight gas analyzers or sensors required for drones may exhibit drift over time that degrades detection limits and increases measurement uncertainty. We have developed a UAS (uncrewed aerial system) based approach with all instrumentation onboard, mapping gases, here focusing on simultaneous measurements of the GHGs methane (CH₄), carbon dioxide (CO₂), nitrous oxide (N₂O), and ethane (C₂H₆). The key innovations are the combination of onboard multi-gas measurements, in-flight drift correction using onboard reference air, and integration of controlled tracer gas (C₂H₆) release to constrain the area attribution of detected fluxes. We explore four different flight patterns (box, two-wall, long wall, and 2D-mapping), each suited to different measurement scenarios, and demonstrate their application in diverse environments, including a rewetted peatland, the littoral zone of a lake, manure wells, and a barn housing dairy cows. Our results show the importance of in-flight drift correction or drift control, and that this can reduce baseline-related uncertainty of UAS-based mass balance approaches, which can be key for improving detection limits and estimation of GHG fluxes in a wide range of environments and settings. Furthermore, combining tracer gas emissions with drone flights aids in separation of sources in the area of interest, verification that targeted emissions are intercepted by the sampling walls, and determination of the upper integration height needed to capture source-related transport.

Measurements of surface-atmosphere carbon dioxide (CO ₂ ) and methane (CH ₄ ) fluxes have been relatively sparse across the Arctic tundra and boreal biomes, causing significant uncertainties in carbon budget estimates from the region. While the availability of Arctic-boreal carbon flux data has increased substantially over the past decade, the data have remained spread across different repositories, scientific articles, and unpublished sources, making it difficult to leverage. Here we present a new dataset of monthly Arctic-boreal carbon fluxes (ABCFlux v2) across terrestrial (wetlands and uplands) and freshwater (lakes and rivers) ecosystems compiled from previous syntheses including the Arctic-boreal CO ₂ flux database (ABCFlux v1), the Boreal-Arctic Wetland and Lake Methane Dataset (BAWLD-CH4), and the Global River Methane Database (GRiMeDB). In addition, we consider data from general-purpose (e.g., Zenodo) and flux network repositories, literature, and site principal investigators. The dataset includes surface-atmosphere CO ₂ fluxes of gross primary production (GPP), ecosystem respiration (Reco), and net ecosystem exchange (NEE), alongside CH ₄ fluxes. For aquatic ecosystems, we split CH ₄ fluxes into diffusive and ebullitive flux pathways, and included potential emissions from transient storage in the water column (“storage fluxes”), alongside CO ₂ and CH ₄ concentrations dissolved in the surface water. Fluxes are measured through a variety of methods including chamber and eddy covariance techniques alongside bubble traps, ice-surveys, and concentration-based turbulence-driven modelling in aquatic ecosystems. The monthly flux data are reported together with supporting methodological and environmental metadata. The resulting ABCFlux v2 has 23 847 flux site-months, 8182 concentration site-months, and 199 seasonal observations from 1024 sites, and includes 56 139 reported fluxes (i.e. sum of GPP, Reco, NEE, and CH ₄ fluxes) from the years 1984 to 2024. The majority of monthly observations occurred after 1999. Wetlands had the highest number of site-month observations (8758), followed by boreal forest (6981), lotic ecosystems (6275), lentic ecosystems (3799) and upland tundra (3308). Measurements of CO ₂ dominated the dataset across most ecosystem types (25 222) except for lentic ecosystems, where CH ₄ flux site-months (3098) were more frequent than CO ₂ flux site-months (2915). Overall, ABCFlux v2 includes 160 % more site-months for terrestrial CO ₂ flux data compared to ABCFlux v1. Integrating and updating BAWLD-CH4 flux data from growing season averages to monthly fluxes resulted in 5671 site-months of chamber CH ₄ data compared to 762 site-years. This collaborative initiative, involving contributions from over 260 researchers, provides a comprehensive overview of the current state of the Arctic-boreal carbon flux network and its data, and serves as an important step in reducing uncertainties in Arctic-boreal carbon budgets and in enhancing our understanding of climate feedbacks. The data can be accessed at ORNL DAAC at https://doi.org/10.3334/ORNLDAAC/2448 (Virkkala et al., 2026).

Convenient in situ methods are key for detecting, quantifying, and mitigating gas emissions. Uncrewed aerial vehicles (UAVs), comprising drones equipped with lightweight integrated instruments, offer a promising platform for mapping greenhouse gas (GHG) emissions. However, flux area attribution can be challenging, and the low-weight gas analyzers or sensors required for drones may exhibit drift over time that degrades detection limits and increases measurement uncertainty. We have developed a UAS (uncrewed aerial system) based approach with all instrumentation onboard, mapping gases, here focusing on simultaneous measurements of the GHGs methane (CH4), carbon dioxide (CO2), nitrous oxide (N2O), and ethane (C2H6). The key innovations are the combination of onboard multi-gas measurements, in-flight drift correction using onboard reference air, and integration of controlled tracer gas (C2H6) release to constrain the area attribution of detected fluxes. We explore four different flight patterns (box, two-wall, long wall, and 2D-mapping), each suited to different measurement scenarios, and demonstrate their application in diverse environments, including a rewetted peatland, the littoral zone of a lake, manure wells, and a barn housing dairy cows. Our results show the importance of in-flight drift correction or drift control, and that this can reduce baseline-related uncertainty of UAS-based mass balance approaches, which can be key for improving detection limits and estimation of GHG fluxes in a wide range of environments and settings. Furthermore, combining tracer gas emissions with drone flights aids in separation of sources in the area of interest, verification that targeted emissions are intercepted by the sampling walls, and determination of the upper integration height needed to capture source-related transport.

Extractable organic fluorine (EOF) analysis is used to assess fluorinated organic content in, e.g., water and solid sample extracts. EOF content is often determined by combustion ion chromatography (CIC). However, contamination from inorganic fluoride (F^-) in extracts risks overestimating actual EOF. Despite this known interference, a standardized and optimized methodology to mitigate such contamination remains lacking. In this study, we evaluated the presence of F^- in EOF extracts and designed and validated a method for F^- determination in small aliquots (∼250 μL) of complex aqueous and solvent matrices. The method is based on derivatization of F^- to triphenylfluorosilane (TPSiF) and subsequent analysis with gas-chromatographic tandem mass spectrometry analysis (GC-MS/MS). Calibration was linear from 1 to 1000 μg L^-1 (R² > 0.99), and the limit of detection and the limit of quantification were 0.98 and 4.5 μg F^- L^-1, respectively. The relative standard deviation was below 7% across the calibrated range. A certified reference material (CRM River water) and F^--spiked minced meat were used to assess F^- recovery to 103 ± 3% (p = 0.10) and 95 ± 6% (p = 0.31) of certified/spiked concentrations. Analysis of sample extracts showed that (1) solid-phase extraction extracts of river water, (2) solvent extracts from aqueous-film-forming foam (AFFF)-impacted soil, and (3) extracts of a fish sample contained 29-49, 61 ± 4.7, and 17-90 μg F^- L^-1, respectively. F^- accounted for 3-59% of the measured EOF, indicating a substantial overestimation. Therefore, the analysis and discount of F^- in EOF extracts are essential for accurate EOF determination by CIC.

Different aquatic ecosystems may have opposing effects on global climate acting as sources and/or sinks of greenhouse gases. The conversion of sediment organic carbon to the powerful greenhouse gas methane is a key indicator of the potential climate impact of a given ecosystem. Here, we assess the lifetime climatic role of aquatic ecosystems by contrasting methane (CH ₄ ) emissions with long-term organic carbon burial. Global compilations revealed that the ecosystem-specific ratio of organic carbon burial (kg CO ₂ ) to CH ₄ emissions (kg CH ₄ ) ranged from 20:1 in lakes to 2500:1 in continental shelves. Using 100-year sustained-flux global warming potential and a radiative balance model, we show that most ecosystems currently exhibit a net negative radiative balance (i.e., net cooling or a CO ₂ -equivalent sink). The lifetime cooling effect per area was strongest in the coastal ocean and fjords. Freshwater ponds, lakes, and inland wetlands had lowest organic carbon burial to CH ₄ emission ratios, requiring ~ 0-700 years after their establishment to shift from a positive to net negative radiative balance. All aquatic ecosystems gradually increase their net climate benefit via long-term enhancement of the ratio of carbon sequestration to CH ₄ emissions. Most aquatic ecosystems will thus achieve negative radiative balance over their lifetime.

Lakes represent one of the main sources of methane (CH₄) to the atmosphere, contributing roughly 3–25 % of the total global yearly emissions. While the scientific interest in understanding and modelling these emissions is increasing rapidly, methodologically consistent long-term flux measurement programs of integrated lake CH₄ emissions are largely missing. Here we present results from a systematic and comparable spatiotemporal multi-lake CH₄ flux program initiated by the Swedish Infrastructure for Ecosystem Science (SITES). Five lakes distributed across Sweden covering a latitudinal gradient from 68° N to 57° N, including the arctic subalpine, boreal and north temperate zones, were monitored during 2016–2022 in ways that captured variability in space and time within lakes and that allowed between-lake comparisons. The data includes 2375 unique CH₄ flux measurements (incl. total CH₄ fluxes, diffusive fluxes and surface water concentrations) along with other common physical and chemical lake variables. This paper presents these data (Swedish Infrastructure for Ecosystem Science, 2026, https://doi.org/10.23700/05ax-st65), underlying methodological priorities and procedures, and provides examples of what can be learned from such a coordinated sampling program. Briefly, the data show the need for appropriate consideration of ebullition and space-time integration to properly represent whole lake CH₄ fluxes. The data further show that both diffusive and total CH₄ fluxes have an apparent temperature dependency, which can be modulated by water depth in ways that differ among lakes. Also, yearly open water CH₄ flux estimates were consistently shaped by temperature in all lakes, but the strength of this response differed between lakes; increases of whole season mean water temperature between 0.5 and 3.2 °C corresponded to increases in CH₄ fluxes ranging from 16 to 74 %. Finally, we propose that temperature-normalized CH₄ fluxes should be used in lake emission inter-comparisons.