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Inland waters are important sources of the greenhouse gasses (GHGs) carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) to the atmosphere. While a growing number of global estimates of inland water GHG emissions exists, the integration of inland waters into regional GHG budgets is often hampered by the lack of adequate geo-spatial datasets. Moreover, existing estimates diverge substantially, in part due to persisting uncertainties related to the size and distribution of effective inland water surface areas. In the framework of the 2nd phase of the REgional Carbon Cycle Assessment and Processes (RECCAP-2) initiative, we synthesize existing estimates of GHG emissions from streams, rivers, lakes and reservoirs, and homogenize them with regard to underlying global maps of inland water surface areas and the effects of seasonal ice cover. We then produce estimates of inland water GHG emissions for 10 extensive land regions that are used for the regional land budgets of RECCAP2. According to our synthesis, global inland waters emit 5.6 (3.5-9.1) Pg CO2 yr-1, 101 (83-135) Tg CH4 yr-1 and 326 (254-592) Gg N2O yr-1. South American rivers contribute about one third of global inland water CO2 emissions. North-American and Russian lakes contribute together one third of global inland water CH4 emissions. Finally, North America alone contributes one fourth of global inland water N2O emissions.The global inland water emissions sum up to a global warming potential (GWP) of an equivalent emission of 13.6 (10.0-20.3) and 8.3 (5.8-12.7) Pg CO2 yr-1 at a 20- and 100-year horizon, respectively. At 100-year horizon, the contribution of CO2 dominates the GWP of global inland water GHG emissions, with rivers being the largest emitters. At the 20-year horizon, on the contrary, lakes and rivers are equally important emitters, and the contributions of CH4 to the GWP of inland water GHG emissions even exceed those of CO2. Contributions of N2O to the GWP appear to be less significant at both time horizons. Normalized to the area of the RECCAP-2 land regions, South America and South East Asia show the highest inland water emission rates in terms of GWP, dominated by riverine CO2 emissions.

Mapping wetland types in northern-latitude regions with Earth Observation (EO) data is important for several practical and scientific applications, but at the same time challenging due to the variability and dynamic nature in wetland features introduced by differences in geophysical conditions. The objective of this study was to better understand the ability of Sentinel-1 radar data, Sentinel-2 optical data and terrain derivatives derived from Copernicus digital elevation model to distinguish three main peatland types, two upland classes, and surface water, in five contrasting landscapes located in the northern parts of Alaska, Canada and Scandinavia. The study also investigated the potential benefits for classification accuracy of using regional classification models constructed from region-specific training data compared to a global classification model based on pooled reference data from all five sites. Overall, the results show high promise for classifying peatland types and the three other land cover classes using the fusion approach that combined all three EO data sources (Sentinel-1, Sentinel-2 and terrain derivatives). Overall accuracy for the individual sites ranged between 79.7% and 90.3%. Class specific accuracies for the peatland types were also high overall but differed between the five sites as well as between the three classes bog, fen and swamp. A key finding is that regional classification models consistently outperformed the global classification model by producing significantly higher classification accuracies for all five sites. This suggests for progress in identifying effective approaches for continental scale peatland mapping to improve scaling of for example, hydrological- and greenhouse gas-related processes in Earth system models. Funding: Swedish Research Council Formas [2017-01944, 2018-01794, 2018-00570]; European Space Agency

Knowledge of the spatial distribution of the fluxes of greenhouse gases (GHGs) and their temporal variability as well as flux attribution to natural and anthropogenic processes is essential to monitoring the progress in mitigating anthropogenic emissions under the Paris Agreement and to inform its global stocktake. This study provides a consolidated synthesis of CH4 and N2O emissions using bottom-up (BU) and top-down (TD) approaches for the European Union and UK (EU27 + UK) and updates earlier syntheses (Petrescu et al., 2020, 2021). The work integrates updated emission inventory data, process-based model results, data-driven sector model results and inverse modeling estimates, and it extends the previous period of 1990–2017 to 2019. BU and TD products are compared with European national greenhouse gas inventories (NGHGIs) reported by parties under the United Nations Framework Convention on Climate Change (UNFCCC) in 2021. Uncertainties in NGHGIs, as reported to the UNFCCC by the EU and its member states, are also included in the synthesis. Variations in estimates produced with other methods, such as atmospheric inversion models (TD) or spatially disaggregated inventory datasets (BU), arise from diverse sources including within-model uncertainty related to parameterization as well as structural differences between models. By comparing NGHGIs with other approaches, the activities included are a key source of bias between estimates, e.g., anthropogenic and natural fluxes, which in atmospheric inversions are sensitive to the prior geospatial distribution of emissions. For CH4 emissions, over the updated 2015–2019 period, which covers a sufficiently robust number of overlapping estimates, and most importantly the NGHGIs, the anthropogenic BU approaches are directly comparable, accounting for mean emissions of 20.5 Tg CH4 yr−1 (EDGARv6.0, last year 2018) and 18.4 Tg CH4 yr−1 (GAINS, last year 2015), close to the NGHGI estimates of 17.5±2.1 Tg CH4 yr−1. TD inversion estimates give higher emission estimates, as they also detect natural emissions. Over the same period, high-resolution regional TD inversions report a mean emission of 34 Tg CH4 yr−1. Coarser-resolution global-scale TD inversions result in emission estimates of 23 and 24 Tg CH4 yr−1 inferred from GOSAT and surface (SURF) network atmospheric measurements, respectively. The magnitude of natural peatland and mineral soil emissions from the JSBACH–HIMMELI model, natural rivers, lake and reservoir emissions, geological sources, and biomass burning together could account for the gap between NGHGI and inversions and account for 8 Tg CH4 yr−1. For N2O emissions, over the 2015–2019 period, both BU products (EDGARv6.0 and GAINS) report a mean value of anthropogenic emissions of 0.9 Tg N2O yr−1, close to the NGHGI data (0.8±55 % Tg N2O yr−1). Over the same period, the mean of TD global and regional inversions was 1.4 Tg N2O yr−1 (excluding TOMCAT, which reported no data). The TD and BU comparison method defined in this study can be operationalized for future annual updates for the calculation of CH4 and N2O budgets at the national and EU27 + UK scales. Future comparability will be enhanced with further steps involving analysis at finer temporal resolutions and estimation of emissions over intra-annual timescales, which is of great importance for CH4 and N2O, and may help identify sector contributions to divergence between prior and posterior estimates at the annual and/or inter-annual scale. Even if currently comparison between CH4 and N2O inversion estimates and NGHGIs is highly uncertain because of the large spread in the inversion results, TD inversions inferred from atmospheric observations represent the most independent data against which inventory totals can be compared. With anticipated improvements in atmospheric modeling and observations, as well as modeling of natural fluxes, TD inversions may arguably emerge as the most powerful tool for verifying emission inventories for CH4, N2O and other GHGs. The referenced datasets related to figures are visualized at https://doi.org/10.5281/zenodo.7553800 (Petrescu et al., 2023).

Methane (CH4) emissions from the boreal and arctic region are globally significant and highly sensitive to climate change. There is currently a wide range in estimates of high-latitude annual CH4 fluxes, where estimates based on land cover inventories and empirical CH4 flux data or process models (bottom-up approaches) generally are greater than atmospheric inversions (top-down approaches). A limitation of bottom-up approaches has been the lack of harmonization between inventories of site-level CH4 flux data and the land cover classes present in high-latitude spatial datasets. Here we present a comprehensive dataset of small-scale, surface CH4 flux data from 540 terrestrial sites (wetland and non-wetland) and 1247 aquatic sites (lakes and ponds), compiled from 189 studies. The Boreal–Arctic Wetland and Lake Methane Dataset (BAWLD-CH4) was constructed in parallel with a compatible land cover dataset, sharing the same land cover classes to enable refined bottom-up assessments. BAWLD-CH4 includes information on site-level CH4 fluxes but also on study design (measurement method, timing, and frequency) and site characteristics (vegetation, climate, hydrology, soil, and sediment types, permafrost conditions, lake size and depth, and our determination of land cover class). The different land cover classes had distinct CH4 fluxes, resulting from definitions that were either based on or co-varied with key environmental controls. Fluxes of CH4 from terrestrial ecosystems were primarily influenced by water table position, soil temperature, and vegetation composition, while CH4 fluxes from aquatic ecosystems were primarily influenced by water temperature, lake size, and lake genesis. Models could explain more of the between-site variability in CH4 fluxes for terrestrial than aquatic ecosystems, likely due to both less precise assessments of lake CH4 fluxes and fewer consistently reported lake site characteristics. Analysis of BAWLD-CH4 identified both land cover classes and regions within the boreal and arctic domain, where future studies should be focused, alongside methodological approaches. Overall, BAWLD-CH4 provides a comprehensive dataset of CH4 emissions from high-latitude ecosystems that are useful for identifying research opportunities, for comparison against new field data, and model parameterization or validation. BAWLD-CH4 can be downloaded from https://doi.org/10.18739/A2DN3ZX1R (Kuhn et al., 2021).

Chemical disinfection of water has been commonly applied to protect public health from waterborne infectious diseases. Chemical disinfectants are strong oxidants that react with the building blocks or alter the metabolism of pathogenic organisms, killing them as the final consequence. These oxidative reactions are not substrate-specific, and thus, all organic and inorganic constituents of the water may be involved. The changes of the organic matter and the disinfection by-products (DBPs) formed are dependent of the disinfectant used and the organic and inorganic precursors present in the water. The present work aims at investigating these aspects in disinfected water from four water treatment plants in Sweden. The waterworks investigated were selected according to the type of disinfectant used (chlorine or chloramine) and the characteristics of water entering the plant (groundwater, surface water, or artificially recharged groundwater). Specific and generic extraction approaches, and target, suspect and non-target screening approaches using advanced mass spectrometry have been used to investigate DBPs formed and to characterize the organic matter before and after the chemical disinfection process. Acknowledgments: CP acknowledges support from the Swedish University of Agricultural Sciences through the August T Larsson Guest Researcher Programme. This work was supported by the Government of Catalonia (Consolidated Research Groups 2017 SGR 01404- Water and Soil Quality Unit) and by the Swedish Research Council FORMAS (grant 2013-01077).

Knowledge of the spatial distribution of the fluxes of greenhouse gases and their temporal variability as well as flux attribution to natural and anthropogenic processes is essential to monitoring the progress in mitigating anthropogenic emissions under the Paris Agreement and to inform its Global Stocktake. This study provides a consolidated synthesis of CH4 and N2O emissions using bottom-up (BU) and top-down (TD) approaches for the European Union and UK (EU27+UK) and updates earlier syntheses (Petrescu et al., 2020, 2021). The work integrates updated emission inventory data, process-based model results, data-driven sector model results, inverse modelling estimates, and extends the previous period 1990–2017 to 2020. BU and TD products are compared with European National GHG Inventories (NGHGI) reported by Parties under the United Nations Framework Convention on Climate Change (UNFCCC) in 2021. The uncertainties of NGHGIs were evaluated using the standard deviation obtained by varying parameters of inventory calculations, reported by the EU Member States following the guidelines of the Intergovernmental Panel on Climate Change (IPCC) and harmonized by gap-filling procedures. Variation in estimates produced with other methods, such as atmospheric inversion models (TD) or spatially disaggregated inventory datasets (BU), arise from diverse sources including within-model uncertainty related to parameterization as well as structural differences between models. By comparing NGHGIs with other approaches, the activities included are a key source of bias between estimates e.g. anthropogenic and natural fluxes, which, in atmospheric inversions are sensitive to the prior geospatial distribution of emissions. For CH4 emissions, over the updated 2015–2019 period, which covers a sufficiently robust number of overlapping estimates, and most importantly the NGHGIs, the anthropogenic BU approaches are directly comparable, accounting for mean emissions of 20.5 Tg CH4 yr−1 (EDGAR v5v6.0, last year 2018) and 18.4 Tg CH4 yr−1 (GAINS, 2015), close to the NGHGI estimates of 17.5 ± 2.1 Tg CH4 yr−1. TD inversions estimates give higher emission estimates, as they also detect natural emissions. Over the same period, high resolution regional TD inversions report a mean emission of 34 Tg CH4 yr−1. Coarser-resolution global-scale TD inversions result in emission estimates of 23 Tg CH4 yr−1 and 24 Tg CH4 yr−1 inferred from GOSAT and surface (SURF) network atmospheric measurements, respectively. The magnitude of natural peatland and mineral soils emissions from the JSBACH-HIMMELI model, natural rivers, lakes and reservoirs emissions, geological sources and biomass burning together could account for the gap between NGHGI and inversions and account for 8 Tg CH4 yr−1. For N2O emissions, over the 2015–2019 period, both BU products (EDGAR v5v6.0 and GAINS) report a mean value of anthropogenic emissions of 0.9 Tg N2O yr−1, close to the NGHGI data (0.8 ± 55 % Tg N2O yr−1). Over the same period, the mean of TD global and regional inversions was 1.4 Tg N2O yr−1 (excluding TOMCAT which reported no data). The TD and BU comparison method defined in this study can be "operationalized" for future annual updates for the calculation of CH4 and N2O budgets at the national and EU27+UK scales. Future comparability will be enhanced with further steps involving analysis at finer temporal resolutions and estimation of emissions over intra-annual timescales, of great importance for CH4 and N2O, which may help identify sector contributions to divergence between prior and posterior estimates at the annual/inter-annual scale. Even if currently comparison between CH4 and N2O inversions estimates and NGHGIs is highly uncertain because of the large spread in the inversion results, TD inversions inferred from atmospheric observations represent the most independent data against which inventory totals can be compared. With anticipated improvements in atmospheric modelling and observations, as well as modelling of natural fluxes, TD inversions may arguably emerge as the most powerful tool for verifying emissions inventories for CH4, N2O and other GHGs. The referenced datasets related to figures are visualized at https://doi.org/10.5281/zenodo.6992472 (Petrescu et al., 2022).

Inland waters play an active role in the global carbon cycle and emit large volumes of the greenhouse gases (GHGs), methane (CH4) and carbon dioxide (CO2). A considerable body of research has improved emissions estimates from lakes, reservoirs and rivers but recent attention has been drawn to the importance of small, artificial waterbodies as poorly quantified but potentially important emission hotspots. Of particular interest are emissions from drainage ditches and constructed ponds. These waterbody types are prevalent in many landscapes and their cumulative surface areas can be substantial. Furthermore, GHG emissions from constructed waterbodies are anthropogenic in origin and form part of national emissions reporting, whereas emissions from natural waterbodies do not (according to Intergovernmental Panel on Climate Change guidelines). Here, we present GHG data from two complementary studies covering a range of land uses. In the first, we measured emissions from nine ponds and seven ditches over a full year. Annual emissions varied considerably: 0.1-44.3 g CH4 m(-2) year(-1) and -36-4421 g CO2 m(-2) year(-1). In the second, we measured GHG concentrations in 96 ponds and 64 ditches across seven countries, covering subtropical, temperate and sub-arctic biomes. When CH4 emissions were converted to CO2 equivalents, 93% of waterbodies were GHG sources. In both studies, GHGs were positively related to nutrient status (C, N, P), and pond GHG concentrations were highest in smallest waterbodies. Ditch and pond emissions were larger per unit area when compared to equivalent natural systems (streams, natural ponds). We show that GHG emissions from natural systems should not be used as proxies for those from artificial waterbodies, and that artificial waterbodies have the potential to make a substantial but largely unquantified contribution to emissions from the Agriculture, Forestry and Other Land Use sector, and the global carbon cycle. Funding Agencies|European Research CouncilEuropean Research Council (ERC)European Commission [725546]; FORMASSwedish Research Council Formas [2018-01794, 2020-00950]; NERCUK Research & Innovation (UKRI)Natural Environment Research Council (NERC) [NE/N018087/1]

Rivers are natural biogeochemical systems shaping the fates of dissolved organic matter (DOM) from leaving soils to reaching the oceans. This study focuses on Amazon basin DOM processing employing negative and positive electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI[±] FT-ICR MS) and nuclear magnetic resonance spectroscopy (NMR) to reveal effects of major processes on the compositional space and structural characteristics of black, white and clear water systems. These include non-conservative mixing at the confluences of (1) Solimões and the Negro River, (2) the Amazon River and the Madeira River, and (3) in-stream processing of Amazon River DOM between the Madeira River and the Tapajós River. The Negro River (black water) supplies more highly oxygenated and high molecular weight compounds, whereas the Solimões and Madeira Rivers (white water) contribute more CHNO and CHOS molecules to the Amazon River main stem. Aliphatic CHO and abundant CHNO compounds prevail in Tapajos River DOM (clear water), likely originating from primary production. Sorption onto particles and heterotrophic microbial degradation are probably the principal mechanisms for the observed changes in DOM composition in the Amazon River and its tributaries.

Chlorine (Cl) in the terrestrial environment is of interest from multiple perspectives, including the use of chloride as a tracer for water flow and contaminant transport, organochlorine pollutants, Cl cycling, radioactive waste (radioecology; 36Cl is of large concern) and plant science (Cl as essential element for living plants). During the past decades, there has been a rapid development towards improved understanding of the terrestrial Cl cycle. There is a ubiquitous and extensive natural chlorination of organic matter in terrestrial ecosystems where naturally formed chlorinated organic compounds (Clorg) in soil frequently exceed the abundance of chloride. Chloride dominates import and export from terrestrial ecosystems while soil Clorg and biomass Cl can dominate the standing stock Cl. This has important implications for Cl transport, as chloride will enter the Cl pools resulting in prolonged residence times. Clearly, these pools must be considered separately in future monitoring programs addressing Cl cycling. Moreover, there are indications that (1) large amounts of Cl can accumulate in biomass, in some cases representing the main Cl pool; (2) emissions of volatile organic chlorines could be a significant export pathway of Cl and (3) that there is a production of Clorg in tissues of, e.g. plants and animals and that Cl can accumulate as, e.g. chlorinated fatty acids in organisms. Yet, data focusing on ecosystem perspectives and combined spatiotemporal variability regarding various Cl pools are still scarce, and the processes and ecological roles of the extensive biological Cl cycling are still poorly understood.

Lakes are major global sources of atmospheric methane (CH4), representing an important greenhouse gas. Dissolved molecular Oxygen (DO) in lakes hinders production of CH4 while promoting CH4 oxidation. Consequently, it has been suggested as an important regulator of CH4 emissions from lakes. Presence or absence of DO at the sediment-water interface could therefore influence the extent of CH4 production in top sediment layers, and the amount of CH4 that is stored in the anoxic layer of the water column and potentially emitted during water column mixing events. However, the quantitative importance of DO on CH4 fluxes remains unknown. We studied CH4 fluxes from two lake basins in northern boreal Sweden of which DO was experimentally added to the deep waters in one of the basins (experimental basin) while the other basin was left in a natural state (reference basin). We used spatial and temporally distributed flux chambers to measure CH4 fluxes while the lake basins were stratified (from June to October) and found that there was no significant difference in CH4 fluxes between the two lake basins attributable to the water column experiment. Moreover, we found that the oxygenation of the hypolimnion resulted in a large decrease in CH4 concentration in the experimental basin, in contrast to the reference basin. However, our monthly lake profile measurements indicated that only a small amount of this CH4 may have been emitted during the open-water season. First, the two lake basins were subject to incomplete spring and fall mixing events. Second, our CH4 emission and oxidation model, based on bathymetry, CH4 concentrations, depth distributed 13C/12C measurements, and gas transfer velocities, indicated that 0 – 24 % of the stored CH4 may be emitted on a yearly basis. This shows that the overall impact on CH4 emissions from boreal forest lakes, due to CH4 storage and DO, may be smaller than previously believed. However, Fluxes during the mixing events still represent a large uncertainty for the total yearly lake CH4 emissions.

Forests play an important role in the exchange of radiatively important gases with the atmosphere. Previous studies have shown that in both temperate and tropical wetland forests tree stems are significant sources of methane, yet little is known about tree stem trace greenhouse gas dynamics in drier, free-draining soils that dominate global forested areas. Here, we examine methane fluxes on tree stems spanning a climate gradient of upland forests and floodplain forest across 4 locations in the Amazon, Brazil (Cunia, Rios Negro, Solimoes and Tapajos), lowland tropical forest on free-draining soils in Panama, Central America (Barro Colorado Nature Monument), deciduous woodland in the United Kingdom (Wytham, Oxfordshire) and boreal forest in Sweden. We found that trees behaved as both methane sources (near the tree base) and sinks (higher up the tree stem) across tropical, temperate and boreal sites and are highly variable, yet we were able to identify a broad correlation between the size of tree stem methane uptake fluxes and mean annual temperature across the climate gradient. The vertical spatial patterns of flux up the individual measured trees and climate gradient temperature-methane flux relationship together with revised LiDAR derived tree surface allometry permitted global scaling of fluxes in upland forest. Results of this scaling together with the implications of this refined understanding of the global methane cycle under various scenarios are discussed.

Lakes emit CO2 to the atmosphere at magnitudes significant for the global carbon cycle, in the form of diffusive CO2 flux (FCO2). As direct FCO2 measurements are time-consuming, FCO2 is often estimated from the air-water CO2 concentration gradient (ΔpCO2) and the gas transfer velocity (k), representing the two components considered to regulate FCO2. However, extrapolating measurements of ΔpCO2 and k to whole-year estimates require understanding of their variability in time and across different types of lakes, which is often insufficient. As a result, simple linear interpolations are typically used in extrapolations which risk producing bias as spatiotemporal variability is not included. Further insight to the variability of ΔpCO2 and k may contribute to more representative extrapolations and provide guidance for focusing sampling campaigns on capturing times of high variability. We used floating flux chambers and surface water samples to measure FCO2 and ΔpCO2, respectively, both within-weeks and over seasons during the open water period at 12 locations in each of 15 boreal lakes across a latitudinal gradient in Sweden. We combined these measurements to derive spatially resolved values of k in order to identify: i) the contributions of ΔpCO2 and k to FCO2 variability over time; and ii) if differences in the contributions of ΔpCO2 and k to FCO2 variability can be related to lake characteristics. The results presented are relevant for improved modelling of lake CO2 emissions.

Lakes are responsible for substantial emissions of methane (CH4) to the atmosphere globally, but their contribution is poorly constrained and current estimates vary widely. One of the reasons for this large uncertainty lies in the practical challenges involved in collecting CH4 concentration and flux data at the suitable temporal and spatial scales to capture their natural variability. Here, we present the results of an attempt to account for the spatial and temporal variability of CH4 concentrations and fluxes when deriving whole-lake and yearly average values. We used these average values to investigate the main environmental drivers of CH4 concentrations in the surface water of lakes and CH4 emissions from lakes. We made surface water CH4 concentration and CH4 fluxes measurements using headspace equilibration and floating chambers, respectively, in a set of boreal lakes located in different parts of Sweden and with various morphological and biogeochemical properties. Measurements covered different periods of the open-water season at multiple locations covering various depths/distances to shore in each lake. Individual CH4 flux measurements (150-300 measurements per lake) were interpolated based on relationships with local spatial and temporal variables. Relationships between mean open water season CH4 concentrations and emissions, and one to three independent environmental variables were tested as different models. The results suggest that the frequency and spatial coverage of the measurements is critical for identifying reliable quantitative empirical models of CH4 concentrations and emissions from lakes.

Appropriate methods to measure greenhouse gas (GHG) fluxes are critical for our ability to detect fluxes, understand regulation, make adequate priorities for climate change mitigation efforts, and verify that these efforts are effective. Ideally, we need reliable, accessible, and affordable measurements at relevant scales. We surveyed present GHG flux measurement methods, identified from an analysis of >11000 scientific publications and a questionnaire to sector professionals and analysed method pros and cons versus needs for novel methodology. While existing methods are well-suited for addressing certain questions, this presentation presents fundamental limitations relative to GHG flux measurement needs for verifiable and transparent action to mitigate many types of emissions. Cost and non-academic accessibility are key aspects, along with fundamental measurement performance. These method limitations contribute to the difficulties in verifying GHG mitigation efforts for transparency and accountability under the Paris agreement. Resolving this mismatch between method capacity and societal needs is urgently needed for effective climate mitigation. This type of methodological mismatch is common but seems to get high priority in other knowledge domains. The obvious need to prioritize development of accurate diagnosis methods for effective treatments in healthcare is one example. This presentation provides guidance regarding the need to prioritize the development of novel GHG flux measurement methods.

Aquatic ecosystems are major sources of greenhouse gases (GHGs). Robust measurements of natural GHG emissions are vital for evaluating regional to global carbon budgets and for assessing climate feedbacks of natural emissions to improve climate models. Diffusive and ebullitive (bubble) transport are two major pathways of gas release from surface waters. To capture the high temporal variability of these fluxes in a well-defined footprint, we designed and built an inexpensive device that includes an easily mobile diffusive flux chamber and a bubble counter all in one. In addition to automatically collecting gas samples for subsequent various analyses in the laboratory, this device also utilized a low-cost carbon dioxide (CO2) sensor (SenseAir, Sweden) and methane (CH4) sensor (Figaro, Japan) to measure GHG fluxes. Each of the devices was equipped with an XBee module to enable local radio communication (DigiMesh network) for time synchronization and data readout at a server controller station on the lakeshore. The software of this server controller was operated on a lowcost computer (Raspberry Pi), which has a 3G connection for remote control and monitor functions from anywhere in the world. This study shows the potential of a low-cost automatic sensor network system for studying GHG fluxes on lakes in remote locations. Funding Agencies|US National Science Foundation (NSF) (MacroSystems Biology, EF)National Science Foundation (NSF) [1241937]; US National Science Foundation (NSF) (Northern Ecosystems Research for Undergraduates program, NSF REU site EAR) [1063037]; Swedish Research Council (VR)Swedish Research Council [2012-00048, 2016-04829]; European Research Council (ERC)European Research Council (ERC) [725546]; VINNOVAVinnova [2015-03529]

Disinfection by-products (DBPs) are potentially toxic compounds formed upon chemical disinfection of drinking water. Controlling the levels and characteristics of dissolved organic matter (DOM) as precursor material for DBPs is a major target to reduce DBP formation. A pilot-scale treatment including suspended ion exchange (SIX (R)), a ceramic microfilter (CeraMac (R)) with in-line coagulation and optional pre-ozonation followed by granular activated carbon (GAC) filtration was compared with a conventional full-scale treatment based on DOM removal and DBP formation using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), rapid fractionation, liquid chromatography organic carbon detection (LC-OCD), adsorbable organic halogens (AOX) and trihalomethane (THM) analysis. The new treatment combination showed different selectivity for DOM removal, compared to the conventional, leading to changes in composition of the DBPs formed. SIX (R) and GAC had the largest impacts on reducing AOX and THM formation potentials but the high adsorptive capacity of GAC affected the diversity of detected DBPs most. Chlorination and chloramination of pilot treated water with doses normally used in Sweden produced low levels of AOX compared to the full-scale treatment, but FT-ICR MS revealed an abundance of brominated DBP species in contrast with the conventional treatment, which were dominated by chlorinated DBPs. This finding was largely linked to the high DOM removal by the pilot treatment, causing an increased Br-/C ratio and a higher formation of HOBr. Potential increases in Br-DBPs are important to consider in minimizing health risks associated with DBPs, because of the supposed higher toxicity of Br-DBPs compared to Cl-DBPs. Funding Agencies|Swedish Research Council for Sustainable Development, FORMASSwedish Research Council Formas [2013-1077]; Svenskt Vatten Utveckling [16-104]; Stockholm Vatten och Avfall; Norrvatten

This study is an attempt to assess CH4 and N2O emissions from all the treatment steps of a wastewater treatment plant (WWTP) in Sweden, serving 145 000 persons, and an adjacent biogas production facility. We have used novel mid-IR ground-based remote sensing with a hyperspectral camera to visualize and quantify the emissions on 21 days during a year, with resulting yearly fluxes of 90.4 +/- 4.3 tonne CH4/yr and 10.9 +/- 1.3 tonne N2O/yr for the entire plant. The most highly emitting CH4 source was found to be sludge storage, which is seldom included in literature as in-situ methods are not suitable for measuring emissions extended over large surfaces, still contributing 90 % to the total CH4 emission in our case. The dominating N2O source was found to be a Stable High rate Ammonia Removal Over Nitrite reactor, contributing 89 % to the total N2O emissions. We also discovered several unexpected CH4 sources. Incomplete flaring of CH4 gave fluxes of at least 30 kg CH4/min, corresponding to plume concentrations of 2.5 %. Such highly episodic fluxes could double the plant-wide yearly emissions if they occur 2 days per year. From a distance of 250 m we found a leak in the biogas production facility, corresponding to 1.1 % of the CH4 produced, and that loading of organic material onto trucks from a biofertilizer storage tank contributed with high emissions during loading events. These results indicate that WWTP emissions globally may have been grossly underestimated and that it is essential to have effective methods that can measure all types of fluxes, and discover new potential sources, in order to make adequate priorities and to take effective actions to mitigate greenhouse gas emissions from WWTPs. Funding Agencies|Swedish Research Council VRSwedish Research Council [2016-04829]; FormasSwedish Research Council Formas [2018-01794]; European Unions Horizon 2020 research and innovation programme [101015825]; Knut and Alice Wallenberg FoundationKnut & Alice Wallenberg Foundation [KAW2010.0126]; European Research Council (ERC) under the European Unions Horizon 2020 research and innovation programmeEuropean Research Council (ERC) [725546]

Este artículo contiene 5 páginas, 2 figuras.

Many biochemical processes and dynamics are strongly controlled by terrain topography, making digital elevation models (DEM) a fundamental dataset for a range of applications. This study investigates the quality of four pan-Arctic DEMs (Arctic DEM, ASTER DEM, ALOS DEM and Copernicus DEM) within the Kalix River watershed in northern Sweden, with the aim of informing users about the quality when comparing these DEMs. The quality assessment focuses on both the vertical accuracy of the DEMs and their abilities to model two fundamental elevation derivatives, including topographic wetness index (TWI) and landform classification. Our results show that the vertical accuracy is relatively high for Arctic DEM, ALOS and Copernicus and in our study area was slightly better than those reported in official validation results. Vertical errors are mainly caused by tree cover characteristics and terrain slope. On the other hand, the high vertical accuracy does not translate directly into high quality elevation derivatives, such as TWI and landform classes, as shown by the large errors in TWI and landform classification for all four candidate DEMs. Copernicus produced elevation derivatives with results most similar to those from the reference DEM, but the errors are still relatively high, with large underestimation of TWI in land cover classes with a high likelihood of being wet. Overall, the Copernicus DEM produced the most accurate elevation derivatives, followed by slightly lower accuracies from Arctic DEM and ALOS, and the least accurate being ASTER.

Methane (CH4) and carbon dioxide emissions from lakes are relevant for assessing the greenhouse gas output of wetlands. However, only few standardized datasets describe concentrations of these gases in lakes across different geographical regions. We studied concentrations and stable carbon isotopic composition (δ13C) of CH4 and dissolved inorganic carbon (DIC) in 32 small lakes from Finland, Sweden, Germany, the Netherlands, and Switzerland in late summer. Higher concentrations and δ13C values of DIC were observed in calcareous lakes than in lakes on non-calcareous areas. In stratified lakes, δ13C values of DIC were generally lower in the hypolimnion due to the degradation of organic matter (OM). Unexpectedly, increased δ13C values of DIC were registered above the sediment in several lakes. This may reflect carbonate dissolution in calcareous lakes or methanogenesis in deepwater layers or in the sediments. Surface water CH4 concentrations were generally higher in western and central European lakes than in Fennoscandian lakes, possibly due to higher CH4 production in the littoral sediments and lateral transport, whereas CH4 concentrations in the hypolimnion did not differ significantly between the regions. The δ13C values of CH4 in the sediment suggest that δ13C values of biogenic CH4 are not necessarily linked to δ13C values of sedimentary OM but may be strongly influenced by OM quality and methanogenic pathway. Our study suggests that CH4 and DIC cycling in small lakes differ between geographical regions and that this should be taken into account when regional studies on greenhouse gas emissions are upscaled to inter-regional scales.

Wetlands can potentially affect global climate change through their role in modulating the atmospheric concentrations of methane (CH4). Their overall CH4 emissions, however, remain the greatest uncertainty in the global CH4 budget. One reason for this is the paucity of long-term field measurements to characterize the variability of CH4 emissions from different types of wetlands. In this study, we quantified CH4 emissions from a brackish, oligohaline Cyperus malaccensis marsh ecosystem in the Min River Estuary in southeast China over five years. Our results showed substantial temporal variability of CH4 emissions from this brackish marsh, with hourly fluxes ranging from 0.7 +/- 0.6 to 5.1 +/- 3.7 mg m(-2) h(-1) (mean +/- 1 SD) during the study period. The inter-annual variability of CH4 emissions was significantly correlated with changes in soil temperature, precipitation and salinity, which highlighted the importance of long-term observations in understanding wetland CH4 dynamics. Distinct seasonal patterns in soil CH4 production rates and porewater CH4 concentrations also were observed, and were both positively correlated with CH4 emissions. The seasonal variations of CH4 emissions and production were highly correlated with salinity and porewater sulfate levels. The mean annual CH4 efflux from our site over the five-year period was 23.8 +/- 18.1 g CH4 m(-2) yr(-1), indicating that subtropical brackish tidal marsh ecosystems could release a large amount of CH4 into the atmosphere. Our findings further highlight the need to obtain high-frequency and continuous field measurements over the long term at multiple spatial scales to improve our current estimates of wetland CH4 emissions. Funding Agencies|National Natural Science Foundation of China [41801070, 41877335, 41671088]; Program for Innovative Research Team at Fujian Normal University [IRTL1205]; Key Sciences and Technology Project of Fujian Province [2014R1034-1]; Study-Abroad Grant Project for Graduates of the School of Geographical Sciences; Graduated Student Science and Technology Innovation Project of the School of Geographical Science, Fujian Normal University [GY201601]; Research Grants Council of the Hong Kong Special Administrative Region, China [CUHK458913, CUHK14302014, CUHK14305515]; Chinese University of Hong Kong [SS16914]; Swedish Research Council VR; European Research Council ERC [725546]; Linkoping University

This study is an attempt to assess CH

Methane (CH4) emissions from the Boreal and Arctic region are globally significant and highly sensitive to climate change. There is currently a wide range in estimates of high-latitude annual CH4 fluxes, where estimates based on land cover inventories and empirical CH4 flux data or process models (bottom-up approaches) generally are greater than atmospheric inversions (top-down approaches). A limitation of bottom-up approaches has been the lack of harmonization between inventories of site-level CH4 flux data and the land cover classes present in high-latitude spatial datasets. Here we present a comprehensive dataset of small-scale, surface CH4 flux data from 540 terrestrial sites (wetland and non-wetland) and 1247 aquatic sites (lakes and ponds), compiled from 189 studies. The Boreal-Arctic Wetland and Lake Methane Dataset (BAWLD-CH4) was constructed in parallel with a compatible land cover dataset, sharing the same land cover classes to enable refined bottom-up assessments. BAWLD-CH4 includes information on site-level CH4 fluxes, but also on study design (measurement method, timing, and frequency) and site characteristics (vegetation, climate, hydrology, soil, and sediment types, permafrost conditions, lake size and depth, and our determination of land cover class). The different land cover classes had distinct CH4 fluxes, resulting from definitions that were either based on or co-varied with key environmental controls. Fluxes of CH4 from terrestrial ecosystems were primarily influenced by water table position, soil temperature, and vegetation composition, while CH4 fluxes from aquatic ecosystems were primarily influenced by water temperature, lake size, and lake genesis. Models could explain more of the between-site variability in CH4 fluxes for terrestrial than aquatic ecosystems, likely due to both less precise assessments of lake CH4 fluxes and fewer consistently reported lake site characteristics. Analysis of BAWLD-CH4 identified both land cover classes and regions within the Boreal and Arctic domain where future studies should be focused, alongside methodological approaches. Overall, BAWLD-CH4 provides a comprehensive dataset of CH4 emissions from high-latitude ecosystems that are useful for identifying research opportunities, for comparison against new field data, and model parameterization or validation. BAWLD-CH4 can be downloaded from https://doi.org/10.18739/A27H1DN5S.

The process of chemosynthesis can represent an important source of organic matter and energy across the benthic zone. However, its detailed vertical distribution and importance in relation to other microbial processes are still poorly investigated in inland aquatic ecosystems. Here, we determined the rates of dark inorganic carbon fixation (DCF) compared to heterotrophic bacterial production (BP) and oxygen consumption (SOC) across a depth profile of oxic to anoxic sediments in the littoral zone of nine tropical lakes located in one of the most important coastal conservation areas, the Jurubatiba Sandbank National Park (Rio de Janeiro, Brazil). Rates of DCF were highly variable (means of 0.1–1.2 mmol C m−2 d−1) among the studied lakes, with mostly production occurring below 10 mm of sediment in the anoxic zone. Although presenting a relatively low contribution in relation to BP and SOC, our study showed extensive microbial metabolism in the anaerobic sediment below the top centimeter, highlighting the importance of studying microbial processes across depth at fine scales. To our knowledge, it is the first study to show detailed vertical DCF rates in coastal tropical lake sediments, thus contributing to a better comprehension of the microbial role in the biogeochemical cycles of aquatic systems.