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The CO( 2)flux (FCO2) from lakes to the atmosphere is a large component of the global carbon cycle anddepends on the air-water CO2concentration gradient (Delta CO2) and the gas transfer velocity (k). Both Delta CO2 and k can vary on multiple timescales and understanding their contributions toFCO(2)is important for explaining var-iability influxes and developing optimal sampling designs. We measuredFCO2 and Delta CO(2 )and derivedkforone full ice-free period in 18 lakes usingfloating chambers and estimated the contributions of Delta CO2 and k to FCO2 variability. Generally, kcontributed more than Delta CO2to short-term (1-9d) FCO2 variability. With in creased temporal period, the contribution of k to FCO2 variability decreased, and in some lakes resulted in Delta CO2 contrib-uting more thank to FCO2 variability over the full ice-free period. Increased contribution of Delta CO2 to FCO2 vari-ability over time occurred across all lakes but was most apparent in large-volume southern-boreal lakes and indeeper (>2m) parts of lakes, whereaskwas linked to FCO(2 )variability in shallow waters. Accordingly, knowing the variability of bothk and Delta CO(2 )over time and space is needed for accurate modeling of F CO2 from these vari-ables. We conclude that priority in FCO(2 )assessments should be given to direct measurements of FCO2 at multiplesites when possible, or otherwise from spatially distributed measurements of Delta CO(2 )combined with k- models that incorporate spatial variability of lake thermal structure and meteorology., Funding Agencies|Knut and Alice Wallenberg Foundation [2016.0083]; European Research Council (ERC) [725546]; Swedish Research Council (VR) [2016-04829]; Swedish Research Council for Sustainable Development (FORMAS) [2018-01794]; VR [2017-00635]; US National Science Foundation (Division of Environmental Biology) [1753856]

Methane (CH4) emissions (FCH4) from northern freshwater lakes are not only significant but also highly variable in time and one driver variable suggested to be important is precipitation. Rain can have various, potentially large effects on FCH4 across multiple time frames, and verifying the impact of rain on lake FCH4 is key to understand both contemporary flux regulation, and to predict future FCH4 related to possible changes in frequency and intensity of rainfall from climate change. The main objective of this study was to assess the short-term impact of typically occurring rain events with different intensity on FCH4 from various lake types located in hemiboreal, boreal, and subarctic Sweden. In spite of high time resolution automated flux measurements across different depth zones and covering numerous commonly types of rain events in northern areas, in general, no strong impact on FCH4 during and within 24 h after the rainfall could be observed. Only in deeper lake areas and during longer rain events FCH4 was weakly related to rain (R2 = 0.29, p < 0.05), where a minor FCH4 decrease during the rain was identified, suggesting that direct rainwater input, during greater rainfall, may decrease FCH4 by dilution of surface water CH4. Overall, this study indicates that typical rain events in the studied regions have minor direct short-term effects on FCH4 from northern lakes and do not enhance FCH4 from shallow and deeper parts of lakes during and up to 24-h after the rainfall. Instead, other factors such as wind speed, water temperature and pressure changes were more strongly correlated with lake FCH4., Funding Agencies|European Research Council (ERC) under the European Union [725546]; Swedish Research Council [2021-00164]; FORMAS [2016-04829]; Knut and Alice Wallenberg Foundation [2017-00635]; [2018-01794]; [2016.0083]

Lakes contribute 9%–19% of global methane (CH4) emissions to the atmosphere. Dissolved molecular oxygen (DO) in lakes can inhibit the production of CH4 and promote CH4 oxidation. DO is therefore often considered an important regulator of CH4 emissions from lakes. Presence or absence of DO in the water above the sediments can affect CH4 production and emissions by (a) influencing if methane production can be fueled by the most reactive organic matter in the top sediment layer or rely on deeper and less degradable organic matter, and (b) enabling CH4 accumulation in deep waters and potentially large emissions upon water column turnover. However, the relative importance of these two DO effects on CH4 fluxes is still unclear. We assessed CH4 fluxes from two connected lake basins in northern boreal Sweden where one was experimentally oxygenated. Results showed no clear difference in summer CH4 emissions attributable to water column DO concentrations. Large amounts of CH4 accumulated in the anoxic hypolimnion of the reference basin but little of this may have been emitted because of incomplete mixing, and effective methane oxidation of stored CH4 reaching oxic water layers. Accordingly, ≤24% of the stored CH4 was likely emitted in the experimental lake. Overall, our results suggest that hypolimnetic DO and water column CH4 storage might have a smaller impact on CH4 emissions in boreal forest lakes than previous estimates, yet potential fluxes associated with water column turnover events remain a significant uncertainty in lake CH4 emission estimates.

2023-04-06 Version 2.0 published. Minor changes in the structure of the data file. There were no changes in the data.2023-03-23 The title was changed fromSource data for “The effects of water column dissolved oxygen concentrations on lake methane emissions: Results from a whole-lake oxygenation experiment” to "Source data for ”Higher apparent gas transfer velocities for CO2 compared to CH4 in small lakes”"2022-11-30 Version 1.0 published.

History:2022-08-22 Version 1.0 published 2022-09-09 Version 1.1 of the dataset with minor revisions published. Version 1.0 hidden.2023-04-17 Version 1.2 of the dataset with minor revisions published. Version 1.1 was hidden, and had been downloadet 20 times in total.2023-09-25 Version 2.0 of the dataset with minor revisions published. Version 1.2 was hidden, and had been downloadet 11 times in total.

Lakes are generally supersaturated in carbon dioxide (CO2) and emitters of CO2 to the atmosphere. However, estimates of CO2 flux (FCO2) from lakes are seldom based on direct flux measurements and usually do not account for nighttime emissions, yielding risk of biased assessments. Here, we present direct FCO2 measurements from automated floating chambers collected every 2-3 hr and spanning 115 24 hr periods in three boreal lakes during summer stratification and before and after autumn mixing in the most eutrophic lake of these. We observed 40%-67% higher mean FCO2 in daytime during periods of surface water CO2 supersaturation in all lakes. Day-night differences in wind speed were correlated with the day-night FCO2 differences in the two larger lakes, but in the smallest and most wind-sheltered lake peaks of FCO2 coincided with low-winds at night. During stratification in the eutrophic lake, CO2 was near equilibrium and diel variability of FCO2 insignificant, but after autumn mixing FCO2 was high with distinct diel variability making this lake a net CO2 source on an annual basis. We found that extrapolating daytime measurements to 24 hr periods overestimated FCO2 by up to 30%, whereas extrapolating measurements from the stratified period to annual rates in the eutrophic lake underestimated FCO2 by 86%. This shows the importance of accounting for diel and seasonal variability in lake CO2 emission estimates., Funding Agencies: Knut & Alice Wallenberg Foundation [2016.0083]; European Research Council (ERC) [725546]; Swedish Research Council, European Commission [2017-00635, 2016-04829]; FORMAS (the Swedish Research Council for Sustainable Development) [2018-01794]

Particulate pyrogenic carbon (PyC) transported by rivers and aerosols, and deposited in marine sediments, is an important part of the carbon cycle. The chemical composition of PyC is temperature dependent and levoglucosan is a source-specific burning marker used to trace low-temperature PyC. Levoglucosan associated to particulate material has been shown to be preserved during riverine transport and marine deposition in high- and mid-latitudes, but it is yet unknown if this is also the case for (sub)tropical areas, where 90% of global PyC is produced. Here, we investigate transport and deposition of levoglucosan in suspended and riverbed sediments from the Amazon River system and adjacent marine deposition areas. We show that the Amazon River exports negligible amounts of levoglucosan and that concentrations in sediments from the main Amazon tributaries are not related to long-term mean catchment-wide fire activity. Levoglucosan concentrations in marine sediments offshore the Amazon Estuary are positively correlated to total organic content regardless of terrestrial or marine origin, supporting the notion that association of suspended or dissolved PyC to biogenic particles is critical in the preservation of PyC. We estimate that 0.5-10 x 10(6) g yr(-1) of levoglucosan is exported by the Amazon River. This represents only 0.5-10 ppm of the total exported PyC and thereby an insignificant fraction, indicating that riverine derived levoglucosan and low-temperature PyC in the tropics are almost completely degraded before deposition. Hence, we suggest caution in using levoglucosan as tracer for past fire activity in tropical settings near rivers., Funding Agencies|European Research Council (ERC) under the European Unions Seventh Framework ProgramEuropean Research Council (ERC) [FP7/2007-2013, 339206]; DFG Excellence ClusterGerman Research Foundation (DFG) [307, KNR/97-4, MSM20/3]; FAPESPFundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP) [2018/15123-4, 2019/24349-9, 2011/06609-1, 2012/502260-6, 2016/02656-9, 2018/23899-2, 2019/24977-0]; CAPESCoordenacao de Aperfeicoamento de Pessoal de Nivel Superior (CAPES) [564/2015, 88881.313535/201901]; CNPqConselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPQ) [302607/2016-1, 422255/2016-5, 304727/20172]; Alexander von Humboldt FoundationAlexander von Humboldt Foundation; Eidgenossische Technische Hochschule Zurich

Winter methane (CH4) accumulation in seasonally ice-covered lakes can contribute to large episodic emissions to the atmosphere during spring ice melt. Biological methane oxidation can significantly mitigate such CH4 emissions, but despite favorable CH4 and O-2 concentrations, CH4 oxidation appears constrained in some lakes for unknown reasons. Here we experimentally test the hypothesis that phosphorus (P) availability is limiting CH4 oxidation, resulting in differences in ice-out emissions among lakes. We observed a positive relationship between potential CH4 oxidation and P concentration across 12 studied lakes and found an increase in CH4 oxidation in response to P amendment, without any parallel change in the methanotrophic community composition. Hence, while an increase in sedimentary CH4 production and ebullitive emissions may happen with eutrophication, our study indicates that the increase in P associated with eutrophication may also enhance CH4 oxidation. The increase in CH4 oxidation may hence play an important role in nutrient-rich ice-covered lakes where bubbles trapped under the ice may to a greater extent be oxidized, reducing the ice-out emissions of CH4. This may be an important factor regulating CH4 emissions from high latitude lakes., Funding Agencies|European Research Council (ERC) grant METLAKEEuropean Research Council (ERC) [725546]; Knut and Alice Wallenberg FoundationKnut & Alice Wallenberg Foundation [2016.0083]; FORMASSwedish Research Council Formas [2016-00874]; Swedish Research CouncilSwedish Research CouncilEuropean Commission [2016-04829, 2017-04422]; Science for Life Laboratory

The current resurgence of hydropower expansion toward tropical areas has been largely based on run-of-the-river (ROR) dams, which are claimed to have lower environmental impacts due to their smaller reservoirs. The Belo Monte dam was built in Eastern Amazonia and holds the largest installed capacity among ROR power plants worldwide. Here, we show that postdamming greenhouse gas (GHG) emissions in the Belo Monte area are up to three times higher than preimpoundment fluxes and equivalent to about 15 to 55 kg CO(2)eq MWh(-1). Since per-area emissions in Amazonian reservoirs are significantly higher than global averages, reducing flooded areas and prioritizing the power density of hydropower plants seem to effectively reduce their carbon footprints. Nevertheless, total GHG emissions are substantial even from this leading-edge ROR power plant. This argues in favor of avoiding hydropower expansion in Amazonia regardless of the reservoir type., Funding Agencies|Sao Paulo Research Foundation (FAPESP)Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP) [2014/21564-2, 2015/09187-1, 2016/11141-2, 2016/02656-9, 2019/24977-0, 2018/15123-4, 2019/24349-9, 2011/14502-2, 2018/18491-4]; National Science FoundationNational Science Foundation (NSF) [DEB-1754317]; Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq)Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPQ) [304727/2017-2]; European Research Council (ERC)European Research Council (ERC)European Commission [725546]; Swedish Research Council VRSwedish Research Council; FORMASSwedish Research Council Formas

The global development of hydropower dams has rapidly expanded over the last several decades and has spread to historically non-impounded systems such as the Amazon Rivers main low land tributaries in Brazil. Despite the recognized significance of reservoirs to the global methane (CH4) emission, the processes controlling this emission remain poorly understood, especially in Tropical reservoirs. Here we evaluate CH4 dynamics in the main channel and downstream of the Santo Antonio hydroelectric reservoir, a large tropical run-of-the-river (ROR) reservoir in Amazonia. This study is intended to give a snapshot of the CH4 dynamics during the falling water season at the initial stage after the start of operations. Our results show substantial and higher CH4 production in reservoirs littoral sediment than in the naturally flooded areas downstream of the dam. Despite the large production in the reservoir or naturally flooded areas, high CH4 oxidation in the main channel keep the concentration and fluxes of CH4 in the main channel low. Similar CH4 concentrations in the reservoir and downstream close to the dam suggest negligible degassing at the dam, but stable isotopic evidence indicates the presence of a less oxidized pool of CH4 after the dam. ROR reservoirs are designed to disturb the natural river flow dynamics less than traditional reservoirs. If enough mixing and oxygenation remain throughout the reservoirs water column, naturally high CH4 oxidation rates can also remain and limit the diffusive CH4 emissions from the main channel. Nevertheless, it is important to highlight that our results focused on emissions in the deep and oxygenated main channel. High emissions, mainly through ebullition, may occur in the vast and shallow areas represented by bays and tributaries. However, detailed assessments are still required to understand the impacts of this reservoir on the annual emissions of CH4., Funding Agencies|FAPESPFundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP) [2011/14502-2, 2012/17359-9, 12/51187-0, 2014/21564-2, 2015/09187-1, 2018/18491-4]; Swedish Research Council VR grants [2012-00048, 2016-04829]; STINT grant [2012-2085]; European Research Council (ERC)European Research Council (ERC)European Commission [METLAKE 725546]; "Cientista do Nosso Estado" grant from FAPERJ; NSFNational Science Foundation (NSF) [DEB 1754317]

The Amazon Basin is at the center of an intensifying discourse about deforestation, land-use, and global change. To date, climate research in the Basin has overwhelmingly focused on the cycling and storage of carbon (C) and its implications for global climate. Missing, however, is a more comprehensive consideration of other significant biophysical climate feedbacks [i.e., CH4, N2O, black carbon, biogenic volatile organic compounds (BV0Cs), aerosols, evapotranspiration, and albedo] and their dynamic responses to both localized (fire, land-use change, infrastructure development, and storms) and global (warming, drying, and some related to El Nino or to warming in the tropical Atlantic) changes. Here, we synthesize the current understanding of (1) sources and fluxes of all major forcing agents, (2) the demonstrated or expected impact of global and local changes on each agent, and (3) the nature, extent, and drivers of anthropogenic change in the Basin. We highlight the large uncertainty in flux magnitude and responses, and their corresponding direct and indirect effects on the regional and global climate system. Despite uncertainty in their responses to change, we conclude that current warming from non-CO2 agents (especially CH4 and N2O) in the Amazon Basin largely offsets- and most likely exceeds-the climate service provided by atmospheric CO2 uptake. We also find that the majority of anthropogenic impacts act to increase the radiative forcing potential of the Basin. Given the large contribution of less-recognized agents (e.g., Amazonian trees alone emit similar to 3.5% of all global CH4), a continuing focus on a single metric (i.e., C uptake and storage) is incompatible with genuine efforts to understand and manage the biogeochemistry of climate in a rapidly changing Amazon Basin., Funding Agencies|National Geographic SocietyNational Geographic Society; Rolex partnership; National Geographic Society research grantNational Geographic Society; FAPESPFundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP) [2018/14006-4, 2018/14423-4, 2014/508489]; National Coordination for High Level Education and Training (CAPES) [88887.136402-00INCT]; National Institute of Science and Technology for Climate Change Phase 2 (CNPq) [465501/2014-1]; CNPqNational Council for Scientific and Technological Development (CNPq) [311103/2015-4, 429795/2016-5]; FAPEAM [708565]; INPA [PRJ15.125]; Rede Clima (INPE) FINEP [01.13.0353-00]

The goal of this work was to study the species composition, the use of breeding sites, and the seasonal patterns of breeding activity of the anuran fauna from Parque Estadual Carlos Botelho - Nucleo Sete Barras, state of Sao Paulo, southeastern Brazil. Fieldwork was carried out from September 2005 to October 2007 through two main methods: active visual search inside a 10 ha- permanent plot and aural and visual search in seven previously selected aquatic breeding habitats. Species richness was related to the sampling effort by means of species accumulation curve and through non-parametric estimators. Thirty-three species distributed in 12 families were recorded, from which 69% are endemic to the Atlantic Forest. Trachycephalus mesophaeus represents a new record for the park. Cycloramphus lutzorum is included as Data Deficient in the IUCN list. The species accumulation curve did not stabilize, showing some tendency to rise. The use of breeding sites by 20 species was compared using cluster analysis, which revealed two major groups: the first with five species (two habitat generalists and three stream specialists) and the second composed by the other species (with different reproductive modes associated with flooded environments). The breeding period of most species was associated to the rainy season (October to February), and only Scinax hayii showed continuous breeding activity during the entire period of study., Funding Agencies|FAPESPFundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP) [04/15938-5, 99/09635-0]

Processes controlling the biogenic production of CH4 and CO2 are relevant not only to environmental issues related to greenhouse gases emissions, but also in the energy scenario, since the biogenic generation of CH4 can be associated with the formation of natural gas reserves over time. This work aimed to evaluate the influence of water and calcium sulfate in the production of CH4 and CO2 from petroleum biodegradation in tar sandstones. Water saturation and sulfate concentration are taken to be important factors of influence in the oil biodegradation process. Long-term incubation experiments (up to 363 days) were carried out with samples of sandstone impregnated with high-viscosity hydrocarbons. The rocks used in this study were collected from outcrops of the Piramboia Formation, a known heavy-oil reservoir of the Parana Basin, Brazil. The net accumulation of both CH4 and CO2 was crescent during all the experiments performed, but with decreasing production rates through time. Average potential production rates obtained were 18 mL CH4/t.y (milliliter per ton of sandstone per year) and 54,000 mL CO2/t.y. The addition of water resulted in an average increase of 11% and 10% in the CH4 and CO2 cumulative production, respectively, in comparison with the dry incubation experiments. The water influence was stronger in the first 30 days of incubations when average production was around 70% higher in wet samples. Once the pH remained constant in the presence of calcium sulfate, the experiments indicate that calcium sulfate may function as buffer for pH, limiting acidification, which has a known negative influence on CH4 and CO2 production. Thus, the present work aims to alert for the potential of CO2 and CH4 production from tar sands in Brazil and for the importance of water as a positive influence on CH4 and CO2 generation from tar sandstones. This helps to evaluate the influence of environmental conditions on biogenic gas systems as well as on green-house gases emissions fr, Funding Agencies|Project "Avaliacao da geracao de metano biogenico nas formacoes Ponta Grossa e Irati, Bacia do Parana" (CNPq) [454362/2014-5]; Programa de Formacao de Recursos Humanos em Geologia do Petroleo e Meio Ambiente [PFRH-241-Petrobras]; CNPqNational Council for Scientific and Technological Development (CNPq) [304727/2017-2]