| 1. |
- Almeida, Nazare da Silva, et al.
(author)
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Incubation experiments to constrain the production of methane and carbon dioxide in organic-rich shales of the Permian Irati Formation, Parana Basin
- 2020
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In: Marine and Petroleum Geology. - : Elsevier. - 0264-8172 .- 1873-4073. ; 112
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Journal article (peer-reviewed)abstract
- The Permian Irati Formation in Brazil hosts organic-rich shales and heavy hydrocarbons suitable for biogenic production of methane (CH4) and carbon dioxide (CO2). In this study, shale samples from the irati Formation were used in laboratory incubation experiments performed under different temperatures (22 degrees C, 50 degrees C, 70 degrees C and 80 degrees C) to evaluate the generation of CH4 and CO2 under thermal conditions compatible with biodegradation in shallow gas systems (< 80 degrees C). Despite our laboratory experiments do not represent natural subsurface temperature conditions, it is observed that the concentrations of CH4 and CO2 increase when shale samples are incubated under temperature higher than 22 degrees C. Samples incubated at 80 degrees C presented a maximum CH4 yield of 2.45 ml/t.d (milliliter per ton of shale per day) compared to 0,49 ml/t.d at 22 degrees C, 1.75 ml/t.d at 50 degrees C and 2.09 ml/t.d at 70 degrees C. The same trend of increasing production rates with higher temperatures was observed for CO2, with maximum potential production observed under a laboratory temperature of 80 degrees C, reaching 23.47 ml/t.d. Stable carbon isotopes (delta C-13) on CH4 and CO2 suggest a mixture of thermogenic and secondary microbial gas. However, the measured CH4 and CO2 can be generated through methanogenic degradation of heavy hydrocarbons present in the studied shales, difficulting the use of carbon isotope composition to discriminate between biogenic and thermogenic gases. The studied shale samples showed significant differences in CH4 and CO2 production rates, which are possibly related to the major elements composition of the mineral matrix. Higher CH4 and CO2 production rates occurred in samples with higher amount of sulfur. Besides sulfur, we highlight that others soluble elements in the mineral matrix, such as Ca and Mg, can play an important role for the generation of biogenic CH4 and CO2. The present work intends to alert for the importance of thermal conditions as well as the geochemical composition of the mineral matrix to build conceptual models about shallow gas systems, acting on organic-rich shales in sedimentary basins.
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| 2. |
- Bertassoli, Dailson J. Jr., et al.
(author)
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How green can Amazon hydropower be? : Net carbon emission from the largest hydropower plant in Amazonia
- 2021
-
In: Science Advances. - : American Association for the Advancement of Science. - 2375-2548. ; 7:26
-
Journal article (peer-reviewed)abstract
- 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.
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| 3. |
- Covey, Kristofer, et al.
(author)
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Carbon and Beyond : The Biogeochemistry of Climate in a Rapidly Changing Amazon
- 2021
-
In: Frontiers in Forests and Gobal Change. - : Frontiers Media S.A.. - 2624-893X. ; 4
-
Research review (peer-reviewed)abstract
- 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.
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| 4. |
- de Araujo, Kleiton R., et al.
(author)
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Carbon dioxide (CO2) concentrations and emission in the newly constructed Belo Monte hydropower complex in the Xingu River, Amazonia
- 2019
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In: Biogeosciences. - Gottingen : Copernicus Gesellschaft MBH. - 1726-4170 .- 1726-4189. ; 16:18, s. 3527-3542
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Journal article (peer-reviewed)abstract
- The Belo Monte hydropower complex located in the Xingu River is the largest run-of-the-river (ROR) hydroelectric system in the world and has one of the highest energy production capacities among dams. Its construction received significant media attention due to its potential social and environmental impacts. It is composed of two ROR reservoirs: the Xingu Reservoir (XR) in the Xingu's main branch and the Intermediate Reservoir (IR), an artificial reservoir fed by waters diverted from the Xingu River with longer water residence time compared to XR. We aimed to evaluate spatiotemporal variations in CO2 partial pressure (pCO(2)) and CO2 fluxes (FCO2) during the first 2 years after the Xingu River impoundment under the hypothesis that each reservoir has contrasting FCO2 and pCO(2) as vegetation clearing reduces flooded area emissions. Time of the year had a significant influence on pCO(2) with the highest average values observed during the high-water season. Spatial heterogeneity throughout the entire study area was observed for pCO(2) during both low-and high-water seasons. FCO2, on the other hand, only showed significant spatial heterogeneity during the high-water period. FCO2 (0.90 +/- 0.47 and 1.08 +/- 0.62 mu mol m(2) d(-1) for XR and IR, respectively) and pCO(2) (1647 +/- 698 and 1676 +/- 323 mu atm for XR and IR, respectively) measured during the high-water season were on the same order of magnitude as previous observations in other Amazonian clearwater rivers unaffected by impoundment during the same season. In contrast, during the low-water season FCO2 (0.69 +/- 0.28 and 7.32 +/- 4.07 mu mol m(2) d(-1) for XR and IR, respectively) and pCO(2) (839 +/- 646 and 1797 +/- 354 mu atm for XR and IR, respectively) in IR were an order of magnitude higher than literature FCO2 observations in clearwater rivers with naturally flowing waters. When CO2 emissions are compared between reservoirs, IR emissions were 90% higher than values from the XR during low-water season, reinforcing the clear influence of reservoir characteristics on CO2 emissions. Based on our observations in the Belo Monte hydropower complex, CO2 emissions from ROR reservoirs to the atmosphere are in the range of natural Amazonian rivers. However, the associated reservoir (IR) may exceed natural river emission rates due to the preimpounding vegetation influence. Since many reservoirs are still planned to be constructed in the Amazon and throughout the world, it is critical to evaluate the implications of reservoir traits on FCO2 over their entire life cycle in order to improve estimates of CO2 emissions per kilowatt for hydropower projects planned for tropical rivers.
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| 5. |
- Häggi, C., et al.
(author)
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Negligible Quantities of Particulate Low-Temperature Pyrogenic Carbon Reach the Atlantic Ocean via the Amazon River
- 2021
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In: Global Biogeochemical Cycles. - : American Geophysical Union (AGU). - 0886-6236 .- 1944-9224. ; 35:9
-
Journal article (peer-reviewed)abstract
- 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.
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| 6. |
- Pelissari, Maria Rogieri, et al.
(author)
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Water influence on CH4 and CO2 generation from tar sandstones: Insights from incubation experiments in the Piramboia Formation, Parana Basin
- 2021
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In: Journal of South American Earth Sciences. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0895-9811 .- 1873-0647. ; 106
-
Journal article (peer-reviewed)abstract
- 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 from geological sources, which are taken to be important sources of carbon to the atmosphere in a context of climate change.
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| 7. |
- Sawakuchi, A. O., et al.
(author)
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Luminescence of quartz and feldspar fingerprints provenance and correlates with the source area denudation in the Amazon River basin
- 2018
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In: Earth and Planetary Science Letters. - : Elsevier. - 0012-821X .- 1385-013X. ; 492, s. 152-162
-
Journal article (peer-reviewed)abstract
- The Amazon region hosts the world's largest watershed spanning from high elevation Andean terrains to lowland cratonic shield areas in tropical South America. This study explores variations in optically stimulated luminescence (OSL) and infrared stimulated luminescence (IRSL) signals in suspended silt and riverbed sands retrieved from major Amazon rivers. These rivers drain Pre-Cambrian to Cenozoic source rocks in areas with contrasting denudation rates. In contrast to the previous studies, we do not observe an increase in the OSL sensitivity of quartz with transport distance; for example, Tapajos and Xingu Rivers show more sensitive quartz than Solimbes and Madeira Rivers, even though the latter have a significantly larger catchment area and longer sediment transport distance. Interestingly, high sensitivity quartz is observed in rivers draining relatively stable Central Brazil and Guiana shield areas (denudation rate xi = 0.04 mm yr(-1)), while low sensitivity quartz occurs in less stable Andean terrains (xi = 0.24 mm yr(-1)). An apparent linear correlation between quartz OSL sensitivity and denudation rate suggests that OSL sensitivity may be used as a proxy for erosion rates in the Amazon basin. Furthermore, luminescence sensitivity measured in sand or silt arises from the same mineral components (quartz and feldspar) and clearly discriminates between Andean and shield sediments, avoiding the grain size bias in provenance analysis. These results have implications for using luminescence sensitivity as a proxy for Andean and shield contributions in the stratigraphic record, providing a new tool to reconstruct past drainage configurations within the Amazon basin.
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| 8. |
- Sawakuchi, Henrique O., et al.
(author)
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Methane emissions from Amazonian Rivers and their contribution to the global methane budget
- 2014
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In: Global Change Biology. - : Wiley-Blackwell. - 1354-1013 .- 1365-2486. ; 20:9, s. 2829-2840
-
Journal article (peer-reviewed)abstract
- Methane (CH4) fluxes from world rivers are still poorly constrained, with measurements restricted mainly to temperate climates. Additional river flux measurements, including spatio-temporal studies, are important to refine extrapolations. Here we assess the spatio-temporal variability of CH4 fluxes from the Amazon and its main tributaries, the Negro, Solimoes, Madeira, Tapajos, Xingu, and Para Rivers, based on direct measurements using floating chambers. Sixteen of 34 sites were measured during low and high water seasons. Significant differences were observed within sites in the same river and among different rivers, types of rivers, and seasons. Ebullition contributed to more than 50% of total emissions for some rivers. Considering only river channels, our data indicate that large rivers in the Amazon Basin release between 0.40 and 0.58 Tg CH4 yr(-1). Thus, our estimates of CH4 flux from all tropical rivers and rivers globally were, respectively, 19-51% to 31-84% higher than previous estimates, with large rivers of the Amazon accounting for 22-28% of global river CH4 emissions.
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| 9. |
- Sawakuchi, Henrique O., et al.
(author)
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Oxidative mitigation of aquatic methane emissions in large Amazonian rivers
- 2016
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In: Global Change Biology. - : WILEY-BLACKWELL. - 1354-1013 .- 1365-2486. ; 22:3, s. 1075-1085
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Journal article (peer-reviewed)abstract
- The flux of methane (CH4) from inland waters to the atmosphere has a profound impact on global atmospheric greenhouse gas (GHG) levels, and yet, strikingly little is known about the dynamics controlling sources and sinks of CH4 in the aquatic setting. Here, we examine the cycling and flux of CH4 in six large rivers in the Amazon basin, including the Amazon River. Based on stable isotopic mass balances of CH4, inputs and outputs to the water column were estimated. We determined that ecosystem methane oxidation (MOX) reduced the diffusive flux of CH4 by approximately 28-96% and varied depending on hydrologic regime and general geochemical characteristics of tributaries of the Amazon River. For example, the relative amount of MOX was maximal during high water in black and white water rivers and minimal in clear water rivers during low water. The abundance of genetic markers for methane-oxidizing bacteria (pmoA) was positively correlated with enhanced signals of oxidation, providing independent support for the detected MOX patterns. The results indicate that MOX in large Amazonian rivers can consume from 0.45 to 2.07 Tg CH4 yr(-1), representing up to 7% of the estimated global soil sink. Nevertheless, climate change and changes in hydrology, for example, due to construction of dams, can alter this balance, influencing CH4 emissions to atmosphere.
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| 10. |
- Bastviken, David, et al.
(author)
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The importance of plants for methane emission at the ecosystem scale
- 2023
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In: Aquatic Botany. - : ELSEVIER. - 0304-3770 .- 1879-1522. ; 184
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Journal article (peer-reviewed)abstract
- Methane (CH4), one of the key long-lived atmospheric greenhouse gases, is primarily produced from organic matter. Accordingly, net primary production of organic matter sets the boundaries for CH4 emissions. Plants, being dominant primary producers, are thereby indirectly sustaining most global CH4 emissions, albeit with delays in time and with spatial offsets between plant primary production and subsequent CH4 emission. In addition, plant communities can enhance or hamper ecosystem production, oxidation, and transport of CH4 in multiple ways, e.g., by shaping carbon, nutrient, and redox gradients, and by representing a physical link be-tween zones with extensive CH4 production in anoxic sediments or soils and the atmosphere. This review focuses on how plants and other primary producers influence CH4 emissions with the consequences at ecosystem scales. We outline mechanisms of interactions and discuss flux regulation, quantification, and knowledge gaps across multiple ecosystem examples. Some recently proposed plant-related ecosystem CH4 fluxes are difficult to reconcile with the global atmospheric CH4 budget and the enigmas related to these fluxes are highlighted. Overall, ecosystem CH4 emissions are strongly linked to primary producer communities, directly or indirectly, and properly quantifying magnitudes and regulation of these links are key to predicting future CH4 emissions in a rapidly changing world.
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| 11. |
- Bertoluci, Jaime, et al.
(author)
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Anuran fauna of the Parque Estadual Carlos Botelho - Nficleo Sete Barras, southeastern Brazil: species composition, use of breeding sites, and seasonal patterns of breeding activity
- 2021
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In: Biota neopropica. - : REVISTA BIOTA NEOTROPICA. - 1678-6424 .- 1676-0603. ; 21:1
-
Journal article (peer-reviewed)abstract
- 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.
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| 12. |
- Kuhn, Catherine, et al.
(author)
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Performance of Landsat-8 and Sentinel-2 surface reflectance products for river remote sensing retrievals of chlorophyll-a and turbidity
- 2019
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In: Remote Sensing of Environment. - : Elsevier. - 0034-4257 .- 1879-0704. ; 224, s. 104-118
-
Journal article (peer-reviewed)abstract
- Rivers and other freshwater systems play a crucial role in ecosystems, industry, transportation and agriculture. Despite the > 40 years of inland water observations made possible by optical remote sensing, a standardized reflectance product for inland waters is yet forthcoming. The aim of this work is to compare the standard USGS land surface reflectance product to two Landsat-8 and Sentinel-2 aquatic remote sensing reflectance products over the Amazon, Columbia and Mississippi rivers. Landsat-8 reflectance products from all three routines are then evaluated for their comparative performance in retrieving chlorophyll-a and turbidity in reference to ship borne, underway in situ validation measurements. The land surface product shows the best agreement (4% Mean Absolute Percent Difference) with field measurements of radiometry collected on the Amazon River and generates 36% higher reflectance values in the visible bands compared to aquatic methods (ACOLITE and SeaDAS) with larger differences between land and aquatic products observed in Sentinel-2 (0.01 sr(-1)) compared to Landsat-8 (0.001 sr(-1)). Choice of atmospheric correction routine can bias Landsat-8 retrievals of chlorophyll-a and turbidity by as much as 59% and 35% respectively. Using a more restrictive time window for matching in situ and satellite imagery can reduce differences by 5-31% depending on correction technique. This work highlights the challenges of satellite retrievals over rivers and underscores the need for future optical and biogeochemical research aimed at improving our understanding of the absorbing and scattering properties of river water and their relationships to remote sensing reflectance.
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| 13. |
- Pajala, Gustav, et al.
(author)
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Higher apparent gas transfer velocities for CO2 compared to CH4 in small lakes
- 2023
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In: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 57:23, s. 8578-8587
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Journal article (peer-reviewed)abstract
- Large greenhouse gas emissions occur via the release of carbon dioxide (CO2) and methane (CH4) from the surface layer of lakes. Such emissions are modeled from the air-water gas concentration gradient and the gas transfer velocity (k). The links between k and the physical properties of the gas and water have led to the development of methods to convert k between gases through Schmidt number normalization. However, recent observations have found that such normalization of apparent k estimates from field measurements can yield different results for CH4 and CO2. We estimated k for CO2 and CH4 from measurements of concentration gradients and fluxes in four contrasting lakes and found consistently higher (on an average 1.7 times) normalized apparent k values for CO2 than CH4. From these results, we infer that several gas-specific factors, including chemical and biological processes within the water surface microlayer, can influence apparent k estimates. We highlight the importance of accurately measuring relevant air-water gas concentration gradients and considering gas-specific processes when estimating k.
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| 14. |
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| 15. |
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| 16. |
- Pajala, Gustav, et al.
(author)
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The effects of water column dissolved oxygen concentrations on lake methane emissions : results from a whole-lake oxygenation experiment
- 2023
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In: Journal of Geophysical Research - Biogeosciences. - : American Geophysical Union (AGU). - 2169-8953 .- 2169-8961. ; 128:11
-
Journal article (peer-reviewed)abstract
- 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.
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| 17. |
- Rudberg, David, et al.
(author)
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Contribution of gas concentration and transfer velocity to CO2 flux variability in northern lakes
- 2024
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In: Limnology and Oceanography. - : WILEY. - 0024-3590 .- 1939-5590.
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Journal article (peer-reviewed)abstract
- 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.
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| 18. |
- Rudberg, David, et al.
(author)
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Diel Variability of CO2 Emissions From Northern Lakes
- 2021
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In: Journal of Geophysical Research - Biogeosciences. - Hoboken, United States : John Wiley & Sons. - 2169-8953 .- 2169-8961. ; 126:10
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Journal article (peer-reviewed)abstract
- Lakes are generally supersaturated in carbon dioxide (CO2) and emitters of CO2 to the atmosphere. However, estimates of CO2 flux ((Formula presented.)) 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 (Formula presented.) 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 (Formula presented.) in daytime during periods of surface water CO2 supersaturation in all lakes. Day-night differences in wind speed were correlated with the day-night (Formula presented.) differences in the two larger lakes, but in the smallest and most wind-sheltered lake peaks of (Formula presented.) coincided with low-winds at night. During stratification in the eutrophic lake, CO2 was near equilibrium and diel variability of (Formula presented.) insignificant, but after autumn mixing (Formula presented.) 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 (Formula presented.) by up to 30%, whereas extrapolating measurements from the stratified period to annual rates in the eutrophic lake underestimated (Formula presented.) by 86%. This shows the importance of accounting for diel and seasonal variability in lake CO2 emission estimates.
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| 19. |
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| 20. |
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| 21. |
- Sawakuchi, Henrique, et al.
(author)
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Low Diffusive Methane Emissions From the Main Channel of a Large Amazonian Run-of-the-River Reservoir Attributed to High Methane Oxidation
- 2021
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In: Frontiers in Environmental Science. - : Frontiers Media S.A.. - 2296-665X. ; 9
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Journal article (peer-reviewed)abstract
- 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.
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| 22. |
- Sawakuchi, Henrique Oliveira, et al.
(author)
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Phosphorus Regulation of Methane Oxidation in Water From Ice-Covered Lakes
- 2021
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In: Journal of Geophysical Research - Biogeosciences. - : Wiley-Blackwell Publishing, Inc.. - 2169-8953 .- 2169-8961. ; 126:9
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Journal article (peer-reviewed)abstract
- 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 O2 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.
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| 23. |
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| 24. |
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| 25. |
- Schenk, Jonathan, 1992-, et al.
(author)
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Methane in Lakes : Variability in Stable Carbon Isotopic Composition and the Potential Importance of Groundwater Input
- 2021
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In: Frontiers in Earth Science. - Lausanne, Switzerland : Frontiers Media S.A.. - 2296-6463. ; 9
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Journal article (peer-reviewed)abstract
- Methane (CH4) is an important component of the carbon (C) cycling in lakes. CH4 production enables carbon in sediments to be either reintroduced to the food web via CH4 oxidation or emitted as a greenhouse gas making lakes one of the largest natural sources of atmospheric CH4. Large stable carbon isotopic fractionation during CH4 oxidation makes changes in 13C:12C ratio (δ13C) a powerful and widely used tool to determine the extent to which lake CH4 is oxidized, rather than emitted. This relies on correct δ13C values of original CH4 sources, the variability of which has rarely been investigated systematically in lakes. In this study, we measured δ13C in CH4 bubbles in littoral sediments and in CH4 dissolved in the anoxic hypolimnion of six boreal lakes with different characteristics. The results indicate that δ13C of CH4 sources is consistently higher (less 13C depletion) in littoral sediments than in deep waters across boreal and subarctic lakes. Variability in organic matter substrates across depths is a potential explanation. In one of the studied lakes available data from nearby soils showed correspondence between δ13C-CH4 in groundwater and deep lake water, and input from the catchment of CH4 via groundwater exceeded atmospheric CH4 emissions tenfold over a period of 1 month. It indicates that lateral hydrological transport of CH4 can explain the observed δ13C-CH4 patterns and be important for lake CH4 cycling. Our results have important consequences for modelling and process assessments relative to lake CH4 using δ13C, including for CH4 oxidation, which is a key regulator of lake CH4 emissions.
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| 26. |
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| 27. |
- Sieczko, Anna Katarzyna, 1978-, et al.
(author)
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Diel variability of methane emissions from lakes
- 2020
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In: Proceedings of the National Academy of Sciences of the United States of America. - Washington, DC 20001 United States : National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 117:35, s. 21488-21494
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Journal article (peer-reviewed)abstract
- Lakes are considered the second largest natural source of atmospheric methane (CH4). However, current estimates are still uncertain and do not account for diel variability of CH4 emissions. In this study, we performed high-resolution measurements of CH4 flux from several lakes, using an automated and sensor-based flux measurement approach (in total 4,580 measurements), and demonstrated a clear and consistent diel lake CH4 flux pattern during stratification and mixing periods. The maximum of CH4 flux were always noted between 10:00 and 16:00, whereas lower CH4 fluxes typically occurred during the nighttime (00:00–04:00). Regardless of the lake, CH4 emissions were on an average 2.4 higher during the day compared to the nighttime. Fluxes were higher during daytime on nearly 80% of the days. Accordingly, estimates and extrapolations based on daytime measurements only most likely result in overestimated fluxes, and consideration of diel variability is critical to properly assess the total lake CH4 flux, representing a key component of the global CH4 budget. Hence, based on a combination of our data and additional literature information considering diel variability across latitudes, we discuss ways to derive a diel variability correction factor for previous measurements made during daytime only.
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| 28. |
- Sieczko, Anna, et al.
(author)
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Minor impacts of rain on methane flux from hemiboreal, boreal, and subarctic lakes
- 2023
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In: Science of the Total Environment. - : ELSEVIER. - 0048-9697 .- 1879-1026. ; 895
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Journal article (peer-reviewed)abstract
- 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.
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| 29. |
- Valerio, Aline de Matos, et al.
(author)
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Using CDOM optical properties for estimating DOC concentrations and pCO2 in the lower Amazon river
- 2018
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In: Optics Express. - : Optical Society of America. - 1094-4087. ; 26:14, s. A657-A677
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Journal article (peer-reviewed)abstract
- Coloured dissolved organic matter (CDOM) is one of the major contributors to the absorption budget of most freshwaters and can be used as a proxy to assess non-optical carbon fractions such as dissolved organic carbon (DOC) and the partial pressure of carbon dioxide (pCO2). Nevertheless, riverine studies that explore the former relationships are still relatively scarce, especially within tropical regions. Here we document the spatial-seasonal variability of CDOM, DOC and pCO2, and assess the potential of CDOM absorption coefficient (aCDOM(412)) for estimating DOC concentration and pCO2 along the Lower Amazon River. Our results revealed differences in the dissolved organic matter (DOM) quality between clearwater (CW) tributaries and the Amazon River mainstream. A linear relationship between DOC and CDOM was observed when tributaries and mainstream are evaluated separately (Amazon River: N = 42, R2 = 0.74, p<0.05; CW: N = 13, R2 = 0.57, p<0.05). However, this linear relationship was not observed during periods of higher rainfall and river discharge, requiring a specific model for these time periods to be developed (N = 25, R2 = 0.58, p<0.05). A strong linear positive relation was found between aCDOM(412) and pCO2(N = 69, R2 = 0.65, p<0.05) along the lower river. pCO2 was less affected by the optical difference between tributaries and mainstream waters or by the discharge conditions when compared to CDOM to DOC relationships. Including the river water temperature in the model improves our ability to estimate pCO(2) (N = 69; R2 = 0.80, p<0.05). The ability to assess both DOC and pCO2 from CDOM optical properties opens further perspectives on the use of ocean colour remote sensing data for monitoring carbon dynamics in large running water systems worldwide.
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| 30. |
- Valerio, Aline M., et al.
(author)
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CO2 partial pressure and fluxes in the Amazon River plume using in situ and remote sensing data
- 2021
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In: Continental Shelf Research. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0278-4343 .- 1873-6955. ; 215
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Journal article (peer-reviewed)abstract
- Estimations of the global carbon budget include a quantitative understanding of the evolving processes that occur along river-to-ocean gradients. However, high spatiotemporal resolution observations of these processes are limited. Here we present in situ measurements of the partial pressure of CO2 (pCO(2)) made through the Amazon River plume (ARP) during different discharge seasons, from 2010 to 2012. We evaluated the spatiotemporal distribution of pCO(2) using Soil Moisture and Ocean Salinity (SMOS) satellite observations for each hydrologic period in the ARP. Regression models were used to estimate pCO(2) at the ARP for the period of 2010-2014. From these distributions we calculated sea-air gas exchange of CO2 between the plume waters and the atmosphere (F-co2(sea)). Intra-annual variability of Fseaco(2) was related to discharge at the river mouth and ocean currents as well as trade winds in the plume. Climatic events during the study period had a significant impact on the Fsea co(2). Including the plume area closer to the river mouth makes the ARP a net source of CO2 with an annual net sea-air flux of 8.6 +/- 7.1 Tg C y(-1) from 2011 to 2014.
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| 31. |
- Ward, Nicholas D., et al.
(author)
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Enhanced Aquatic Respiration Associated With Mixing of Clearwater Tributary and Turbid Amazon River Waters
- 2019
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In: Frontiers in Earth Science. - : Frontiers Media S.A.. - 2296-6463. ; 7
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Journal article (peer-reviewed)abstract
- When water bodies with unique biogeochemical constituents mix together there is potential for diverse responses by aquatic microbial communities and associated ecosystem functions. Here we evaluate bulk respiration under varying mixtures of turbid Amazon River water and two lowland tributaries-the Tapajos and Xingu rivers-based on O-2 drawdown in dark rotating incubation chambers. Experiments containing 5, 17, 33, and 50% tributary water mixed with Amazon River water were performed for the Tapajos and Xingu rivers at three different rotation velocities (0, 0.22, and 0.66 m s(-1)) during the falling water period. Pseudo first order reaction coefficients (k'), a measure of respiration potential, ranged from -0.15 to -1.10 d(-1), corresponding to respiration rates from 1.0 to 8.1 mg O-2 L d(-1). k'-values consistently increased with the rate of chamber rotation, and also was generally higher in the tributary-mainstem mixtures compared to pure endmembers. For both the Tapajos and Xingu rivers, the 17% mixture of tributary water yielded maximal k'-values, which were up to 2.9 and 2.2 times greater than in the tributary endmembers, respectively. The 50% mixtures, on the other hand, did not result in large increases in k'. We hypothesize that enhanced respiration potential after mixing unique water is driven, in part, by microbial priming effects that have been previously identified on a molecular level for these rivers. The results of this study suggest that there may be an optimal mixture for priming effects to occur in terms of the relative abundance of "priming" and "primed" substrates.
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| 32. |
- Ward, Nicholas D., et al.
(author)
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Pathways for Methane Emissions and Oxidation that Influence the Net Carbon Balance of a Subtropical Cypress Swamp
- 2020
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In: Frontiers in Earth Science. - : FRONTIERS MEDIA SA. - 2296-6463. ; 8
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Journal article (peer-reviewed)abstract
- We evaluated the major pathways for methane emissions from wetlands to the atmosphere at four wetland sites in the Big Cypress National Preserve in southwest Florida. Methane oxidation was estimated based on the delta C-13-CH4 of surface water, porewater, and bubbles to evaluate mechanisms that limit surface water emissions. Spatially-scaled methane fluxes were then compared to organic carbon burial rates. The pathway with the lowest methane flux rate was diffusion from surface waters (3.50 +/- 0.22 mmol m(-2) d(-1)). Microbial activity in the surface water environment and/or shallow oxic sediment layer oxidized 26 +/- 3% of the methane delivered from anerobic sediments to the surface waters. The highest rates of diffusion were observed at the site with the lowest extent of oxidation. Ebullition flux rates were 2.2 times greater than diffusion and more variable (7.79 +/- 1.37 mmol m(-2) d(-1)). Methane fluxes from non-inundated soils were 1.6 times greater (18.4 +/- 5.14 mmol m(-2) d(-1)) than combined surface water fluxes. Methane flux rates from cypress knees (emergent cypress tree root structures) were 3.7 and 2.3 times higher (42.0 +/- 6.33 mmol m(-2) d(-1)) than from surface water and soils, respectively. Cypress knee flux rates were highest at the wetland site with the highest porewater methane partial pressure, suggesting that the emergent root structures allow methane produced in anaerobic sediment layers to bypass oxidation in aerobic surface waters or shallow sediments. Scaled across the four wetlands, emissions from surface water diffusion, ebullition, non-inundated soils, and knees contributed to 14 +/- 2%, 25 +/- 6%, 34 +/- 10%, and 26 +/- 5% of total methane emissions, respectively. When considering only the three wetlands with cypress knees present, knee emissions contributed to 39 +/- 5% of the total scaled methane emissions. Finally, the molar ratio of CH4 emissions to OC burial ranged from 0.03 to 0.14 in the wetland centers indicating that all four wetland sites are net sources of atmospheric warming potential on 20-100 yr timescales, but net sinks over longer time scales (500 yr) with the exception of one wetland site that was a net source even over 500 yr time scales.
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