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Abstract. Abundant research has been devoted to understanding the complexity of the biogeochemical and physical processes that are responsible for greenhouse gas (GHG) emissions from hydropower reservoirs. These systems may have spatially complex and heterogeneous GHG emissions due to flooded biomass, river inflows, primary production and dam operation. In this study, we investigated the relationships between the water-air CO 2 fluxes and the phytoplanktonic biomass in the Funil Reservoir, which is an old, stratified tropical reservoir that exhibits intense phytoplankton blooms and a low partial pressure of CO 2 (pCO 2 ). Our results indicated that the seasonal and spatial variability of chlorophyll concentrations (Chl) and pCO 2 in the Funil Reservoir are related more to changes in the river inflow over the year than to environmental factors such as air temperature and solar radiation. Field data and hydrodynamic simulations revealed that river inflow contributes to increased heterogeneity during the dry season due to variations in the reservoir retention time and river temperature. Contradictory conclusions could be drawn if only temporal data collected near the dam were considered without spatial data to represent CO 2 fluxes throughout the reservoir. During periods of high retention, the average CO 2 fluxes were 10.3 mmol m −2 d −1 based on temporal data near the dam versus −7.2 mmol m −2 d −1 with spatial data from along the reservoir surface. In this case, the use of solely temporal data to calculate CO 2 fluxes results in the reservoir acting as a CO 2 source rather than a sink. This finding suggests that the lack of spatial data in reservoir C budget calculations can affect regional and global estimates. Our results support the idea that the Funil Reservoir is a dynamic system where the hydrodynamics represented by changes in the river inflow and retention time are potentially a more important force driving both the Chl and pCO 2 spatial variability than the in-system ecological factors.

Peatlands are carbon‐rich ecosystems that cover 185–423 million hectares (Mha) of the earth's surface. The majority of the world's peatlands are in temperate and boreal zones, whereas tropical ones cover only a total area of 90–170 Mha. However, there are still considerable uncertainties in C stock estimates as well as a lack of information about depth, bulk density and carbon accumulation rates. The incomplete data are notable especially in tropical peatlands located in South America, which are estimated to have the largest area of peatlands in the tropical zone. This paper displays the current state of knowledge surrounding tropical peatlands and their biophysical characteristics, distribution and carbon stock, role in the global climate, the impacts of direct human disturbances on carbon accumulation rates and greenhouse gas (GHG) emissions. Based on the new peat extension and depth data, we estimate that tropical peatlands store 152–288 Gt C, or about half of the global peatland emitted carbon. We discuss the knowledge gaps in research on distribution, depth, C stock and fluxes in these ecosystems which play an important role in the global carbon cycle and risk releasing large quantities of GHGs into the atmosphere (CO2 and CH4) when subjected to anthropogenic interferences (e.g., drainage and deforestation). Recent studies show that although climate change has an impact on the carbon fluxes of these ecosystems, the direct anthropogenic disturbance may play a greater role. The future of these systems as carbon sinks will depend on advancing current scientific knowledge and incorporating local understanding to support policies geared toward managing and conserving peatlands in vulnerable regions, such as the Amazon where recent records show increased forest fires and deforestation.

Tropospheric trace gases were measured from an aircraft platform. The flights were organized to sample air masses from the geographic area of central Brazil, where the vegetation, a savanna‐type environment with the local name of “cerrado”, is subject to burning every year, especially through August, September, and October. These measurements were made as a Brazilian local contribution to the international field campaign organized by NASA, the Transport and Atmospheric Chemistry Near the Equator‐Atlantic (TRACE A) mission, and the Southern African Fire Atmospheric Research Initiative (SAFARI). The major NASA TRACE A mission used the NASA DC 8 aircraft, with most flights over the South Atlantic Ocean region. In Brazil, missions using small aircraft measured ozone and carbon dioxide continuously, and carbon monoxide, nitrous oxide, and methane using grab sampling. In addition, ground‐based measurements were made continuously over most of the dry months of 1992, and ozonesondes were launched at three different sites. Geostationary Operational Environment Satellite‐East (GOES E) images and a special network of radio soundings provided meteorological information, and advanced very high resolution radiometer (AVHRR) images indicated the distribution of fire pixels in the region of interest. Most of the biomass burning in 1992 occurred in the state of Tocantins, with about 22% of all the burning in Brazil. The state of Mato Grosso was second, with 19% of all burning. The Brazilian aircraft was used mostly in these two states, near the cities of Porto Nacional and Cuiabá, for in situ sampling; 31 vertical profiles were made in air masses considered to be well mixed, that is, not in fresh plumes. Although the major interest was the dry season, sampling was also made during the previous wet season period in April 1992 for comparison; 10 vertical profiles were obtained using the same aircraft and measurement techniques. There is a clear difference between these two opposite seasonal periods, most evident in the O3 and CO data. Both Cuiabá and Porto Nacional show some 30–60 parts per billion by volume (ppbv) larger methane concentrations, for example, during the dry season, in comparison to the wet season, the difference at Cuiabá being larger. The methane data for the wet season show no significant differences between Cuiabá and Porto Nacional mixing ratios, which seems to exclude the existence of significant sources or sinks at these sites during this wet season. The ozone mixing ratios vary around 15 ± 5 ppbv in the wet season, and from a minimum of 35 to a maximum of 70 ± 10 ppbv, depending on height, in the dry season. The largest variability is seen in the carbon monoxide mixing ratios which vary from 90–100 ppbv in the wet season to maxima of 300 at 3.3 km and 600 ppbv at 1.2 km height in the dry season.

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Abstract. Much research has been devoted to understanding the complexity of biogeochemical and physical processes responsible for the greenhouse gas (GHG) emissions from hydropower reservoirs. Spatial complexity and heterogeneity of GHG emission may be observed in these systems because it is dependent on flooded biomass, river inflow, primary production and dam operation. In this study, we investigate the relationships between water–air CO2 fluxes and phytoplanktonic biomass in Funil Reservoir, an old and stratified tropical reservoir, where intense phytoplankton blooms and low partial pressure of CO2 (pCO2) are observed. Our results showed that Funil Reservoir seasonal and spatial variability of chlorophyll concentration (Chl) and pCO2 is more related to changes in river inflow over the year than environmental factor such as air temperature and solar radiation. Field data and hydrodynamic simulations reveal that the river inflow contributes to increased heterogeneity in dry season due to the variation of reservoir retention time and river temperature. Contradictory conclusion can be drawn if temporal data collected only near the dam is considered instead of spatial data to represent CO2 fluxes in whole reservoir. The average CO2 fluxes was −17.6 and 22.1 mmol m−2d−2 considering data collected near the dam and spatial data, respectively, in periods of low retention time. In this case, the lack of spatial information can change completely the role of Funil Reservoir regarding GHG emissions. Our results support the idea that Funil Reservoir is a dynamic system where the hydrodynamics represented by changes in river inflow and retention time is potentially more important force driving both Chl and pCO2 spatial variability than in-system ecological factors.

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