The carbon and water cycles for a southwestern Amazonian forest site were investigated using the longest time series of fluxes of CO2 and water vapor ever reported for this site. The period from 2004 ...to 2010 included two severe droughts (2005 and 2010) and a flooding year (2009). The effects of such climate extremes were detected in annual sums of fluxes as well as in other components of the carbon and water cycles, such as gross primary production and water use efficiency. Gap-filling and flux-partitioning were applied in order to fill gaps due to missing data, and errors analysis made it possible to infer the uncertainty on the carbon balance. Overall, the site was found to have a net carbon uptake of ≈5 t C ha(-1) year(-1), but the effects of the drought of 2005 were still noticed in 2006, when the climate disturbance caused the site to become a net source of carbon to the atmosphere. Different regions of the Amazon forest might respond differently to climate extremes due to differences in dry season length, annual precipitation, species compositions, albedo and soil type. Longer time series of fluxes measured over several locations are required to better characterize the effects of climate anomalies on the carbon and water balances for the whole Amazon region. Such valuable datasets can also be used to calibrate biogeochemical models and infer on future scenarios of the Amazon forest carbon balance under the influence of climate change.
The water level at the Manaus Port on the Negro River reached its record value of 29.97 m on 29 May 2012. This is higher than the previous record in the year 2009 by 20 cm. The rise of the level from ...November 2011 till the record maximum is the highest in the past several decades. A cooler South Atlantic and a normal or slightly warmer North Atlantic were associated with a record flood in the Amazon Basin in 2012. The seasonal atmospheric moisture convergence and the precipitation over the Amazon Basin are well correlated. During the period October 2011 through May 2012 the moisture‐flux convergence was 38% more intense than climatology. The rainfall equivalence of this excess moisture convergence is about 2.5 mm d–1 in the western Amazon Basin and 1.8 mm d–1 in the whole Amazon Basin.
Key PointsIn May 2012 the Negro River level reached record high valueAmazon's convergence was 30% more than its climatological the rainy seasonLa Nina condition produced rainfall in excess in the rainy season in the Amazon
Isoprene photochemistry over the Amazon rainforest Liu, Yingjun; Brito, Joel; Dorris, Matthew R. ...
Proceedings of the National Academy of Sciences - PNAS,
05/2016, Letnik:
113, Številka:
22
Journal Article
Recenzirano
Odprti dostop
Isoprene photooxidation is a major driver of atmospheric chemistry over forested regions. Isoprene reacts with hydroxyl radicals (OH) and molecular oxygen to produce isoprene peroxy radicals ...(ISOPOO). These radicals can react with hydroperoxyl radicals (HO₂) to dominantly produce hydroxyhydroperoxides (ISOPOOH). They can also react with nitric oxide (NO) to largely produce methyl vinyl ketone (MVK) and methacrolein (MACR). Unimolecular isomerization and bimolecular reactions with organic peroxy radicals are also possible. There is uncertainty about the relative importance of each of these pathways in the atmosphere and possible changes because of anthropogenic pollution. Herein, measurements of ISOPOOH and MVK + MACR concentrations are reported over the central region of the Amazon basin during the wet season. The research site, downwind of an urban region, intercepted both background and polluted air masses during the GoAmazon2014/5 Experiment. Under background conditions, the confidence interval for the ratio of the ISOPOOH concentration to that of MVK + MACR spanned 0.4–0.6. This result implies a ratio of the reaction rate of ISOPOO with HO₂ to that with NO of approximately unity. A value of unity is significantly smaller than simulated at present by global chemical transport models for this important, nominally low-NO, forested region of Earth. Under polluted conditions, when the concentrations of reactive nitrogen compounds were high (>1 ppb), ISOPOOH concentrations dropped below the instrumental detection limit (<60 ppt). This abrupt shift in isoprene photooxidation, sparked by human activities, speaks to ongoing and possible future changes in the photochemistry active over the Amazon rainforest.
•We assess mechanisms regulating evapotranspiration (E) in Amazonia and cerrado.•Groundwater and deep root uptake can both sustain E during the dry season.•Canopy stomatal conductance regulates E ...even at sites with little water limitation.•Models capturing observed patterns in E may still poorly represent these mechanisms.•Model developments should focus on improved biological controls on E.
Evapotranspiration (E) in the Amazon connects forest function and regional climate via its role in precipitation recycling However, the mechanisms regulating water supply to vegetation and its demand for water remain poorly understood, especially during periods of seasonal water deficits In this study, we address two main questions: First, how do mechanisms of water supply (indicated by rooting depth and groundwater) and vegetation water demand (indicated by stomatal conductance and intrinsic water use efficiency) control evapotranspiration (E) along broad gradients of climate and vegetation from equatorial Amazonia to Cerrado, and second, how do these inferred mechanisms of supply and demand compare to those employed by a suite of ecosystem models? We used a network of eddy covariance towers in Brazil coupled with ancillary measurements to address these questions With respect to the magnitude and seasonality of E, models have much improved in equatorial tropical forests by eliminating most dry season water limitation, diverge in performance in transitional forests where seasonal water deficits are greater, and mostly capture the observed seasonal depressions in E at Cerrado However, many models depended universally on either deep roots or groundwater to mitigate dry season water deficits, the relative importance of which we found does not vary as a simple function of climate or vegetation In addition, canopy stomatal conductance (gs) regulates dry season vegetation demand for water at all except the wettest sites even as the seasonal cycle of E follows that of net radiation In contrast, some models simulated no seasonality in gs, even while matching the observed seasonal cycle of E. We suggest that canopy dynamics mediated by leaf phenology may play a significant role in such seasonality, a process poorly represented in models Model bias in gs and E, in turn, was related to biases arising from the simulated light response (gross primary productivity, GPP) or the intrinsic water use efficiency of photosynthesis (iWUE). We identified deficiencies in models which would not otherwise be apparent based on a simple comparison of simulated and observed rates of E. While some deficiencies can be remedied by parameter tuning, in most models they highlight the need for continued process development of belowground hydrology and in particular, the biological processes of root dynamics and leaf phenology, which via their controls on E, mediate vegetation-climate feedbacks in the tropics.
The occurrence of nonliquid and liquid physical states of submicron atmospheric particulate matter (PM) downwind of an urban region in central Amazonia was investigated. Measurements were conducted ...during two intensive operating periods (IOP1 and IOP2) that took place during the wet and dry seasons of the GoAmazon2014/5 campaign. Air masses representing variable influences of background conditions, urban pollution, and regional- and continental-scale biomass burning passed over the research site. As the air masses varied, particle rebound fraction, an indicator of physical state, was measured in real time at ground level using an impactor apparatus. Micrographs collected by transmission electron microscopy confirmed that liquid particles adhered, while nonliquid particles rebounded. Relative humidity (RH) was scanned to collect rebound curves. When the apparatus RH matched ambient RH, 95 % of the particles adhered as a campaign average. Secondary organic material, produced for the most part by the oxidation of volatile organic compounds emitted from the forest, produces liquid PM over this tropical forest. During periods of anthropogenic influence, by comparison, the rebound fraction dropped to as low as 60 % at 95 % RH. Analyses of the mass spectra of the atmospheric PM by positive-matrix factorization (PMF) and of concentrations of carbon monoxide, total particle number, and oxides of nitrogen were used to identify time periods affected by anthropogenic influences, including both urban pollution and biomass burning. The occurrence of nonliquid PM at high RH correlated with these indicators of anthropogenic influence. A linear model having as output the rebound fraction and as input the PMF factor loadings explained up to 70 % of the variance in the observed rebound fractions. Anthropogenic influences can contribute to the presence of nonliquid PM in the atmospheric particle population through the combined effects of molecular species that increase viscosity when internally mixed with background PM and increased concentrations of nonliquid anthropogenic particles in external mixtures of anthropogenic and biogenic PM.
The Amazon Basin plays key role in atmospheric chemistry, biodiversity and climate change. In this study we applied nanoelectrospray (nanoESI) ultra-high-resolution mass spectrometry (UHRMS) for the ...analysis of the organic fraction of PM2.5 aerosol samples collected during dry and wet seasons at a site in central Amazonia receiving background air masses, biomass burning and urban pollution. Comprehensive mass spectral data evaluation methods (e.g. Kendrick mass defect, Van Krevelen diagrams, carbon oxidation state and aromaticity equivalent) were used to identify compound classes and mass distributions of the detected species. Nitrogen- and/or sulfur-containing organic species contributed up to 60 % of the total identified number of formulae. A large number of molecular formulae in organic aerosol (OA) were attributed to later-generation nitrogen- and sulfur-containing oxidation products, suggesting that OA composition is affected by biomass burning and other, potentially anthropogenic, sources. Isoprene-derived organosulfate (IEPOX-OS) was found to be the most dominant ion in most of the analysed samples and strongly followed the concentration trends of the gas-phase anthropogenic tracers confirming its mixed anthropogenic–biogenic origin. The presence of oxidised aromatic and nitro-aromatic compounds in the samples suggested a strong influence from biomass burning especially during the dry period. Aerosol samples from the dry period and under enhanced biomass burning conditions contained a large number of molecules with high carbon oxidation state and an increased number of aromatic compounds compared to that from the wet period. The results of this work demonstrate that the studied site is influenced not only by biogenic emissions from the forest but also by biomass burning and potentially other anthropogenic emissions from the neighbouring urban environments.
•Turbulent exchange processes in the forest atmosphere interface.•Different turbulence regimes present in the Amazon nocturnal boundary layer.•Coherent structures with different time scales ...associated with turbulent regimes.•Aerodynamic instabilities associated with different turbulent regimes.
The structure of atmospheric turbulence is analyzed based on the existence of three different night-time turbulent regimes observed in the Amazon forest, classified according to Sun's criteria: regime 1: weak turbulence, low wind speed; regime 2: strong turbulence, with high wind speed, and regime 3: intermittent turbulence events. Next, we have investigated some of the main statistical characteristics of turbulent regimes. In situations with strong winds and high values of turbulent kinetic energy (4% of cases) sensible heat fluxes are about 40 times higher than the ones under light winds and low turbulent kinetic energy values (95% of cases). Furthermore, the inflection point height in the wind profile and shear length scale Lh=uh/(du/dz) (where uh is the mean wind velocity at canopy top) increases with the regime 2, with the occurrence of strong mixing in the atmospheric boundary layer. In addition the coherent structure time scale in the regime 2 is greater than regime 1. Regime 3 is essentially nonstationary.
From April 2014 to January 2015, ozone (O3) dynamics were investigated as part of GoAmazon 2014/5 project in the central Amazon rainforest of Brazil. Just above the forest canopy, maximum hourly O3 ...mixing ratios averaged 20 ppbv (parts per billion on a volume basis) during the June–September dry months and 15 ppbv during the wet months. Ozone levels occasionally exceeded 75 ppbv in response to influences from biomass burning and regional air pollution. Individual convective storms transported O3-rich air parcels from the mid-troposphere to the surface and abruptly enhanced the regional atmospheric boundary layer by as much as 25 ppbv. In contrast to the individual storms, days with multiple convective systems produced successive, cumulative ground-level O3 increases. The magnitude of O3 enhancements depended on the vertical distribution of O3 within storm downdrafts and origin of downdrafts in the troposphere. Ozone mixing ratios remained enhanced for > 2 h following the passage of storms, which enhanced chemical processing of rainforest-emitted isoprene and monoterpenes. Reactions of isoprene and monoterpenes with O3 are modeled to generate maximum hydroxyl radical formation rates of 6×106 radicals cm−3s−1. Therefore, one key conclusion of the present study is that downdrafts of convective storms are estimated to transport enough O3 to the surface to initiate a series of reactions that reduce the lifetimes of rainforest-emitted hydrocarbons.
•In the rainforest, convective storms transport ozone-rich air to the surface.•Ozone levels remain enhanced for more than 2 h after the passage of storms.•Enhanced ozone drives oxidation of rainforest-emitted hydrocarbons.
•Turbulence structure in and above the Amazon forest canopy.•Canopy absorbs linear momentum differs greatly between different sites.•Canopy exchanges heat with the air above differ among the ...different wind regimes.•The shear production is at least an order of magnitude greater than the buoyancy above the forest.
Atmospheric turbulence characteristics within and above rain forest canopies are investigated at several sites located in the Amazon region of Brazil. Turbulence data provided by bi- and three-dimensional sonic anemometers, which were deployed at heights ranging from near the forest floor to about 80 m, are analyzed to describe the principal features of atmospheric turbulence, sensible heat flux (H), and components of the turbulent kinetic energy (TKE) budget equation. The analyses focused on weak (WW) and strong (SW) wind conditions to achieve the research objectives of evaluating the turbulence structure above and below the rain forest canopy and estimating the degree of coupling between air layers above the forest and deep in the canopy. Turbulence statistical moments show that atmospheric eddies, generated above the canopy, hardly penetrate the region below 0.5h (h is the canopy height). Forest-atmosphere exchanges of heat differ depending on the observed wind regimes. Sensible heat fluxes decrease with canopy depth for SW conditions and are approximately constant with the height for WW above the canopy. Sensible heat flux profiles reveal a transition layer (around 0.6h) which sometimes exchanges heat with the upper and sometimes with the lower forest canopy, depending on time of day and weather conditions. TKE balance results show that during the daytime period in SW conditions the shear production is at least an order of magnitude greater than the buoyancy above the forest canopy. This turbulence, however, is practically all dissipated in the region above 0.5h. Thus, the air layer from the soil surface to 0.5h is largely decoupled from the upper part of the forest canopy. This feature of having the bottom of the canopy mostly decoupled from the air aloft in the dense and tall rain forest can exert control on the residence times and turbulent transport of plant-emitted gases out of the forest canopy.
PDF
