Displays

The rapid rise in atmospheric CO₂ concentration over the past century is unprecedented. It has unambiguously influenced Earth’s climate system and terrestrial ecosystems. Elevated atmospheric CO₂ concentrations (eCO₂) have induced an increase in biomass and thus, a carbon sink in forests worldwide. It is assumed that eCO₂ stimulates photosynthesis and plant productivity and enhances water-use efficiency – the so-called CO₂-fertilization effect, which may provide an important buffering effect for plants during adverse climate conditions. For these reasons, current global climate simulations consistently predict that tropical forests will continue to sequester more carbon in aboveground biomass, partially compensating human emissions and decelerating climate change by acting as a carbon sink. In contrast to model simulations, several lines of evidence point towards a decreasing carbon sink strength of the Amazon rainforest. Reliable predictions of eCO₂ effects in the Amazon rainforest are hindered by a lack of process-based information gained from ecosystem scale eCO₂ experiments. Here we report on baseline measurements from the Amazon Free Air CO₂ Enrichment (AmazonFACE) experiment and preliminary results from open-top chamber (OTC) experiments with eCO₂. After three months of eCO₂, we find that understory saplings increased carbon assimilation by 17% (under light saturated conditions) and water use efficiency by 39% in the OTC experiment. We present our main hypotheses for the FACE experiment, and discuss our expectations on the potential driving processes for limiting or stimulating the Amazon rainforest carbon sink under eCO₂. We focus on possible effects of eCO₂ on carbon uptake and allocation, nutrient cycling, water-use and plant-herbivore interactions, which need to be implemented in dynamic vegetation models to estimate future changes of the Amazon carbon sink.

How to cite: Rammig, A., Fleischer, K., Garcia, S., Martins, N., Menezes, J., Fuchslueger, L., Schaap, K., Pereira, I., Takeshi, B., Quesada, C., Kruijt, B., Norby, R., Araujo, A., Domingues, T., Grams, T., Hartley, I., De Kauwe, M., Hofhansl, F., and Lapola, D.: AmazonFACE – Assessing the response of Amazon rainforest functioning to elevated atmospheric carbon dioxide concentrations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18290, https://doi.org/10.5194/egusphere-egu2020-18290, 2020.

Amazon is the major tropical land region, with critical processes, such as the carbon cycle, not yet fully understood. Only very few long-term greenhouse gas measurements regionally represented is available in the tropics. The Amazon accounts for 50% of Earth’s tropical rainforests hosting the largest carbon pool in vegetation and soils (~200 PgC). The net carbon exchange between tropical land and the atmosphere is critically important because the stability of carbon in forests and soils can be disrupted in short time-scales. The main processes releasing C to the atmosphere are deforestation, degradation, fires and changes in growing conditions due to increased temperatures and droughts. Such changes may thus cause feedbacks on global climate.

In the last 40 years, Amazon mean temperature increased by 1.1ºC. The length and intensity of the dry season is also increasing, causing a strong stress each year higher to the forest.

We observed a reduction of 17% in precipitation during dry season and the transition dry to wet season during this same period. This reduction in precipitation and the increase in temperature during the dry season exacerbate vegetation water stress, with consequences for carbon balance.

To understand the consequences of human-driven and climate changes on the C budget of Amazonia, we put in place the first program with regional representativeness, from 2010 onwards, aiming to quantify greenhouse gases based on extensive collection of vertical profiles of CO2 and CO. Regular vertical profiles from the ground up to 4.5 km height were performed at four sites along the main air-stream over the Amazon. Along this period from 2010 to 2018, we performed 669 vertical profiles, over four strategic regions that represent fluxes over the entire Amazon region.

The observed variability of carbon fluxes during these 9 years is correlated with climate variability (Temperature, precipitation, GRACE, EVI) and human-driven changes (Biomass Burning). The correlations were performed inside each influenced area for each studied site and show how high temperature and water stress during dry season are affecting the Amazon Carbon Balance. At Southeast of Amazon these extreme conditions are dominating the annual balance. Fire emission is the main source of carbon to the atmosphere, which is not compensate by the C removal from old-growth Amazon forest. The west Amazon almost compensate the east carbon source. During wet/normal years Amazon Carbon Balance is around neutral, but during dry years the uptake capacity is very compromised.

How to cite: Gatti, L. V., Basso, L., Domingues, L., Cassol, H., Marani, L., Miller, J., Gloor, M., Aragao, L., Arai, E., Tejada, G., Anderson, L., Von Randow, C., Peters, W., Ipia Sanchez, A., Correia, C., Crispim, S., and Neves, R.: Amazon Carbon Balance affected by human activities and Climate change, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11182, https://doi.org/10.5194/egusphere-egu2020-11182, 2020.

Tropical forests such as Amazon is repository of ecological services. Understanding how tropical forest responds to the climate helps to improve ecosystem modeling and declining the uncertainty in calculation of carbon balance. Nowadays, the availability of very high resolution satellite imagery such as Sentinel-2 are powerful tools for analyzing the canopy structural and functional shifts over time, especially for tropical forest.

In this study, we examined the effect of the nutrient availability (nitrogen (N) and phosphorus (P)) on canopy and structural properties in tropical forest of French Guiana. In situ observations of canopy structure and functioning (i.e. photosynthesis, leaf N, chlorophyll content) were collected at two experimental sites (Paracou and Nouragues). Three topographical positions in each site were considered (top of the hills, middle and bottom end of the slope) and four plots were manipulated with different level of fertilization (Control, N, P, NP) in September 2016. Statistical analysis were conducted to analyze how the fertilization affect the forest canopy seasonality and if differences between sites and across positions existed. Furthermore, we tested whether Sentinel-2 data could help or not to describe the canopy changes observed in the field. Therefore, all Sentinel-2 images available before the start of the experiment, which date represent the natural situation, and two years after the intensive and repeated fertilization were collected. Greenness, chlorophyll and N, P related indicators were calculated from Sentinel-2 images.

Key words: Sentinel-2, Tropical forest, soil fertilization, topographical position.

How to cite: Maleki, M., Verryckt, L., Barrios, J. M., Peñuelas, J., Janssens, I., and Balzarolo, M.: Analysis of canopy structural and functional properties of tropical forests in a fertilisation experiment by Sentinel-2 images, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17538, https://doi.org/10.5194/egusphere-egu2020-17538, 2020.

Wetland emissions are considered the main natural global Methane (CH₄) source, but it is budget remains highly uncertain. Tropical regions like the Amazon, host some of the largest wetlands/seasonally flooded areas on the globe. However, tropical regions are still poorly observed with large-scale integrating observations. Here we present the first atmospheric sampling of the lower troposphere over the Amazon using regular vertical profile greenhouse gas and carbon monoxide (CO) observations at four sites. Since 2010 we collected bimonthly CH₄, to provide solid seasonal and annual CH₄ budgets with large spatial resolution. Vertical profiles are sampled using light aircraft, high-precision greenhouse gas and CO analysis of flask air, fortnightly between 2010 to 2018. The results show a regional variation in CH₄ emissions. There are comparably high emissions from the northeast part of the Amazon exhibiting strong variability, with particularly high CH₄ fluxes in the beginning of the wet season (January to March). A second period of high emissions occurs during the dry season. The cause of the high emissions is unclear. In the other three sites located further downwind along the main air-stream are observed lower emissions, that represents approximately 25-30% of what is observed in the northeast region and with a clear annual seasonality. In addition, these data show an interannual variability in emissions magnitude, so we discuss how these data can be correlate to climate variables (like temperature and precipitation) and with human-driven changes (like biomass burning) that could be influencing this variability. Over the full period the Amazon (total area of around 7.2 million km²) was a source of CH₄, of approximately 46 ± 6 Tg/year, which represent 8% of the global CH₄ flux to the atmosphere. Using a CO/CH₄ emission ratio calculated in this study we find a biomass burning contribution varying between 10 and 23% of the total flux at each site.

Acknowledgment: FAPESP (2019/23654-2, 2018/14006-4, 2016/02018-2, 2008/58120-3, 2011/51841-0), NASA, ERC (GEOCARBON, Horizon 2020/ASICA), NERC (NE/F005806/1), CNPq (480713/2013-8).

How to cite: Basso, L., Gatti, L., Marani, L., Cassol, H., Tejada, G., Domingues, L., Correia, C., Crispim, S., Neves, R., Ipia, A., Arai, E., Aragão, L., Miller, J., and Gloor, M.: Amazon CH4 budget and its controls based on atmospheric data from vertical profiles measurements, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-558, https://doi.org/10.5194/egusphere-egu2020-558, 2020.

Amazon rainforests and soils contain large amounts of carbon, which is under pressure from ongoing climate and land use change in the Amazon basin. It is estimated that methane (CH₄), an important greenhouse gas, is largely released from the flooded wetlands of the Amazon, but the trends and balances of CH₄ in the Amazon rainforest are not yet well understood. In addition, the change in atmospheric CH₄ concentration is strongly associated with a change in carbon monoxide (CO) concentration, often caused by the human-induced combustion of biomass that usually peaks during dry season. Understanding the long-term fluctuations in the fluxes of greenhouse gases in the Amazon rainforest is essential for improving our understanding of the carbon balance of the Amazon rainforest.

Since March 2012, we have continuously measured atmospheric CO₂/CH₄/CO concentrations at five levels (79, 53, 38, 24, and 4 m a.g.l.) using two wavelength-scanned cavity ring-down spectroscopy analyzers (G1301 and G1302, Picarro Inc., USA), which are automatically calibrated on site every day. In addition, we measured the CO₂ flux by the eddy covariance method at the same tower. We estimated the CO₂/CH₄/CO fluxes by combining the vertical profile of the CO₂/CH₄/CO concentrations with the flux gradient method. Our results generally show no major difference in CO₂ flux between the wet and dry seasons except for year 2017, when an elevated CO₂ uptake was documented during the dry season despite the lowest precipitation between 2014 and 2018. The CH₄ flux showed the largest CH₄ emission during the dry season in year 2016. Further results will be analyzed and discussed in the presentation.

How to cite: Komiya, S., Lavric, J., Walter, D., Botia, S., Araujo, A., Sá, M., Sörgel, M., Wolff, S., Asperen, H., Kondo, F., and Trumbore, S.: Temporal variations of CH4/CO2/CO fluxes in the central Amazon rainforest, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16019, https://doi.org/10.5194/egusphere-egu2020-16019, 2020.

Atmospheric CO₂ concentrations have had a significant increase in recent years reaching levels never seen before. In the Amazon region, the main CO₂ emissions come from land use and cover change (LUCC), especially for the deforestation of natural forests. It is very important to understand the impacts of climate change and deforestation on the Amazon forests to understand their role in the current carbon balance at different scales. The lower-troposphere greenhouse gas (GHG) monitoring program “CARBAM project”, has been collecting bimonthly GHGs vertical profiles in four sites of the Amazon since 2010, filling a very important gap in regional GHGs measurements. Here we compare different LUCC datasets for the Amazon region to see if there is a relation between annual LUCC and bimonthly CO₂ aircraft measurements in the Amazon. We compared the annual (2010-2018) LUCC area from IBGE, PRODES and mapbiomas pan-amazon datasets for each mean influence area of the CARBAM sites and relate this LUCC areas with the annual CO₂ fluxes. We found differences in the classification methods of the LUCC data, showing differences in the total deforested area. The LUCC data have different tendencies in each CARBAM influence area having more deforestation in the east side of the Amazon CARBAM sites. There is no clear trend between LUCC and carbon fluxes in the last 8 years. Inter-annual CO₂ fluxes variability could be related with the several droughts that influence the photosynthesis/respiration. Here we highlight the scale issues regarding LUCC datasets, atmospheric CO₂ measurements and CO₂ modeling to better understand the current Amazon carbon balance.  

Acknowledgment: FAPESP (2018/18493-7; 2018/14006-4; 2016/2016/02018-2), NASA, ERC (GEOCARBON, Horizon 2020/ASICA), NERC (NE/F005806/1), CNPq (480713/2013-8).

How to cite: Tejada, G., Gatti, L., Basso, L., Marani, L., Cassol, H., Arai, E., Aragão, L., Crispim, S., Neves, R., Domingues, L., Correia, C., Ipia, A., Gloor, M., Miller, J., and von Randow, C.: Is it feasible to relate CO2 atmospheric measurements with land use and cover change data? -A primary assessment of land use and cover change datasets in the Amazon, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-561, https://doi.org/10.5194/egusphere-egu2020-561, 2020.

 Abstract: It is challenged to get an accurate estimate of surface energy budget for the investigation of land atmosphere and global ecosystems. In this study, we established a novel tool based the maximum entropy production (MEP) method for the simulation of global energy flux as well as evapotranspiration (ET) processes. This tool (named as RMEP) was built in R for its great convenient for open-source and the feature of easy-use. As only three variables (net radiation, surface temperature, and specific humidity) are need for MEP model, it shows great advantages in simulation for both global or site scales. Firstly, we compare the performances of RMEP in two flux sites, BR-Sa1and BR-Sa3 of Amazon basin, with the simulation of heat fluxes. Although the substantial bias of G flux exist, both the latent and sense heat flux show high R² in hourly temporal scale. Then, the RMEP was test in large scale by employing the global scale dataset. Since the Global Land Data Assimilation System (GLDAS) product integrates satellite data and ground-based observations at global scale, the variables of radiation, surface temperature, as well as specific humidity of GLDAS were used as inputs for RMEP and the outputs of RMEP were validated with the variables of fluxes and evapotranspiration in GLDAS. The MEP model shows a high performances in simulating surface energy budget in global scale and Amazon basin area of 3-hourly temporal scale. The performances of MEP model using GLDAS data are superior to that of EC data, with higher R², lower RMSE and higher, positive NSE. In addition, the MEP accurately estimated ET over regional or global scale. Especially for Amazon area, MEP simulated results of heat fluxes and ET are used in comparisons at their original (3-hourly and daily) and aggregated monthly temporal scales. Generally, the original 3-hourly simulations had a higher accuracy and smaller bias than daily simulations, take the aggregated monthly ET for example, the monthly 3-hourly ET (R²=0.91, NSE=0.85) outperformed than that of daily scale (R²=0.29, NSE=-0.98). Results indicated the excellent performances of the MEP model in estimating ET with 3-hourly temporal scale in Amazon area. In summary, the RMEP shows great performances in both site and global scale. It also can deal with the input file with both site measured table and global netcdf types. The resulted figures, global ET values (in netcdf file), source code, and R package can be shared by the request to the first author.

Appendix. List of figures and tables.

Table 1. Information for two flux sites

Figure 1. 

How to cite: Yang, Y., Sun, H., and Wang, J.: An R tool for Capturing Dynamics of Actual Evapotranspiration with MEP model and its application in Amazon, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1034, https://doi.org/10.5194/egusphere-egu2020-1034, 2020.

Isoprene regulates large-scale biogeochemical cycles by influencing atmospheric chemical and physical processes, and its dominant sources to the global atmosphere are the tropical forests. Although global and regional model estimates of isoprene emission have been optimized in the last decades, modeled emissions from tropical vegetation still carry high uncertainty due to a poor understanding of the biological and environmental controls on emissions. It is already known that isoprene emission quantities may vary significantly with plant traits, such as leaf phenology, and with the environment; however, current models still lack of good representation for tropical plant species due to the very few observations available. In order to create a predictive framework for the isoprene emission capacity of tropical forests, it is necessary an improved mechanistic understanding on how the magnitude of emissions varies with plant traits and the environment in such ecosystems. In this light, we aimed to quantify the isoprene emission capacity of different tree species across leaf ages, and combine these leaf measurements with long-term canopy measurements of isoprene and its biological and environmental drivers; then, use these results to better parameterize isoprene emissions estimated by MEGAN. We measured at the Amazon Tall Tower Observatory (ATTO) site, central Amazonia: (1) isoprene emission capacity at different leaf ages of 21 trees species; (2) isoprene canopy mixing ratios during six campaigns from 2013 to 2015; (3) isoprene tower flux during the dry season of 2015 (El-Niño year); (3) environmental factors – air temperature and photosynthetic active radiation (PAR) - from 2013 to 2018; and (4) biological factors – leaf demography and phenology (tower based measurements) from 2013 to 2018. We then parameterized the leaf age algorithm of MEGAN with the measurements of isoprene emission capacity at different leaf ages and the tower-based measurements of leaf demography and phenology. Modeling estimates were later compared with measurements (canopy level) and five years of satellite-derived isoprene emission (OMI) from the ATTO domain (2013-2017). Leaf level of isoprene emission capacity showed lower values for old leaves (> 6 months) and young leaves (< 2 months), compared to mature leaves (2-6 months); and our model results suggested that this affects seasonal ecosystem isoprene emission capacity, since the demography of the different leaf age classes varied a long of the year. We will present more results on how changes in leaf demography and phenology and in temperature and PAR affect seasonal ecosystem isoprene emission, and how modeling can be improved with the optimization of the leaf age algorithm. In addition, we will present a comparison of ecosystem isoprene emission of normal years (2013, 2014, 2017 years) and anomalous years (2015 - El-Niño; and 2016 - post El-Niño), and discuss how a strong El-Niño year can influence plant functional strategies that can be carried over to the consecutive year and potentially affect isoprene emission.

How to cite: Gomes-Alves, E., Taylor, T., Assis, P., Martins, G., Souza, R., Duvoisin-Junior, S., Guenther, A., Gu, D., Yáñez-Serrano, A. M., Kesselmeier, J., Tsokankunku, A., Sörgel, M., Nelson, B., Pinho, D., Lopes, A., Gonçalves, N., Stavrakou, T., Bauwens, M., Manzi, A., and Trumbore, S.: Isoprene emission in central Amazonia - from measurements to model estimates, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1618, https://doi.org/10.5194/egusphere-egu2020-1618, 2020.

Sesquiterpenes (C₁₅H₂₄) are highly reactive biogenic volatile organic compounds playing an important role in atmospheric chemistry. Once emitted from the Earth’s surface, primarily by vegetation, they are rapidly oxidized to semivolatile oxygenated organic species that can lead to secondary organic aerosols (SOA) that influence climate. In the pristine Amazon rainforest environment oxidation of sesquiterpenes is initiated by OH and ozone.

We measured sesquiterpenes in March 2018 (wet season) and November 2018 (dry season) from central Amazonia, at the remote field site ATTO (Amazonian Tall Tower Observatory), Brazil. Samples were collected on adsorbent filled tubes equipped with ozone scrubbers at different heights above the forest canopy ; every three hours for two weeks at 80m and 150m (wet season) and every hour for three days at 80m, 150m and 320m (dry season). Samples were then analysed in the laboratory with a TD-GC-TOF-MS (Thermodesorption-Gas Chromatographer-Time Of Flight-Mass Spectrometer, Markes International). Simultaneous measurements of ozone and meteorological parameters were made at the nearby INSTANT tower. Identification of the chromatographic peaks was achieved by injection of standard molecules and by matching literature mass spectra. Quantification of the chemical compounds was achieved by injection of a standard mixture containing terpenes.The most abundant sesquiterpene measured at ATTO is (-)-α-copaene. Its diel profile varies with photosynthetically active radiation (PAR) and temperature, suggesting the canopy to be the main emission source. Interestingly, other identified sesquiterpenes show a consistent mirrored cycle, with their concentration being higher by night than by day. These varied mostly with RH suggesting the soil to be the main source of the emissions. Air samples taken at the ground are qualitatively and quantitatively different to those collected at different altitudes from the tower. Sesquiterpenes show a common maximum at sunrise (5 :00-7 :00 local time, UTC-4h) coincident with a strong decrease in ozone concentration (>50% decrease on average during the dry season). The strongest effect is registered during the dry season, when sesquiterpenes and ozone concentrations are highest and ozone loss is largest. The atmospheric impact of the measured sesquiterpenes will be discussed including ozone reactivity contributions and OH generation.

How to cite: Zannoni, N., Wolff, S., Tsokankunku, A., Soergel, M., Sa, M., Araujo, A., and Williams, J.: Atmospheric impact of sesquiterpenes in the Amazon rainforest, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9967, https://doi.org/10.5194/egusphere-egu2020-9967, 2020.

The Amazon Rainforest is one of the most important pristine ecosystems for atmospheric chemistry and biodiversity. This region allows the study of organic aerosol particles as well as their nucleation into clouds. However, the rainforest is subject to constant change due to human influences. Thus, it is essential to acquire climate data of trace gases and aerosols over the next decades for a better understanding of the atmospheric oxidant cycle. Therefore, the research site Amazon Tall Tower Observatory (ATTO) was established in the central Amazon Basin to perform long-term measurements under almost natural conditions.

Biogenic emissions of volatile organic compounds (VOCs) mainly consist of isoprene and terpenes. They are responsible for the production of a large fraction of atmospheric particulate matter. Isoprene represents the largest source of non-methane VOCs in the atmosphere and is primarily emitted from vegetation. Its global emissions were estimated in the magnitude of about 500 ‒ 600 Tg per year. Originally, the isoprene photooxidation was not expected to contribute to the secondary organic aerosol (SOA) budget, due to the high volatility of resulting oxidation products. However, several studies have proven evidence for the importance of isoprene SOA formation. Based on the two double bonds, isoprene is highly reactive towards atmospheric oxidants like OH and NO radicals. The subsequent reactive uptake on acidic particles is strongly dependent on the NO concentration. Therefore, anthropogenic sources have a substantial impact on the isoprene photooxidation.

The chemical composition of atmospheric aerosols in the rainforest highly depends on the current season, since the Amazon basin exhibits huge variations of gaseous and particulate matter with clean air conditions during the wet season and polluted conditions during the dry season, due to biomass burning events. For a comprehensive statement, it is necessary to perform field measurements under both conditions to study the isoprene and terpene SOA contribution. For that reason, filter samples were collected at ATTO at different heights to analyze the aerosol composition emitted both from local and regional sources.

High-resolution mass spectrometry combined with data mining techniques will help to link characteristic SOA compounds to certain climate conditions in order to get insights into the Amazon aerosol life cycle.

How to cite: Leppla, D., Kremper, L., Zannoni, N., Praß, M., Ditas, F., Holanda, B., Pöhlker, C., Williams, J., Sá, M., Wolff, S., Solci, M. C., and Hoffmann, T.: Chemical characterization of submicrometer organic aerosol particles from the Amazon rainforest with high-resolution mass spectrometry, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8977, https://doi.org/10.5194/egusphere-egu2020-8977, 2020.

Being the largest mineral dust source, Africa contributes over half of the global mineral dust emission. The trans-Atlantic transport of the large amount of mineral dust is shown to enter the Amazon basin frequently, not only perturbing the near pristine condition in the Amazon during the wet season, but also fertilizing the Amazon rainforest due to dust deposition and associated nutrients input. In this study, we use a global chemical transport model (GEOS-Chem) to simulate the emission, the long-range trans-Atlantic transport, and the deposition flux of African mineral dust to the Amazon basin during the period of 2013-2017, with observational constraints from AERONET data, MODIS data, as well as the observation from the Amazon Tall Tower Observatory (ATTO). With optimized size distribution of African dust, we improve the simulation of dust over both source (north Africa) and remote region (Amazon basin). The trans-Atlantic transport of African dust reaching the Amazon Basin generally occurs in winter and spring (Northern Hemisphere) associated with the northeasterly trade wind advection. In winter, the transport of dust layer occurs below 2 km height while in other seasons it occurs between 1 Km and 3 Km. With average annual emission of 0.78 (±0.14) Pg a^-1, African dust entering the amazon basin could reach 3.93 (± 0.76) ug m^-3 at ATTO, account for 19% (± 2.5%) of total particle concentrations. However, the contribution could be up to 91% during strong dust events. Assuming mass fraction of 4.4% and 0.082% of iron and phosphorus in the mineral dust, we estimate an annual mass flux of 35.3 (± 4.49) mg m^-2 a^-1 and 0.66 (± 0.084) mg m^-2 a^-1 of iron and phosphorus deposit in the Amazon rainforest, respectively.

How to cite: Wang, X., Ma, N., Prass, M., Pöhlker, C., and Wang, Q.: The long-range transport of African mineral dust to the Amazon basin, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12009, https://doi.org/10.5194/egusphere-egu2020-12009, 2020.

Scaling from individuals or species to ecosystems is a fundamental challenge of modern ecology and understanding tropical forest response to drought is a key challenge of predicting responses to global climate change.  We here synthesize our developing understanding of these twin challenges by examining individual and ecosystem responses to the 2015 El Niño drought at two sites in the central Amazon of Brazil, near Manaus and Santarem, which span a precipitation gradient from moderate (Manaus) to long (Santarem) dry seasons.  We will focus on how ecosystem water and carbon cycling, measured by eddy flux towers, emerges from individual trait-based responses, including photosynthetic responses of individual leaves, and water cycle responses in terms of stomatal conductance and hydraulic xylem embolism resistance.  We found the Santarem forest (with long dry seasons) responded strongly to drought: sensible heat values significantly increased and evapotranspiration decreased.  Consistent with this, we also observed reductions in photosynthetic activity and ecosystem respiration, showing levels of stress not seen in the nearly two decades since measurements started at this site.  Forests at the Manaus site showed significant, however, less consistent reductions in water and carbon exchange and a more pronounced water deficit.  We report an apparent community level forest composition selecting for assemblies of traits and taxa manifest of higher drought tolerance at Santarem, compared to the Manaus forest (short dry seasons) and other forest sites across Amazonia.  These results suggest that we may be able to use community trait compositions (as selected by past climate conditions) and environmental threshold values (e.g. cumulative rainfall, atmospheric moisture and radiation) as to help forecast ecosystem responses to future climate change.

How to cite: Saleska, S. R., Restrepo-Coupe, N., Barros, F. V., Bittencourt, P. R. L., Prohaska, N., Penha, D. V., Albert, L. P., Brum, M., Pereira, L., Leal, L. S. M., Araujo, A. C., Stark, S. C., Alves, L., Tribuzy, E., Camargo, P. B., Cosme de Oliveira, R., Ivanov, V., Mauro, J., Aragao, L., and Oliveira, R. S.: Amazon forest responses to drought: scaling from individuals to ecosystems., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12746, https://doi.org/10.5194/egusphere-egu2020-12746, 2020.

The Amazon forests are one of the largest ecosystem carbon pools on Earth. While more frequent and prolonged droughts have been predicted under future climate change there, the vulnerability of Amazon forests to drought has yet remained largely uncertain, as previous studies have shown that few land surface models succeeded in capturing the vegetation responses to drought. In this study, we present an improved version of the land surface model JSBACH, which incorporates new formulations of leaf phenology and litter production based on intensive field measurement from the artificial drought experiments in the Amazon. Coupling the new JSBACH with the atmospheric model ECHAM, we investigate the drought responses of the Amazon forests and the resulting feedbacks under RCP8.5 scenario. The climatic effects resulted from (1) direct effects including declining soil moisture and stomatal responses, and (2) soil moisture-induced canopy responses are separated to give more insights, as the latter was poorly simulated. Preliminary results show that for net primary production and soil respiration, the direct effects and canopy responses have similar spatial patterns with the magnitude of the latter being 1/5 to 1/3 of the former. In addition, declining soil moisture enhances rainfall in Northern Amazon and suppresses rainfall in the south, while canopy responses have negligible effects on rainfall. Based on our findings, we suggest cautious interpretation of results from previous studies. To address this uncertainty, better strategy in modeling leaf phenology such as implemented in this study should be adopted.

How to cite: Wey, H., Naudts, K., Pongratz, J., Nabel, J., and Boysen, L.: Drought responses of Amazon forests under climate change: Separating the roles of soil moisture and canopy responses, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12511, https://doi.org/10.5194/egusphere-egu2020-12511, 2020.

Direct eddy covariance flux measurements of O₃ in tropical forests are sparse and deposition velocities of O₃ for tropical forest have large uncertainties in models. Therefore, we measured O₃ fluxes at different heights ( 4 m, 12 m, 46 m and 81 m), which is 2 levels within canopy (below crown layer) and two levels above. At the same levels heat and CO₂ fluxes were measured by eddy covariance to differentiate upper canopy fluxes from understory and soil fluxes and to infer stomatal conductance based on the inverted Penman-Monteith equation. Further measurements include the profiles of O₃, NO_x, CO₂ and H₂O which are used to calculate storage fluxes and reactions of O₃ with NO_x within the air volume. Additionally, leaf surface temperature and leaf wetness were measured in the upper canopy (26 m) to infer their influence on the non-stomatal deposition. The measurements took place at the ATTO (Amazon Tall Tower Observatory) site that is located about 150 km northeast of the city of Manaus in the Amazon rainforest. (02°08’38.8’’S, 58°59’59.5’’W). The climate in this region is characterized by a rainy (350 mm around March) and a dry season (ca. 80 mm in September). During the wet months, the air quality is close to pristine, while strong pollution from biomass burning is evident in the dry season. Therefore, we will present results from two intensive campaigns (3- 4 flux levels) for the rainy season (March to May) and the dry season (September to December) 2018.

The focus of the analysis is the partitioning between a) the crown layer and understory and b) stomatal and non-stomatal deposition with a further analysis of the non-stomatal pathways. Non-stomatal deposition is analyzed by quantifying gas-phase reactions of O₃ with NO_x and an estimate of O₃ reactivity by VOCs. Furthermore, the remaining (surface) deposition is analyzed according to its relations with leaf surface temperature and leaf wetness.

How to cite: Sörgel, M., Tsokankunku, A., Wolff, S., Araùjo, A., Assis, P., Harder, H., Martins, G., Sá, M., Souza, R., Williams, J., and Zannoni, N.: Quantifying deposition pathways of Ozone at a rainforest site (ATTO) in the central Amazon basin, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19455, https://doi.org/10.5194/egusphere-egu2020-19455, 2020.

The Wavelet and the Multiresolution analysis are applied to ten nocturnal hours of observations of 3-D wind velocity taken within and above a forest canopy in Central Amazonia. Data from the ATTO Project, consisting in 7 levels of turbulence observations along both 81 and 325-meter towers, are used. The presented night is dynamically rich presenting three distinct periods. In the first one the boundary layer is characterized by canopy waves and coherent structures generated at the canopy top. In the second period an intense orographic gravity wave generated at around 150 m strongly influences the boundary layer structure, both above and below the canopy. In the third period, a very stable stratification at the canopy top enables the development of a low-level jet that interferes and disrupts the vertical orographic wave. During the night the wavelet cospectra identified turbulent and non-turbulent structures with different length and time-scales that are generated at different levels above the canopy and propagated inside it. The contributions of the different temporal scales of the flow above and within the canopy were identified using Wavelet and Multiresolution two-point cospectra. The analysis showed how turbulent and wave-like structures propagates in different ways and, further, the ability of low-frequency processes to penetrate within the canopy and to influence the transport of energy and scalar in the roughness sublayer and within canopy.

Keywords: Coherent structures, Canopy Waves, Gravity Waves, Stable Boundary Layer, Low-Level Jet, wave-turbulence interaction.

How to cite: Mortarini, L., Corrêa, P. B., Cava, D., Dias-Júnior, C. Q., Manzi, A. O. M., Acevedo, O., Araújo, A., Sörgel, M., and Machado, L. A. T.: Orographic gravity wave and low-level jet interaction above a tall and dense Amazonian forest, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7341, https://doi.org/10.5194/egusphere-egu2020-7341, 2020.