Characterization of the radiative impact of aerosols on CO₂ and energy fluxes in the Amazon deforestation arch using artificial neural networks

In vegetation canopies with complex architectures, diffuse solar radiation can enhance carbon assimilation through photosynthesis because isotropic light is able to reach deeper layers of the canopy. Although this effect has been studied in the past decade, the mechanisms and impacts of this enhancement over South America remain poorly understood. Over the Amazon deforestation arch large amounts of aerosols are released into the atmosphere due to biomass burning, which provides an ideal scenario for further investigation of this phenomenon in the presence of canopies with complex architecture. In this paper, the relation of aerosol optical depth and surface fluxes of mass and energy are evaluated over three study sites with artificial neural networks and radiative transfer modeling. Results indicate a significant effect of the aerosol on the flux of carbon dioxide between the vegetation and the atmosphere, as well as on energy exchange, including that surface fluxes are sensitive to second-order radiative impacts of aerosols on temperature, humidity, and friction velocity. CO₂ exchanges increased in the presence of aerosol in up to 55 % in sites with complex canopy architecture. A decrease of approximately 12 % was observed for a site with shorter vegetation. Energy fluxes were negatively impacted by aerosols over all study sites

DINÂMICA DE SERAPILHEIRA EM UMA ÁREA DE FLORESTA DE TERRA FIRME, AMAZÔNIA OCIDENTAL

O objetivo deste estudo foi avaliar a produção e decomposição de serapilheira em uma área de floresta primária de terra firme na Reserva Biológica do Jaru. Para tanto, foi implantada uma parcela permanente de 1 hectare, onde foram demarcadas 25 subparcelas com 20 x 20 m cada. Para a coleta de serapilheira, instalou-se 25 coletores de PVC (1 em cada centro da subparcela), medindo 0,25 m², a 1 metro do solo, com malha de nylon de 1 mm. Para estimar o estoque de serapilheira, utilizou-se 25 coletores de madeira, medindo 0,25 m², com malha de nylon de 1 mm, dispostos no solo de cada subparcela. As coletas da pesquisa foram realizadas quinzenalmente, entre os meses de outubro de 2016 a setembro de 2017, e a serapilheira triada nas frações: folha, galho, material reprodutivo e miscelânea. No laboratório, os materiais amostrados foram secos em estufa à 80 ºC e pesados em balança de precisão centesimal, sendo que a decomposição de serapilheira foi estimada através da relação entre produção e estoque. De acordo com os resultados obtidos, a produção de serapilheira total foi de 14,13 Mg ha-1 e as frações seguiram o padrão: folha>miscelânea>galho>material reprodutivo. As maiores produções aconteceram na estação seca e a taxa de decomposição foi 1,37, indicando que a atividade microbiana na área de estudo é acelerada.Palavras-chave: dinâmica sazonal; nutrição de plantas; ecologia florestal; decomposição. LITTER DYNAMICS IN A FOREST AREA OF GROUND FIRM, WESTERN AMAZON ABSTRACT:The objective of this study was to evaluate the litter production and decomposition in an area of primary upland forest in the Jaru Biological Reserve. For that, a permanent plot of 1 hectare was implanted, where 25 subplots with 20 x 20 m each were demarcated. For the collection of litter, 25 PVC collectors were installed (1 in each center of the subplot), measuring 0.25 m², 1 meter from the ground, with 1 mm nylon mesh. To estimate the litter stock, 25 wood collectors, measuring 0.25 m², with 1 mm nylon mesh, were used, arranged in the soil of each subplot. The collections of the research were carried out fortnightly, between the months of October 2016 and September 2017, and the litter is sorted in the fractions: leaf, branch, reproductive material and miscellaneous. In the laboratory, the sampled materials were dried in an oven at 80 ºC and weighed on a centesimal precision scale, and the litter decomposition was estimated through the relationship between production and stock. According to the results obtained, the total litter production was 14.13 Mg ha-1 and the fractions followed the pattern: leaf>miscellaneous>branch>reproductive material. The highest yields occurred in the dry season and the decomposition rate was 1.37, indicating that the microbial activity in the study area is accelerated.Keyword: seasonal dynamics; plant nutrition; forest ecology; decomposition

A comparison of the spatial heterogeneities of surface fluxes simulated by INLAND model with observations at a valley and a nearby plateau stations in Central Amazon Forest

An improved version of the Integrated Land Surface Model (INLAND), incorporating the physical, ecological and hydrological parameters and processes pertaining to two subclasses of tropical forest in the central Amazon basin, a poorly drained flat plateau and a well-drained adjacent broad valley, is used to simulate the hydrological, energy and CO2 fluxes. The model is forced with observed meteorological data. The experimental output data from the model runs are compared with observational data at the two locations. The seasonal variabilities of water table depth at the valley site and the soil moisture at the plateau site are satisfactorily simulated. The two locations exhibit large differences in energy, carbon and water fluxes, both in the simulations and in the observations. Results validate the INLAND model and indicate the need for incorporating sub-grid scale variability in the relief, soil type and vegetation type attributes to improve the representation of the Amazonian ecosystems in land-surface models.This work was supported by the São Paulo Research Foundation (FAPESP) Grant Number 2017/22269-2. The first author was funded by The National Council of Scientific and Technological Development (CNPq) and National Coordination for High Level Education and Training (CAPES). The second author was supported by CNPq Grant Number 314780/2020-3. The fourth author was supported by Grant Number 2308.019802/2018-7, PVNS (National Senior Visiting Professor) program by CAPES in Brazil and CNPq in Brazil for research Grant number PQ 306595/2013-3.Peer ReviewedPostprint (published version

The CO2 record at the Amazon Tall Tower Observatory : A new opportunity to study processes on seasonal and inter-annual scales

High-quality atmospheric CO2 measurements are sparse in Amazonia, but can provide critical insights into the spatial and temporal variability of sources and sinks of CO2. In this study, we present the first 6 years (2014-2019) of continuous, high-precision measurements of atmospheric CO2 at the Amazon Tall Tower Observatory (ATTO, 2.1 degrees S, 58.9 degrees W). After subtracting the simulated background concentrations from our observational record, we define a CO2 regional signal (Delta CO2obs) that has a marked seasonal cycle with an amplitude of about 4 ppm. At both seasonal and inter-annual scales, we find differences in phase between Delta CO2obs and the local eddy covariance net ecosystem exchange (EC-NEE), which is interpreted as an indicator of a decoupling between local and non-local drivers of Delta CO2obs. In addition, we present how the 2015-2016 El Nino-induced drought was captured by our atmospheric record as a positive 2 sigma anomaly in both the wet and dry season of 2016. Furthermore, we analyzed the observed seasonal cycle and inter-annual variability of Delta CO2obs together with net ecosystem exchange (NEE) using a suite of modeled flux products representing biospheric and aquatic CO2 exchange. We use both non-optimized and optimized (i.e., resulting from atmospheric inverse modeling) NEE fluxes as input in an atmospheric transport model (STILT). The observed shape and amplitude of the seasonal cycle was captured neither by the simulations using the optimized fluxes nor by those using the diagnostic Vegetation and Photosynthesis Respiration Model (VPRM). We show that including the contribution of CO2 from river evasion improves the simulated shape (not the magnitude) of the seasonal cycle when using a data-driven non-optimized NEE product (FLUXCOM). The simulated contribution from river evasion was found to be 25% of the seasonal cycle amplitude. Our study demonstrates the importance of the ATTO record to better understand the Amazon carbon cycle at various spatial and temporal scales.Peer reviewe

The CO2 record at the Amazon Tall Tower Observatory: A new opportunity to study processes on seasonal and inter-annual scales

Abstract High-quality atmospheric CO2 measurements are sparse in Amazonia, but can provide critical insights into the spatial and temporal variability of sources and sinks of CO2. In this study, we present the first 6 years (2014?2019) of continuous, high-precision measurements of atmospheric CO2 at the Amazon Tall Tower Observatory (ATTO, 2.1°S, 58.9°W). After subtracting the simulated background concentrations from our observational record, we define a CO2 regional signal () that has a marked seasonal cycle with an amplitude of about 4 ppm. At both seasonal and inter-annual scales, we find differences in phase between and the local eddy covariance net ecosystem exchange (EC-NEE), which is interpreted as an indicator of a decoupling between local and non-local drivers of . In addition, we present how the 2015?2016 El Niño-induced drought was captured by our atmospheric record as a positive 2σ anomaly in both the wet and dry season of 2016. Furthermore, we analyzed the observed seasonal cycle and inter-annual variability of together with net ecosystem exchange (NEE) using a suite of modeled flux products representing biospheric and aquatic CO2 exchange. We use both non-optimized and optimized (i.e., resulting from atmospheric inverse modeling) NEE fluxes as input in an atmospheric transport model (STILT). The observed shape and amplitude of the seasonal cycle was captured neither by the simulations using the optimized fluxes nor by those using the diagnostic Vegetation and Photosynthesis Respiration Model (VPRM). We show that including the contribution of CO2 from river evasion improves the simulated shape (not the magnitude) of the seasonal cycle when using a data-driven non-optimized NEE product (FLUXCOM). The simulated contribution from river evasion was found to be 25% of the seasonal cycle amplitude. Our study demonstrates the importance of the ATTO record to better understand the Amazon carbon cycle at various spatial and temporal scales

Evapotranspiration and gross primary productivity of secondary vegetation in Amazonia inferred by eddy covariance

The conversion of primary forest (PF) to other types of land cover, such as pasture and agriculture, in Amazonia, affects regional carbon and water balances, significantly contributing to increased carbon emissions and reduced evapotranspiration. However, secondary forest (SF) growth, resulting from the abandonment of low-productivity pasture areas, offers a potential alternative to counterbalance the effects of deforestation on carbon release to the atmosphere and evapotranspiration reduction. In this work, we present four years of eddy flux measurements of a SF that is approximately 20 years old, located in Central Amazonia, and we compare these measurements with those of a PF in the same region, analyzing daily and seasonal variations in evapotranspiration, gross primary productivity of carbon and water use efficiency. On average, evapotranspiration is 20% higher in the SF (3.6 mm day−1) than in the PF (3.1 mm day−1), while gross primary productivity is only 5% higher in the SF (8.1 gC m−2 day−1) than in the PF (7.8 gC m−2 day−1). Despite robust evidence of higher evapotranspiration and gross primary productivity in SF, the estimated uncertainty range of WUE is large to reach definite conclusions about the differences on carbon gain per water loss between the sites. Nonetheless, the significantly higher evapotranspiration and gross primary productivity of SF may counterbalance both water and C losses from deforestation and has important implications for regional budgets.</p

Fluxos de CO2 em Plantio de Palma de Óleo no Leste da Amazônia

Resumo Os ecossistemas terrestres são importantes para compreender as trocas de CO2 entre superfície e atmosfera. Este trabalho apresenta as condições atmosféricas e medidas de CO2 em palma de óleo com híbrido interespecífico no leste da Amazônia, durante ano de El niño. O experimento foi realizado em Moju - Pará, onde foi instalada uma torre micrometeorológica para obtenção de dados meteorológicos e de CO2 durante o período de janeiro-dezembro de 2015. Os valores médios diurnos de absorção de CO2 atingiram o máximo por volta do meio dia, com 22,3 (± 0,98) μmol m-2 s-1 no período chuvoso e 21,0 (± 0,47) μmol m-2 s-1 no período menos chuvoso. Houve pouca variação noturna nos valores médios de emissão de CO2, 5 (± 0,20) μmol m-2 s-1, em ambos os períodos. Os valores médios diurnos da concentração de CO2 foram menores e os valores médios noturnos foram maiores. Em geral, o ciclo diário de troca de CO2 apresentou diferença entre o período chuvoso e menos chuvoso. Esses resultados contribuem para melhor compreensão da tendência temporal dos fluxos de CO2 em cultivo agrícola em ano de seca no leste da Amazônia, gerando informações novas sobre a interação entre palma de óleo e atmosfera