Balanço de radiação, energia e fechamento do balanço em uma floresta prístina na Amazônia oriental.

A Floresta Nacional de Caxiuanã, localizada no Estado do Pará, ocupa uma área de 324.060 ha, próxima da baía de Caxiuanã, entre os rios Xingu e Amazonas e compreende aproximadamente 70% do município de Portel e 30% do município de Melgaço. O fluxo de energia foi obtido pelo sistema “Eddy Covariance” localizado a 54 metros de altura. Nota-se uma redução de 10,93% comparando os anos de 2015 (2108,1 mm) e 2016 (2367,8 mm), tendo em vista que a redução da precipitação em determinados sítios é uma consequência das mudanças no balanço de energia e água. O albedo médio do dossel na Flona Caxiuanã foi de 8,5% para ambos os anos avaliados. O fechamento do balanço de energia durante o ano de 2015 e 2016 foi da ordem de 74,83% e 69%, valor este abaixo do que é considerado satisfatório (entre 80 e 90%) como encontrado na literatura. A inclusão do termo (S) na equação melhora substancialmente o fechamento do balanço, principalmente para áreas de florestas primárias devido a quantidade de biomassa. Visando a melhora do fechamento, o fluxo de calor latente foi descartado e então estimado como o resíduo da equação Rn – H – G – S, obtendo um fechamento da ordem de 92,05 e 97,26% para 2015 e 2016.Palavras chave: Eddy covariância, balanço de energia, Caxiuanã, fluxo. Balance of radiation, energy and balance closure in a pristine forest in the eastern Amazon A B S T R A C TThe Caxiuanã National Forest, located in the State of Pará, occupies an area of 324,060 ha, close to Caxiuanã Bay, between the Xingu and Amazonas rivers and comprises approximately 70% of the municipality of Portel and 30% of the municipality of Melgaço. The energy flow was obtained by the “Eddy Covariance” system located 54 meters high. A reduction of 10.93% can be seen comparing the years 2015 (2108.1 mm) and 2016 (2367.8 mm), considering that the reduction of precipitation in certain sites is a consequence of changes in the energy balance and water. The average canopy albedo in Flona Caxiuanã was 8.5% for both years evaluated. The closing of the energy balance during the years 2015 and 2016 was of the order of 74.83% and 69%, a value below what is considered satisfactory (between 80 and 90%) as found in the literature. The inclusion of the term (S) in the equation substantially improves the balance sheet closing, mainly for primary forest areas due to the amount of biomass. In order to improve the closure, the latent heat flow was discarded and then estimated as the residue of the Rn - H - G - S equation, obtaining a closure of the order of 92.05 and 97.26% for 2015 and 2016.Key words: Eddy covariance, energy balance, Caxiuanã, flow.

Evapotranspiration and its components over a rainfed spring maize cropland under plastic film on the Loess Plateau, China

Aim of study: To determine seasonal variations in evapotranspiration (ET) and its components; and ascertain the key factors controlling ET and its components in a rainfed spring maize field under plastic film.Area of study: Shouyang County in Shanxi Province on the eastern Loess Plateau, ChinaMaterial and methods: Eddy covariance system combined with micro-lysimeters and meteorological observing instruments were used in the field. The manual method was used to measure the green leaf area index (GLAI) during the growing season.Main results: In 2015 and 2016, the growing season ET accounted for 80% and 79% of annual ET, respectively. Soil evaporation (E) accounted for 36% and 33% of the growing season ET in 2015 and 2016, respectively. The daily crop coefficient increased with increasing GLAI until a threshold of ~3 m2 m−2 in the canopy-increasing stage, and decreased linearly with decreasing GLAI in the canopy-decreasing stage. At equivalent GLAI, daily basal crop coefficient and soil water evaporation coefficient were generally higher in the canopy-increasing and -decreasing stages, respectively. During the growing season, the most important factor controlling daily ET, T, and E was net radiation (Rn), followed by GLAI for daily ET and T, and soil water content at 10-cm depth for daily E; during the non-growing season, daily ET was mainly controlled by Rn.Research highlights: The daily crop coefficient and its components reacted differently to GLAI in the canopy-increasing and -decreasing stages.

First application of low-cost eddy covariance for CO2 fluxes over agroforestry

<p>Agroforestry is a combination of monoculture agriculture and trees. Studies of net ecosystem exchange of CO<sub>2</sub> (NEE) of agroforestry systems are rare, in comparison to the extensive studies of NEE of agricultural systems (croplands and grasslands). Agroforestry has been shown to alter the microclimate, productivity, and nutrient and water usage – as compared to standard agricultural practise. The, potentially, higher carbon sequestration of agroforestry, relative to monoculture systems, provides an interesting option for mitigating climate change, highlighting the need for improved study of agroforestry systems. The current study, as part of the SIGNAL (sustainable intensification of agriculture through agroforestry) project, investigates NEE of agroforestry compared to that of monoculture agriculture. The study employs paired comparisons of flux measurements above agroforestry and monoculture agronomy, replicated at five locations across Germany. Fluxes are measured, using innovative low-cost CO<sub>2</sub> eddy covariance sensors (slow response Vaisala GMP343 IRGA with custom made housing), which have been successfully used in a study over grassland. Continuous data series from mid-summer until winter 2019 show that both systems acted as a sink with comparable fluxes during summer. The diurnal CO<sub>2</sub> cycle and the response to management activities are distinguishable and in autumn preliminary results suggest a small difference in fluxes between the two systems. The low-cost eddy covariance system is able to capture the turbulence and to measure the CO<sub>2</sub> flux over the agroforestry and monoculture agricultural system. We aim to further improve the quality of the CO<sub>2</sub> fluxes, by adapting post-processing software to better estimate the difference in carbon uptake between the agroforestry and monoculture systems.</p>

Turbulent flux estimation in the atmospheric surface layer through flux-gradient similarity during the ALEX17 field campaign

<p>Turbulent flux measurements require high frequency sampling in order to characterize appropriately all the variability scales of the atmosphere. A 3D sonic anemometer coupled with a gas detector allows for applying the eddy-covariance method which has become the standard. However, the high cost of this system often implies to look for alternative methods, specially when multiple stations are required. Turbulent fluxes can also be estimated through the flux-gradient similarity theory, requiring observations of mean quantities of (at least) air temperature and humidity at two levels and wind at one height. This approach is more sensitive to the disturbing influence of heterogeneous and complex surfaces and a comparison between methodologies is required under these conditions.<br><br>The data used in this study is part of the ALaiz EXperiment 2017-2018 (ALEX17). This campaign was the last within the New European Altas project. It had a duration of over a year with measurements in complex terrain. The location of the experiment is a valley bounded by two mountain ranges that rise 150 m north and over 600 m south. A central site in the centre of the valley was instrumented with a sodar-RASS, an 80-m tower, a surface energy balance (SEB) station with an eddy-covariance system and a surface-layer station (SLS) with the necessary measurements to estimate the turbulent fluxes. In addition, eight supplementary SLS were deployed along the longitudinal and transverse valley axes to characterize the surface layer variability within the valley.<br><br>This communication will present a comparison of the friction velocity and sensible heat flux obtained from both the eddy-covariance system and the flux-gradient method at the central site for a time series of 8 months. Friction velocity is highly comparable between methodologies with a correlation of 0.92 and a standard deviation of 0.05. The performance of the sensible heat flux estimation differs between stable and unstable cases, with a correlation of 0.70 and 0.89, respectively, after applying a quality control procedure. The poorer results obtained under stable conditions points out the need for alternative estimations of the sensible heat flux for these cases.</p>