Banca de QUALIFICAÇÃO: ALAN RANDSON VARELA BARRETO

Uma banca de QUALIFICAÇÃO de MESTRADO foi cadastrada pelo programa.
STUDENT : ALAN RANDSON VARELA BARRETO
DATE: 27/08/2026
TIME: 09:00
LOCAL: Link remoto
TITLE:

BIOSPHERE–ATMOSPHERE INTERACTION: MASS AND ENERGY DYNAMICS IN TROPICAL PASTURE ENVIRONMENTS IN THE AMAZON

KEY WORDS:

Urochloa brizantha. Micrometeorology. Energy Balance. Net Ecosystem Exchange. Eddy Covariance.

PAGES: 44
BIG AREA: Ciências Exatas e da Terra
AREA: Geociências
SUBÁREA: Meteorologia
SPECIALTY: Micrometeorologia
SUMMARY:

Global climate change and the conversion of primary forests into rainfed tropical pasture areas profoundly alter albedo, surface energy partitioning, and regional carbon sinks in the Amazon. Continuous monitoring of these gas exchanges is essential, since pastures operate under combined biological and atmospheric controls that may shift the ecosystem from a seasonal carbon sink to an active carbon source. This study aims to quantify energy, carbon dioxide, and evapotranspiration fluxes at two experimental sites located in tropical pasture monocultures in the Amazon region. For this purpose, the eddy covariance method is applied at two observation sites in the state of Pará, Brazil: Castanhal and Santarém. The analyzed time series cover the seasonal transition period from June 27 to July 4. High-frequency raw data were processed using EddyPro software and subsequently post-processed in the R environment. Preliminary results show that, during the daytime, both sites act as net carbon sinks (NEE < 0), with Castanhal reaching a greater instantaneous carbon uptake capacity at 13:30 (approximately −27 μmol m⁻² s⁻¹) compared with Santarém at 12:00 (approximately −20 μmol m⁻² s⁻¹). At night, the absence of solar radiation ceases photosynthetic activity, and both sites become CO₂ sources (NEE > 0). Anomalous morning emission peaks indicate a ventilation effect associated with the release of carbon accumulated within the stable nocturnal boundary layer. Net radiation partitioning is predominantly directed toward latent heat flux, indicating soil water availability during this early phase of the less rainy season. Energy balance closure based on linear regression was 67.6% (R² = 0.97) for Castanhal and 63.3% (R² = 0.90) for Santarém, suggesting that the unaccounted fraction may be associated with systematic errors and intermittent cloud cover. The wind regime in Santarém showed a lower mean wind speed (0.83 m s⁻¹) than in Castanhal (1.36 m s⁻¹), favoring persistent nocturnal carbon accumulation near the canopy. The results indicate that pasture ecosystems maintain substantial metabolic and evapotranspirative activity during the analyzed period but require advanced post-processing procedures, such as those implemented in the REddyProc package, to correct storage terms and accurately quantify the ecosystem carbon balance.

COMMITTEE MEMBERS:
Presidente - ***.400.082-** - GABRIEL BRITO COSTA - UFOPA
Interno - 2086472 - BERGSON GUEDES BEZERRA
Interno - 1753398 - PABLO ELI SOARES DE OLIVEIRA
Externo à Instituição - ROSEILSON SOUZA DO VALE - UFOPA