Interações biosfera-atmosfera em uma savana tropical no leste da Amazônia

Abstract

Sensitive heat, latent heat, soil heat and carbon dioxide flux measurements were made in a natural savanna ecosystem in eastern Amazonia, using the eddy covariance method. Data collection was carried out in a savanna area in the municipality of Santarém, Pará, from September to November 2018, a period corresponding to part of the dry season in the region. In this experimental site, the patterns of variability of the daily cycle for energy and CO2 flows were analyzed, as well as an attempt to understand the structure of the local turbulence. The average air temperature in the year 2018 at the savanna site was 29 ºC, being 2 ºC warmer than the historical average of the region, with the occurrence of occasional and low intensity rain episodes. The average radiation balance at the surface was 125 W m-2, with an average daily latent heat flow (LE) in the period of 59 W m-2, while the sensitive heat flow (H) was 69 W m- 2. The average Bowen ratio for the data period was 1.4, representing the preponderance of air heating processes over evaporative processes. During the day, about 36% of the available energy (Rn) in the savanna was used in the evapotranspiration process and H corresponded to 51% of Rn on average. In the study's time interval, an incomplete surface energy balance was observed, with a deficit of 8%. With respect to carbon dioxide flows, the maximum carbon absorption was -8.8 µmol.m-2 s-1, during the day, while the maximum emission was 4.6 µmol.m- 2 s-1 , during dawn. In general, it was found that, in terms of energy balance, the studied savanna has characteristics of a typical savanna, despite the more humid climate in this region compared to other savanna regions. Regarding the structure of turbulence in the savanna atmosphere, it is not possible to apply the Monin-Obukhov Similarity Theory, following the behavior observed in the Amazon rainforest, which requires an adaptation of the theory for the biome in the correct quantification of mass and energy flows.