An unprecedented study was carried out in a mangrove ecosystem in the northeastern coast of the Brazilian Amazon to understand the behavior of climatic elements in a year with the occurrence of El Niño (2015), associated with the seasonal function source/sink of CO2 by the ecosystem. Global radiation (Rg), net radiation (Rn), temperature, relative humidity, precipitation, horizontal wind speed and direction, as well as turbulent flows of sensible heat (H), latent heat (LE), and carbon (f_CO2) were recorded using eddy covariance, a system for studying turbulent flows of heat and gases in the atmosphere. We observed a drastic reduction in rainfall volumes, which accounts for 63.7% of the expected total according to the region’s climatology. Regarding f_ CO2, the highest values of photosynthesis, autotrophic, and heterotrophic respiration of the ecosystem occurred in the wet season due to precipitation, ideal photosynthetically active radiation, lower soil salinity, and higher NDVI of the ecosystem. In the 2nd semester of the year, we observed that the decrease in cloudiness, causing a higher radiation supply in the forest canopy, accompanied by a reduction in precipitation and an increase in the value of H and soil salinity, favored the increase of foliar abscission by the dominant genus Rhizophora and Avicennia, thus influencing the reduction of magnitudes of carbon source/sink functions in the ecosystem during this season, even on high tide days.

The effects of diffuse solar radiation (DSR), precipitation, and air temperature on survival and mortality of seedlings of açai (Euterpe oleracea Mart.) were evaluated in an estuarine floodplain forest located in the environmental protection area of Combu Island, Belém, Pará, Brazil, in the period from April 2010 to January 2011. An automatic weather station was installed in the understory of Combu Island to collect from the elements, whose location was defined by taking into account the sheer number of seedlings of açai and the incidence of diffuse radiation through canopy sunflecks on the solar panel. Six plots of 2 m × 20 m were demarcated and divided into 10 subplots of 2 m × 2 m in the directions of north, south, east, and west and two others at random around the station. The seedlings with a height between 10 cm and 2 m were quantified and monitored biweekly for survival and mortality. Data were statistically analyzed by a Pearson correlation. Initially, 1072 individuals were recorded, with a significant survival rate of 764 (71.3%) and a mortality rate of 308 (28.7%); therefore, a positive correlation between precipitation and survival was seen, while DSR directly influenced the mortality in the months of May–July 2010, mainly in continuous days of radiation above 34.56 MJ m−2 day−1.