Analysing the time scales of variability in carbon dioxide and energy balance components of a tropical Amazon rainforest in central Peru

The Amazon Rainforest plays a vital role in the global carbon and water cycle, yet responses of old growth tropical rainforests to climate change and rising CO₂ concentrations remain poorly understood. Especially the western part of the Amazon is underrepresented in ecohydrological studies. At the Panguana research station, as part of the AndesFlux Network, fluxes of CO₂, water vapor and the dynamics of the CO₂, CH₄ and water vapor profile inside the forest and above the 35 m tall canopy have been continuously monitored since December 2023 to fill this gap and determine whether this site acts as a net source or sink for carbon. Building on this objective, our focus extends to understanding the timescales and ecosystem drivers responsible for flux variability, a crucial step toward predicting ecosystem responses to future changes.

As the main objective, we aim at understanding what are the main drivers for ecosystem flux variability, e.g. incoming solar radiation, water availability, or water vapor deficit and on which timescale we can detect the highest variability of ecosystem fluxes. In a tropical region the highest variability in an annual dataset would be expected to occur on a seasonal timescale. However, we did not observe the expected difference in latent heat flux when comparing the mean dial course on a seasonal basis. Surprisingly, we found the highest variability of latent heat flux to occur on much shorter timescales of up to ten days, coinciding with variability of incoming shortwave radiation for which a timescale of highest variability of eight days was detected. Understanding the processes causing this periodicity in latent heat flux in a tropical region and resulting effects on CO₂ flux is the primary objective of this analysis.

A further objective of this study presented here is to calculate a CO₂-based carbon budget, with the inclusion of the storage term change to understand the effect of ecosystem respiration at night. While the methane exchange to the carbon budget may be significant at this site, it is outside the scope of the current study. Additional objectives of this project include calculating the energy balance of this site and analysing at the surface water balance to better understand seasonal differences and their impact on the carbon cycle.

After calculating the 4h-daytime energy balance closure with different perturbation time scales, we selected a perturbation timescale of 20 min as the best compromise between reducing the systematic and random flux errors. This choice leads to a high energy balance closure of 75% over the course of one year maximizing to 80% when calculated for the rainy season.

These analyses contribute to a deeper understanding of the driving processes of ecosystem exchange in the tropical rainforest near the Andes and help to assess how this part of the Amazon basin may respond to future changes in water availability and atmospheric circulation.