Carbon Dioxide Fluxes to the Atmosphere From Waters Within Flooded Forests in the Amazon Basin

Inundated tropical forests are underrepresented in analyses of the global carbon cycle and constitute 80% of the surface area of aquatic environments in the lowland Amazon basin. Diel variations in CO₂ concentrations and exchanges with the atmosphere were investigated from August 2014 to September 2016 in two flooded forests sites with different wind exposure within the central Amazon floodplain (3°23'S, 60°18'W). CO₂ profiles and estimates of air-water gas exchange were combined with ancillary environmental measurements. Surface CO₂ concentrations ranged from 19 to 329 μM, CO₂ fluxes ranged from -0.8 to 55 mmol m^-2 hr^-1 and gas transfer velocities ranged from 0.2 to 17 cm hr^-1. CO₂ concentrations and fluxes were highest during the high water period. CO₂ fluxes were three times higher at a site with more wind exposure (WE) compared to one with less exposure (WP). Emissions were higher at the WP site during the day, whereas they were higher at night at the WE site due to vertical mixing. CO₂ concentrations and fluxes were lower at the W P site following an extended period of exceptionally low water. The CO₂ flux from the water in the flooded forest was about half of the net primary production of the forest estimated from the literature. Mean daily fluxes measured in our study (182 ± 247 mmol m^-2d^-1) are higher than or similar to the few other measurements in waters within tropical and subtropical flooded forests and highlight the importance of flooded forests in carbon budgets.