Diurnal sampling reveals significant variation in CO₂ emission from a tropical productive lake

Amostragem diurna demonstra variação significativa na emissão de CO₂ em um lago tropical produtivo

It is well accepted in the literature that lakes are generally net heterotrophic and supersaturated with CO₂ because they receive allochthonous carbon inputs. However, autotrophy and CO₂undersaturation may happen for at least part of the time, especially in productive lakes. Since diurnal scale is particularly important to tropical lakes dynamics, we evaluated diurnal changes in pCO₂and CO₂ flux across the air-water interface in a tropical productive lake in southeastern Brazil (Lake Carioca) over two consecutive days. Both pCO₂ and CO₂ flux were significantly different between day (9:00 to 17:00) and night (21:00 to 5:00) confirming the importance of this scale for CO₂ dynamics in tropical lakes. Net heterotrophy and CO₂ outgassing from the lake were registered only at night, while significant CO₂ emission did not happen during the day. Dissolved oxygen concentration and temperature trends over the diurnal cycle indicated the dependence of CO₂ dynamics on lake metabolism (respiration and photosynthesis). This study indicates the importance of considering the diurnal scale when examining CO₂emissions from tropical lakes.

pCO₂; CO₂ flux; diurnal variations; tropical productive lake