Reis P C J, Barbosa F A R
Laboratório de Limnologia, Ecotoxicologia e Ecologia Aquática - LIMNEA, Instituto de Ciências Biológicas, Universidade Federal de Minas Gerais - UFMG, Belo Horizonte, MG, Brazil.
Braz J Biol. 2014 Aug;74(3 Suppl 1):S113-9. doi: 10.1590/1519-6984.01713.
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 CO2 undersaturation 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 pCO2 and 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 CO2 emissions from tropical lakes.
文献中普遍认为，湖泊通常是净异养的，且由于接受外源碳输入而二氧化碳过饱和。然而，至少在部分时间内可能会出现自养和二氧化碳不饱和的情况，特别是在富营养湖泊中。由于日尺度对热带湖泊动态尤为重要，我们连续两天评估了巴西东南部一个热带富营养湖泊（卡里奥卡湖）中pCO2和空气-水界面二氧化碳通量的日变化。白天（9:00至17:00）和夜间（21:00至5:00）的pCO2和二氧化碳通量均存在显著差异，这证实了该尺度对热带湖泊中二氧化碳动态的重要性。仅在夜间记录到湖泊的净异养和二氧化碳排放，而白天未发生显著的二氧化碳排放。日周期内溶解氧浓度和温度趋势表明二氧化碳动态对湖泊代谢（呼吸作用和光合作用）的依赖性。这项研究表明，在研究热带湖泊的二氧化碳排放时，考虑日尺度非常重要。
