Effects of nutrients and organic matter inputs in the gases CO2 and O2: A mesocosm study in a tropical lake

Lakes are important components in the carbon cycling and threatened by direct and indirect human activities, which ultimately affect metabolic processes. We analyzed the daily dynamics of the air-water CO2 and O2 fluxes over nine days in a mesocosm experiment to determine how the inputs of inorganic nutrients (+NUTRI) and allochthonous organic matter (+OM) affected the metabolic processes. The control, representing the original state of the lake, showed low coefficient of variability among the days sampled and a predominant FCO2 to the atmosphere, but with mean values close to zero (0.2 ± 0.3 mmol m−2 d−1). In +NUTRI and +NUTRI+OM treatments mesocosms, the FCO2 and FO2 showed similar response, where the FCO2 was negative during all days (mean −1.8 ± 1.1 and −1.9 ± 1.2 mmol m−2 d−1, respectively) and FO2 was initially negative, becoming positive after day 4, and decreasing again after day 6. The +OM treatment intensified the FCO2 to the atmosphere (mean 0.4 ± 0.9 mmol m−2 d−1) with highest values at day 7. The ecosystem in +NUTRI and +NUTRI+OM treatments showed a similar recovery (8 days), while +OM treatment mesocosm was similar to the control conditions. The models showed that nutrients promoted larger overall changes and higher daily variability in both FCO2 and FO2, leading to a CO2 influx, followed by organic matter addition. In conclusion, this mesocosm experiment showed the fast response of the lakes to even small disturbances (e.g organic matter addition), which can intensify the sink or the source of carbon to the atmosphere and change the role of the lakes in the global carbon cycling.