The role played by aquatic macrophytes regarding CO2 balance in a tropical coastal lagoon (Cabiúnas Lagoon, Macaé, RJ)
Anderson da Rocha Gripp, Claudio Cardoso Marinho, Lúcia Fernandes Sanches, Antonella Petruzzella, Francisco de Assis Esteves
Acta Limnologica Brasiliensia
The role played by aquatic macrophytes regarding CO 2 balance in a tropical coastal lagoon (Cabiúnas Lagoon, Macaé, RJ) O papel desempenhado pelas macrófitas aquáticas em relação ao balanço de CO 2 em uma lagoa costeira tropical (Lagoa Cabiúnas, Macaé, RJ) Abstract: Aim: Carbon dioxide (CO 2 ) is an important atmospheric trace gas that is involved in both the biological carbon cycle and global warming. Inland waters -mainly lakes -contribute to C cycling and have been considered a large source
... f atmospheric CO 2 . However, scientific studies usually neglect lake morphometry and the presence of aquatic macrophytes in littoral zones, which have a great potential for CO 2 absorption and for C storage. This study aimed to evaluate the importance of the littoral region on the CO 2 balance in the Cabiúnas Lagoon, while also considering the contribution of the limnetic region and of Typha domingensis and Eichhornia azurea, prominent species in the area. Methods: CO 2 flux was estimated by a linear integration of CO 2 concentrations measured in the internal atmospheric of a single-component static closed chambers at the studied sites. The distribution of macrophyte stands throughout lagoon surface was taken into account to evaluate the effects of macrophytes on CO 2 supersaturation. Other factors were also measured throughout the sampling process to evaluate their relationship with CO 2 flux data by means of Akaike model selection criterion. The area covered by aquatic macrophytes at the Cabiúnas lagoon was estimated by profiles and transects. Results and discussion: CO 2 flux through the water surface ranged from -7.39 to 17.56 mgCO2m -2 h -1 . An emission pattern predominated, suggesting that water columns are CO 2 supersaturated at all sampling sites. Rates were similar among all the sampling sites, suggesting that aquatic macrophytes do not influence CO 2 saturation in the water column at Cabiúnas lagoon. On the other hand, CO 2 fluxes from macrophyte tissues showed a clear assimilation pattern. Influxes were higher in T. domingensis (-229.1 ± 320.9 mg CO2.m -2 .h -1 ) than in E. azurea stands (-43.8 ± 39.5 mg CO2.m -2 .h -1 ). Once these macrophytes covered a considerable area of the lagoon and CO 2 absorption strongly overwhelmed the emission processes, then we were able to extrapolate data from the total estimated area of the evaluated sites (75% of the Cabiúnas lagoon), which resulted in a net influx of 46.6 mg CO2.m -2 .h -1 . The strong Typha domingensis contribution to CO 2 absorption and other C cycling processes indicate that it is one of the most important species to Carbon cycling in the studied ecosystem. Thus, it is worth considering C cycling in lake littoral zones as a key process when estimating C balance in shallow aquatic ecosystems.