POSITIVE RELATIONSHIP AMONG RAINFALL, DOC AND CO2 SUPERSATURATION IN A TROPICAL COASTAL LAGOON

Abstract

Lakes are potentially important conduit for carbon from terrestrial sources to the atmosphere. Our hypothesis was that both dissolved organic carbon (DOC) and CO2 supersaturation might increase in a tropical oligotrophic lagoon during rainy months. The study design included three sampling stations in Carapebus coastal lagoon (RJ, Brazil): CAR 1 (central area colonized by submerged aquatic macrophytes), CAR 2 (central area without macrophytes) and CAR 3 (marginal area colonized by emerged aquatic macrophytes). Four months in a rainy period and three in a dry were analyzed between 2003 and 2004. Rainy months showed signi?cant higher values of DOC, CO2 and coloration than dry ones (Tukey-Kramer; p<0.05). CAR 1 was characterized by CO2 undersaturation during the dry period, while CAR 3 showed higher CO2 supersaturation, coloration and DOC among sampling stations. A high positive relationship between DOC and CO2 along the study time was also observed in all sampling stations
(Pearson correlation; p<0.05). In conclusion, intra-lake and temporal heterogeneity for CO2 saturation might be important features in tropical lakes. The balance between submerged vegetation reducing CO2 and emerged aquatic macrophytes or terrestrial sources increasing it contributed to this heterogeneity. Our results suggested that Brazilian lagoons might show strong enhancements in CO2 saturation in rainy periods probably supported by terrestrial inputs.
Keywords: Tropical lakes, rainfall, DOC, CO2 supersaturation.