Emissions of methane and carbon dioxide during anaerobic decomposition of aquatic macrophytes from a tropical lagoon (São Paulo, Brazil)

Abstract

AIM: Massive accumulations of aquatic sedimentary plant are the main source of CH4 and CO2 emissions in floodplain lakes. To examine this connection, this study measured CO2 and CH4 formation during anaerobic decomposition of aquatic macrophytes from a floodplain lake; METHODS: Methane formation was determined to the intrinsic characteristics of the debris, and the experimental (physical and chemical) conditions. Production of CH4 and CO2 were measured during anaerobic degradation of seven aquatic macrophytes: Cabomba furcata, Cyperus giganteus, Egeria najas, Eichhornia azurea, Ludwigia inclinata, Oxycaryum cubense, and Utricularia breviscapa, all of which inhabit the littoral zone of the lagoon studied; RESULTS: Overall, methanogenesis was more sensitive to temperature variation than gross anaerobic mineralization. Although the metabolic routes that generate CO2 were always predominant, as a competing process methanogenesis was favored by increasing temperature to the detriment of CO2 formation. Although several factors (such as pH, redox potential, salinity and nutrients availability) influenced yields of the final degradation products, temperature and detritus chemical composition were, in a first approach, the key factors in CH4 formation. In the oxbow lakes of the Mogi-Guacu River Floodplain, especially Oleo Lagoon, on average, 10% of the total carbon can be regarded as the yield of CH4 formation derived from aquatic macrophyte decay, while the remaining carbon (90%) became CO2.