Implication of anaerobic and aerobic decomposition of Eichhornia azurea (Sw.) Kunth. on the carbon cycling in a subtropical reservoir

Abstract

This study aimed at describing kinetic aspects of aerobic and anaerobic mineralization of Eicchornia azurea. The samples of aquatic macrophyte and water were collected in the Monjolinho Reservoir (22° 00′ S and 47° 54′ W). To determine the leachate potential, dried plant fragments were added to reservoir water, with sampling lasting for 4 months, where the particulate and dissolved organic carbon concentrations were measured. The kinetics of mass loss was obtained with 10 mineralization chambers for both aerobic and anaerobic conditions, with the plant fragments and reservoir water. Two additional chambers were used to monitor the volume of gases produced from anaerobic mineralization, with bioassays to determine oxygen uptake. The results were fitted to a first-order kinetic model, from which 27.21% of detritus corresponded to labile/soluble fractions and 72.62% to the refractory fractions. The decay rates for the global mass losses of the labile/soluble components were 2.07 day–1. DOC mineralization was not verified for either condition. Under aerobic condition, the mass loss constant rate (0.0029 day–1) for the refractory fractions was 2.4 the value for the anaerobic one. Under anaerobic condition, the gases formation occurred in three phases. Based on these results, in the Monjolinho Reservoir, the decomposition of E. azurea that undergo within the water column and in upper layers of sediment is a faster process, favoring the mineralization. In contrast, in the lower layers of sediment the diagenetic processes (i.e. humus production and accumulation of organic matter) are favored.