Anaerobic decomposition of different parts of Scirpus cubensis: kinetics

and gas production

ROMEIRO¹, F. & BIANCHINI JR.^1,2, I.

¹ Programa de Pós-Graduação em Ecologia e Recursos Naturais, Universidade Federal de São Carlos. Via Washington Luiz, km 235. C.P. 676. CEP: 13565-905. São Carlos, SP, Brasil.

e-mail: romeiro@rocketmail.com

² Departamento de Hidrobiologia, Universidade Federal de São Carlos, Via Washington Luiz, km 235, C.P. 676. CEP: 13565-905. São Carlos, SP, Brasil.

e-mail: irineu@power.ufscar.br

 ABSTRACT: We report the anaerobic decomposition of rhizomes, roots and aerial portions (leaves and fertile branches) of Scirpus cubensis, as well as the detritus from the entire plant; in this context, the hypothesis was that the aerial portion of S. cubensis is the most degradable source. Samples of water and plants were collected in the Óleo lagoon (Ecological Station of Jataí; 21º 36’ S and 47º 49’ W). The labile, soluble and refractory fractions of the fragments were quantified and the contents of carbon, nitrogen and ash were determined. For each kind of detritus, three incubations were prepared (7.0 g DW L-1) in the laboratory, using as controls two prepared with lagoon water. During 140 days, all flasks were maintained under controlled conditions, in the dark, at 20 ºC. The results of periodic measurements of CO2 and CH4 were analyzed with an ANOVA (Kruskal-Wallis), with the consumptions of detritus being fitted to a 1s t order kinetics model. After 140 days, 47% of S. cubensis detritus was mineralized. Conversely the expected, the roots were the most mineralized structure (40%), while the rhizomes were the most refractory (26%); overall, the degradability of detritus was attributed to high ash contents. In addition, the detritus with the highest ash contents (roots) presented the most elevated CH4 productions (21.7%).

Key-words: aquatic macrophytes, anaerobic decomposition, Scirpus cubensis, methanogenesis, kinetic model.