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.Keywords: decay, oxygen consumption, gases formation, aquatic macrophyte, Monjolinho Reservoir. Implicações da decomposição aeróbia e anaeróbia de Eichhornia azurea (Sw.)Kunth. na ciclagem de carbono em um reservatório subtropical ResumoNesse estudo descreveram-se aspectos cinéticos da decomposição aeróbia e anaeróbia de Eichhornia azurea. As amostras da macrófita aquática e de água foram coletadas no reservatório do Monjolinho (22° 00' S e 47° 54' O). Para a determinação do potencial de lixiviação, adicionaram-se fragmentos de planta (previamente secos) em água do reservatório. Nos experimentos de decomposição, as amostragens foram realizadas durante 4 meses e quantificaram-se as frações particuladas e dissolvidas de carbono. Para descrever as cinéticas de perda de massa, para cada condição (aeróbia e anaeróbia) foram preparadas 10 incubações contento fragmentos de plantas e água do reservatório. A cada dia de amostragem as frações particuladas e dissolvidas de carbono orgânico foram quantificadas. Foram também preparadas 2 câmaras para registrar a formação de gases da degradação anaeróbia e o consumo de oxigênio na degradação aeróbia. Os resultados foram ajustados a um modelo cinético de 1ª ordem. Verificou-se que 27,21% dos detritos corresponderam à fração lábil/solúvel e 72,62% à refratária. O coeficiente global de perda de massa das frações lábeis/solúveis foi 2,07 dia -1 . Nas duas condições não houve mineralização ...

Leaf decomposition of the macrophyte Eichhornia azurea and associated microorganisms and invertebrates

“…Analysis of the percent mass loss of E. azurea observed in this study reveals that its decomposition ratio was very slow in comparison to others reported in the literature (Pagioro and Thomaz 1998, Stripari and Henry 2002, Padial and Thomaz 2006, Martins et al 2011, Bianchini Jr. et al 2014. In contrast, the half-life (t 1/2 = 468 days) calculated up to the 35 th day of incubation was similar to that reported by Cunha-Santino et al (2010) for refractory fractions of E. azurea (t 1/2 = 385 to 462 days) in the laboratory.…”

“…Plant decomposition rates in aquatic environments are controlled by multiple physical, chemical and biological processes (Sangiorgio et al 2010). These processes may be intrinsic or extrinsic, such as the type of decomposition (e.g., aerobic or anaerobic), the enzymatic capacity of the microbial community in the degradation of organic matter, environmental variables (e.g., temperature, availability of dissolved oxygen, pH, redox potential) and detritus quality (Bianchini Jr. et al 2014).…”

Chironomidae larvae associated with Eichhornia azurea leaf detritus: decomposition community structure and colonization dynamics

“…However, the methodological procedures used may have interfered with the dynamics of decomposition of E. azurea, as it was slower than in other studies Martins et al 2011;Bianchini et al 2014). Since aquatic plants generally begin to decompose at the senescence stage, part of the labile compounds may have been lost even before incubation in water (Pagioro and Thomaz 2006).…”

Pb and Zn contamination as rate-regulation agents on decomposition of two emergent macrophytes: a systemic approach

“…Anaerobic microcosms were setup in glass bottles (volume 450 ml) with lids wherein 4.0 g plant dry mass were added to 400 ml of filtered water (Gimenes et al, 2013) and 4 ml of microbial indigenous inoculant (based on experiments from . According to Bianchini Jr. et al (2014) based on the kinetics of oxygen consumption during macrophytes decomposition the anaerobic condition was achieved on maximum of 2 h after the introduction of plant fragments in the water. To ensure the anaerobic conditions, after being prepared, the chambers used in the anaerobic processes were closed, being opened only on the sampling days.…”