Eichhornia azurea decomposition and the bacterial dynamic: an experimental research

Abstract Organic decomposition is a complex interaction between chemical, physical and biological processes, where the variety of aquatic vascular plants is essential for the trophic dynamics of freshwater ecosystems. The goal of this study was to determine the aquatic macrophyte Eichhornia azurea (Sw.) Kunth decomposition rate, the time relation with the limnological parameters, and whether this relationship is a result of decomposition processes. To that end, we collected water and leaves of E. azurea in Surf Leopoldo, PR. The experiment consisted of two treatments: 25 containers with 450 mL of water and 0.8 g of biomass dry weight were used with or without the addition of macrophytes. Samples were collected in triplicate at times 0, 3 h, 6 h, 12 h, 24 h, 72 h, 120 h, 168 h and 240 h. When the container was removed, the plant material was dried in an oven. After 48 h, the material was measured to obtain the final dry weight. Analyses of pH, conductivity, dissolved oxygen, total phosphorus N-ammonia (NH4), soluble reactive phosphorus (PO4) and dissolved organic carbon were performed, and the decomposition rate was calculated. The results showed significant temporal variation of limnological parameters in the study. Additionally, dissolved oxygen, conductivity, dissolved organic carbon and total phosphorus were correlated with the dry weight of the biomass, suggesting that E. azurea decomposition significantly interferes with the dynamics of these variables.

Relationship between bacterial density and abiotic factors at different sediment depths of lakes in the Upper Paraná River floodplain / Relação entre densidade bacteriana e fatores abióticos em diferentes profundidades do sedimento em lagoas da planície de inundação do Alto Rio Paraná

River-floodplain systems are known for their heterogeneity of habitats and the hydrological pulse, the main driving force, which increases nutrient concentrations at the onset of the flood due to leaching from the littoral region and decomposition. This decaying organic matter tends to be deposited in the sediment, where occur biogeochemical processes associated with microorganisms. This study aimed to characterize the vertical distribution of bacterial density in the sediment strata of six environments of the Upper Paraná River floodplain, checking similarity as for bacterial density and physical and chemical conditions. To this end, we analyzed the following factors: total phosphorus, total Kjeldahl nitrogen, levels of organic and inorganic material, oxidation potential and particle size. The results evidenced a gradient of vertical distribution of bacterial density, with predominance of cocci, which possibly indicates no nutrient limitation in this limnic compartment. The analysis of variance was applied to determine significant differences between the layers of the sediment and environments. It can be observed a tendency of deposition of total-P and MI within the upper layers of all environments. More reducing potentials in the initial layers indicate a higher bacterial activity, since this region possesses a greater availability of most easily decomposable material.

Sistemas rios-planície de inundação são conhecidos pela sua heterogeneidade de habitats e pelo pulso hidrológico, principal função de força atuante, que aumenta as concentrações de nutrientes no início devido à lixiviação da região litorânea e à decomposição. Essa matéria orgânica tende a ser depositada no sedimento, onde ocorrem processos biogeoquímicos associados a microrganismos. O objetivo deste estudo foi caracterizar a distribuição vertical da densidade bacteriana em estratos do sedimento de seis ambientes da planície de inundação do Alto Rio Paraná, verificando a similaridade entre os mesmos em relação à densidade bacteriana e condições físicas e químicas. Foram analisados os seguintes fatores: Fósforo total (P-total), nitrogênio total Kjeldahl (NTK), material orgânico (MO) e inorgânico (MI), potencial oxidativo e granulometria. Os resultados mostraram um gradiente de distribuição vertical da densidade bacteriana, com predomínio da forma cocos, possivelmente indicando que não há limitação de nutrientes nos estratos. Análise multivariada mostrou grupamentos por ambientes, ressaltando a grande heterogeneidade de condições limnológicas e de habitats. Pôde-se observar uma tendência de deposição de P-total e MI nas ultimas camadas de todos os ambientes. Potenciais mais redutores nas camadas iniciais indicam maior atividade bacteriana, visto que nesta região há maior disponibilidade material mais facilmente decomponível.

Large scale distribution of bacterial communities in the upper Paraná River floodplain

A bacterial community has a central role in nutrient cycle in aquatic habitats. Therefore, it is important to analyze how this community is distributed throughout different locations. Thirty-six different sites in the upper Paraná River floodplain were surveyed to determine the influence of environmental variable in bacterial community composition. The sites are classified as rivers, channels, and floodplain lakes connected or unconnected to the main river channel. The bacterial community structure was analyzed by fluorescent in situ hybridization (FISH) technique, based on frequency of the main domains Bacteria and Archaea, and subdivisions of the phylum Proteobacteria (Alpha-proteobacteria, Beta-proteobacteria, Gamma-proteobacteria) and the Cytophaga-Flavobacterium cluster. It has been demonstrated that the bacterial community differed in density and frequency of the studied groups. And these differences responded to distinct characteristics of the three main rivers of the floodplain as well as to the classification of the environments found in this floodplain. We conclude that dissimilarities in the bacterial community structure are related to environmental heterogeneity, and the limnological variables that most predicted bacterial communities in the upper Paraná River floodplain was total and ammoniacal nitrogen, orthophosphate and chlorophyll-a.

Photo-degradation effect on dissolved organic carbon availability to bacterioplankton in a lake in the upper Paraná river floodplain / Photo-degradation effect on dissolved organic carbon availability to bacterioplankton in a lake in the upper Paraná river floodplain

Dissolved organic carbon (DOC) is nowadays recognized as the main substrate and source of energy for aquatic microbial community. The great part of available organic carbon for bacterioplankton might be formed after photolytic degradation of humic material, which constitutes the major part of DOC in almost all natural waters. The effects of DOC photo-degradation were evaluated, as was its utilization by bacterioplankton, through a two-step experiment, one involving photo-degradation of DOC and the other bacterial growth on the photo-degraded substrate. Photo-degradation was responsible for the consumption of 19% of DOC, reduced SUVA254, an increase in the E2/E3 and E3/E4 ratios, in addition to modifications in the fluorescence spectra that indicated a rise in the labile fraction of DOC. However, these alterations on DOC were not reflected in differences in bacterioplankton growth, as shown by the fact that there were no significant differences in density, biomass, bacterial production, bacterial respiration and bacterial growth efficiency between treatment and control.

O carbono orgânico dissolvido (COD) é reconhecido atualmente como o principal substrato e fonte de energia para a comunidade microbiana aquática. Grande parte do COD biodisponível para o bacterioplâncton pode ser gerada após degradação fotolítica do material húmico dissolvido, que constitui a maior parte do carbono orgânico total. Neste trabalho foram avaliados os efeitos da fotodegração no COD de um ambiente húmico e a sua posterior utilização pelo bacterioplâncton, por meio de um experimento em duas etapas, uma de fotodegradação do COD e outra de crescimento microbiano sobre o substrato fotodegradado. A fotodegradação causou consumo de 19% do COD, diminuição na SUVA254, aumento nas razões E2/E3 e E3/E4 e modificações nos espectros de fluorescência apontando aumento da fração lábil. No entanto, as alterações no COD não se refletiram em diferenças no crescimento do bacterioplâncton, não havendo diferenças significativas com relação à densidade, biomassa, produção, respiração e eficiência de crescimento bacteriano.

Bacterioplankton features and its relations with doc characteristics and other limnological variables in Paraná river floodplain environments (PR/MS-Brazil)

Since the introduction of the Microbial Loop concept, many studies aimed to explain the role of bacterioplankton and dissolved organic carbon (DOC) in aquatic ecosystems. Paraná River floodplain system is a very complex environment where these subjects were little explored. The aim of this work was to characterize bacterial community in terms of density, biomass and biovolume in some water bodies of this floodplain and to verify its temporal variation and its relation with some limnological variables, including some indicators of DOC quality, obtained through Ultraviolet-visible (UV-VIS) and fluorescence spectroscopic analysis. Bacterial density, biomass and biovolume are similar to those from other freshwater environments and both density and biomass were higher in the period with less rain. The limnological and spectroscopic features that showed any relation with bacterioplankton were the concentrations of N-NH4 and P-PO4, water transparency, and some indicators of DOC quality and origin. The analysis of these relations showed a possible competition between bacterioplankton and phytoplankton for inorganic nutrients and that the DOC used by bacterioplankton is labile and probably from aquatic macrophytes.