Marcela Bianchessi da Cunha-Santino

Humic substance mineralization in a tropical oxbow lake (São Paulo, Brazil)

We evaluated the mineralization rates of humic substances in Infernão oxbow lake (State of São Paulo, Brazil). Experiments were conducted under aerobic and anaerobic conditions using fulvic acid and humic acid from four sources: Scirpus cubensis and Cabomba piauhyensis leachate submitted to a 120-day degradation process, sediment, and dissolved organic matter from the lake water. A fixed amount of substrate was added to 450 ml of water from Infernão lake, filtered over glass wool. After adding substrate, the flasks were incubated at 21.0°C under aerobic and anaerobic conditions. The dissolved organic carbon was monitored during 95 days. The results were fitted to first-order kinetics model, which pointed to one labile and one refractory fraction. The refractory fractions predominated, ranging from 71.4 to 84.3% for fulvic acid and from 73.4 to 85.0% for humic acid. Mineralization rates of the labile fractions of dissolved organic carbon were higher under aerobic than anaerobic conditions, while the converse was true for the refractory fractions.We evaluated the mineralization rates of humic substances in Infernão oxbow lake (State of São Paulo, Brazil). Experiments were conducted under aerobic and anaerobic conditions using fulvic acid and humic acid from four sources: Scirpus cubensis and Cabomba piauhyensis leachate submitted to a 120-day degradation process, sediment, and dissolved organic matter from the lake water. A fixed amount of substrate was added to 450 ml of water from Infernão lake, filtered over glass wool. After adding substrate, the flasks were incubated at 21.0°C under aerobic and anaerobic conditions. The dissolved organic carbon was monitored during 95 days. The results were fitted to first-order kinetics model, which pointed to one labile and one refractory fraction. The refractory fractions predominated, ranging from 71.4 to 84.3% for fulvic acid and from 73.4 to 85.0% for humic acid. Mineralization rates of the labile fractions of dissolved organic carbon were higher under aerobic than anaerobic conditions, while the converse was true for the refractory fractions.

XYLANASE AND CELLULASE ACTIVITIES DURING ANAEROBIC DECOMPOSITION OF THREE AQUATIC MACROPHYTES

Enzymatic activity during decomposition is extremely important to hydrolyze molecules that are assimilated by microorganisms. During aquatic macrophytes decomposition, enzymes act mainly in the breakdown of lignocellulolytic matrix fibers (i.e. cellulose, hemicellulose and lignin) that encompass the refractory fraction from organic matter. Considering the importance of enzymatic activities role in decomposition processes, this study aimed to describe the temporal changes of xylanase and cellulose activities during anaerobic decomposition of Ricciocarpus natans (freely-floating), Oxycaryum cubense (emergent) and Cabomba furcata (submersed). The aquatic macrophytes were collected in Óleo Lagoon, Luiz Antonio, São Paulo, Brazil and bioassays were accomplished. Decomposition chambers from each species (n = 10) were set up with dried macrophyte fragments and filtered Óleo Lagoon water. The chambers were incubated at 22.5°C, in the dark and under anaerobic conditions. Enzymatic activities and remaining organic matter were measured periodically during 90 days. The temporal variation of enzymes showed that C. furcata presented the highest decay and the highest maximum enzyme production. Xylanase production was higher than cellulase production for the decomposition of the three aquatic macrophytes species.

The decomposition of aquatic macrophytes: bioassays versus in situ experiments

In aquatic sciences, the agreement between laboratory and field observations remains a challenge. Using kinetic modeling, this research aims to compare the decomposition in laboratory and in situ conditions. In the in situ incubations, the mass decreases of the aquatic macrophytes (Echinodorus tenellus, Hydrocotyle verticillata, Najas microcarpa and Pontederia parviflora) were described using a litter bag technique and in the laboratory their decomposition was maintained under controlled conditions. The plants and water samples were collected from a tropical reservoir (Brazil). To describe the particulate organic carbon (POC) decay we adopted a two stage kinetic model that considered the heterogeneity of resources. The released organic carbon (i.e., losses related to mineralization, dissolution and sedimentation of smaller particles than the litter bag mesh) were used to compare the results derived from the field and laboratory incubations. Despite the methodological differences, the results show equivalence among the POC decay. The decomposition measured by litter bags method was 1.32 faster, owing to the effects of losses by sedimentation of the smaller particles, abrasion, action of decomposer organisms (e.g., fragmentation and enzymatic attack) and synergy among these factors. From a mathematical modeling approach, the results validate the use of decomposition data obtained under controlled conditions providing estimations of energy and matter fluxes within aquatic ecosystems. However, it is necessary to adopt a coefficient to acquire the similarity (e.g., 1.32).

Cellulase and xylanase activity during the decomposition of three aquatic macrophytes in a tropical oxbow lagoon

Due to the connection between enzymatic activity and degradation of different fractions of organic matter, enzyme assays can be used to estimate degradation rates of particulate and dissolved organic carbon in freshwater systems. The aim of this study was to quantify and model the enzymatic degradation involving the decomposition of macrophytes, describing temporal activity of cellulases (EC 3.2.1.4 and EC 3.2.1.91) and xylanase (EC 3.2.1.8) during in situ decomposition of three aquatic macrophytes (Salvinia sp., Eichhornia azurea and Cyperus giganteus) on the surface and water-sediment interface (w-s interface) of an oxbow lagoon (Óleo lagoon) within a natural Brazilian Savanna Reserve. Overall, the enzymatic degradation of aquatic macrophytes in Óleo lagoon occurred during the whole year and was initiated together with leaching. Xylanase production was ca. 5 times higher than cellulase values due to easy access to this compound by cellulolytic microorganisms. Enzymatic production and detritus mass decay were similar on the surface and w-s interface. Salvinia sp. was the most recalcitrant detritus, with low mass decay and enzymatic activity. E. azurea and C. giganteus decomposition rates and enzymatic production were high and similar. Due to the physicochemical homogeneity observed in the Óleo lagoon, the differences between the decay rates of each species are mostly related with detritus chemical quality.

Oxygen consumption during mineralization of organic compounds in water samples from a small sub-tropical reservoir (Brazil)

ABSTRACT Assays were carried out to evaluate the oxygen consumption resulting from mineralization of different organiccompounds: glucose, sucrose, starch, tannic acid, lysine and glycine. The compounds were added to 1 l of watersample from Monjolinho Reservoir. D issolved oxygen and dissolved organic carbon were monitored during 20 daysand the results were fitted to first order kinetics model. During the 20 days of experiments, the oxygen consumptionvaried from 4.5 mg.l -1 (tannic acid) to 71.5 mg.l -1 (glucose). The highest deoxygenation rate ( k D ) was observed formineralization of tannic acid (0.321 day -1 ) followed by glycine, starch, lysine, sucrose and glucose (0.1004, 0.0504,0.0486, 0.0251 and 0.0158 day -1 , respectively). From theoretical calculations and oxygen and carbonconcentrations we obtained the stoichiometry of the mineralization processes. S toichiometric values varied from 0.17(tannic acid) to 2.55 (sucrose).Key words: Oxygen consumption; aerobic mineralization; Reservoir of Monjolinho ( UFSCar - Sao Carlos, SP)

How does leaf litter chemistry influence its decomposition and colonization by shredder Chironomidae (Diptera) larvae in a tropical stream

The nutritional quality of leaf litter can influence shredder chironomid larvae activities and affect leaf litter decomposition in tropical streams. The invasion of riparian areas by exotic plants may alter the nutritional quality of allochthonous material in streams, which would influence litter decomposition in these systems. We carried out an in situ experiment to verify the relationship between the initial leaf litter chemistry of two invasive plants (Hedychium coronarium and Pteridium arachnoideum) and a native one (Magnolia ovata) and the shredder chironomid larvae density and decomposition rates in a tropical stream. We found differences in the initial leaf litter chemistry and mass loss between leaf litter species. Differences in leaf litter chemistry influenced the colonization behavior by chironomid larvae. Larval densities differed among litter species, both taxonomically and functionally. The density of shredders was similar between M. ovata and H. coronarium, although they were colonized by different taxa: Endotribelos was more abundant in M. ovata and Stenochironomus in H. coronarium. P. arachnoideum was colonized by fewer shredders probably due to its high secondary compounds and lignin concentration. The invasion of riparian areas by exotic plants can alter the colonization of chironomid shredder assemblages and therefore the decomposition rates in aquatic systems.

Cellulase activity in anaerobic degradation of aquatic macrophytes tissues

Resumo Macrophytes are responsible for a large input of detrital organic matter in tropical lentic aquatic systems, thus this study aimed to evaluate the different aspects involved in anaerobic decomposition (i.e. cellulase activity, leaching and mineralization) of Cyperus giganteus, Eichhornia azurea and Egeria najas. Decomposition chambers comprising macrophyte detritus and lagoon water were set up and incubated at 17.4 and 27.8 degrees C in the dark. In each sampling day, the mass of the detritus particulate fraction, the cellulose content and the cellulolytic activity were evaluated. The detritus presented a labile and/or soluble (POMLS) and a refractory (POMR) fraction. Based on the decomposition kinetics, the leaching process was faster than the degradation of refractory compounds. C. giganteus detritus presented the highest contents of POMR and longer half-life times, and the higher cellulose content. The cellulose degradation was higher for E. najas regardless of temperature incubation, although the highest accumulated cellulolytic activity was observed in the degradation of E. azurea. In conclusion: (i) temperature affected the leaching coefficient but did not alter the decay velocity of POMR; (ii) regardless of temperature, the POMR contents and the decomposition times were shorter for E. najas and higher for C. giganteus and (iii) higher temperature increased the cellulase activity in C. giganteus and E. najas tissues, but a reduced activity was observed during degradation of E. azurea, indicating that temperature displays a different pattern depending on macrophyte life form. (AU)

Formation and mineralization kinetics of dissolved humic substances from aquatic macrophytes decomposition

PurposeAquatic macrophytes are an important source of autochthonous dissolved organic carbon in aquatic ecosystems. Yield and mass loss of aquatic humic substances released from macrophytes decomposition could be affected by the plant species and oxygen availability. Our aim was to describe the kinetics of dissolved fulvic and humic acids formed from decomposition of four aquatic macrophytes under aerobic and anaerobic conditions.Materials and methodsSamples of Eichhornia azurea (Sw.) Kunth, Egeria najas Planch, Oxycaryum cubense (Poepp. and Kunth), and Salvinia molesta (Mitchell) were incubated under aerobic and anaerobic conditions. On sampling days, the remaining particulate detritus were weighted and were measured for the pH, the electrical conductivity, and the organic carbon in the dissolved fraction. Humic substances were extracted from the dissolved fraction, separated into fulvic and humic acids, and then quantified. The mass loss of particulate and dissolved fractions were fitted to first order kinetic models.Results and discussionAerobic environment favored mineralization of aquatic macrophyte detritus and humification of organic dissolved carbon. Incubations under aerobic conditions formed 3.6 times more humic acid than incubations under anaerobic conditions. However, incubations in an anaerobic environment formed 1.84 times more fulvic acid. The dissolved humic compounds presented low mineralization rates probably due to the presence of the macrophyte detritus in the incubation representing a more attractive source of resource for microorganisms.ConclusionsIn many cases, the mineralization of HS was not noticed, leading to an increase in humic and fulvic acid concentration in the water. O. cubense detritus presented the highest carbon concentration, were related to refractory features, and generated the highest amounts of dissolved HA (mainly under aerobic condition). Egeria najas detritus presented the lowest carbon concentration, were related to labile features, and generated the highest amounts of dissolved FA (mainly under anaerobic condition). Besides that, high humic substance concentrations in the dissolved organic carbon were related to low mineralization of this fraction.

First record of herbivory of the invasive macrophyte Hedychium coronarium J. König (Zingiberaceae)

Invasive species can cause structural and functional changes in their non-native habitats, such as changes in the trophic chain. We describe ramet herbivory of butterfly ginger, an aggressive aquatic weed in Brazil, by capybaras in a floodplain area of a Cerrado reserve. This is the first record of herbivory of H. coronarium in invaded areas. Capybaras could be using the butterfly ginger as habitat and as a food resource, which could cause changes in apparent competition between these invasive and native macrophytes.

AVALIAÇÃO PRELIMINAR DA QUALIDADE DOS SEDIMENTOS DE DUAS NASCENTES, CÓRREGO ESPRAIADO E RIO MONJOLINHO, SÃO CARLOS - SP

An effective way to analyze hydric bodies is through their sediments characterization, once this compartment accumulates compounds arising from the surroundings. The present study aimed at comparing the environmental quality of two springs, the Espraiado stream spring (preserved) and the Monjolinho river spring (anthropized). Toxicity, organic matter, pH, density, humidity, metals and granulometry analyses were performed during the drought and raining seasons in 2012. The monitoring of sediments and analysis of the surroundings of the spring supplied an environmental diagnosis. The existence of riparian vegetation around the Espraiado spring constitutes a landscape factor that effectively ensures the maintenance of the environmental quality of this spring, without compromising matter and energy flows, which are innate characteristics of a natural ecosystem. However, in the Monjolinho spring this quality pattern was not observed, also presenting various other problems such as erosion, lack of riparian vegetation and anthropic uses on the surroundings (agriculture and pasture).