Highly segregated trophic niche of two congeneric fish species in Neotropical floodplain lakes.

The diets of two sympatric, morphologically similar species of Moenkhausia were studied to investigate whether the manner in which they exploit food resources can help to explain their coexistence. Fish diets were evaluated during the low-water season in six lakes of the upper Paraná River floodplain (Brazil). The results indicate that these two species segregate in relation to food resources and that the differential use of resources is probably a strategy that reduces competition during periods of a potential food shortage (the low-water season).

Isolation of bovine immunoglobulins resistant to peptic digestion: new perspectives in the prevention of failure in passive immunization of neonatal calves.

In calves, neonatal mortality and disease susceptibility are greatly influenced by failure in passive immunization, normally provided by colostrum ingestion just after birth. Formulations projected to replace natural colostrum have not been successful, and one of the possible reasons for such failure is that orally administered Ig are probably digested in the gastrointestinal tract, so they are not absorbed as intact functional molecules. With the aim of finding an adequate colostrum substitute, we used columns of immobilized jacalin, a lectin known by its ability to bind O-linked oligosaccharides, to obtain a colostral Ig population putatively protected against enzymatic cleavage by the presence of sugar chains. Immunoglobulin G1 is a major constituent of colostrum Ig bound to jacalin (JB-Ig). This preparation contains 10% of the total colostral Ig and is typically 3 to 6 times more resistant to pepsin digestion than the Ig contained in the fraction that is not bound to jacalin, which presumably does not contain O-glycans. Mass spectrometry analysis demonstrated that the tryptic peptides obtained from JB-Ig and unbound Ig were similar, indicating that their distinct susceptibility to enzyme hydrolysis was associated with differences in their sugar chains. Therefore, the present research suggests that the bovine colostrum JB-Ig has potential application in the immunotherapy of neonatal calves that have not been supplied with colostrum.

Effects of temperature on decomposition of a potential nuisance species: the submerged aquatic macrophyte Egeria najas Planchon (Hydrocharitaceae).

Decomposition of aquatic plants is influenced by several biotic and abiotic factors. Among them, temperature plays an important role. Despite the increasing number of studies describing the effects of temperature on the decomposition of aquatic macrophytes, little attention has been given to the decay of submerged macrophytes. In this paper, we assessed the effect of temperature on weight loss and chemical composition of detritus of the submerged aquatic macrophyte Egeria najas Planchon (Hydrocharitaceae). Fresh plant material was maintained at 17 degrees C and 27 degrees C, in the dark, in incubation chambers. The overall decay process was best described by a linear model, with rates of 0.014 day(-1) (R2= 94%) and 0.045 day(-1) (R2= 96%) obtained at 17 degrees C and 27 degrees C, respectively. The analysis of covariance (ANCOVA) indicated a significant difference between the decomposition rates at the two temperatures. The rapid breakdown of E. najas detritus, indicated by the decay coefficient, may be explained by its low content of resistant compounds such as cellulose and lignin. The variables analyzed in this study (pH, electrical conductivity, dissolved oxygen in the water and organic matter, total nitrogen and total phosphorus concentration in detritus) showed accentuated responses at 27 degrees C. It is likely that the higher temperature increased microbial activity and, therefore, oxygen consumption in the water, consequently affecting the pH and the rate of ion and nutrient liberation into the aquatic ecosystem. Due to the rapid decomposition of E. najas at high temperatures, a small exportation is expected of this species from its stands to distant regions in tropical reservoirs, where it is considered a potential nuisance species.

Microbial respiration and chemical composition of different sediment fractions in waterbodies of the upper Paraná River floodplain, Brazil.

Four size fractions of the sediment of six environments of the upper Paraná River floodplain were analyzed for carbon, nitrogen, and phosphorus contents and microbial respiration (oxygen consumption). Particle size did not affect nitrogen and phosphorus content or microbial activity, but did affect carbon content (F = 4.274, df = 3; 20, p = 0.020). The carbon concentration of ultra-fine particles was significantly lower than that of other sizes of sediment particles. Microbial respiration values were well predicted by sediment chemical composition, as shown by multiple regression (microbial respiration = -0.39 - 0.210C + 0.108N + 0.796P; F = 7.0495, p = 0.0022). However, phosphorus was the element which best explained the microbial respiration (partial coefficient = 0.796, p = 0.0039, n = 23). Considering that i) phosphorus was the best predictor of microbial respiration; ii) phosphorus is trapped in the series of reservoirs located upstream from the section of the floodplain studied; and iii) microbial respiration is a measure of decomposition rates and nutrient cycling, we hypothesize that the long-term accumulation of litter detritus and reduction of nutrient cycling in environments of the upper Paraná River floodplain are probable impacts of this decrease in phosphorus caused by the upstream reservoirs.

Toxicity and genotoxicity of water and sediment from streams on dotted duckweed (Landoltia punctata).

Most rivers are used as a source to supply entire cities; the quality of water is directly related to the quality of tributaries. Unfortunately men have neglected the importance of streams, which receive domestic and industrial effluents and transport nutrients and pesticides from rural areas. Given the complexity of the mixtures discharged into these water bodies, this study aimed to evaluate the quality of water and sediment of ten tributaries of Pirapó River, in Maringá, Paraná State, Brazil. To this end, the free-floating macrophyte Landoltia punctata (G. Meyer) Les & D.J.Crawford was used as test organism in microcosm, and the toxicity of water and sediment samples was evaluated by the relative growth rate, dry/fresh biomass ratio, and genotoxic effects (comet assay). Samples of water and sediment of each stream were arranged in microcosms with L. punctata. Seven days later, plants were collected for analysis. Nutrient levels were higher than the reference location, indicating eutrophication, but the results indicated a toxic effect for only three streams, and a genotoxic effect for all streams.

Identifying and modeling patterns of tetrapod vertebrate mortality rates in the Gulf of Mexico oil spill.

The accidental oil spill in the Gulf of Mexico in 2010 has caused perceptible damage to marine and freshwater ecosystems. The large quantity of oil leaking at a constant rate and the long duration of the event caused an exponentially increasing mortality of vertebrates. Using data provided by NOAA and USFWS, we assessed the effects of this event on birds, sea turtles, and mammals. Mortality rates (measured as the number of carcasses recorded per day) were exponential for all three groups. Birds were the most affected group, as indicated by the steepest increase of mortality rates over time. For sea turtles and mammals, an exponential increase in mortality was observed after an initial delay. These exponential behaviors are consistent with a unified scenario for the mortality rate for tetrapod vertebrates. However, at least for mammals, pre-spill data seem to indicate that the growth in the mortality rate is not entirely a consequence of the spill.

Modeling chlorophyll-a and dissolved oxygen concentration in tropical floodplain lakes (Paraná River, Brazil).

The need for prediction is widely recognized in limnology. In this study, data from 25 lakes of the Upper Paraná River floodplain were used to build models to predict chlorophyll-a and dissolved oxygen concentrations. Akaike's information criterion (AIC) was used as a criterion for model selection. Models were validated with independent data obtained in the same lakes in 2001. Predictor variables that significantly explained chlorophyll-a concentration were pH, electrical conductivity, total seston (positive correlation) and nitrate (negative correlation). This model explained 52% of chlorophyll variability. Variables that significantly explained dissolved oxygen concentration were pH, lake area and nitrate (all positive correlations); water temperature and electrical conductivity were negatively correlated with oxygen. This model explained 54% of oxygen variability. Validation with independent data showed that both models had the potential to predict algal biomass and dissolved oxygen concentration in these lakes. These findings suggest that multiple regression models are valuable and practical tools for understanding the dynamics of ecosystems and that predictive limnology may still be considered a powerful approach in aquatic ecology.

Temporal and spatial patterns of aquatic macrophyte diversity in the Upper Paraná River floodplain.

Although the importance of long-term data has been emphasized by ecologists in recent years, little is known about how communities may change over time. In this study, we describe the general patterns of aquatic macrophyte diversity in the Paraná River floodplain observed during six years of study. Temporal changes in community composition were also evaluated. Data on the presence or absence of aquatic macrophytes were collected between March 2002 and March 2008, in six lakes associated with three rivers. Different analytical strategies were used to evaluate the dynamics of aquatic macrophyte communities between the different systems in the floodplain. The composition of aquatic macrophytes differed among the rivers, mainly with respect to the different vegetation life forms (floating, submersed, emergent and rooted with floating stems). The temporal similarity of species composition during the six years and the beta-diversity index indicated that the month-to-month species turnover was, in general, lower in the connected lakes, which are directly influenced by the river. Probably the water level fluctuation is a selective force that contributes to maintaining diversity or richness. Our findings indicated the importance of abiotic characteristics and connectivity of the lakes in determining macrophyte composition and community stability over a long time frame.

Limnology in the Upper Paraná River floodplain: large-scale spatial and temporal patterns, and the influence of reservoirs.

Knowledge of abiotic limnological factors is important to monitor changes caused by humans, and to explain the structure and dynamics of populations and communities in a variety of inland water ecosystems. In this study, we used a long term data-set (eight years) collected in 10 habitats with different features (river channels, and connected and isolated lakes) to describe the spatial and temporal patterns of some of the principal limnological factors. In general, the degree of connectivity of the lakes, together with the rivers to which the lakes are connected, were important determinants of their limnological characteristics. These differences are expected, because rivers entering the floodplain come from different geological regions and are subject to different human impacts. At large spatial scales, these differences contribute to the increased habitat diversity of the floodplain and thus to its high biodiversity. With regard to temporal variation, Secchi-disk transparency increased, and total phosphorus decreased in the Paraná River main channel during the last 20 years. Although these changes are directly attributed to the several reservoir cascades located upstream, the closing of the Porto Primavera dam in 1998 enhanced this effect. The increase in water transparency explains biotic changes within the floodplain. The lower-phosphorus Paraná River water probably dilutes concentrations of this element in the floodplain waterbodies during major floods, with future consequences for their productivity.

The study of aquatic macrophytes in Neotropics: a scientometrical view of the main trends and gaps.

Aquatic macrophytes comprises a diverse group of organisms including angiosperms, ferns, mosses, liverworts and some macroalgae that occur in seasonally or permanently wet environments. Among other implications, aquatic macrophytes are highly productive and with an important structuring role on aquatic environments. Ecological studies involving aquatic plants substantially increased in the last years. However, a precise view of researches devoted to aquatic macrophytes in Neotropics is necessary to reach a reliable evaluation of the scientific production. In the current study, we performed a scientometrics analysis of the scientific production devoted to Neotropical macrophytes in an attempt to find the main trends and gaps of researches concerning this group. The publication devoted to macrophytes in Neotropics increased conspicuously in the last two decades. Brazil, Argentina, Mexico and Chile were the most productive among Neotropical countries. Our analyses showed that the studies dealt mostly with the influences of aquatic macrophytes on organisms and abiotic features. Studies with a predictive approach or aiming to test ecological hypothesis are scarce. In addition, researches aiming to describe unknown species are still necessary. This is essential to support conservation efforts and to subsidize further investigations testing ecological hypotheses.

[(3)H]Leucine incorporation methodology to estimate epiphytic bacterial biomass production.

[(3)H]leucine incorporation into protein, as a method of measuring bacterial biomass production (BBP), was adapted to epiphytic bacteria. Incorporation of the isotope was saturated at concentrations higher than 400 nM. Disruption of thicker biofilms by sonication resulted in higher values of BBP and ratios of BBP/biomass when compared to those of intact biofilm. Thin biofilms formed early in the decomposition process did not show this phenomenon. These results support to evidence that more internally located cells of the matrices either have greatly reduced access to the leucine from the overlying medium or that fast recycling of leucine occurs in the biofilm.

Limnology in the Upper Paraná River floodplain: large-scale spatial and temporal patterns, and the influence of reservoirs / Limnologia na planície de inundação do Alto Rio Paraná: padrões em amplas escalas espaciais e temporais e influência de reservatórios

Knowledge of abiotic limnological factors is important to monitor changes caused by humans, and to explain the structure and dynamics of populations and communities in a variety of inland water ecosystems. In this study, we used a long term data-set (eight years) collected in 10 habitats with different features (river channels, and connected and isolated lakes) to describe the spatial and temporal patterns of some of the principal limnological factors. In general, the degree of connectivity of the lakes, together with the rivers to which the lakes are connected, were important determinants of their limnological characteristics. These differences are expected, because rivers entering the floodplain come from different geological regions and are subject to different human impacts. At large spatial scales, these differences contribute to the increased habitat diversity of the floodplain and thus to its high biodiversity. With regard to temporal variation, Secchi-disk transparency increased, and total phosphorus decreased in the Paraná River main channel during the last 20 years. Although these changes are directly attributed to the several reservoir cascades located upstream, the closing of the Porto Primavera dam in 1998 enhanced this effect. The increase in water transparency explains biotic changes within the floodplain. The lower-phosphorus Paraná River water probably dilutes concentrations of this element in the floodplain waterbodies during major floods, with future consequences for their productivity.

Fatores limnológicos abióticos têm sido importante para monitorar as mudanças causadas pelo homem e para explicar a estrutura e a dinâmica de populações e comunidades em uma variedade de ecossistemas aquáticos. Neste estudo, foram usados dados de vários anos (oito anos) coletados em 10 habitats com características distintas (rios, canais, lagoas isoladas e conectadas) para descrever padrões espaciais e temporais de alguns fatores limnológicos. Em geral, o grau de conectividade das lagoas com o rio ao qual estão conectadas foi importante para determinar as suas características limnológicas. Estas diferenças são esperadas porque os rios que chegam à planície de inundação vêm de diferentes regiões geológicas e estão sujeitos a diferentes impactos humanos. Em grandes escalas espaciais, tais diferenças contribuem para o aumento da diversidade de habitats da zona sujeita a inundações e assim, a sua alta biodiversidade. A respeito da variação temporal, observou-se um aumento nos valores de disco de Secchi e diminuição na carga de fósforo total no canal principal do rio Paraná nos últimos 20 anos. Embora estas mudanças estejam diretamente atribuídas ao efeito cascata de vários reservatórios a montante, o fechamento da represa de Porto Primavera em 1998 realçou este efeito. O aumento na transparência da água explica as mudanças bióticas observadas na planície de inundação. Em função das baixas concentrações de fósforo no rio Paraná, este está provavelmente diluindo a sua planície de inundação durante as grandes cheias, o que poderá acarretar em efeitos negativos para a sua produtividade no futuro.

Modeling chlorophyll-a and dissolved oxygen concentration in tropical floodplain lakes (Paraná River, Brazil) / Predição das concentrações de clorofila-a e oxigênio dissolvido em lagoas da planície de inundação do Alto Rio Paraná

The need for prediction is widely recognized in limnology. In this study, data from 25 lakes of the Upper Paraná River floodplain were used to build models to predict chlorophyll-a and dissolved oxygen concentrations. Akaike's information criterion (AIC) was used as a criterion for model selection. Models were validated with independent data obtained in the same lakes in 2001. Predictor variables that significantly explained chlorophyll-a concentration were pH, electrical conductivity, total seston (positive correlation) and nitrate (negative correlation). This model explained 52 percent of chlorophyll variability. Variables that significantly explained dissolved oxygen concentration were pH, lake area and nitrate (all positive correlations); water temperature and electrical conductivity were negatively correlated with oxygen. This model explained 54 percent of oxygen variability. Validation with independent data showed that both models had the potential to predict algal biomass and dissolved oxygen concentration in these lakes. These findings suggest that multiple regression models are valuable and practical tools for understanding the dynamics of ecosystems and that predictive limnology may still be considered a powerful approach in aquatic ecology.

O objetivo desse estudo foi o de construir modelos para predizer as concentrações de clorofila-a e oxigênio dissolvido em lagoas da planície de inundação do Alto Rio Paraná. Para tanto, foram selecionadas 25 lagoas na planície de inundação. O critério de Akaike (AIC) foi utilizado para a seleção dos modelos. Posteriormente, os modelos foram validados utilizando dados independentes obtidos nas mesmas lagoas. As variáveis que explicaram significativamente as concentrações de clorofila-a (52 por cento) foram pH, condutividade elétrica, material em suspensão (relação positiva) e nitrato (relação negativa). As variáveis que melhor explicaram as concentrações de oxigênio dissolvido (54 por cento) foram pH, área das lagoas, nitrato (relação positiva), temperatura da água e condutividade elétrica (relação negativa). A elevada capacidade preditiva desses modelos foi demonstrada através da utilização de dados independentes. Esses resultados demonstraram que a limnologia preditiva continua sendo uma importante área de pesquisa na ecologia aquática.

Temporal and spatial patterns of aquatic macrophyte diversity in the Upper Paraná River floodplain / Padrões temporais e espaciais da diversidade de macrófitas aquáticas na planície de inundação do Alto Rio Paraná

Although the importance of long-term data has been emphasized by ecologists in recent years, little is known about how communities may change over time. In this study, we describe the general patterns of aquatic macrophyte diversity in the Paraná River floodplain observed during six years of study. Temporal changes in community composition were also evaluated. Data on the presence or absence of aquatic macrophytes were collected between March 2002 and March 2008, in six lakes associated with three rivers. Different analytical strategies were used to evaluate the dynamics of aquatic macrophyte communities between the different systems in the floodplain. The composition of aquatic macrophytes differed among the rivers, mainly with respect to the different vegetation life forms (floating, submersed, emergent and rooted with floating stems). The temporal similarity of species composition during the six years and the beta-diversity index indicated that the month-to-month species turnover was, in general, lower in the connected lakes, which are directly influenced by the river. Probably the water level fluctuation is a selective force that contributes to maintaining diversity or richness. Our findings indicated the importance of abiotic characteristics and connectivity of the lakes in determining macrophyte composition and community stability over a long time frame.

Estudos utilizando ampla escala temporal ainda são escassos na ecologia, mesmo considerando sua importância no estudo de comunidades. Esse trabalho teve como objetivo principal descrever padrões gerais sobre a diversidade de macrófitas aquáticas na planície de inundação do Alto Rio Paraná utilizando uma ampla escala temporal (seis anos de estudo). Mudanças na composição das comunidades ao longo do tempo também foram avaliadas. Dados de presença ou ausência de macrófitas foram obtidos entre Março de 2002 e Março de 2008 em seis lagoas associadas a três rios na planície de inundação. Diferentes técnicas foram utilizadas para avaliar a dinâmica das comunidades de macrófitas aquáticas entre os diferentes ambientes. De maneira geral, a composição das comunidades foi dissimilar entre os diferentes rios, principalmente considerando os diferentes grupos funcionais de macrófitas (flutuante livre, submersa, emergente e enraizada com folha flutuante). A similaridade temporal na composição de espécies e o índice de diversidade beta indicaram que a substituição de espécies ao longo dos meses foi, de maneira geral, menor nas lagoas conectadas ao rio principal. Provavelmente, a flutuação no nível da água representa uma pressão seletiva que ajuda a manter a diversidade de espécies nas lagoas diretamente influenciadas pelo rio. Os resultados desse estudo indicaram a importância das características abióticas e da conectividade das lagoas na composição e estabilidade temporal das comunidades de macrófitas aquáticas na planície de inundação do Alto Rio Paraná.

A neutrophil migration-inducing lectin from Artocarpus integrifolia.

A neutrophil migration-inducing protein has been isolated from the saline extract of Artocarpus integrifolia seeds by successive sugar affinity chromatography steps during which the protein was not absorbed by D-galactose resin, and then was absorbed to and eluted from D-mannose resin by 0.1 M D-mannose. Gel filtration on Superdex 75 HR indicated a molecular mass of 52 kDa when 0.1 M D-mannose was present in the elution buffer. A single band of apparent molecular mass of 13 kDa was demonstrable by SDS-PAGE only after heating, both in the presence and absence of reducing agent, suggesting that the molecule is a tetramer formed by the noncovalent association of 13 kDa chains. Isoelectric forms corresponding to isoelectric points of 4.0, 4.2, 5.0, and 5.2 were demonstrable by isoelectric focusing-PAGE, and four active forms having the same isoelectric points were separated by chromatofocusing. The minimal m.w. calculated from amino acid analysis data was 13,193. The protein, denoted KM+, stimulated neutrophil migration in the rat peritoneal cavity assay in a dose-related manner in the range of 1 to 300 micrograms per rat. The dose-response curve of the in vitro chemotactic activity of KM+ was bell shaped and its ascending limb was dose dependent in the range of 1 ng to 10 micrograms/well. D-Mannose (0.1 M) inhibited the in vitro (80%) and in vivo (60%) neutrophil migration-inducing activities of KM+ and also its hemmaglutinating activity. The chemotactic activity was shown to be caused by haptotaxis rather than chemokinesis. The physical and biologic properties of KM+ suggest that this lectin may attract neutrophils by a mechanism involving a haptotactic gradient as has been proposed for IL-8. KM+ might be used as tool to study protein-carbohydrate interactions during neutrophil migration through the extracellular matrix.

The study of aquatic macrophytes in Neotropics: a scientometrical view of the main trends and gaps / O estudo de macrófitas aquáticas na região neotropical: uma visão cienciométrica dos principais padrões e lacunas

Aquatic macrophytes comprises a diverse group of organisms including angiosperms, ferns, mosses, liverworts and some macroalgae that occur in seasonally or permanently wet environments. Among other implications, aquatic macrophytes are highly productive and with an important structuring role on aquatic environments. Ecological studies involving aquatic plants substantially increased in the last years. However, a precise view of researches devoted to aquatic macrophytes in Neotropics is necessary to reach a reliable evaluation of the scientific production. In the current study, we performed a scientometrics analysis of the scientific production devoted to Neotropical macrophytes in an attempt to find the main trends and gaps of researches concerning this group. The publication devoted to macrophytes in Neotropics increased conspicuously in the last two decades. Brazil, Argentina, Mexico and Chile were the most productive among Neotropical countries. Our analyses showed that the studies dealt mostly with the influences of aquatic macrophytes on organisms and abiotic features. Studies with a predictive approach or aiming to test ecological hypothesis are scarce. In addition, researches aiming to describe unknown species are still necessary. This is essential to support conservation efforts and to subsidize further investigations testing ecological hypotheses.

Macrófitas compreendem um diverso grupo de organismos macrofíticos, incluindo angiospermas, samambaias, musgos, hepáticas e algumas macroalgas que ocorrem em ambientes sazonalmente ou permanentemente inundados. Dentre outras implicações, as macrófitas aquáticas são altamente produtivas e com um importante papel na estruturação nos ambientes aquáticos. Estudos ecológicos envolvendo plantas aquáticas cresceram substancialmente nos últimos anos. Entretanto, uma visão precisa das pesquisas sobre macrófitas na região Neotropical é necessária para uma avaliação confiável da produção científica. No presente estudo, uma análise cienciométrica sobre macrófitas Neotropicais foi realizada com o intuito de identificar os principais padrões e lacunas nas pesquisas sobre esse grupo biológico. As publicações sobre macrófitas na região Neotropical cresceu conspicuamente nas últimas duas décadas. Brasil, Argentina, México e Chile foram os mais produtivos dentre os países Neotropicais. As análises mostraram que os estudos enfocaram principalmente as influências das macrófitas nos organismos e nas características abióticas. Estudos com uma abordagem preditiva ou testando hipóteses ecológicas são escassos. Adicionalmente, pesquisas com o objetivo de descrever espécies desconhecidas ainda são necessárias. Isso é essencial para subsidiar esforços de conservação e investigações futuras testando hipóteses ecológicas.

Effects of temperature on decomposition of a potential nuisance species: the submerged aquatic macrophyte Egeria najas planchom (Hydrocharitaceae)

Inúmeros fatores bióticos e abióticos influenciam a decomposição de plantas aquáticas, destacando-se, entre eles, a temperatura. Apesar do grande número de estudos descrevendo os efeitos da temperatura sobre a decomposição de macrófitas aquáticas, pouca atenção tem sido dada à decomposição de espécies submersas. O objetivo do presente trabalho foi avaliar o efeito da temperatura sobre a perda de peso e composição química do detrito da macrófita aquática submersa Egeria najas Planchon (Hydrocharitaceae). O material vegetal fresco foi mantido em temperaturas constantes de 17ºC e 27ºC, no escuro, em uma câmara de incubação. O modelo que melhor descreveu o processo de decomposição foi o modelo linear, com taxas de 0,014 dia-1 (R2 = 94%) e 0,045 dia-1 (R2 = 96%) obtidas às temperaturas de 17ºC e 27ºC, respectivamente. A análise de covariância (ANCOVA) indicou diferença significativa entre as taxas de decomposição nas duas temperaturas estudadas. É possível que o baixo conteúdo de compostos de resistência presentes na planta, como celulose e lignina, seja o responsável pela alta taxa de decomposição de E. najas, indicada pelo coeficiente de decomposição. As variáveis analisadas (pH, condutividade elétrica, oxigênio dissolvido na água, concentração de matéria orgânica, nitrogênio total e fósforo total no detrito) demonstraram resposta acentuada a 27ºC. Provavelmente, as maiores temperaturas aumentam a atividade microbiana, aumentando, assim, o consumo de oxigênio na água e, conseqüentemente, afetando o pH e a taxa de liberação de íons e nutrientes para o ecossistema aquático. Em razão da rápida decomposição de E. najas em altas temperaturas, espera-se uma baixa taxa de exportação dessa espécie de seus estandes para regiões distantes em reservatórios tropicais, onde é considerada uma espécie potencialmente daninha.

Microbial respiration and chemical composition of different sediment fractions in waterbodies of the upper Paraná River floodplain, Brazil

Four size fractions of the sediment of six environments of the upper Paranß River floodplain were analyzed for carbon, nitrogen, and phosphorus contents and microbial respiration (oxygen consumption). Particle size did not affect nitrogen and phosphorus content or microbial activity, but did affect carbon content (F = 4.274, df = 3; 20, p = 0.020). The carbon concentration of ultra-fine particles was significantly lower than that of other sizes of sediment particles. Microbial respiration values were well predicted by sediment chemical composition, as shown by multiple regression (microbial respiration = -0.39 - 0.210C + 0.108N + 0.796P; F = 7.0495, p = 0.0022). However, phosphorus was the element which best explained the microbial respiration (partial coefficient = 0.796, p = 0.0039, n = 23). Considering that i) phosphorus was the best predictor of microbial respiration; ii) phosphorus is trapped in the series of reservoirs located upstream from the section of the floodplain studied; and iii) microbial respiration is a measure of decomposition rates and nutrient cycling, we hypothesize that the long-term accumulation of litter detritus and reduction of nutrient cycling in environments of the upper Paraná River floodplain are probable impacts of this decrease in phosphorus caused by the upstream reservoirs