Cyanopeptides occurrence and diversity in a Brazilian tropical reservoir: Exploring relationships with water quality.

Microcystins (MCs) are a class of toxic secondary metabolites produced by some cyanobacteria strains that endanger aquatic and terrestrial organisms in various freshwater systems. Although patterns in MC occurrence are being recognized, divergences in the global data still hamper our ability to predict the toxicity of cyanobacterial blooms. This study aimed (i) to determine the dynamics of MCs and other cyanopeptides in a tropical reservoir, (ii) to investigate the correlation between peptides and potential cyanotoxin producers (iii) identifying the possible abiotic factors that influence the peptides. We analyzed, monthly, eight MC variants (MC-RR, -LA, -LF, -LR, -LW, -YR, [D-Asp3]-RR and [D-Asp3]-LR) and other peptides in 47 water samples collected monthly, all season long, from two sampling sites in a tropical eutrophic freshwater reservoir, in southeastern Brazil. The cyanopeptides were assessed by liquid chromatography-tandem mass spectrometry (LC-MS/MS). The biomass of potential cyanobacterial producers and water quality variables were measured. MCs were detected in both sampling sites year-round; the total MC concentration varied from 0.21 to 4.04 µg L-1, and three MC variants were identified and quantified (MC-RR, [D-Asp3]-RR, -LR). Additionally, we identified 28 compounds belonging to three other cyanopeptide classes: aeruginosin, microginin, and cyanopeptolin. As potential MC producers, Microcystis spp. and Dolichospermum circinalis were dominant during the study, representing up to 75% of the total phytoplankton. Correlational and redundancy analysis suggested positive effects of dissolved oxygen, nitrate, and total phosphorus on MC and microginins concentration, while water temperature appeared to favor aeruginosins. A comparison between our results and historical data showed a reduction in total phosphorus and cyanobacteria, suggesting increased water quality in the reservoir. However, the current MC concentrations indicate a rise in cyanobacterial toxicity over the last eight years. Moreover, our study underscores the pressing need to explore cyanopeptides other than MCs in tropical aquatic systems.

New lake in a changing world: the construction and filling of a small hydropower reservoir in the tropics (Rio de Janeiro, Brazil).

Climate change has affected rainfall patterns in tropical regions, where simultaneous demands for water and energy, habitat loss, declining biodiversity, and spread of invasive species have reflected a rapidly changing world underway. In Brazil, hydropower generation accounts for 64% of the electricity matrix, which presently includes 1007 small hydropower plants (SHPs) having many others under construction or planned. This paper aimed to evaluate changes in water quality, plankton communities, and benthic macroinvertebrates during dam construction, filling, and the first year of operation of a SHP. Suspended solids, turbidity, and silica were variables that highlighted the impact of this construction on the river. Fast changes in water quality (increases in calcium, chlorides, and nitrate) and on aquatic communities (i.e. euglenophyceans and testate amoebae increased in numbers) were detected during the filling phase. Following SHP construction, the concentrations of metals and total phosphorus tended to decrease. Two striking findings observed in the aquatic communities from the riverine conditions to the new lake were the increase in picocyanobacteria abundance, expanding population stocks throughout the river basin, and the constant presence of the invasive mollusc Corbicula fluminea in the macroinvertebrate assemblage, revealing once again its resistance to environmental variability. The lake soon became a natural trap for ions from the drainage basin, as revealed by the increase in electrical conductivity, ammonium, potassium, and magnesium concentrations and the abundance of cyanobacteria, highlighting the need for watershed management to improve ecological conditions in the lake.

Environmental factors affecting chlorophyll-a concentration in tropical floodplain lakes, Central Brazil.

Chlorophyll-a (Chl-a) has been widely used in the assessment and monitoring of aquatic environments. Local and regional factors can influence Chl-a concentrations; moreover, the connection between terrestrial and aquatic ecosystems is a major paradigm within aquatic ecology. Here, we investigate the spatial distribution of Chl-a concentrations in a tropical savannah floodplain in Central Brazil using a broad spatial data set (a 900-km north-south transect; 30 lakes). We determine the relative importance of local environmental variables (limnological and morphometric) and regional (land use) and spatial distances (spatial eigenvector) on Chl-a concentrations using partial linear regression. We evaluate the direct and indirect effects of local and regional variables on Chl-a with a path analysis. Our results indicate spatially autocorrelated patterns wherein lakes in closer proximity showed more similar levels of Chl-a than more distant lakes. Local environmental factors explained most variance in Chl-a (R 2adj = 0.28; P = 0.02); more specifically, both lake area and total nitrogen significantly (P < 0.05) explained Chl-a concentrations (direct effects). Meanwhile, regional factors neither directly nor indirectly predicted Chl-a. Thus, internal processes, such as the resuspension of sediment (which is frequent in tropical floodplains), rather than external influences, were the main factors that explained Chl-a concentrations in this study. The importance of local variables in structuring Chl-a concentration may be used to guide the conservation of the aquatic ecosystems in these tropical floodplain lakes.

Environmental rather than spatial factors structure bacterioplankton communities in shallow lakes along a > 6000 km latitudinal gradient in South America.

Metacommunity studies on lake bacterioplankton indicate the importance of environmental factors in structuring communities. Yet most of these studies cover relatively small spatial scales. We assessed the relative importance of environmental and spatial factors in shaping bacterioplankton communities across a > 6000 km latitudinal range, studying 48 shallow lowland lakes in the tropical, tropicali (isothermal subzone of the tropics) and tundra climate regions of South America using denaturing gradient gel electrophoresis. Bacterioplankton community composition (BCC) differed significantly across regions. Although a large fraction of the variation in BCC remained unexplained, the results supported a consistent significant contribution of local environmental variables and to a lesser extent spatial variables, irrespective of spatial scale. Upon correction for space, mainly biotic environmental factors significantly explained the variation in BCC. The abundance of pelagic cladocerans remained particularly significant, suggesting grazer effects on bacterioplankton communities in the studied lakes. These results confirm that bacterioplankton communities are predominantly structured by environmental factors, even over a large-scale latitudinal gradient (6026 km), and stress the importance of including biotic variables in studies that aim to understand patterns in BCC.

Zooplankton community in fish farming / Comunidades zooplanctônicas em sistemas de criação de peixes

The aim of this study was to evaluate the richness and the abundance and biomass of the zooplankton community of different fish farming systems in the Rio de Janeiro state. In the first stage of the study, 30 fish ponds were analyzed and ten of these were selected for the second stage. The total number of taxa found in the samples was 127: 71 rotifers, 13 cladocerans, seven copepods and 26 protozoans. About the abundance, rotifers predominated in the mostly systems and, in the second stage, the copepods showed higher abundance. Although the rotifers have highlighted the richness and abundance, biomass values were in the majority of low carbon systems (µg C L-1) compared to biomass values presented by cladocerans and copepods in the entire study. The species Brachionus calyciflorus and Moina micrura were associated with higher nitrogenous compounds concentration, and were suggested as indicators of eutrophication of these studied systems.

O objetivo desse estudo foi avaliar a riqueza, abundância e biomassa da comunidade zooplanctônica em sistemas de criação de peixes em diversos municípios do Estado do Rio de Janeiro. As amostragens foram realizadas dentro dos viveiros de criação, sendo que, em uma primeira etapa, 30 sistemas foram analisados e, dentre estes, dez sistemas foram selecionados para uma segunda etapa de estudo. O número total de táxons encontrados nas amostras foi de 127, sendo 71 rotíferos, 13 cladóceros, sete copépodes e 26 protozoários. Os rotíferos foram predominantes na densidade total na maioria dos sistemas na primeira amostragem, e os copépodes, na segunda. Apesar de os rotíferos terem destaque na riqueza e abundância, nos valores de biomassa apresentaram na maioria dos sistemas baixos valores de carbono (µg C L-1) quando comparados aos valores de biomassa apresentados pelos cladóceros e copépodes, em todo o estudo. As espécies Brachionus calyciflorus e Moina micrura foram associadas a maiores concentrações de compostos nitrogenados, sendo sugeridas como indicadoras de eutrofização dos sistemas estudados.

Zooplankton community in fish farming / Comunidades zooplanctônicas em sistemas de criação de peixes

The aim of this study was to evaluate the richness and the abundance and biomass of the zooplankton community of different fish farming systems in the Rio de Janeiro state. In the first stage of the study, 30 fish ponds were analyzed and ten of these were selected for the second stage. The total number of taxa found in the samples was 127: 71 rotifers, 13 cladocerans, seven copepods and 26 protozoans. About the abundance, rotifers predominated in the mostly systems and, in the second stage, the copepods showed higher abundance. Although the rotifers have highlighted the richness and abundance, biomass values were in the majority of low carbon systems (µg C L-1) compared to biomass values presented by cladocerans and copepods in the entire study. The species Brachionus calyciflorus and Moina micrura were associated with higher nitrogenous compounds concentration, and were suggested as indicators of eutrophication of these studied systems.

O objetivo desse estudo foi avaliar a riqueza, abundância e biomassa da comunidade zooplanctônica em sistemas de criação de peixes em diversos municípios do Estado do Rio de Janeiro. As amostragens foram realizadas dentro dos viveiros de criação, sendo que, em uma primeira etapa, 30 sistemas foram analisados e, dentre estes, dez sistemas foram selecionados para uma segunda etapa de estudo. O número total de táxons encontrados nas amostras foi de 127, sendo 71 rotíferos, 13 cladóceros, sete copépodes e 26 protozoários. Os rotíferos foram predominantes na densidade total na maioria dos sistemas na primeira amostragem, e os copépodes, na segunda. Apesar de os rotíferos terem destaque na riqueza e abundância, nos valores de biomassa apresentaram na maioria dos sistemas baixos valores de carbono (µg C L-1) quando comparados aos valores de biomassa apresentados pelos cladóceros e copépodes, em todo o estudo. As espécies Brachionus calyciflorus e Moina micrura foram associadas a maiores concentrações de compostos nitrogenados, sendo sugeridas como indicadoras de eutrofização dos sistemas estudados.

Estrutura da comunidade fitoplanctônica da lagoa de Juturnaíba, Araruama, RJ, Brasil: uma comparaçäo entre o centro da regiäo limnética, tributários e canal de drenagem / Structure of phytoplankton community of lagoa de Juturnaíba, Araruama, RJ, Brazil: a comparison between centrum of limnetical region, tributaries and drainage channel

Foi comparada a estrutura da comunidade fitoplanctônica da regiäo limnética da Lagoa, com seus tributários e seu canal de drenagem. A composiçäo florística, diversidade, equitabilidade, abundância e análise qualitativa da afinidade, mostraram maiores semelhanças entre o centro da Lagoa e seu canal de drenagem, sendo estes diferenciados dos tributários. A análise quantitativa da afinidade separou os ambientes em funçäo das concentraçöes das populaçöes de algas, e evidenciou a formaçäo de grupos de espécies abundantes, onde destacam-se o grupo de espécies de Oscillatoria, exclusivo das estaçöes lóticas, e o grupo de espécies que apresentam uma maior adaptaçäo às variaçöes ambientais