Efeitos da tilápia do Nilo (Oreochromis niloticus) e do enriquecimento por nutrientes sobre a comunidade planctônica em um lago artificial no semi-árido brasileiro

The major aim of this study was to test the hypothesis that the introduction of the Nile tilapia (Oreochromis niloticus) and the enrichment with nutrients (N and P) interact synergistically to change the structure of plankton communities, increase phytoplankton biomass and decrease water transparency of a semi-arid tropical reservoir. One field experiment was performed during five weeks in twenty enclosures (8m3) to where four treatments were randomly allocated: with tilapia addition (T), with nutrients addition (NP), with tilapia and nutrients addition (T+NP) and a control treatment with no tilapia or nutrients addition (C). A two-way repeated measures ANOVA was done to test for time (t), tilapia (T) and nutrient (NP) effects and their interaction on water transparency, total phosphorus, total nitrogen, phytoplankton and zooplankton. The results show that there was no effect of nutrient addition on these variables but significant fish effects on the biomass of total zooplankton, nauplii, rotifers, cladocerans and calanoid copepods, on the biovolume of Bacillariophyta, Zygnemaphyceae and large algae (GALD ≥ 50 μm) and on Secchi depth. In addition, we found significant interaction effects between tilapia and nutrients on Secchi depth and rotifers. Overall, tilapia decreased the biomass of most zooplankton taxa and large algae (diatoms) and decreased the water transparency while nutrient enrichment increased the biomass of zooplankton (rotifers) but only in the absence of tilapia. In conclusion, the influence of fish on the reservoir plankton community and water transparency was greater than that of nutrient loading. This finding suggests that biomanipulation should be a greater priority in the restoration of eutrophic reservoirs in tropical semi-arid regions

Efeito dos nutrientes (nitrogênio e fósforo) sobre o desenvolvimento da Gracilaria birdiae: crescimento e possível uso como biofiltro

Marine shrimp farming has grown exponentially during the last years in Brazil. In spite of the promising economical situation, this activity is facing an increasing criticism due to its environmental impact. Thus, the necessity of alternatives to mitigate environmental degradation caused by this activity. An alternative that is being studied is the policulture that is the integrated culture of two or more organisms, normally one of them a filtering organism. Among filtering organisms, macroalgae are very practicable because they are efficient in the removal of the exceeding nutrients of the water and do not leave residues in the water. Besides, the integrated culture with macroalgae allows the economical exploration of the seaweed (for the manufacture of jelly and jam, for the dairy industry, pharmaceuticals, etc.) along with possibility of a sustainable aquaculture. In the present experiment, the development of the seaweed Gracilaria birdiae, the influence and tolerance of this species to the environmental parameters, and its absorption efficiency in relation with the three kinds of macronutrients (NH4+, NO3- and PO4-3) found in the effluents of marine shrimp farming was studied. The experiment was divided in two parts: a laboratorial part and one part carried under natural conditions. The water used in the laboratory trial was collected in the shrimp ponds of Tecnarão farm and distributed in aquaria containing 20 g of G. birdiae. In the field trial, 0.5 kg of G. birdiae was inserted in PVC cages cultivated in the farm. The results of the study showed a modest growth of G. birdiae, probably due to its low tolerance to highly eutrophicated environments. However, the removal of nutrients was very expressive. Ammonia was reduced in approximately 34 %. Ortho-phosphate showed a reduction of 93.5 %. The capacity of biofiltration of the NO3- by the macro algae was of 100 %, showing that G. birdiae is a seaweed-filtered with a high level of removal for this nutrient under laboratorial conditions. In spite of the low growth of the macro algae in the experiment, the results in relation to the removal of nutrients of the water was encouraging, suggesting that this species can be an efficient biofilter and thus, a strong candidate to be used in a sustainable aquaculture

Utilização da macroalga Ulva lactuca linnaeus na redução de nutrientes (NH4+,NO3- e PO4-2) provenientes da carcinicultura

Dentre as macroalgas capazes de absorver altas concentrações de N e P dissolvidos na água, destaca-se a Chlorophyta Ulva lactuca, bastante adaptável e resistente às adversidades ambientais, como grandes variações de temperatura, salinidade, matéria orgânica e metais pesados. Trata-se também de uma espécie bastante comum nas áreas intertidais do litoral norte-riograndense. Devido a suas características ecológicas, fisiológicas e nutricionais, foi avaliado nesse estudo, o seu potencial como biofiltro na redução de NH4+, NO3- e PO4-2, tanto em condições controladas como também em um viveiro de camarão. No experimento laboratorial, foram utilizados quatro aquários de vidro de 30 x 20 x 20cm com 10L de água, sendo três aquários experimentais contendo 20g de U. lactuca e um controle. O acréscimo de biomassa foi de 2,92g (22,92 ± 6,29g; p < 0,05) em relação ao inóculo inicial de 20g, sob temperatura (28,50 ± 0,58ºC), salinidade (35,00 ± 0,00 ), pH (8,26 ± 0,02) e luz constante (250 μmol.m2s-1). O crescimento positivo (1,78 ± 4,38%dia-1; p < 0,05), juntamente com a alta eficiência de absorção de amônio (83%; p < 0,001), nitrato (83%; p < 0,001) e ortofosfato (53%; p < 0,001), demonstrou que, nessas condições, a Ulva lactuca absorveu os nutrientes e aumentou sua biomassa. Já no experimento de campo, realizado na fazenda TECNARÃO, situada no município de Arez/RN (06° 11 40 Latitude Sul, e 35º 09 37 Longitude Oeste), foram utilizadas três gaiolas de PVC, posicionadas a 12cm da superfície da água, cada uma com dimensões de aproximadamente 59 x 59 x 15cm, onde foram colocadas 200g de U. lactuca. O ganho de biomassa de 3g (203,00 ± 41,02g; p < 0,001) foi muito semelhante às condições controladas, demonstrando a adaptabilidade da espécie em condições ambientais variáveis, onde, apesar da temperatura pouco variável (27,45 ± 0,64ºC), houve progressiva diminuição de salinidade (25 - 15 ), devido ao período de fortes chuvas (34,70 ± 23,78mm). Somado a isso, foram observados vários fatores biológicos interferindo no viveiro, como a presença de epífitas, organismos endofíticos, fouling e a herbivoria por parte dos próprios camarões. Houve aumento nas concentrações de NH4+ (4,36 ± 1,69 μmol.L-1), NO3- (0,17 ± 0,25μmol.L-1) e PO4-2 (0,41 ± 0,13μmol.L-1), coincidindo com o crescimento da espécie até a terceira semana. Todos os parâmetros ambientais analisados, assim como a biomassa e a Taxa de Crescimento Relativo (TCR), obtidos no campo, apresentaram variações altamente significativas (p < 0,001). As correlações observadas entre biomasa e NH4+ (r = 0,82; p < 0,001) e entre biomassa e PO4-2 (r = 0,87; p < 0,001), indicam que esta espécie é capaz de ter um crescimento satisfatório nas condições eutróficas de um viveiro de camarão, sendo possível seu uso como biofiltro.

Estudo do crescimento, eficiência de biofiltração e cinética de absorção de nutrientes (N-NH, N-NO e P-PO4³) da macroalga Gracilaria cervicornis (Turner) J. Agardh

The objective of this study was to examine the growth of Gracilaria cervicornis cultured in a shrimp (Litopenaeus vannamei) pond and to determine the absorption efficiency and the kinetics parameters (Vmax, Ks e Vmax:Ks) of this macroalgae for the nutrients N-NO3-, N-NH4+ and P-PO4-3, aiming at its use as bioremediatory of eutrophicated environments. For this study, two experiments (field and laboratory) were developed. In the field study, the seaweed was examined in relation to the growth and the biomass. In the laboratory experiment, the absorption efficiency of G. cervicornis was measured through the monitoring of the concentration of the three nutrients (N-NO3-, N-NH4+ e P-PO4-3) during 5 hours and the kinetic parameters were determined through the formula of Michaelis-Menten. The results obtained in this study demonstrated that G. cervicornis benefited from the available nutrients in the pond, increasing 52.4% of its biomass value after 30 days of culture. It was evidenced that the variability of the biomass could be explained through the salinity, availability of light (transparency and solid particle in suspension) and concentration of N-NO3- in the environment. In the laboratory experiment, the highest absorption efficiency was found in the treatments with low concentration (5 µmol.L-1), being evidenced a reduction of up to 85,3%, 97,5% and 81,2% of N-NH4+, N-NO3- and P-PO43-, respectively. Regarding the kinetic parameters, G. cervicornis presented better ability in absorbing N-NH4+ in high concentrations (Vmax = 158,5 µmol g-1 dry wt h-1) and P-PO43- in low concentrations (Ks = 5 µmol.L-1 e Vmax:Ks = 10,3). The results of this study show that G. cervicornis could be cultivated in shrimp ponds, presents a good capacity of absorption for the tested nutrients and is a promising candidate for biorremediation in shrimp pond effluent

Interação de microorganismos na solubilização de fósforo e potássio de rochas para produção de biofertilizantes

he present model of agriculture is based on intensive use of industrial inputs, due to its rapid response, but it brings harmful consequences to the environment, and it is necessary the use of modern inputs. And an alternative is the use of rock biofertilizers in agriculture, a product easy to use, with higher residual effect and does not harm the environment. The objective of study was to evaluate the inoculation and co-inoculation of different microorganisms in the solubilization of rock phosphate and potash ground microbial evaluating the best performance in the production of biofertilizers comparing with rocks pure in soil chemical properties and, verify effect of inoculation of the bacterium Paenibacillus polymyxa in the absorption of minerals dissolved in the development of cowpea (Vigna unguiculata [L.] Walp.). The first bioassay was conducted in Laboratory (UFRN) for 72 days in Petri dishes, where the rock powder was increased by 10% and sulfur co-inoculated and inoculated with bacterial suspension of Paenibacillus polymyxa grown in medium tryptone soy broth, Ralstonia solanacearum in medium Kelman, Cromobacterium violaceum in medium Luria-Bertani and Acidithiobacillus thiooxidans in medium Tuovinen and Kelly,and fungi Trichoderma humatum and Penicillium fellutanum in malt extract. Every 12 days, samples were removed in order to build up the release curve of minerals. The second bioassay was conducted in a greenhouse of the Agricultural Research Corporation of Rio Grande do Norte in experimental delineation in randomized block designs, was used 10 kg of an Yellow Argissolo Dystrophic per pot with the addition of treatments super phosphate simple (SS), potassium chloride (KCl), pure rock, biofertilizers in doses 40, 70, 100 and 200% of the recommendation for SS and KCl, and a control, or not inoculated with bacteria P. polymyxa. Were used seeds of cowpea BRS Potiguar and co-inoculated with the bacterial suspension of Bradyrhizobium japonicum and P. polymyxa. The first crop was harvested 45 days after planting, were evaluated in the dry matter (ADM), macronutrients (N, P, K, Ca, Mg) and micronutrients (Zn, Fe, Mn) in ADM. And the second at 75 days assessing levels of macro end micronutrients in plants and soil, and the maximum adsorption capacity of P in soil. The results showed synergism in co-inoculations with P. polymyxa+R. solanacearum and, P. polymyxa+C. violaceum solubilizations providing higher P and K, respectively, and better solubilization time at 36 days. The pH was lower in biofertilizers higher doses, but there was better with their addition to P at the highest dose. Significant reduction of maximum adsorption capacity of phosphorus with increasing dose of biofertilizer. For K and Ca was better with SS+KCl, and Mg to pure rock. There was an effect of fertilization on the absorption, with better results for P, K and ADM with SS+KCL, and N, Ca and Mg for biofertilizers. Generally, the P. polymyxa not influence the absorption of the elements in the plant. In treatments with the uninoculated P. polymyxa chemical fertilizer had an average significantly higher for weight and number of grains. And in the presence of the bacteria, biofertilizers and chemical fertilizers had positive values in relation to rock and control. The data show that the rocks and biofertilizers could meet the need of nutrients the plants revealed as potential for sustainable agriculture

Síntese e caracterização do poli(ácido láctico) para potencial uso em sistemas de liberação controlada de fármacos

With the advances in medicine, life expectancy of the world population has grown considerably in recent decades. Studies have been performed in order to maintain the quality of life through the development of new drugs and new surgical procedures. Biomaterials is an example of the researches to improve quality of life, and its use goes from the reconstruction of tissues and organs affected by diseases or other types of failure, to use in drug delivery system able to prolong the drug in the body and increase its bioavailability. Biopolymers are a class of biomaterials widely targeted by researchers since they have ideal properties for biomedical applications, such as high biocompatibility and biodegradability. Poly (lactic acid) (PLA) is a biopolymer used as a biomaterial and its monomer, lactic acid, is eliminated by the Krebs Cycle (citric acid cycle). It is possible to synthesize PLA through various synthesis routes, however, the direct polycondensation is cheaper due the use of few steps of polymerization. In this work we used experimental design (DOE) to produce PLAs with different molecular weight from the direct polycondensation of lactic acid, with characteristics suitable for use in drug delivery system (DDS). Through the experimental design it was noted that the time of esterification, in the direct polycondensation, is the most important stage to obtain a higher molecular weight. The Fourier Transform Infrared (FTIR) spectrograms obtained were equivalent to the PLAs available in the literature. Results of Differential Scanning Calorimetry (DSC) showed that all PLAs produced are semicrystalline with glass transition temperatures (Tgs) ranging between 36 - 48 °C, and melting temperatures (Tm) ranging from 117 to 130 °C. The PLAs molecular weight characterized from Size Exclusion Chromatography (SEC), varied from 1000 to 11,000 g/mol. PLAs obtained showed a fibrous morphology characterized by Scanning Electron Microscopy (SEM)

Novos sistemas de liberação de fármacos à base de xilana

The aim of this work was to perform the extraction and characterization of xylan from corn cobs and prepare xylan-based microcapsules. For that purpose, an alkaline extraction of xylan was carried out followed by the polymer characterization regarding its technological properties, such as angle of repose, Hausner factor, density, compressibility and compactability. Also, a low-cost and rapid analytical procedure to identify xylan by means of infrared spectroscopy was studied. Xylan was characterized as a yellowish fine powder with low density and poor flow properties. After the extraction and characterization of the polymer, xylan-based microcapsules were prepared by means of interfacial crosslinking polymerization and their characterization was performed in order to obtain gastroresistant multiparticulate systems. This work involved the most suitable parameters of the preparation of microcapsules as well as the study of the process, scale-up methodology and biological analysis. Magnetic nanoparticles were used as a model system to be encapsulated by the xylan microcapsules. According to the results, xylan-based microcapsules were shown to be resistant to several conditions found along the gastrointestinal tract and they were able to avoid the early degradation of the magnetic nanoparticles

Desenvolvimento de microemulsões liofilizadas como um potencial sistema de liberação de fármacos usando planejamento experimental fatorial

Conselho Nacional de Desenvolvimento Científico e Tecnológico

Obtenção de sistemas multiparticulados de isoniazida revestidos com polímero de liberação entérica

Known for thousands of years, tuberculosis (TB) is the leading cause of mortality by a single infectious disease due to lack of patient adherence to available treatment regimens, the rising of multidrug resistant strains of TB (MDR-TB) and co-infection with HIV virus. Isoniazid and rifampicin are the most powerful bactericidal agents against M. tuberculosis. Because of that, this couple of drugs becomes unanimity in anti-TB treatment around the world. However, the rifampicin in acidic conditions in the stomach can be degraded rapidly, especially in the presence of isoniazid, which reduces the amount of available drug for absorption, as well as its bioavailability, contributing to the growing resistance to tuberculostatic drugs. Rifampicin is well absorbed in the stomach because of its high solubility between pH 1 and 2 and the gastric absorption of isoniazid is considered poor, therefore it is mostly intestinal. This work has as objective the development of gastro-resistant multiple-systems (granules and pellets) of isoniazid aiming to prevent the contact with rifampicin, with consequent degradation in acid stomach and modulate the release of isoniazid in the intestine. Granules of isoniazid were obtained by wet method using both alcoholic and aqueous solutions of PVP K-30 as aggregating and binder agent, at proportions of 5, 8 and 10%. The influence of the excipients (starch, cellulose or filler default) on the physical and technological properties of the granules was investigated. The pellets were produced by extrusionesferonization technique using isoniazid and microcrystalline cellulose MC 101 (at the proportion of 85:15) and aqueous solution of 1% Methocel as platelet. The pellets presented advantages over granular, such as: higher apparent density, smaller difference between apparent and compaction densities, smoother surface and, especially, smaller friability, and then were coated with an organic solution of Acrycoat L 100 ® in a fluidized bed. Different percentages of coating (15, 25 and 50%) were applied to the pellets which had their behavior evaluated in vitro by dissolution in acidic and basic medium. Rifampicin dissolution in the presence of uncoated and coated isoniazid pellets was evaluated too. The results indicate that the gastro resistance was only achieved with the greatest amount of coating and isoniazid is released successfully in basic step. The amount of rifampicin in the dissolution medium when the isoniazid pellets were not coated was lower than in the presence of enteric release pellets. Therefore, the polymer Acrycoat L 100 ® was efficient for coating with gastro-resistant function and can solve the problem of low bioavailability of rifampicin and help to reduce its dosage

Micropartículas poliméricas à base de xilana e Eudragit® S-100 contendo mesalazina visando à liberação cólon-específica

Colon-specific drug delivery systems have attracted increasing attention from the pharmaceutical industry due to their ability of treating intestinal bowel diseases (IBD), which represent a public health problem in several countries. In spite of being considered a quite effective molecule for the treatment of IBD, mesalazine (5-ASA) is rapidly absorbed in the upper gastrointestinal tract and its systemic absorption leads to risks of adverse effects. The aim of this work was to develop a microparticulate system based on xylan and Eudragit® S- 100 (ES100) for colon-specific delivery of 5-ASA and evaluate the interaction between the polymers present in the systems. Additionaly, the physicochemical and rheological properties of xylan were also evaluated. Initially, xylan was extracted from corn cobs and characterized regarding the yield and rheological properties. Afterwards, 10 formulations were prepared in different xylan and ES100 weight ratios by spray-drying the polymer solutions in 0.6N NaOH and phosphate buffer pH 7.4. In addition, 3 formulations consisting of xylan microcapsules were produced by interfacial cross-linking polymerization and coated by ES100 by means of spray-drying in different polymer weight ratios of xylan and ES100. The microparticles were characterized regarding yield, morphology, homogeneity, visual aspect, crystallinity and thermal behavior. The polymer interaction was investigated by infrared spectroscopy. The extracted xylan was presented as a very fine and yellowish powder, with mean particle size smaller than 40μm. Regarding the rheological properties of xylan, they demonstrated that this polymer has a poor flow, low density and high cohesiveness. The microparticles obtained were shown to be spherical and aggregates could not be observed. They were found to present amorphous structure and have a very high thermal stability. The yield varied according to the polymer ratios. Moreover, it was confirmed that the interaction between xylan and ES100 occurs only by means of physical aggregation

Micropartículas de poli (ácido lático-co-ácido glicólico) obtidas por spray drying para a liberação prolongada de metotrexato

Methotrexate (MTX) is a drug used in the chemotherapy of some kind of cancers, autoimmune diseases and non inflammatory resistant to corticosteroids uveits. However, the rapid plasmatic elimination limits its therapeutic success, which leads to administration of high doses to maintain the therapeutic levels in the target tissues, occurring potential side effects. The aim of this study was to obtain spray dried biodegradable poly-lactic acid co-glycolic acid (PLGA) microparticles containing MTX. Thus, suitable amounts of MTX and PLGA were dissolved in appropriate solvent system to obtain solutions at different ratios drug/polymer (10, 20, 30 and 50% m/m). The physicochemical characterizing included the quantitative analysis of the drug using a validate UV-VIS spectrophotometry method, scanning electron microscopy (SEM), infrared spectrophotometry (IR), thermal analyses and X-ray diffraction analysis. The in vitro release studies were carried out in a thermostatized phosphate buffer pH 7.4 (0.05 M KH2PO4) medium at 37°C ± 0.2 °C. The in vitro release date was subjected to different kinetics release models. The MTX-loaded PLGA microparticles showed a spherical shape with smooth surface and high level of entrapped drug. The encapsulation efficiency was greater then 80%. IR spectroscopy showed that there was no chemical bond between the compounds, suggesting just the possible occurrence of hydrogen bound interactions. The thermal analyses and X-ray diffraction analysis shown that MTX is homogeneously dispersed inside polymeric matrix, with a prevalent amorphous state or in a stable molecular dispersion. The in vitro release studies confirmed the sustained release for distinct MTX-loaded PLGA microparticles. The involved drug release mechanism was non Fickian diffusion, which was confirmed by Kornmeyer-Peppas kinetic model. The experimental results demonstrated that the MTX-loaded PLGA microparticles were successfully obtained by spray drying and its potential as prolonged drug release system.

Micropartículas de poli (ácido láctico)/ poloxámero obtids por spray drying para liberação modificada de metotrexatro

New drug delivery systems have been used to increase chemotherapy efficacy due the possible drug resistance of cancer cells. Poly (lactic acid) (PLA) microparticles are able to reduce toxicity and prolong methotrexate (MTX) release. In addition, the use of PLA/poloxamer polymer blends can improve drug release due to changes in the interaction of particles with biological surfaces. The aim of this study was developing spray dried biodegradable MTX-loaded microparticles and evaluate PLA interactions with different kinds of Pluronic® (PLUF127 and PLUF68) in order to modulate drug release. The variables included different drug:polymer (1:10, 1:4.5, 1:3) and polymer:copolymer ratios (25:75, 50:50, 75:25). The precision and accuracy of spray drying method was confirmed assessing drug loading into particles (75.0- 101.3%). The MTX/PLA microparticles showed spherical shape with an apparently smooth surface, which was dependent on the PLU ratio used into blends particles. XRD and thermal analysis demonstrated that the drug was homogeneously dispersed into polymer matrix, whereas the miscibility among components was dependent on the used polymer:copolymer ratio. No new drug- polymer bond was identified by FTIR analysis. The in vitro performance of MTX-loaded PLA microparticles demonstrated an extended-release profile fitted using Korsmeyer- Peppas kinetic model. The PLU accelerated drug release rate possible due PLU leached in the matrix. Nevertheless, drug release studies carried out in cell culture demonstrated the ability of PLU modulating drug release from blend microparticles. This effect was confirmed by cytotoxicity observed according to the amount of drug released as a function of time. Thus, studied PLU was able to improve the performance of spray dried MTX-loaded PLA microparticles, which can be successfully used as carries for modulated drug delivery with potential in vivo application

Produção, acúmulo e decomposição da serrapilhadeira e repartição da precipitação pluviométrica por espécies da caatinga

This study aimed to establish patterns of dynamics of litter and redistribution of rainfall of Caatinga vegetation. Sampling was done monthly for twenty three months in four areas: degraded, successional primary stage, secondary stage and late stage. We installed 72 collectors of 1.0 mx 1.0 m, with nylon fabric background in three areas. Litter deposited was fractionated into leaves, twigs, reproductive structures and miscellaneous, dried and weighed. To assess the stock of accumulated litter we used metal frame with dimensions of 0.5 mx 0.5 m, thrown randomly and collected monthly, taken to the laboratory for oven drying and weighed. To evaluate the decomposition, 40g of litter were placed in nylon bags (litterbags) mesh 1 mm ², dimensions 20.0 x 20.0 cm, being distributed on the soil surface and removed monthly, cleaned, dried and weighed. To evaluate the contribution of rainfall we used interceptometers installed 1.0 m above the ground surface, distributed under the canopy of six species of the caatinga, which evaluated the stemflow through collecting system installed around the stems of these species. The deposition of litter in the primary stage was 2.631,26 kg ha-1; 3.144,89 kg ha-1 in the secondary stage; 3.144,89 kg ha-1 in the late stage. The fraction of leaves was the largest contributor to the formation of litter in three stages. The degraded area showed greater accumulation of litter and decomposition has been sluggish during the dry period. We conclude that occurred greater litterfall in later stages. The late successional stage showed faster decomposition of litter, the evidence that is a better use of litter in nutrient cycling processes and incorporation of organic matter to the soil. The time required to decompose 50 % of the litter in the later stages of succession was lower indicating greater speed of release and reuse of nutrients by the vegetation. The specie jurema preta with less leaf area and consists of leaflets, showed greater internal precipitation in rain events of greater magnitude. The stemflow was not influenced by DAP and basal area. The water lost by trapping represented the largest proportion of total rainfall in all species studied

Efeitos de peixes zooplanctívoros e onívoros sobre a resposta de comunidades planctônicas à fertilização por nutrientes

The food chain theory predict that presence of omnivory prevent the trophic cascade and could be a strong stabilizing factor over resource and consumer community dynamics, and that the nutrient enrichment destabilize populations dynamics. Most of the freshwater tropical reservoirs are eutrophic, and strategies that seek improve the water quality through the control of phytoplankton biomass and nutrient input, become essential for the improvement and preservation of water quality. The aim of this study was test the zooplanktivory (when larvae) and omnivory (when young and adult) effects of Nile Tilapia over the structure and dynamics of plankton communities, in addition or absence of nutrients enrichment. For this, one field experiment was performed with a factorial design 2x3 resulting in six treatments: control, without fish and nutrient (C); with omnivorous fish (O); with zooplanktivorous fish (Z); without fish and with enrichment of nutrients (NP); with omnivorous fish and nutrients (ONP); and, with zooplanktivorous fish and nutrients (ZNP). The two planktivory types reduced the zooplankton biomass and increased the phytoplankton biomass, but the omnivory of filter-feeding fish attenuated the trophic cascade magnitude. The fertilization by nutrients increases the nutrient concentrations in water and the phytoplankton biomass, but the effect on zooplankton is dependent of the trophic structure. In a general way, the effects of the fish and nutrient addition were addictive, but significant interactions among those factors were observed in the answer of some zooplankton groups. The effects of omnivorous fish over the temporal variability of phytoplankton and zooplankton biomass were very variable, the increase or reduce in variability of the plankton depending of the level of nutrients and of the analyzed variable. With base in this study, we conclude that the planktivory type exercised by the fish and the concentrations of nutrients in the water affects the force of pelagic trophic cascades and probably the success of biomanipulation programs for the handling of water quality in lakes and tropical reservoirs

Efeitos do enriquecimento com nutrientes (N e P) em diferentes condições de luz sobre o crescimento do fitoplâncton em um reservatório eutrófico no semi-árido brasileiro

The increasing of pollution in aquatic ecosystems in the last decades has caused an expansion of eutrophication and loss of water quality for human consumption. The increase of frequency and intensity of cyanobacteria blooms have been recognized as a major problem connected to water quality and eutrophication. The knowledge of environmental factors controlling these blooms is a key step towards the management for recovering aquatic ecosystems from eutrophic conditions. Primary productivity in aquatic ecosystems is dependent on light and nutrients availability. In the present work we evaluated the relative importance of the concentration of major nutrients, such as phosphorus and nitrogen, and light for phytoplankton growth in the main water reservoir of Rio Grande do Norte State, named Engenheiro Armando Ribeiro Gonçalves (EARG), which is an eutrophic system, dominated by potentially toxic cyanobacteria populations. Limitation of phytoplankton growth was evaluated through bioassays using differential enrichment of nutrients (N and/or P) under two light conditions (low light and high light) and monthly monitoring of chlorophyll-a and nutrients (total nitrogen and phosphorus) concentrations, and water transparency (Secchi depth) at the pelagic region. Our results confirm that EARG reservoir is an eutrophic system with a low water quality. Results of bioassays on the growth of phytoplankton limitation (N or P) were conflicting with the results predicted by the TN:TP ratios, which indicates that these ratios were not a good indicator of algal growth limitation. Nitrogen was the limiting nutrient, considering both frequency and magnitude. Light and hidrology affected phytoplankton response to nutrient enrichment. The extreme eutrophic conditions of this reservoir, dominated by cyanobacteria blooms, demand urgent managing strategies in order to guarantee the multiple uses for this system, including water supply for human population. Although nitrogen is the limiting nutrient, an effective management program must focus on the reduction of both phosphorus and nitrogen input