La destruction par brûlage de munitions chimiques de la Première Guerre Mondiale a provoqué une contamination importante de la partie supérieure du sol du site de la Place-à-Gaz par l’arsenic, le zinc, le cuivre et le plomb. Le traitement thermique a eu pour effet de minéraliser l’As des agents de guerre organoarséniés, et de former un assemblage minéral inattendu composé d’arséniates de Zn, Cu et Fe, et d’une phase amorphe riche en Fe, As, Zn, Cu et Pb. Ce matériel amorphe est la principale phase porteuse de l’As et des métaux dans la zone la plus polluée. Le site est sujet à des changements environnementaux pouvant affecter la stabilité des contaminants inorganiques. Afin d’évaluer l’impact d’épisodes de saturation en eau et de l’apport de matière organique sur les cycles biogéochimiques des métaux et de l’As, une étude en mésocosme a été menée. Les résultats montrent que la phase amorphe est instable en conditions saturées, et libère des contaminants dans l’eau interstitielle du sol. Comme sur le site, les contaminants les plus mobiles sont le Zn et l’As. L’addition de matière organique a induit une immobilisation de l’As, par piégeage de l’As V sur les oxyhydroxydes de fer, dans la partie saturée du sol. La caractérisation du compartiment microbien a été effectuée via des dénombrements, une analyse de la diversité bactérienne et des tests d’activités d’oxydation de l’As III et de respiration et. Les résultats montrent que les microorganismes ont contribué activement au métabolisme du C et de l’As. L’apport de matière organique a promu la croissance des microorganismes As III-oxydants et As Vréducteurs et modifié la structure des communautés bactériennes. Cependant, un effet négatif de la matière organique sur la vitesse d’oxydation de l’As III a été observé, entrainant une augmentation des concentrations d’As III en solution. Cette étude en mésocosme a montré que le dépôt naturel de litière organique a des conséquences antagonistes sur le transfert des contaminants inorganiques. Ces résultats fournissent de plus amples informations sur l’impact environnemental de la Grande Guerre et, de façon plus générale, sur les processus biogéochimiques contrôlant le comportement des métaux/métalloïdes sur les sites pollués. / The thermal destruction of chemical munitions from World War I, on the site of “Place-à-Gaz”, induced intense local top soil contamination by arsenic and heavy metals. The heat treatment mineralized As from organoarsenic warfare agents, resulting in a singular mineral assemblage, composed of Zn, Cu and Fe arsenates and of an amorphous phase rich in Fe, As, Zn, Cu and Pb. The amorphous material was the principal carrier of As and metals in the central part of the site. The site undergoes environmental changes which may alter the stability of inorganic contaminants. To assess the impact of water saturation episodes and input of bioavailable organic matter on the biogeochemical cycles of metal(loid)s, a mesocosm study was conducted. Results showed that amorphous phase was instable in saturated conditions, and released contaminants in soil water. As previously observed on site, the most mobile contaminants were Zn and As. The addition of organic matter induced the immobilization of As by trapping of As V onto hydrous ferric oxides in the saturated soil. Microbial characterizations including counting, bacterial community structure, respiration, and determination of As IIIoxidizing activities were performed. Results showed that microorganisms actively contribute to the metabolisms of C and As.The addition of organic matter induced the increase of As III-oxidizing and As V-reducing microorganisms concentrations and modified the bacterial diversity. However, a negative effect of organic matter on the activity of As III oxidation was observed resulting in higher As III concentration in soil water. This study showed that the natural deposition of forest organic litter on the site, induced antagonist effects on the transfer of inorganic pollutants did not immobilize all the Zn and As and even contributed to As III transport to the surrounding environment. These results provide more information about the environmental impact of the Great War and more generally about the processes driving the behavior of metals/metalloids on polluted sites.

The objective of this work was to understand microbial population density and diversity, both spatially and temporally, in wetland mesocosms to gain a better fundamental understanding for use in the optimization and design of constructed wetlands (CWs). A standardized community level physiological profiling (CLPP) data analysis protocol was adapted and utilized for CW mesocosms. A new one-dimensional metric was developed to track community divergence using BIOLOGTM ECO plate data. The method proved easy to use, did not require a background in multivariate statistics, and accurately described community divergence in mesocosm systems. To study mesocosm biofilm-bound bacterial communities an appropriate detachment protocol was required. Various shaking protocols were evaluated for their effectiveness in the detachment of bacteria from mesocosm pea gravel, with a focus on detachment of viable and representative bacterial communities. A protocol based on mechanical shaking with buffer and enzymes was identified as an optimal approach and used further in this study. The bacterial communities associated with the interstitial water, pea gravel media, and rhizospheric regions from both planted and unplanted CW mesocosms were profiled using the CLPP method and compared. Vertical community stratification was observed for all mesocosm systems. Rhizospheric communities were found to be significantly more active than their gravel-associated counterparts, suggesting that although rhizospheric bacteria were less abundant in the mesocosms they may play a more significant role in the removal and fate of water born contaminants. The start-up dynamics of CW mesocosms was investigated using the CLPP and standard CW characterization methods over an eight month period. All mesocosms showed a steep increase in interstitial community divergence until day 75-100, at which point a steady-state was reached. The interstitial communities were also characterized in terms of similarity based on experimental design treatments (planted/unplanted and origin of seeding inoculum). Four stages were identified during the start-up consisting of an initial stage where mesocosm communities were differentiated based on origin of the inoculum, a period where adjustments and shifts occurred in all mesocosm, a time where all mesocosm communities were quite similar, and a final state where community differentiations were made based plant presence in the mesocosms.

The objective of this work was to understand microbial population density and diversity, both spatially and temporally, in wetland mesocosms to gain a better fundamental understanding for use in the optimization and design of constructed wetlands (CWs). A standardized community level physiological profiling (CLPP) data analysis protocol was adapted and utilized for CW mesocosms. A new one-dimensional metric was developed to track community divergence using BIOLOGTM ECO plate data. The method proved easy to use, did not require a background in multivariate statistics, and accurately described community divergence in mesocosm systems. To study mesocosm biofilm-bound bacterial communities an appropriate detachment protocol was required. Various shaking protocols were evaluated for their effectiveness in the detachment of bacteria from mesocosm pea gravel, with a focus on detachment of viable and representative bacterial communities. A protocol based on mechanical shaking with buffer and enzymes was identified as an optimal approach and used further in this study. The bacterial communities associated with the interstitial water, pea gravel media, and rhizospheric regions from both planted and unplanted CW mesocosms were profiled using the CLPP method and compared. Vertical community stratification was observed for all mesocosm systems. Rhizospheric communities were found to be significantly more active than their gravel-associated counterparts, suggesting that although rhizospheric bacteria were less abundant in the mesocosms they may play a more significant role in the removal and fate of water born contaminants. The start-up dynamics of CW mesocosms was investigated using the CLPP and standard CW characterization methods over an eight month period. All mesocosms showed a steep increase in interstitial community divergence until day 75-100, at which point a steady-state was reached. The interstitial communities were also characterized in terms of similarity based on experimental design treatments (planted/unplanted and origin of seeding inoculum). Four stages were identified during the start-up consisting of an initial stage where mesocosm communities were differentiated based on origin of the inoculum, a period where adjustments and shifts occurred in all mesocosm, a time where all mesocosm communities were quite similar, and a final state where community differentiations were made based plant presence in the mesocosms.

L'écotoxicité de différentes nanoparticules de carbone (NPC) a été évaluée chez des organismes aquatiques, en particulier chez Xenopus laevis. Il a été montré que la surface des NPC est le paramètre le plus pertinent pour décrire l'inhibition de croissance chez le xénope, indépendamment de leur forme allotropique et de leur état de dispersion. L'induction des micronoyaux a aussi été étudiée chez le xénope, et l'oxyde de graphène (GO) s'est révélé génotoxique à faible dose, résultat corroboré par l'étude de l'expression des gènes. Les mécanismes de toxicité impliqués seraient notamment liés aux fonctions oxygénées de la particule. De plus, le GO a aussi entrainé de la génotoxicité chez Pleurodeles waltl. et de la tératogénicité, des retards de développement et de l'inhibition de croissance chez Chironomus riparius. La mise en interaction de ces organismes au sein d'un mésocosme a également conduit à l'observation de génotoxicité chez le pleurodèle en présence de GO. / The ecotoxicity of different carbon-based nanoparticles (CNPs) was assessed in freshwater organisms, especially in Xenopus laevis. The surface of the CNPs was shown to be the more relevant parameter to describe the growth inhibition in Xenopus, regardless of their allotropic form and their state of dispersion. Micronucleus induction was also studied in Xenopus and graphene oxide (GO) was found genotoxic at low dose. This result was in compliance with the study of genes expression. The involved toxicity mechanisms would be related to the oxidized functions of the CNP. Moreover, GO was also found responsible for genotoxicity in Pleurodeles waltl. and for teratogenicity, development delay and growth inhibition in Chironomus riparius. These organisms have finally been put together in a mesocosm, which has also led to genotoxicity in Pleurodeles in the presence of GO.

Une approche in situ et expérimentale sont menées en baie de Marseille. Des mesures simultanées de PB, de RB, de la phosphatase alcaline (phos) et de la protéase (prot) sont réalisées. Des gradients de températures (12-32°C) de ces 4 activités sont effectués. Les résultats montrent que 1) les températures optimales et les Q10 varient saisonnièrement, 2) le BGE ne diminue pas nécessairement lorsque la température augmente et 3) quelles que soit les conditions in situ, l'assemblage bactérien possède un BGE à la température in situ proche de sa température optimale. Des expériences d'enrichissements en PO4 et glucose incubées à température in situ et température in situ + 3°C montrent que la nature de l'interaction entre la température et les ressources est principalement synergétique. L'hypothèse d'un scénario supposant des changements relatifs de PB, prot et phos lors d'un changement de température suggère que les taux prot/PB et phos/PB diminuent lors d'un réchauffement et augmentent lors d'un refroidissement. Enfin, ces expériences témoignent que la température et la disponibilité du PO4 sont les principaux facteurs limitant les activités hétérotrophes. L'étude du mode d'apport de la MO (pulsé ou en continu) menée sur 4 cultures saisonnières montre que selon les conditions environnementales et le mode d'apport de la MO, l'AB, la PB et la RB varient significativement. Toutefois, l'AB, la PB, la RB et le BGE ne montrent pas de différences significatives entre les réservoirs d'ajouts pulsés et d'ajouts continus de MO suggérant des communautés bactériennes peu sensibles à la nature de la perturbation nutritionnelle alors que leurs activités en sont fortement dépendantes. / In this work, in situ and experimental approaches have been carried out in Marseilles' Bay. Simultaneous measurements of bacterial production (BP), bacterial respiration (BR), alkaline phosphatase activity (phos) and protease activity (prot) have been performed. Kinetic temperatures (12-32°C) of these 4 activities have been also conducted. The results demonstrate that i) the optimum temperature and Q10 values vary seasonally, ii) BGE value does not necessarily decrease with increasing temperature and iii) whatever the in situ conditions, the bacterial assemblage has a in situ temperature BGE value close to its optimal temperature. Enrichments experiments in PO4 and glucose incubated at in situ temperature and in situ temperature + 3°C allow to observe that the synergistic nature of the interaction between temperature and resources. The assumption of a scenario assuming that BP, prot and phos changes during a temperature change suggests that prot:BP and phos:BP ratios decrease with a warming and increase with a cooling. Finally, these experiments show that temperature and PO4 availability are the main factors controlling heterotrophic activities. The study on OM availability and associated timing (pulsed or continuous) conducted during 4 seasonal cultures demonstrates that at different seasons and according to the delivery mode of OM, BA, BP and BR are varying significantly. However, the BA, BP and the BR does not show significant differences between the tanks with pulse OM addition and continuous OM addition suggesting that predominant bacterial communities are insensitive to the nature of nutritional disturbance whereas bacterial activities are highly dependent.

Cette thèse a pour but de comprendre les implications des relations entre réseau trophique vert et réseau trophique brun sur la stabilité et le fonctionnement des réseaux trophiques. Les interactions entre ces deux réseaux, respectivement fondés sur la photosynthèse et la consommation de la matière organique morte, sont essentielles au fonctionnement des écosystèmes : l'un produit de la matière organique à partir de nutriments minéraux et l'autre recycle les nutriments contenus dans la matière organique morte. Cette question est abordée à l'aide de deux modèles théoriques et d'une étude expérimentale. Mon premier modèle montre que la boucle de rétroaction induite par le recyclage des nutriments dans un réseau trophique exclusivement vert a un effet stabilisant sur les dynamiques d'une chaîne trophique et un effet enrichissement à cause de la remise à disposition pour les producteurs primaires des nutriments excrétés par l'ensemble des organismes du réseau trophique. Cependant seul l'effet enrichissement, qui est déstabilisant, persiste dans un modèle de réseau trophique. Mon second modèle intègre le réseau brun de manière explicite et montre que ce réseau est davantage déstabilisé que le réseau vert lorsque la disponibilité en nutriments augmente. Cette effet est amplifié si la majeure partie de l'excrétion se fait sous forme de détritus qui déstabilisent le réseau brun par un effet d'enrichissement. Ce modèle montre également que la survie des consommateurs est améliorée lorsqu'ils peuvent consommer des proies provenant des deux réseaux. Mon expérience en mésocosmes aquatiques a permis d'étudier les effets en cascades entre réseaux vert et brun via une filtration de la lumière (manipulation directe du réseau vert), l'ajout de carbone organique dissous (manipulation directe du réseau brun) et l'ajout de poissons (manipulation de la structure du réseau trophique). Nous n'avons pas observé d'effets en cascade du réseau vert sur le réseau brun et inversement, notamment à cause d'un ajout probablement trop faible de carbone dissout. Les poissons ont eux eu un fort effet sur les deux réseaux avec des effets positifs sur le phytoplancton lorsque la lumière est réduite à cause de la diminution de la limitation par les nutriments grâce à l'excrétion des poissons, une augmentation de la concentration en carbone organique dissout et une modification du profil métabolique de la communauté bactérienne benthique. Un modèle annexe montre quant à lui que la plasticité du métabolisme chez les organismes, c'est-à-dire leur capacité à réduire ou à augmenter leur métabolisme en fonction de la disponibilité en ressources afin de maximiser leur bilan énergétique permet de stabiliser les dynamiques d'une chaine trophique en diminuant la variabilité temporelle des biomasses des espèces. Dans un réseau trophique, cette stabilisation se traduit par une augmentation de la persistance des espèces. Cette thèse a permis de mieux relier l'écologie des communautés à l'écologie fonctionnelle, améliorant ainsi notre compréhension des conséquences de grands processus écosystémiques comme le recyclage des nutriments sur la stabilité des réseaux trophiques et des effets de la structure de ces réseaux sur le fonctionnement des écosystèmes. / The aim of this thesis is to understand the implications of the relationships between green and brown food webs on the stability and functioning of food webs. The interactions between these two food webs, based respectively on photosynthesis and the consumption of dead organic matter, are essential for the functioning of ecosystems: one produces organic matter from mineral nutrients and the other one recycles the nutrients contained in dead organic matter. I address this by using two theoretical models and an experimental study. My first model shows that the feedback loop induced by nutrient cycling in an exclusively green food web has a stabilising effect on species dynamics in a food chain and an enrichment effect due to the excretion of nutrients that are available again for primary producers. However, only the enrichment effect, which is destabilising, persists in a food web model. My second model integrates a true brown food web and shows that this food web is more destabilised than the green food web when nutrient availability increases. This effect is amplified if most of nutrients are excreted as detritus that destabilises the brown food web through an enrichment effect. This model also shows that consumer survival is improved when they can consume prey from both green and brown food webs. My experiment in aquatic mesocosms enabled me to study the cascading effects between green and brown food webs thanks to light filtration (direct manipulation of the green food web), the addition of dissolved organic carbon (direct manipulation of the brown food web) and the addition of fish (manipulation of food web structure). We did not observe any cascading effects of the green food web on the brown food web and vice versa, probably because of a too low addition of dissolved carbon. The fish had a strong effect on both green and brown food webs with positive effects on phytoplankton when light is filtered because of the decreased nutrient limitation thanks to fish excretion, an increased concentration of dissolved organic carbon and a change in the metabolic profile of the benthic bacterial community. An additional model shows that the plasticity of metabolic rate, that is the ability of organisms to increase or decrease their metabolic rate depending on resource availability in order to optimise their energy budget, stabilises species dynamics in a food chain model by decreasing biomass time variability. Such a stabilising effect results in increase of species persistence in a complex food web model. This thesis is an additional step to better link community ecology to functional ecology, thus improving our understanding of the consequences on food web stability of major ecosystem processes such as the nutrient cycling and the effects of food web structure on ecosystem functioning.

The University of North Texas Stream Research Facility (UNTSRF) was designed to examine contaminant impacts on effluent-dominated stream ecosystems. Stream mesocosms, fed municipal effluent from the City of Denton, TX, Pecan Creek Water Reclamation Plant (PCWRP), were treated with 0, 15 or 140 µg/L cadmium for a 10-day study in August 2000. Laboratory toxicity test and stream macroinvertebrate responses indicated that cadmium bioavailability was reduced by constituents of effluent-dominated streams. The Biotic Ligand Model (BLM) for Cd was used to predict a 48 hour Cd EC50 for Ceriodaphnia dubia of 280 µg/L in these effluent-dominated streams. This value is higher that an EC50 of 38.3 µg/L Cd and a 7-day reproduction effect level of 3.3 µg/L Cd generated for C. dubia in reconstituted laboratory hard water. These results support use of a cadmium BLM for establishing site-specific acute water quality criteria in effluent-dominated streams. Although not affected by 15 µg/L treatments, organisms accumulated Cd in 15 µg/L treated streams. Hence, over longer exposure periods, Cd accumulation may increase and a no effect level may be lower than the observed 10-day no effect level of 15 µg/L. A toxicity identification evaluation procedure was utilized with in vitro and in vivo bioassays to identify estrogenic compounds in PCWRP effluent, previously identified to seasonally induce vitellogenin (VTG) in male fathead minnows. Steroids, nonylphenol ethoxylate metabolites, and other unidentified compounds were identified as causative effluent estrogens. These findings suggest that in vivo VTG bioassays should be used to confirm in vitro Yeast Estrogen Screening assay activity when effluents are fractionated or screened for estrogenicity. A subsequent 90-day cadmium study was initiated to assess long-term effluent and cadmium effects on fish endocrine function. Juvenile fathead minnows were placed in UNTSRF pool sections of replicate streams treated with 0, 5, 20 or 80 µg/L Cd. Male VTG was induced at each treatment level, indicating that PCWRP effluent was estrogenic during fall 2001. 20 and 80 µg/L Cd treatments reduced male circulating estradiol levels and critical swimming performance. Future studies are needed to assess impacts of environmental estrogen exposure on fish calcium metabolism and vertebral integrity.

Phytoplankton blooms compromise the quality of freshwater ecosystems and the efficient processing of water by treatment works worldwide. This research aims to determine whether in-situ filamentous biofiltration processes mediated by living roots and synthetic filters as media can reduce or remove the phytoplankton loading (micro-algae and cyanobacteria) prior to a potable water treatment works intake. The underlying biofiltration mechanisms were investigated using field and laboratory studies. A novel macroscale biofilter with three plant species, named the "Living-Filter", installed in Farmoor II reservoir, UK, was surveyed weekly for physicochemical and biological variables under continuous flow conditions during 17 weeks. The efficiency of a mesoscale biofilter using the aquatic plant Phalaris arundinacea and synthetic filters, was tested with Microcystis aeruginosa under continuous flow conditions and in batch experiments. The 'simultaneous allelochemical method' was developed for quantifying allelochemicals from Phalaris in aqueous samples. Microscale studies were used to investigate biofilter allelochemical release in response to environmental stressors and Microcystis growth inhibition in filtered and unfiltered aqueous root exudate. Results demonstrate that the removal of phytoplankton biomass by physical mechanisms has a removal efficiency of ≤45% in the "Living-Filter" (filamentous biofilter plus synthetic fabric) and that the removal of Microcystis biomass using only biofilters was 25%. Chemical mechanisms that reduce Microcystis cell numbers are mediated by allelochemicals released from biofilter roots. Root exudate treatments on Microcystis revealed that Microcystis growth is inhibited by allelochemicals, not by nutrient competition, and that protists and invertebrates play a role in removing Microcystis. Filamentous biofilters can remove phytoplankton biomass by physical, chemical and biological mechanisms. Biofilters and synthetic filters in combination improve removal efficiency. Application of macroscale biofilters prior to potable water treatment works benefits the ecosystem. Plant properties, biofilter size to surface water ratio, and retention time must be considered to maximise the benefits of biofiltration processes.

Made available in DSpace on 2014-12-17T14:33:02Z (GMT). No. of bitstreams: 1 MariaMLC.pdf: 1068178 bytes, checksum: 2211aebe12426e9f45d52a507df28c0f (MD5) Previous issue date: 2009-05-29 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / 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 / A teoria de cadeias alimentares prev? que a presen?a de onivoria pode atenuar os efeitos de cascata tr?fica e estabilizar as popula??es de aut?trofos e herb?voros, as quais s?o desestabilizadas pela fertiliza??o por nutrientes. Tendo em vista que muitos lagos e reservat?rios tropicais encontram-se eutrofizados, estrat?gias que visem o controle do aporte de nutrientes e a redu??o da biomassa fitoplanct?nica s?o essenciais para a melhoria da qualidade da ?gua desses ambientes. O presente estudo teve como objetivo avaliar o efeito da zooplanctivoria e onivoria por uma mesma esp?cie de peixe (Til?pia do Nilo), que quando larva ? zooplanct?vora e quando jovem e adulta torna-se filtradora on?vora, sobre a estrutura e din?mica das comunidades planct?nicas, na presen?a e aus?ncia de enriquecimento por nutrientes. Para tanto, foi realizado um experimento com desenho fatorial 2 x 3, resultando em 6 tratamentos: sem adi??o de peixes ou nutrientes (C); com adi??o de peixes zooplanct?voros (Z); com adi??o de peixes on?voros (O); com adi??o de nutrientes (NP); com adi??o de peixes zooplanct?voros e nutrientes (ZNP); e com adi??o de peixes on?voros e nutrientes (ONP). Os resultados mostram que os dois tipos de planct?voros reduziram a biomassa zooplanct?nica e aumentaram a biomassa fitoplanct?nica, mas que a onivoria dos peixes filtradores atenuou a magnitude das cascatas tr?ficas. Os resultados tamb?m mostram que a fertiliza??o por nutrientes aumenta as concentra??es de nutrientes na ?gua e a biomassa fitoplanct?nica, mas que o efeito sobre o zoopl?ncton depende da estrutura tr?fica. De um modo geral, os efeitos da adi??o de peixes e nutrientes foram aditivos, mas intera??es significativas entre esses fatores foram observadas na resposta de alguns grupos zooplanct?nicos. Os efeitos dos peixes on?voros sobre a variabilidade temporal da biomassa do fitopl?ncton e do zoopl?ncton foram muito vari?veis, aumentando ou reduzindo a variabilidade do pl?ncton dependendo do n?vel de nutrientes e da vari?vel analisada. ? poss?vel concluir, com base neste estudo, que o tipo de planctivoria exercido pelos peixes e as concentra??es de nutrientes na ?gua afetam a for?a das cascatas tr?ficas pel?gicas e provavelmente o sucesso dos programas de biomanipula??o para o manejo da qualidade da ?gua de lagos e reservat?rios tropicais