The role of communities associated to a substrate as fundamental components of an aquatic system has been recognized by many authors. Although periphyton has been considered of great importance in shallow lakes, its inclusion in different ecological models has been unusual. Phillips et al. (1978) were the first in considering epiphyton as an internal mechanism leading the system to a change in its state from greater water transparecy to more turbid conditions. In contrast, Scheffer et al. (1993) proposed the Alternative Equilibria Hypothesis (AEH), which considers that a shallow lake can alternate between two states, a Clear Water State (stabilized by the presence of submerged macrophytes) and a Turbid Water State (stabilized by an elevated phytoplankton biomass), excluding in this scheme the periphytic communities. Later only the conceptual model coined by Goldsborough and Robinson (1996, G&R model) emphasizes again the importance of epiphyton as well as that of epipelon and metaphyton by establishing the possibility of occurrence of four states according to the contributions to the total algal biomass of each of the algal taxocenosis. Some analyses of the system’s dynamics have been performed in pampean lakes in the context of the AEH. On the other hand, knowledge regarding periphytic and benthic communities is still poor. We propose as an hypothesis that phytoperiphyton will respond to the occurrence of different equilibria states, displaying, at the same time, strong interrelationships with the phytobenthos as well as with the phytoplankton. On the other hand, we consider the possibility that the phytoperiphytic and phytobenthic assemblages may function as internal mechanisms both, as state change or as state stability factors. Finally, we assess the importance of phytoperiphyton as regards its contributions to the total algal biomass in the context of the G&R model, comparing then the results with those obtained in the case of the AEH. The general objectives of the present investigation are to gather information about the structure and dynamics of the phytoperiphyton and its relationships with environmental factors as well as with the phytobenthon and phytoplankton in a pampean shallow lake; and to analyze phytoperiphytic dynamics under the AEH and the G&R model contexts, evaluating periphytic contributions to the total algal biomass. This investigation was carried out in an seepage shallow lake, Lacombe Lake, which is included in the “Grupo Marginal de lagunas” group in the pericoastal region of Provincia de Buenos Aires. Sampling was performed from July 2001 to June 2002 at four sites according to their exposure to environmental factors and the presence of macrophytes: bulrush beds, (JP and JC); and sites devoided of emergent vegetation but with stands of submerged macrophytes during the growing season (ALe and ALr). J sites and ALe were also representative of deeper zones and ALr of a site near the shore. Environmental variables were measured in situ and water samples were collected for chemical analysis and for plankton identification and quantification, following a vertical profile (excepting in ALr). In the case of phytoperiphyton, bulrush epiphyte samples (epiphyton) were taken following a vertical profile and those of submerged macrophytes were collected from the first 25 cm of the stems. Benthon (epipelon) was sampled using a corer. Aliquots for chemical analysis were also extracted from those samples. Vegetal substrate dynamics was also evaluated during sampling. At the laboratory, concentrations of algal nutrients, of the eight principal ions and of soluble polyphenols, as well as alkalinity and total hardness were measured. Phytoplanktonic, epiphytic and epipelic samples were treated for active a chlorophyll and pheopigment determinations. Organism identification and quantification were made according to standardized and own developed methods. First, variations in biotic and abiotic variables were analyzed for the determination of different equilibrium states occurrence. Three perturbation events were registered: precipitations in August, October and March. All of them involved water level increases and conductivity diminutions. Especially in the first two events, nutrient input from runoff was observed; meanwhile in March the input of water determined the dilution in nutrients concentrations. On the other hand, light conditions improved, particularly from October onwards, when stands of submerged macrophytes developed and a decrease of phytoplankton density and a change in its specific composition was detected. The latter being generated by the dilution effects of water input, the shading of the aquatic plants and algal consumption by cladocerans. March event also involved an improvement of light underwater climate but the increase in the water level affected macrophyte stands which mainly withdrawed to the shallowest zones. As regards phytoplankton, changes in the specific composition were recorded again. The statistic evaluation of these facts in conjunction with the analysis of permanence, resiliency and resistance properties of the dominating taxocenosis leads to interpret in the context of the AEH that two equilibria states occurred in the shallow lake. During the first three months a Turbid Water State developed, given by the phytoplankton domination given by an oscilatorial cyanophyte, minor transparency and relatively higher nutrient concentrations. In October and November the passage between states occurred, thus considering these months as transitional. From December onwards a Clear Water State established given by extended development of stands of submerged macrophytes, greater water transparency and minor nutrient concentrations. Finally, from March to May, given the submerged macrophyte withdrawal to shallowest sectors it can be interpreted that the system oscillated around a clear water state, or else, taking into account changes in the planktonic community, it is suggested that a third different state established, the “mixed phytoplankton” state. It is also suggested that states developed in Lacombe could be alternative. Next, the structure and dynamics of phytoperiphyton on bulrush and submerged macrophytes was analyzed. Vertical spatial and temporal variations of bulrush epiphyton showed to be more important than differences between sites. These variations involved smaller biomass values and a simpler physiognomy during turbid water phase and along the vertical gradient in all sampling occasions. In October, related to better light underwater conditions and the nutrient input, epiphytic biomass increased, principally promoted by species typical of the turbid phase. Nonetheless, a structural change started in this month, driven by herbivores but also by the modification of internal relationships between members of the same taxocenosis (shading and less bare substrate to be colonized). This resulted in the establishment of the characteristic assemblages of the clear water phase. During the first three months domination by stalked diatoms structured the community in a unique stratum, resistant to the less favourable light conditions and resilient to August perturbations. From December onwards Spirogyra species dominated, constituting the upper stratum, followed by Oedogonium species in the middle stratum and diatoms in the lower one. These assemblages were stabilized by mechanisms mainly displayed by the zignematalean taxon (shading, epifitism inhibition), allowing to considerer that they were resilient to March perturbation event (de novo establishment on non previously colonized surfaces). In face of the permanence, resistance and resilience properties showed by the taxocenosis, two different states of bulrush phytoperiphyton are considered: turbid water and clear water assemblages. This temporal pattern appeared less well delimited with depth and showed up later in time. Epiphyton data suggested that both states could be alternative. Differences between sites could be observed in respect to phytoperiphyton growing on submerged macrophytes, but the same temporal pattern showed by bulrush periphyton couldn’t be detected due to a great variability in the data gathered. In the next section, the analysis of the structure and dynamics of the phytobenton was carried out. It was showed that differences between the deepest sampling points and the shallowest site were greater than temporal ones. The composition of the assemblages was scarcely variable in time. The taxocenosis was principally related to the poor light conditions recorded on the sediment surface throughout the entire sampling period, even during the clear water phase. The examination of the specific composition in function of its origin evidenced the influence that the epipelon receives from other taxocenosis, constituting a refuge site for allochthonous taxa during unfavourable situations. The scarce variability of the epipelic fraction is also showed. In this way, it is considered that the taxocenosis maintained itself in only one state, indifferent to state changes in the lake and principally resisting the darkness and bearing to live in the unstable sediments. Subsequently, first the roles of the phytoperiphyton and complementary those of phytobenton, as state change or state stability agents were evaluated. The harmful effect of the phytoperiphyton on submerged macrophytes was probably counteracted by plant ramification production and allelopathy. The evidence suggested that its role as nutrient sequestrator is of minor importance in this case, due to other factors that might have disturbed phytoplankton more intensely than competition with phytoperiphyton. Much evidence supported the role of phytobenton as a source of epiphytic and planktonic species belonging either to turbid and clear water state assemblages. The results did not support the hypothesis that phytobenton may play a role as a sediment-stabilizing factor. On the contrary, it may be perturbating agent. Next, an analysis of the contributions of each community to the total algal biomass in the context of the G&R model was performed. Comparisons with AEH results were also carried out. This leaded to the consideration of the occurrence of the following states in Lacombe Lake: a Lake State consistent with the Turbid Water phase, an Open State consistent with the Clear Water phase and local Dry States in ALr site occurred both during the turbid water phase (July) or the clear water situation (March-April). The substantial contribution of epiphyton especially, that growing on submerged macrophytes, is emphasized. The importance of the discrimination of different fractions of epipelon material according to its origin when evaluating the contributions of each community to total algal biomass is also highlighted. Finally, a new interpretation is presented based on algal taxocenosis dynamics, which incorporates elements from both, the AEH and the G&R model. In conclusion, phytoperiphyton in this pampean shallow lake is strongly affected by the factors that determine the establishment or passage from one equilibrium state to another. These assemblages respond to changes through modifications in their own internal structure. These structures gradually alter with depth, remaining these changes more fully explained by the comparison with phytobenton dynamics. Besides the possible roles that the taxocenosis might undertake as an internal mechanism in the change or stabilization of systems states in different situations other than those encountered during this study, epiphyton importance in the systems context, is principally evidenced by the great contribution that these taxocenosis make to the total algal biomass, constituting the dominant compartment during clear water states. / El rol de las comunidades relacionadas a un sustrato como componentes fundamentales dentro de un sistema acuático ha sido reconocido por varios autores. A pesar de la importancia dada al perifiton en lagos someros, su inclusión dentro de diferentes modelos ecológicos ha sido inusual. Phillips et al. (1978) son los primeros en considerar al epifiton como un mecanismo interno en el pasaje de un estado de aguas transparentes a otro más turbio. En contraste, Scheffer et al. (1993), proponen la Hipótesis de Estados de Equilibrio Alternativos (HEEA) que considera que un lago somero puede alternar entre dos estados, uno de Aguas Claras, (estabilizado por la presencia de macrófitas sumegidas) y otro de Aguas Turbias (estabilizado por la elevada biomasa de fitoplancton), no tomando en consideración a las comunidades perifiticas. Sólo el marco conceptual propuesto por Goldsborough y Robinson (1996, modelo G&R) da nuevamente relevancia al epifiton, incluyendo al epipelon, al metafiton y al fitoplancton dentro de un modelo ecológico, discriminando cuatro estados de acuerdo a la dominancia en la biomasa algal total de alguna de estas taxocenosis. En las lagunas pampeanas se han realizado algunos análisis de la dinámica de los sistemas en el marco de la HEEA. Por otro lado, el conocimiento acerca de las comunidades perifíticas y bentónicas todavía es escaso. Se propone como hipótesis que el fitoperifiton variará de acuerdo a la ocurrencia de los diferentes estados en la laguna (según HEEA), interrelacionándose al mismo tiempo con el fitobenton y el fitoplancton. Por otro lado, también se considera la posibilidad de que tanto los ensambles fitoperifíticos como fitobentónicos sean mecanismos internos en el pasaje o en la estabilización de un estado. Por último, se valora la importancia del fitoperifiton en cuanto a sus aportes a la biomasa algal total en el marco del modelo G&R, realizando comparaciones con los resultados obtenidos en el caso de la HEEA. Los objetivos generales de esta investigación son: obtener información acerca de la dinámica y estructura del fitoperifiton y su relación con factores ambientales así como, también, acerca de sus interrelaciones con el fitobenton y el fitoplancton en una laguna pampeana; y analizar su dinámica en el marco de la HEEA y del modelo G&R valorando los aportes del fitoperifiton a la biomasa algal total. El estudio se realizó en la laguna Lacombe comprendida en el Grupo Marginal de lagunas en la región pericostera de la Provincia de Buenos Aires. Los muestreos se realizaron desde julio 2001 a junio 2002 en cuatro sitios de acuerdo a su grado de exposición a las variables ambientales y la presencia de macrófitas: Juncales (JP y JC); sitios de Aguas Libres con o sin macrófitas sumergidas durante la época de crecimiento (ALe y ALr). Los sitios J y ALe representan, puntos de mayor profundidad y ALr un sitio cercano a la orilla. Siguiendo un perfil vertical (con excepción del sitio cercano a la orilla, ALr) se midieron variables ambientales in situ y se tomaron muestras de agua para realizar análisis químicos del agua y la identificación y la cuantificación del plancton. En el caso del fitoperifiton se tomaron muestras de epifitos sobre junco (epifiton) también en un perfil vertical y en los 25 cm apicales del tallo de plantas sumergidas. El benton (epipelon) fue muestreado con un corer, extrayendo muestras también para realizar análisis químicos de los sedimentos. En el campo también se evaluaron las dinámicas de los sustratos vegetales. En el laboratorio se midieron las concentraciones de nutrientes algales, de los ocho iones principales, de los polifenoles solubles así como también la reserva alcalina y la dureza total. Las muestras de fitoplancton, epifiton y epipelon fueron tratadas para la estimación de clorofila a activa y feopigmentos, y la identificación y cuantificación de organismos según métodos estandarizados y propios. En principio, se analizaron las variables bióticas y abióticas para determinar la ocurrencia de estados de equilibrio en la laguna. Tres eventos principales de perturbación ocurrieron durante el período de estudio: las precipitaciones en agosto, octubre y marzo. Todas ellas involucraron aumentos del nivel hidrométrico y disminuciones en la conductividad. En los dos primeros, especialmente en octubre, se produjo la entrada de nutrientes por escorrentía, en tanto que en marzo el aporte de agua resultó en la dilución de los mismos. Por otro lado, las condiciones lumínicas mejoraron especialmente a partir de octubre, lo que se relacionó con el desarrollo de manchones de macrófitas sumergidas y una menor densidad y composición diferente del fitoplancton. Esto último se produjo por los efectos de dilución de la entrada de agua, el sombreado de las plantas acuáticas y por el pastoreo de cladóceros. El evento de marzo involucró también un mejoramiento de las condiciones de luz en la columna de agua pero, paralelamente, determinó la retracción de los manchones de macrófitas sumergidas hasta zonas más cercanas a la orilla. En el fitoplancton se operaron cambios en la composición específica. La evaluación estadística de estos hechos junto con el análisis de las características de permanencia, resiliencia y resistencia de las taxocenosis dominantes condujeron a interpretar que durante el período de estudio se establecen dos estados de equilibrio según la HEEA. Durante los tres primeros meses se desarrolló un estado de aguas turbias definido por la dominancia del fitoplancton con el predominio de una oscilatorial, menor transparencia y concentraciones de nutrientes relativamente más elevadas. En octubre y noviembre se produjo el pasaje entre estados, considerándose a estos meses como transicionales. De diciembre hasta el final del estudio, se desarrolló un estado de aguas claras definido por la presencia de manchones de macrófitas, mayor transparencia del agua y menores concentraciones de nutrientes. Finalmente, de marzo hasta mayo, dada la retracción de los manchones de macrófitas sumergidas, se puede interpretar que ocurrió una oscilación del sistema alrededor de un estado de aguas claras o, dados los cambios operados en el plancton, un tercer estado “mixed phytoplankton”. Se evidenció que los estados establecidos podrían ser alternativos. Seguidamente se analizaron la estructura y dinámica del fitoperifiton sobre junco y las macrófitas sumergidas. Las variaciones espaciales verticales y temporales en la dinámica del perifiton sobre junco resultaron más marcadas que las espaciales horizontales (entre sitios). Estas variaciones implicaron una menor biomasa y una fisonomía más simple durante la fase de aguas turbias y a lo largo del perfil vertical en todas las fechas. Relacionado con el incremento de la luz en la columna de agua y por la entrada de nutrientes en octubre, la biomasa epifítica aumentó, impulsada por las especies características de la fase turbia. Sin embargo, a partir de ese mes se dió un cambio estructural, generado por el pastoreo pero, también, por la modificación en las relaciones entre los componentes de la taxocenosis (autosombreado y menor disponibilidad de sustrato libre) que desembocó en el establecimiento de los ensambles característicos de la fase clara. Durante los tres primeros meses el predominio de diatomeas pedunculadas conformó una comunidad uniestrato, resistente a una menor disponibilidad de la luz y resiliente frente a las perturbaciones de agosto. De diciembre a febrero se desarrolló un ensamble donde predominan las especies de Spirogyra formando un estrato superior, las de Oedogonium en un estrato medio y las diatomeas en un estrato inferior. Estos ensambles presentaron mecanismos de estabilización dados por los talos de la zignematal (sombreado, inhibición del crecimiento de epifitos secundarios), considerándose resilientes frente a las perturbaciones de marzo (desarrollo de los ensambles en sitios previamente no colonizados). En función de las características de permanencia, resistencia y resiliencia, se diferenciaron dos estados en el fitoperifiton de junco: ensambles de fase turbia y ensambles de fase clara. Este patrón temporal se hizo menos marcado en profundidad y aparece en forma retrasada en el tiempo. Los datos habrían indicado la posibilidad de que ambos estados fuesen alternativos. El fitoperifiton sobre macrófitas sumergidas presentó variaciones definidas en el sentido espacial horizontal (mayor biomasa en sitios más profundos) pero no se detectó un patrón temporal, similar al del perifiton sobre junco, dada la gran variabilidad de los datos obtenidos. En el apartado siguiente se analizaron la estructura y dinámica del fitobenton. Se estableció que las variaciones entre sitios de muestreo fueron más marcadas que las temporales. Los ensambles epipélicos presentaron en general una composición escasamente variable a lo largo del tiempo relacionándose principalmente con la disponibilidad de luz. Ésta fue escasa durante todo el período de estudio por lo que las condiciones de crecimiento para las algas béntonicas no fueron favorables, aún con los cambios de estado en la laguna. El análisis del material en función de su origen evidenció las influencias que esta comunidad recibe desde otros ensambles, siendo un sitio de refugio para organismos alóctonos durante épocas desfavorables. También se evidenció la escasa variabilidad de la fracción epipélica propiamente dicha durante todo el período de estudio. Así, se considera que esta taxocenosis se mantuvo en un solo estado, ajena al pasaje de estado en la laguna, principalmente resistiendo la falta de luz y la inestabilidad de los sedimentos. Posteriormente, se evaluó primeramente el papel del fitoperifiton y, en forma complementaria, el del fitobenton como impulsores del pasaje de estados o como estabilizadores de los mismos en la laguna. El efecto de sombreado del fitoperifiton sobre macrófitas sumergidas probablemente fue contrarrestado por la producción de nuevas ramificaciones de las macrófitas y por alelopatía. Las evidencias señalaron que su rol como secuestradores de nutrientes disponibles para el fitoplancton fue menor en este caso, dado que éste último se halla perturbado por otros factores más que por la competencia con el epifiton. Las evidencias señalaron al epipelon como simiente de especies del epifiton y del fitoplancton tanto pertenecientes a la fase turbia como a la clara. En cambio, los resultados no avalaron su rol como estabilizador de los sedimentos. Al contrario, podría ser una perturbación de éstos. A continuación, se examinaron las contribuciones de las taxocenosis a la biomasa algal total en el marco del modelo G&R. También se realizó la comparación de los resultados con aquellos obtenidos a partir de la HEEA. Se consideró la ocurrencia de un estado Lake State congruente con la fase turbia en la laguna, un estado Open State congruente con la fase clara y estados locales Dry State en ALr tanto en la fase turbia (julio) como en la clara (marzo-abril). Se destacó la substancial contribución del epifiton sobre macrófitas sumergidas. También, se subrayó la importancia de discriminar, en relación con el epipelon, los aportes de cada una de las taxocenosis cuando se evalúan las contribuciones a la biomasa algal total. Finalmente, se ofreció una interpretación basada sobre la dinámica de las taxocenosis algales considerando elementos de la HEEA y del modelo G&R. En conclusión, el fitoperifiton en las lagunas pampeanas fue fuertemente influido por los factores que determinan los estados de equilibrio, respondiendo al cambio de los mismos con la modificación en su estructura interna. Ésta se alteró gradualmente con la profundidad, quedando estos cambios más completamente explicados a través de la comparación con la dinámica del fitobenton. Además de los posibles roles que podría desempeñar como mecanismo interno de pasaje o como estabilizador de estados en situaciones diferentes a las halladas en Lacombe, su importancia en el contexto del sistema se manifiesta en el gran aporte que realiza a la biomasa algal total, constituyendo el compartimiento dominante en los estados de aguas claras.

La presente tesis "estudio de los efectos sobre el medio litoral derivados de la implantación de saneamientos integrales en la costa Cantábrica" pretende evaluar la validez de los diseños ambientales de estos saneamientos integrales como instrumentos predictivos aplicables a la gestión de la calidad de los sistemas acuáticos litorales mediante la realización de estudios dirigidos a analizar la afección que originan los vertidos de aguas tratadas a través del emisario submarino sobre el estado de las aguas costeras, sobre la calidad de los fondos sedimentarios y sobre las comunidades bentónicas establecidas; así como, mediante el análisis de la evolución de la calidad de las masas de agua estuarinas afectadas por los vertidos de tormenta. Los resultados obtenidos han servido para proponer una serie de indicaciones para el diseño de los programas de control operativo planteados en la DMA, a aplicar en las masas de agua afectadas por este tipo de vertidos. / This PhD thesis titled "Effects of coastal sanitations on Cantabrian littoral ecosystems (Bay of Biscay)" was carried out to evaluate the applicability of the environmental design of the sewer systems constructed in the north of Spain to the management of the aquatic ecosystems. This work has analysed the effects caused by the treated effluents discharged by the submarine outfall on the water and sediment quality and on the structure and composition of the hard-bottom benthic communities dwelling the outfall surroundings. On the other hand this study has analysed the recovery of the estuarine ecosystem (water, bacteriology, sediments and benthic organisms) directly affected in the past by the urban effluents and nowadays affected by storm discharges. Results obtained in both surveys have contributed to propose a guidance for the design of the Operative control of the water masses established in the EU Water Framework Directive in the north of Spain.

Vam monitoritzar paràmetres físics i químics, macroinvertebrats bentònics, clorofil·la a, productors primaris i matèria orgànica durant un any (2001-2002) per examinar els efectes d'una font puntual sobre la composició taxonòmica, la estructura de la comunitat, l'organització funcional, la utilització de l'habitat i la estoquiometria al riu la Tordera (Catalunya).Aigües avall de la font puntual, concentració de nutrients, cabal i conductivitat eren majors que al tram d'aigües amunt, mentre que oxigen dissolt era menor. La densitat de macroinvertebrats era més elevada al tram d'aigües avall però la biomassa era similar als dos trams. La riquesa taxonòmica al tram de dalt era un 20% més alt que al tram de baix. Els anàlisis d'ordenació separen clarament els dos trams en el primer eix, mentre que els dos trams presentaven una pauta temporal similar en el segon eix. La similaritat entre els dos trams en composició taxonòmica, densitats i biomasses després de les crescudes d'abril i maig de 2002, indiquen que les pertorbacions del cabal poden actuar com a un mecanisme de reinici de la comunitat bentònica i jugar un paper important per a la restauració d'ecosistemes fluvials.Els dos trams presentaven una biomassa de perifiton, plantes vasculars, CPOM i FPOM similars, mentre que clorofil·la a, algues filamentoses, molses i SPOM eren majors al tram d'aigües avall. La densitat relativa de trituradors era menor sota la font puntual mentre que col·lectors i filtradors van ser afavorits. La biomassa relativa de trituradors també era menor sota la font puntual, però la biomassa de col·lectors i depredadors va augmentar. Les relacions entre densitat de grups tròfics i els seus recursos eren rarament significatives. La relació s'explicava millor amb la biomassa de macroinvertebrats. Els dos trams compartien la mateixa relació per raspadors, col·lectors i filtradors però no per trituradors i depredadors.La densitat i la biomassa de macroinvertebrats es trobaven positivament correlacionades amb la quantitat de recursos tròfics i la complexitat d'habitat, mentre que la riquesa taxonòmica es trobava negativament relacionada amb paràmetres hidràulics. La influència dels substrats inorgànics prenia menor rellevància per a la distribució dels macroinvertebrats. Els anàlisis d'ordenació mostren com les variables del microhabitat de major rellevància eren CPOM, clorofil·la a, algues filamentoses i velocitat. La cobertura de sorra només era significativa per al tram d'aigües amunt i les molses, al d'aigües avall. El número de correlacions significatives entre macroinvertebrats i les variables del microhabitat era més elevat per al tram de dalt que per al de baix, bàsicament per diferències en composició taxonòmica. La biomassa de macroinvertebrats va aportar una informació semblant a la obtinguda per la densitat.Perifiton i molses tenien uns continguts de nutrients similars en els dos trams. Els %C i %N d'algues filamentoses també eren similars en els dos trams però el %P sota la font puntual era el doble que al tram de dalt. Les relacions estoquiomètriques en CPOM, FPOM i SPOM eren considerablement menors sota la font puntual. Els continguts elementals i relacions van ser molt variables entre taxons de macroinvertebrats però no van resultar significativament diferents entre els dos trams. Dípters, tricòpters i efemeròpters presentaven una estoquiometria similar, mentre que el C i el N eren inferiors en moluscs i el P en coleòpters. Els depredadors presentaven un contingut en C i N més elevat que la resta de grups tròfics, mentre que el P era major en els filtradors. Els desequilibris elementals entre consumidors i recursos eren menors en el tram d'aigües avall. A la tardor i l'hivern la major font de nutrients va ser la BOM mentre que a la primavera i a l'estiu va ser el perifiton. / We monitored physical and chemical parameters, benthic macroinvertebrates, chlorophyll a, primary producers, and organic matter for one year (2001-2002) to assess the effect of a point source input on the taxa composition, community structure, functional organization, microhabitat distribution, and elemental stoichiometry in La Tordera stream (Catalonia, NE Spain).Below the point source, nutrient concentrations, discharge, and specific conductance were higher than at the upstream reach, while dissolved oxygen decreased. Total macroinvertebrate density was higher at the downstream reach than at the upstream reach. The two reaches did not differ in macroinvertebrate total biomass. On average, taxa richness at the upstream reach was 20% higher than at the downstream reach. Ordination analysis clearly separated the samples of the two reaches in the first axis and corroborated the effect of the point source on the benthic community. The two reaches followed a similar temporal pattern with respect to the distribution of taxa along the second axis. Higher similarities between the two reaches in taxa composition, densities and biomass after the spates of April and May 2002, suggest that flooding events may act as a reset mechanism for benthic communities and play an important role in stream restoration.The two reaches did not differ in standing stocks of periphyton, vascular plants, CPOM and FPOM. Chlorophyll a, filamentous algae, mosses, and SPOM concentrations were increased by the point source. Relative density of shredders was reduced at the downstream reach, whereas gatherers and filterers were enhanced. Relative biomass of shredders decreased below the point source as well, but gatherers diminished and predators increased. The relationships between density of functional feeding groups and their presumed food resources were rarely significant. The relation between consumers and their food resources was best explained through macroinvertebrate biomass. The two reaches had the same relationship for scrapers, gatherers, and filterers, but differed for shredders and predators.Macroinvertebrate density and biomass were positively correlated with food resources and complexity of habitat architecture while taxa richness was negatively correlated with hydraulic parameters. Inorganic substrate exerted a lesser influence on macroinvertebrate distribution. Ordination analysis revealed that the microhabitat variables of major relevance at the two reaches were CPOM, chlorophyll a, filamentous algae, and maximum water velocity. Sand coverage was only retained at the upstream reach and moss, at the downstream reach. The number of significant correlations between macroinvertebrates and microhabitat variables was higher at the upstream reach than at the downstream reach mainly because of higher taxa richness. Macroinvertebrate biomass provided similar information to that obtained from density in our study case.Periphyton and mosses had similar nutrient contents in the two reaches. The %C and %N filamentous algae was also similar in the two reaches, but %P below the point source was two times higher than that at the upstream reach. Stoichiometric ratios for CPOM, FPOM, and SPOM decreased considerably below the point source. Elemental contents and ratios were highly variable among macroinvertebrate taxa but did not differ significantly between the two reaches, indicating homeostatic regulation. Dipterans, caddisflies, and mayflies had similar elemental contents and stoichiometry, whereas C and N were lower in mollusks and P in beetles. Predators had the higher C and N contents, while %P was higher in filterers and lower in scrapers. Elemental imbalances between consumers and resources were amended at the downstream reach relative to the upstream reach. Macroinvertebrates represented, on average, relatively low nutrient storage in the ecosystem. At the upstream reach, autochthonous production represented the major input of nutrients into the ecosystem food web, whereas the major source of P for heterotrophic production at the downstream reach was represented by allochthonous inputs.

Total phosphorus concentrations in the open waters of the Laurentian Great Lakes are currently at or beneath target concentrations set by international agreement. Despite the success of phosphorus loading controls in remediating nearshore eutrophication problems in the past, nuisance growth of Cladophora has recently returned to the lower Great Lakes. This thesis examines soluble reactive phosphorus (SRP) in a northwestern segment of Lake Ontario to assess whether allochthonous or autochthonous sources of phosphate lead to localized areas of PO43- enrichment that may help to explain the seemingly paradoxical resurgence of Cladophora. As SRP is often an overestimate of PO43- in P-limited waters, measures of SRP made with the standard method were compared with measures of SRP made with modified methods (i.e., using dialysis and magnesium-induced co-precipitation) designed to more accurately measure phosphate when it was expected to be at low concentrations. Measures of SRP made with standard and modified methods did not differ, however, SRP was 1 to 3 orders of magnitude higher than a more sensitive steady-state radiobioassay for PO43- used for comparison in offshore waters. Although the utility of SRP is limited when phosphate concentrations are very low, SRP is useful to measure localized areas of phosphate enrichment, and its relative concentrations can be compared in time and space. To quantify the degree to which allochthonous inputs and dreissenids contribute to PO43- concentrations that permit Cladophora growth, intensive sampling for SRP was carried out prior to, during and following the Cladophora growing season. SRP was higher in the nearshore than offshore and near the mouth of a large tributary and a treated wastewater outfall than in samples from other locations along the shoreline, but only in the spring and autumn. Phosphate turnover times indicated lower P-limitation in the nearshore and near local inputs versus the offshore. Higher concentrations of SRP were measured in samples taken 15 cm and 50 cm above dreissenid mussel-beds than in those obtained at corresponding depths over other substrata and from higher up in the water column through the Cladophora growing season, while Chl a concentrations displayed the reverse trend. These results suggest that PO43- excreted by dreissenids could be more important in time and space than external inputs in supporting nuisance Cladophora growth in the current nearshore environment. Continued research and monitoring of P dynamics in the nearshore combined with model approaches should better predict whether more stringent P controls would be effective in managing Cladophora growth.

Continental margin sediments play an important role in marine biogeochemical cycles, partly due to high primary production rates and efficient export of organic matter to sediments in margin environments. This thesis presents studies of solute exchange in fine-grained sediments representative of slope and rise environments, and carbon and nitrogen cycling in sandy sediments dominant in continental shelves worldwide. Results of these studies advance understanding of the role of benthic processes on marine ecosystems. In fine-grained sediments, solute exchange by diffusion, biological mixing and bioirrigation can be quantified using in situ flux chambers with inert tracer additions. Mechanistic models of chamber tracer transport across the seabed indicate that in organic-rich sediments, bioirrigation and mixing dominate over a wide range of bottom water oxygen levels, reflecting the patchiness and versatility of benthic macrofaunal communities. Positive correlations between benthic oxygen and tracer fluxes appear site-specific. Reliable chamber volume estimates derived from mechanistic models reveal that empirical fits to chamber tracer datasets may overestimate chamber volume and benthic solute fluxes. The biogeochemistry of sandy, highly permeable sediments that dominate continental shelves is largely unknown because of the difficulty in sampling and studying them under natural conditions. Novel sediment reactors were developed and used to mimic in situ porewater advection and natural sedimentary conditions. Compositional changes of natural seawater, with and without the addition of

Total phosphorus concentrations in the open waters of the Laurentian Great Lakes are currently at or beneath target concentrations set by international agreement. Despite the success of phosphorus loading controls in remediating nearshore eutrophication problems in the past, nuisance growth of Cladophora has recently returned to the lower Great Lakes. This thesis examines soluble reactive phosphorus (SRP) in a northwestern segment of Lake Ontario to assess whether allochthonous or autochthonous sources of phosphate lead to localized areas of PO43- enrichment that may help to explain the seemingly paradoxical resurgence of Cladophora. As SRP is often an overestimate of PO43- in P-limited waters, measures of SRP made with the standard method were compared with measures of SRP made with modified methods (i.e., using dialysis and magnesium-induced co-precipitation) designed to more accurately measure phosphate when it was expected to be at low concentrations. Measures of SRP made with standard and modified methods did not differ, however, SRP was 1 to 3 orders of magnitude higher than a more sensitive steady-state radiobioassay for PO43- used for comparison in offshore waters. Although the utility of SRP is limited when phosphate concentrations are very low, SRP is useful to measure localized areas of phosphate enrichment, and its relative concentrations can be compared in time and space. To quantify the degree to which allochthonous inputs and dreissenids contribute to PO43- concentrations that permit Cladophora growth, intensive sampling for SRP was carried out prior to, during and following the Cladophora growing season. SRP was higher in the nearshore than offshore and near the mouth of a large tributary and a treated wastewater outfall than in samples from other locations along the shoreline, but only in the spring and autumn. Phosphate turnover times indicated lower P-limitation in the nearshore and near local inputs versus the offshore. Higher concentrations of SRP were measured in samples taken 15 cm and 50 cm above dreissenid mussel-beds than in those obtained at corresponding depths over other substrata and from higher up in the water column through the Cladophora growing season, while Chl a concentrations displayed the reverse trend. These results suggest that PO43- excreted by dreissenids could be more important in time and space than external inputs in supporting nuisance Cladophora growth in the current nearshore environment. Continued research and monitoring of P dynamics in the nearshore combined with model approaches should better predict whether more stringent P controls would be effective in managing Cladophora growth.

Processes during the meroplanktonic phase regulate population dynamics for many marine benthic invertebrates. I examined changes in vertical distribution of different meroplanktonic larvae in a coastal embayment during a stable period, at high temporal frequencies and spatial resolutions. Plankton samples were collected at 6 depths (3, 6, 9, 12, 18, 24 m) using a pump, every 2-h over a 36- and a 25-h period, during a spring and neap tide, respectively, concurrently with measures of temperature, salinity, fluorescence and current velocity. For 10 gastropod taxa, larval vertical distribution was mostly related to the thermal structure of the water column. Each of 7 taxonomic groups was found either exclusively near the surface, associated with the fluorescence maximum, or showed diel changes in distribution. These larvae that occupy different depths in the water column exhibit different dispersal potentials. / Biogeographical data contained in this thesis will be submitted to the Oceanographic Biogeographic Information System (OBIS) and may be accessed on-line at http://www.iobis.org

Global warming is forecast to cause significant thawing of the permafrost that surrounds lakes and rivers across the Arctic, with potential wide-scale effects on the water quality and biotic characteristics of these water bodies. The benthic environment is believed to be especially sensitive to permafrost-induced ecological change, and this has been the focus of recent field intensive research. Five lakes disturbed and three lakes undisturbed by retrogressive permafrost thaw slumps were sampled during late summer of 2006 to assess the potential effects of slumping on benthos. Water quality parameters, submerged macrophytes, benthic invertebrates, and sediment were collected. A significant difference (p < 0.05) between disturbed and undisturbed lakes was found for macrophyte, invertebrates, underwater light attenuation, and some sediment variables. The results suggest that thaw slumps can affect submerged macrophyte biomass, benthic invertebrate abundance, and also community structure in upland tundra lakes. Such differences between undisturbed and disturbed lakes are suggested to be related to changes in water column transparency, sediment nutrient availability, soil and terrestrial vegetation loading from the landscape, and changes in slope angle of the littoral zone.

Dans le contexte des nouvelles exigences en termes de qualité des eaux du surface, les modèles hydro-écologiques s'avèrent être des outils indispensables pour compléter notre compréhension du fonctionnement du milieu ou prévoir l'impact sur la qualité de l'eau de nouvelles mesures. L'objectif de cette recherche est de tirer parti de l'outil de modélisation ProSe, et de le faire évaluer afin de compléter la compréhension du fonctionnement biogéochimique de la Seine. Dans une première étape, différents processus biogéochimiques sont implémentés, calibrés et validés indépendamment, grâce à des jeux de données disponibles sur un linéaire de 220 km (de Paris jusqu'à l'estuaire), à différents pas de temps, pour la période 2007-2012. Ces améliorations sont réalisées grâce à l'utilisation directe de résultats expérimentaux, à l'extrapolation de résultats de couplage entre expériences de laboratoire et modélisation biogéochimique, ou encore grâce à l'analyse de mesures haute fréquence in-situ. Le modèle ProSe est ensuite utilisé pour établir un bilan du fonctionnement biogéochimique de la Seine dans cette zone fortement anthropisée. L'effet des processus pélagiques et benthiques sur les différents cycles biogéochimiques (carbone, azote, phosphore) est quantifié, pour différentes conditions hydrologiques, en amont et en aval de la plus grosse station d'épuration de l'agglomération parisienne, qui traite les effluents de plus de 5 millions équivalent habitants. La précision spatio-temporelle du modèle est ensuite utilisée pour évaluer l'effet de la fréquence d'échantillonnage sur l'estimation des critères de qualité de l'eau au sens de la Directive Cadre sur l'Eau. Les résultats soulignent l'importance d'une représentation précise des processus physiques (hydrodynamique et processus hydro-sédimentaires) dans les modèles de qualité de l'eau pour parvenir à une simulation fiable des flux biogéochimiques dans le milieu et des échanges entre compartiment benthique et colonne d'eau. Ce travail illustre enfin toute l'utilité des modèles hydro-écologiques pour venir en appui au suivi du milieu dans le cadre des objectifs actuels d'amélioration de la qualité des milieux aquatiques. / Hydro-ecological models are essential to complete our knowledge of the functioning of aquatic systems. They can moreover be used to forecast the impact of new management strategies on the future water quality. The aim of this thesis is to use the hydro-ecological ProSe model to improve our understanding of the biogeochemical functioning of the Seine River downstream the Paris urban area. Simulated biogeochemical processes are first implemented, calibrated, and validated independently for the 2007-2012 period. For each one of these processes, appropriate methodologies are used. These methodologies include the direct use of experimentally obtained parameters, the upscaling of results from coupled laboratory experiments and stand-alone biogeochemical modelling, or the analysis of high frequency in-situ measurements. Different datasets, which are available at various time steps, allow the validation of these processes along the whole 220 km simulated stretch (from Paris to the entrance of the Seine River estuary). Once validated, the ProSe model is then used to assess the biogeochemical functioning of the Seine River along this highly anthropized stretch. The impact of pelagic and benthic processes on the different biogeochemical cycles (carbon, nitrogen, and phosphorus) is quantified for different hydrological conditions, up- and downstream the major waste water treatment plant of the Paris urban area, which treats the effluents of over 5 million population equivalent. The model is then used to assess the effect of the monitoring frequency on the estimation of the water quality as defined by the European Water Framework Directive. The results highlight the importance of a detailed representation of physical processes in hydro-ecological models for a reliable simulation of in-river biogeochemical fluxes and of exchanges at the sediment-water interface. Having in mind the present targets of the improvement of the quality of water bodies, this work illustrates the importance of hydro-ecological modelling as an essential complement to water quality monitoring strategies.

A introdução de espécies exóticas é uma prática que acompanha a história da humanidade, sendo as espécies introduzidas a base da nutrição e economia em vários países. Porém, esse processo contínuo tem levado a uma homogeneização da flora e fauna global. Os ecossistemas aquáticos, que têm recebido menor atenção que os terrestres, têm sofrido perda de diversidade, hibridação, introdução de patógenos, degradação do habitat além da necessidade e alto custo de controle das espécies introduzidas. O desenvolvimento da aqüicultura tem acelerado a introdução de peixes exóticos, que são a base dessa produção em países como o Brasil. Além desta, entre as razões para a introdução citam-se o esporte, a manipulação ecológica com controle de organismos indesejáveis, o melhoramento dos estoques, a ornamentação ou ainda introduções acidentais. No Rio Grande do Sul, nos rios dos Campos de Cima da Serra estão ocorrendo introduções da espécie exótica truta arco- íris (Oncorhynchus mykiss) desde meados da década de 90 como forma de estímulo ao turismo rural. O objetivo dessa prática é a pesca esportiva, que atrai turistas de várias regiões. Porém, os rios da região possuem várias espécies de peixes endêmicas e as conseqüências dessa prática sobre a biota aquática são desconhecidas. O objetivo do presente trabalho é avaliar o efeito da introdução da truta arco-íris sobre o ecossistema de rios de baixa ordem no município de São José dos Ausentes – RS, Brasil. Para tanto foi descrita a biologia da truta arco- íris no novo ambiente, verificando sua alimentação, movimentação, presença e viabilidade da reprodução. A ictiofauna autóctone dos rios com ausência e presença de trutas foi comparada, bem como o efeito da predação sobre a macrofauna bentônica. A ictiofauna foi amostrada com o uso da pesca elétrica, sendo o conteúdo estomacal das trutas avaliado sazonalmente. Três trutas foram marcadas e acompanhadas por ii biotelemetria para determinação da sua área de vida. Um experimento com ninhos artificiais foi conduzido para verificação da sobrevivência de ovos de trutas nas condições dos rios de São José dos Ausentes. O experimento de exclusão de peixes foi feito a fim de avaliar o efeito da predação sobre a macrofauna bentônica, comparando a macrofauna em rios com e sem trutas. Os resultados indicaram que a truta arco- íris tem como alimento principal os invertebrados bentônicos, porém as maiores classes de tamanho incluem peixes em seus alimentos principais. Logo após sua introdução a movimentação é restrita, porém alguns exemplares foram capturados em um rio onde não foi feita introdução dessa espécie. Apesar de baixa, a sobrevivência dos adultos ocorre, assim como a reprodução. A sobrevivência dos ovos também é baixa, porém, uma pós-larva foi encontrada. A ictiofauna autóctone é diferenciada nos rios com presença de truta, apresentando menor riqueza e diversidade e uma tendência a diminuição da biomassa. A macrofauna bentônica também é diferenciada, apesar de não ser possível atribuir essa diferença somente à presença das trutas. / The introduction of exotic species is a practice that accompanies the humanity's history, being the introduced species the base of the nutrition and economy in several countries. Even so, that continuous process has been taking to a homogenization of the global flora and fauna. The aquatic ecosystems, that have been receiving smaller attention than the terrestrial ones, have been suffering diversity loss, hybridization, pathogens introduction, degradation of the habitat and costs of control of the introduced species. The development of aquaculture has been accelerating the introduction of exotic fish, that are the base of that production in countries as Brazil. Among the reasons for the introduction are the sporting fishing, the ecological manipulation with control of undesirable organisms, the improvement of the stocks, the ornamentation or still accidental introductions. In Rio Grande do Sul, in the rivers of Campos de Cima da Serra are occurring introductions of the species exotic rainbow trout (Oncorhynchus mykiss) from middles of the decade of 90 as incentive form to the rural tourism. The objective of that practice is the sporting fishing, which attracts tourists of several areas. Even so, the rivers of the area possess several endemic species of fish and the consequences of that practice on the aquatic biota have been ignored. The objective of the present work is to evaluate the effect of the introduction of the rainbow trout on rivers of low order in the municipal district of São José dos Ausentes - RS, Brazil. Thus the biology of the rainbow trout was described in the new environment, verifying its feeding, movement, presence and viability of reproduction. The autochthonous ictiofauna of the rivers with absence and presence of trouts was compared, as well as the effect of the predation on the benthic macrofauna. The ictiofauna was collected with the use of the electric fishing, being the stomacal content of the trouts evaluated seasonally. Three trouts were marked and accompanied by biotelemetry for determination of its life iv area. An experiment with artificial nests was driven for verification of the survival of eggs of trouts in the conditions of the rivers of São José dos Ausentes. The experiment of exclusion of fish was made in order to evaluate the effect of the predation on the benthic macrofauna, comparing the macrofauna in rivers with and without trouts. The results indicated that the rainbow trout has as main food benthic invertebrates, even so, in larger size classes it include fishes as main food. After its introduction the movement is restricted, even so trout s were found in a river where they were not introduced. Although low, have survival, as well as reproduction. The survival of the eggs is low, but it is happening in Silveira River, a post larvae being found. The autochthonous ictiofauna is differentiated in the rivers with trout presence, presenting smaller richness and diversity. The benthic macrofauna is also differentiated, in spite of not being possible to attribute that difference only to the presence of trouts.