FundaÃÃo Cearense de Apoio ao Desenvolvimento Cientifico e TecnolÃgico / Os estuÃrios sÃo ecossistemas costeiros semifechados, cuja influÃncia das marÃs se reflete em grandes variaÃÃes dos parÃmetros fÃsico-quÃmicos e, conseqÃentemente, na distribuiÃÃo e flutuaÃÃo da abundÃncia das comunidades aquÃticas. Como estÃo sujeitos a receber nutrientes em excesso, em geral provenientes das Ãguas residuÃrias, podendo entrar em processo de eutrofizaÃÃo que pode ser benÃfico ou tornÃ-lo um corpo dâÃgua imprÃprio para qualquer atividade humana. Este trabalho teve por objetivo analisar a ocorrÃncia sazonal de bioindicadores fitoplanctÃnicos de qualidade da Ãgua no estuÃrio do rio Catu, Aquiraz, CearÃ, verificando as variaÃÃes da produtividade primÃria e dos parÃmetros fÃsico-quÃmicos aos quais esta ocorrÃncia està geralmente associada. Coletas mensais foram realizadas de janeiro a dezembro de 2005, na regiÃo da barra do rio Catu para obtenÃÃo dos dados de temperatura da Ãgua e do ar, transparÃncia, profundidade, salinidade, pH, amÃnia, nitrito, oxigÃnio e CO2 dissolvido, fosfato e silicato, bem como, do material biolÃgico. Os resultados mostraram que, com exceÃÃo dos valores de amÃnia, nitrito, fosfato e silicato, os demais parÃmetros ambientais se encontravam dentro dos padrÃes recomendados. A produtividade primÃria foi considerada muito baixa. Foram identificadas 19 famÃlias e 32 gÃneros, sendo possÃvel a identificaÃÃo de 12 organismos atà o tÃxon espÃcie. Estes representeantes do fitoplÃncton estÃo inseridas nas classes Cyanophyceae, Chlorophyceae, Baccillariophyceae, Dinophyceae, Zygnemaphyceae, Chlamydophyceae, em que as Cyanophyceae foram as mais abundantes no perÃodo chuvoso e as Baccillariophyceae as mais abundantes no perÃodo seco. A espÃcie Anabaena cylindrica foi dominante no perÃodo chuvoso e todas as outras espÃcies foram raras. No perÃodo seco Navicula sp. foi classificada como sendo abundante, jà Nitzschia sp. e Anabaena cylindrica foram pouco abundantes, sendo as demais classificadas como raras. As condiÃÃes fÃsico-quÃmicas, a presenÃa de indicadores biolÃgicos do fitoplÃncton, alÃm dos blooms registrados de Anabaena cylindrica, mostraram que as Ãguas estuarinas apresentavam um estado avanÃado de eutrofizaÃÃo artificial / The estuaries are semi closed coastal ecosystems, which reflect a great variation of the physical-chemical parameters influenced by the tides and, consequently, reflecting on the distribution and flotation of the abundance of the aquatic communities. Since they are subjected to excessive nutrition, which generally comes from wastewater, they are able to start an eutrophication process which can be beneficial or they can turn into an inappropriate body of water for any human activity. This paper objected to analyze the seasonal occurrence of phytoplankton bioindicators of the water quality in the estuary of the Catu River, Aquiraz, CearÃ, verifying the variations of the primary productivity and the physical-chemical parameters to which this occurrence is generally associated to. Monthly collections were held from January until December 2005, in the region of CatuÂs River mouth in order to obtain the data referring to the water and air temperature, transparency, depth, salinity, pH, ammonia, nitrite, oxygen and dissolved CO2, phosphate and silicate, as well as, data from the biological material. The results showed that, with the exception of the ammonia values, nitrite, phosphate and silicate, the other environmental parameters were found under the recommended patterns. The primary productivity was considered to be very low. 19 families and 32 genera were identified, making the identification of 12 species possible up to the taxon species. These phytoplankton representatives are inserted in the Cyanophyceae, Chlorophyceae, Baccillariophyceae, Dinophyceae, Zygnemaphyceae, Chlamydophyceae classes, in which the Cyanophyceae were the most abundant in the rainy season and the Baccillariophyceae were more abundant in the dry seasons. The Anabaena cylindrica was dominant in the rainy season and all the other species were rare. In the dry season Navicula sp. was classified as abundant and Nitzschia sp. and Anabaena cylindrica were not so abundant. The physical-chemical conditions, the presence of biological indicators of the phytoplankton, besides the registered blooms of Anabaena cylindrica, showed that the estuarine waters presented an advanced state of artificial eutrophication

As águas continentais existem em menor quantidade na superfície terrestre e apresentam grande importância para a sobrevivência dos seres vivos, motivo pelo qual a preocupação com sua qualidade aumenta a cada dia. As represas de Paraibuna e Paraitinga, localizadas no município de Paraibuna, São Paulo, totalizam 224 km2 de extensão de espelho d´água, com função atual de geração de energia elétrica. Com o objetivo de analisar a qualidade da água destas represas, o presente trabalho apresenta um diagnóstico físico, químico, bem como biológico, no qual foi utilizada a comunidade fitoplanctônica e cálculos de índices de qualidade. Foram realizadas quatro coletas em nove pontos de amostragem distribuídos ao longo das represas. As análises físicas e químicas da água demonstraram baixas concentrações de nutrientes como nitrato (média 0,42 +/- 0,23 mg.L-1) e fosfato (<0,05 mg.L-1). A maior parte dos metais e elementos-traço analisados mostraram-se dentro dos limites estabelecidos pela legislação federal. O elemento fósforo apresentou valores acima (média 0,0293 +/- 0,0153 mg.L-1) do estabelecido pela resolução CONAMA 357/05 (0,020 mg.L-1) em todos os pontos de amostragem no mês de maio, porém este fato pareceu não influenciar a densidade fitoplanctônica. Altos valores de oxigênio dissolvido e transparência, baixos valores de turbidez, condutividade e sólidos dissolvidos, pH próximo à neutralidade, em conjunto com altos índices de diversidade e baixos índices de dominância fitoplanctônica, com predomínio de clorofíceas, demonstraram que as represas estudadas ainda mantêm características de ambiente aquático preservado. Porém, a presença, ainda que em baixas densidades, de cianofíceas e a existência de atividades de monocultura e pecuária no entorno destas represas merecem especial atenção no que tange ao seu correto manejo para que não se tornem fatores prejudiciais à qualidade daquelas águas. / The inland waters are less on the Earth\'s surface and are extremely important for the survival of living things, why the concern for quality increases daily. The dams Paraibuna and Paraitinga, located in Paraibuna city, state of São Paulo, totaling 224 km2 of extension of water surface, with the current function of generating electricity. In order to analyze the water quality of these dams, this paper presents a diagnostic physical, chemical, and biological, which was used in the phytoplankton community and calculation of quality indexes. Four samples were taken at nine sampling points distributed along the dams. The physical and chemical analysis of water showed low concentrations of nutrients such as nitrate (mean 0,42 +/- 0,23 mg.L-1) and phosphate (<0,05 mg.L-1). Most metals and trace elements analyzed were within the limit established by federal law. The element phosphorus (mean 0,0293 +/- 0,0153 mg.L-1) is presented above the values established by CONAMA Resolution 357/05 (0,020 mg.L-1) on all sampling points in the month of May, but this fact did not seem to influence the phytoplankton amount. High levels of dissolved oxygen and transparency, low levels of turbidity, conductivity and dissolved solids, pH close to neutrality, together with high diversity and low dominance of phytoplankton, with a predominance of green algae, showed that the dams still retain features of aquatic environment preserved, which suffer little influence of anthropogenic factors. However, the presence, even at low densities, of cyanobacteria and the existence of plantations and livestock activities in the borders of these dams deserve special attention in terms of their correct management to not become harmful factors to the quality of those waters.

Os reservatórios Billings e Guarapiranga integram uma das principais fontes de abastecimento público da cidade de São Paulo, suprindo água para milhões de pessoas. O aporte de nutrientes em corpos hídricos, advindos de efluentes domésticos e industriais, fertilizantes agrícolas, leva à eutrofização das águas propiciando condições ideais para a proliferação do fitoplâncton. Os objetivos do trabalho foram acompanhar a dinâmica da comunidade fitoplanctônica durante um ciclo sazonal e verificar a influência das variáveis físicas e químicas sobre a estrutura dessa comunidade. A maior densidade (ind.mL-1) da comunidade fitoplanctônica em ambos os reservatórios, foi representada por organismos das classes Chlorophyceae e Cyanobacteria, sendo a última dominante no reservatório Billings e abundante no reservatório Guarapiranga. Os fatores ambientais que interferiram na dinâmica da comunidade fitoplanctônica, em ambos os reservatórios, foram elevados valores de temperatura da água, pH e nutrientes. / Billings and Guarapiranga reservoirs are part of the main public water supply of São Paulo city, supplying water to millions of people. The nutrient input to hidric resources from domestic and industrial effluents, fertilizers causes eutrophication, thus creating ideal conditions to phytoplankton blooms to occur. The objectives of the present work were to follow up the phytoplankton community along one seasonal cycle and to identify the influence of physical and chemical parameters of the water on the community structure. The greatest phytoplankton density (ind.mL-1) in both reservoirs was due to individuals of Chlorophyceae and Cyanobacteria classes, the last being dominant in Billings reservoir and abundant in Guarapiranga reservoir, be it rainy or dry season. The environmental factors that interferred in phytoplankton dynamics were high temperature values, pH and nutrients, in both reservoirs.

A represa de Guarapiranga faz parte da sub-bacia do alto Tietê e situa-se entre a Região Metropolitana de São Paulo e cidades vizinhas: Itapecerica da Serra e Embu-guaçu, SP (230 43\' S e 46° 32\' W). Sua bacia estende-se ainda pelos municípios de Embu e Cotia. Foi construída em 1906 pela barragem do rio Guarapiranga, com o objetivo de regularizar as vazões contribuintes e ampliar a produção de energia elétrica em Santana do Parnaíba. Em 1926 passou a servir ao abastecimento público e atualmente suas finalidades são: controle de enchentes, geração de energia, recreação e abastecimento. É responsável pelo atendimento da demanda hídrica de 60 por cento da população da Região Metropolitana de São Paulo, sendo o segundo sistema produtor da Companhia de Saneamento Básico do Estado de São Paulo, suprindo 21 bairros da cidade de São Paulo e também Taboão da Serra, Osasco e Carapicuíba. Nas últimas décadas a qualidade de suas águas vem sendo submetida a séria deterioração, em virtude da intensa ocupação e usos inadequados do solo de sua bacia de drenagem, bem como dos crescentes aportes de esgotos, que incrementaram sua eutrofização e o desenvolvimento explosivo da comunidade fitoplanctônica. Este trabalho relata aspectos ecológicos, sanitários e indica ações para um manejo mais adequado da represa de Guarapiranga, a partir da análise da comunidade fitoplanctônica e suas relações com as variáveis ambientais, estudadas no período entre maio de 1991 e julho de 1992. Os dados foram obtidos em campanhas semanais de amostragem em dois pontos da área de água aberta superficial da represa. Neste estudo foram analisadas as características e flutuações da comunidade fitoplanctônica (riqueza, densidade, bioárea, biovolume, diversidade de espécies, uniformidade, estratégias adaptativas, bem como taxas de alteração). Propôs-se um método para avaliação da persistência dos grupos analisados, que mostrou-se eficiente, especialmente para a avaliação sanitária. Foram analisadas simultaneamente as características climatológicas e hidrológicas atuantes na represa e também os aspectos fisicos e químicos da qualidade da água (temperatura, profundidade, transparência, cor, turbidez, condutividade, potencial hidrogeniônico, oxigênio dissolvido, demanda bioquímica de oxigênio, alcalinidade, dureza, teor de sólidos totais em suspensão, fósforo solúvel reativo, fosfato total, nitrogênio amoniacal, nitrato, sulfato, cloreto, cálcio, potássio, silício, sódio, magnésio, manganês, cobre, alumínio, ferro e zinco). Os resultados mostraram a ocorrência de 240 táxons, sendo que as clorococales e as zignemaficeas destacaram-se pela riqueza de espécies. A comunidade demonstrou os efeitos da eutrofização, através da alta produção algácea expressa pelas elevadas densidades e biovolumes, especialmente de espécies indicadoras de eutrofização. Os fatores climáticos e a influência antrópica (expressa pela eutrofização, operação hidráulica e controle algáceo) atuaram como as principais forçantes de alterações da comunidade fitoplanctônica. Os dados obtidos para a estação de coleta mais próxima da barragem e captação de água para abastecimento - denominado ponto 1- mostraram a influência da urbanização de suas margens, e os obtidos na estação mais a montante - ponto 4 - indicaram as influências de desmatamentos recentes. Observou-se que as chuvas promovem entrada de nutrientes e contaminantes, magnificando os resultados da degradação ambiental. Estes ingressos de nutrientes favorecem um maior desenvolvimento algáceo. Entre os efeitos da degradação na qualidade da água, o mais deletério é o ingresso de teores elevados de metais, entre estes o alumínio, citado na literatura médica por sua relação com doenças neurológicas crônicas como o mal de Alzheimer. O risco à saúde humana é discutido neste trabalho. O teor deste metal mostrou correlação negativa com densidade, bioárea e riqueza de espécies do fitoplâncton. A espécie que mais se destacou na represa, em densidade e biomassa, foi Dictyosphaerium ehrenberghianum. Criptoficeas e zignemaficeas mostraram maior taxa de alteração das comunidades, devido às aplicações de sulfato de cobre para o controle algáceo, realizadas na área de captação para abastecimento - ponto 1. Rhizosolenia eiriensis mostrou correlação negativa com o teor aplicado deste algicida, o que pode indicar sensibilidade desta espécie ao controle. Espécies de Mougeotia contribuíram expressivamente para a densidade e o biovolume total das algas em água aberta, durante as fases de maior movimentação, períodos estes de intensa pluviosidade. A estabilidade da comunidade fitoplanctônica foi espressa por algumas fases de equilíbrio verificadas apenas na estação de captação, bem como pela persistência de penales nesta estação e de volvocales na estação a montante. Diatomáceas atingiram seu auge nos períodos de inverno, clorococales e zignemaficeas, no verão. O aumento da disponibilidade de nutrientes por aporte da bacia ou por senescência das algas, especialmente de clorococales e zignemaficeas no verão e a concentração de nutrientes durante a seca mais intensa, favoreceram o desenvolvimento de Cyanophyceae/Cyanobacteria como Aphanocapsa, Synechoccocus, Oscillatoria e Pseudoanabaena. As florações de cianoficeas são discutidas sob o aspecto ecológico e sanitário, incluindo os riscos à saúde humana. As espécies que se destacaram em biovolume ou densidade são, em geral, relatadas na literatura como indicadoras de ambiente eutrofizado. Espécies oportunistas, r-estrategistas tiveram seu desenvolvimento favorecido no ambiente estudado, não sendo encontradas quantidades expressivas de espécies estritamente K-estrategistas. A teoria ecológica que mostrou-se mais adequada, provendo maior quantidade de informação foi a teoria do não equilíbrio, com a aplicação do teste da hipótese do distúrbio intermediário. A qualidade ambiental e em especial a da comunidade fitoplanctônica, foi analisada quanto às características sanitárias. A partir dos resultados obtidos e considerando-se também a realidade atual das forças econômicas, políticas e sociais atuantes, propõe-se medidas de melhoramento do manejo e qualidade ambiental, estabelecendo-se prioridades de curto, médio e longo prazo para sua aplicação. Este estudo permitiu concluir que a represa de Guarapiranga é um ambiente de alta taxa de transferência de matéria e energia que as recebe, transforma em biomassa planctônica e as exporta, configurando-se desta forma uma reciclagem muito intensa. Esta reciclagem intensa e o elevado potencial de autodepuração permitem concluir que ações para o melhoramento da qualidade ambiental podem apresentar resultados favoráveis a curto prazo. A importância da eficiência destas ações relaciona-se ao melhoramento da qualidade da água fornecida à população humana, bem como da qualidade de vida dos usuários da represa. / Guarapiranga reservoir belongs to Tietê basin, is located at the Metropolitan Area of São Paulo City, surrounded by other neighbours small Cities as Itapecerica da Serra and Embuguaçu, SP (23° 43\'S and 46° 32\' W). There are two other towns in its basin, Embu and Cotia. The dam was built in 1906, in the Guarapiranga river, in order to provide electric power and to regulate the flow. It started to supply water to São Paulo City in 1926. Nowadays this reservoir which is the second one of São Paulo State\'s Basic Sanitary Company, provides water to 60 per cent of São Paulo\'s Metropolitan Region population, attending 21 districts of São Paulo and another towns, as Osasco and Carapicuiba. It has beeing also used for electric energy production and people recreation. The water quality decreased in the last decades, due to the intensive people migration from other states, attracted to São Paulo\'s economic development. This demographic growth increased the water\'s as well as the land uses and occupation, the degradation of the basin, and also the explosive development of the algae of its waters. This thesis discuss the ecological and sanitary aspects and indicate adequate management measures, supported by the analysis of the phytoplanktonic community and its relationships with the environmental variables, through data weekly sampled from may 1991 to july 1992. The analysis of the phytoplanktonic community characteristics and flutuations (richness, density, bioarea, biovolume, species diversity, eveness, survivor species strategies, alteration rates, and community stability - testing a new method to evaluate community persistance, which showed to be useful), as well as physical and chemical parameters to evaluate the water quality (temperature, depth, transparency, color, turbidity, conductivity, hidrogenionic potencial, dissolved oxygen, biological oxygen demand, alkalinity, hardness, total suspended solids, and PO4-3, TP, NH4+ NO3-, S04-2, CI-, Al, Ca, Fe, K, Mg, Mn, Na, Si and Zn) were carried out from two surface sampling stations in the open water. The analysis showed 240 species, detaching Chloroccocales and Zignemaphyceae by their richness. The community showed eutrofication effects through the high algae productivity, expressed by density and biovolume, specially of high trophic level indicator species. The climatic events and anthropic influences, showed by the eutrophication and hidraulic management, as well as showed by the algae control through copper sulphate were the major umpelling forces promoting phytoplanktonic community changes. Station 1, which was the closest station to the dam and intake for supply, showed the urbanization influence of the surrounding areas as well as of the copper sulphate applications, which were carried out only in this station. The station 4, upper in the reservoir, showed the effects of recent deforestation in its border region. Among these effects of the water quality degradation, the most deleterious one, is the input of elevated concentrations of heavy metals as aluminum, related in the medical literature, as responsible for Alzheimer\'s disease. These inputs occurred during high pluviosity periods, and they are related to a deforestation recently carried out at the basin. The rainy season, which promoted these nutrient and contaminant inputs, favoured also the intensive phytoplankton growth. Dictyosphaerium ehrenberghianum was the specie which showed the highest density and biovolume. Cryptophyceae and Zignemaphyceae showed higher alteration rates due to the copper sulphate, and Rhizosolenia eiriensis showed negative correlation with the applied concentration of this algicide. Mougeotia species contributed expressively to the density and biovolume in the open water, due to the intensive water movement during the higher pluviosity periods. The stability of the community was attained in some phases in the station 1, the lentic one but never in the station 4, the most lotic one. Pennales showed high persistance in the station 1, and Volvoccales in the station 4, throughout this study. Diatoms attained its higher values in cold-dry periods, in the winter and Chloroccocales and Zygnemaphyceae, during the warmer-wet periods in the summer. The inputs of nutrients from the basin and/or the senescence of the algae, specially Chlorococcales and Zygnemaphyceae in the summer and the ionic concentration during the most intensive dry periods favoured the growth of Cyanophyceae/Cyanobacteria like Aphanocapsa, Synechoccocus, Oscillatoria and Pseudoanabaena spp. The species which showed the highest productivity are often mentioned in the literature as indicators of eutrophication. Oportunistic species, r-strategists had its development favoured in this environment. The ecological theory, which showed to be more useful and gave more information, was the \"non equilibrium\" theory, with the Hipothesis of the Intermmediate Disturbance test. The environmental and phytoplankton qualities and sanitary characteristics were analysed. The results obtained, as well as economic, political and social present forces were considered in order to propose management measures for improvement of the environmental quality, priorized to be applied in short, medium and long time. This study showed that Guarapiranga reservoir is an environment with high level of energy and material transference, receiving, changing it in living biomass, and exporting its contents to other environments, in this case, our homes. The recycling is very fast, therefore any improvement of the sanitary level at the basin and at the water will be reflected immediatly in the distributed water supply, as well as in the life quality of the users.

No description available.

The structure of phytoplankton communities was examined seasonally across five rivers with a focus on small cells and their relative importance. Picophytoplankton (0.2-2 μm), previously considered insignificant in rivers, reached densities as high as those observed in lakes and oceans (~ 10e4-10e5 cells/mL). Their relative importance was not a function of trophic state with the highest contribution to algal biomass found in the most eutrophic river. Body size distributions were analyzed from both chlorophyll-a size fractions and taxonomic enumerations; no significant effect of river or season was detected, suggesting that phytoplankton size distribution is not a useful metric of change in rivers. Unlike lake ecosystems, the rivers were uniformly dominated by small cells (< 20 μm). Taxonomic analyses of the seasonal succession did not reveal a common periodicity of particular divisions (e.g. diatoms). However, strong dominance was more typical of eutrophic rivers even though taxa richness was similar.

In the marine environment, export production leading to the traditional food chain is a relatively rare event taking place primarily in hydrographic features such as frontal areas. When export production persists, massive reproduction of herbivores is expected to occur. Since copepod eggs and nauplii are the main prey of a majority of fish postlarvae, the spawning of dominant fish species is expected to be associated with fronts. The aims of this study were to determine the influence of an estuarine plume front upon the phytoplankton dynamics (distribution and physiological status) and to assess the role of the cross-frontal circulation upon the distribution of fish larvae and their prey. The frontal area under study is located in the northwestern part of the Gulf of St. Lawrence, at the interface between a coastal jet (Gaspe Current) flowing along the Gaspe Peninsula and the Anticosti Gyre. In early June, maximum phytoplankton concentrations (up to 35 μg chl a L⁻¹) were found in the Gaspe Current. In the salinity gradient, a significant correlation was found between salinity and phytoplankton concentrations (and seston in general), indicating that physical processes (vertical and horizontal mixing) were more important in controlling the seston distribution than biological processes. The dominance of physical processes is probably due to the high current velocities and shear stress in the Gaspe Current in early June. Later during the season, the cross-frontal mixing was less vigorous due to the lower freshwater runoff, and the front acted as a retention zone for estuarine plankton. Maximum diatom concentrations (up to 50 μg chl a L⁻¹) were measured in the front per se. Measurements of nitrogen and silicate concentrations (ambient and intracellular) and uptake rates suggested that silicate generally limited diatom growth across the front. In June, estuarine larvae (capelin, Mallotus villosus and sand lance, Ammodytes hexapterus) were concentrated in the diatom-rich Gaspe Current and front where immature copepod stages were abundant. The five-fold increase in immature copepod concentrations between the gyre and the current/front resulted probably from a food-induced increase in copepod reproduction. Thus it appears that the dispersion strategy of the estuarine species in relation with local hydrography favours the exploitation of the resource-rich Gaspe current and front by the first-feeding postlarvae. The extrusion of redfish (Sebastes spp.) larvae appears to be synchronized with the copepod reproduction that followed the gyre April/May bloom. Later, redfish larvae were also found in abundance in the resource-rich front. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

Understanding the impact which grazers have on their prey is of vital importance in understanding how aquatic ecosystems function. In an attempt to contribute to this understanding, this study examined, at three levels, the effects of zooplankton on phytoplankton biomass in Placid Lake in summer. Examination of selective feeding by the major herbivorous zooplankton species in in situ enclosures revealed that single phytoplankton cells in the range of 6-20 μm long were the preferred food of these organisms. Colonial algae, when dominated by the cyanophyte Merismopedia, did not appear to be grazed. The effect of zooplankton biomass on phytoplankton biomass was examined in in situ enclosures. Generally, phytoplankton biomass decreased only in enclosures where initial zooplankton biomass was very low or very high. A simple model based on the classical logistic model of predator-prey interactions was developed to explain events in the enclosures. I concluded that in summer, Placid Lake phytoplankton depend on nutrients remineralized by zooplankton for growth. Grazing appears to be an important regulating mechanism of the phytoplankton standing crop in the spring but not summer. A third level of study involved examination of the responses of phytoplankton to lake perturbation, namely removal of zooplankton, compared to plankton patterns in previous and subsequent years. In years lacking zooplankton manipulation, major increases in zooplankton biomass in mid spring were followed by phytoplankton biomass increases in late spring. During the first harvesting season, July and August 1979, a 50% reduction in zooplankton biomass was obtained. An enormous bloom of the inedible Merismopedia developed. I hypothesized that removal of zooplankton caused a shortage of available biologically reactive nitrogen which became limiting to eukaryotic phytoplankton, allowing Merismopedia, a blue-green alga which may be able to fix nitrogen, to thrive. In summer, the positive effect of zooplankton on phytoplankton via nutrient remineralization appeared to be more significant than the negative effect of grazing. During the second harvesting season, May, June, and July 1980, no decrease in zooplankton biomass was apparent. Instead of the usual pattern of zooplankton biomass increase preceeding the phytoplankton biomass increase, both increases occurred simultaneously. I concluded that harvesting delayed the rise in zooplankton biomass and decreased the grazing pressure on phytoplankton, allowing it to peak earlier. Grazing may thus be significant in spring in slowing phytoplankton growth. Seasonal variations were introduced to the model for the enclosure experiments to help understand the normal plankton patterns in Placid Lake. The time lag between maximum solar radiation and lake temperature, and the effects of these two physical parameters on phytoplankton and zooplankton growth appear to be instrumental in establishing the pattern of plankton biomass dynamics observed in Placid Lake. / Science, Faculty of / Zoology, Department of / Graduate

This thesis presents a quantitative model of interactions among phytoplankton, nutrients, bacteria and grazers in an enclosed marine ecosystem. The enclosed system was a 23 m deep, 9.6 m diameter column of surface water in Saanich Inlet, British Columbia. Dynamics of large- and small-celled diatoms and flagellates in response to observed irradiance and zooplankton numbers and observed or simulated nitrogen and silicon concentrations were modelled over a simulated 76-day period between July 12 and September 26. The model's predictions poorly matched the observed events in Controlled Experimental Ecosystem 2 (CEE2), but nevertheless provided some important insights into system behavior. Ciliate grazing probably prevented small-celled phytoplankton from increasing to large concentrations in CEE2. By virtue of their tremendous numbers, colourless flagellates were potentially the most important grazers on bacteria, much more important than larvaceans or metazoan larvae. Whereas small-celled phytoplankton were limited by grazers, large phytoplankton dynamics were not markedly affected by grazing. The average observed rate of 14C fixation in the surface 8 m was roughly consistent with an interpretation in which artificial additions of nitrogen contributed 62% of inferred net uptake of nitrogen by phytoplankton, mixing from subsurface water contributed 18%, bacterial remineralization 12%, and zooplankton excretion 9%. However, independent observations of rapid activity by microheterotrophs (presumably bacteria) suggested that 1*C fixation considerably underestimated net primary production. This yielded an alternative interpretation in which nutrient additions contributed 46% of inferred net uptake of nitrogen in the surface layer, mixing 13%, bacteria 35%, and zooplankton 7%. Dissolution of silica was responsible for the observed accumulation of silicic acid below 8 m depth in CEE2, but the importance of silica dissolution as a source of Si for diatom growth in the surface 8 m is uncertain. The model's major failing was its assumption of unchanging maximum growth rates of phytoplankton, and unchanging rates of exudation, sinking, and respiration. Physiological parameter values which accounted for the huge bloom of Stephanopyxis in CEE2 could not account for the ensuing collapse. Traditional modelling assumptions of slowly changing internal physiology, although adequate for marine systems dominated by physical factors such as seasonality or water movement, cannot capture the behavior of biologically dominated systems like the enclosed system considered here. / Science, Faculty of / Zoology, Department of / Graduate

No description available.