Made available in DSpace on 2014-12-17T14:01:57Z (GMT). No. of bitstreams: 1 VanessaPM.pdf: 789049 bytes, checksum: e9d13460761970df0bf00132d5df08ec (MD5) Previous issue date: 2008-06-03 / ?This study aimed to describe the spatial and temporal patterns of variation in trophic state and its relation with the structure and dynamics of planktonic community of a large reservoir located in semi-arid tropical region of Northeast Brazil. The reservoir Armando Ribeiro Gon?alves is the biggest reservoir of the Rio Grande do Norte State and is responsible for about 53% of all surface water accumulated in the State. The samples of water and plankton were taken monthly in 10 points distributed throughout the longitudinal axis of the reservoir and over a full hydrological cycle. The samples were collected to determine concentrations of total phosphorus, total nitrogen, chlorophyll a and suspended solids (fixed and volatile) and for determining the composition and abundance of phytoplanktonic and zooplanktonic species. During the study period, the reservoir was characterized as eutrophic and there was no trend of increasing the trophic state of the reservoir in the period of drought. The concentrations of total phosphorus and suspended fixed solids decreased towards the dam while the N:P ratios increased in the same direction due to the reduction in the phosphorus concentrations and relative constancy in the nitrogen concentrations. The N:P ratios observed were indicative of greater limitation by phosphorus than by nitrogen. However, as concentrations of both nutrients were high and the water transparency was very low, with secchi depth usually lower than one meter, it seems likely that the planktonic primary production of the reservoir is more limited by the availability of light than the availability of nutrients. High nutrient concentrations coupled with low availability of light may explain the continuing dominance of filamentous cyanobacteria such as Cylindrospermopsis raciborskii in the plankton of the reservoir.These cyanobacteria are potentially toxic and pose a serious environmental problem because it compromises the water quality for public supply, recreation and fishing when present in high densities as in this study. The mesozooplankton of the reservoir was dominated by the calanoid Notodiaptomus cearensis and the cladoceran Diaphanosoma spinulosum. In general, the structure of zooplankton community seems to be particularly influenced by the spatial variation of cyanobacteria. The results of the regression analyses show that both the chlorophyll a concentrations and the cyanobacteria biovolume were more strongly correlated with the nitrogen than with phosphorus and that the water transparency was more strongly correlated with algal biomass than with other sources of turbidity. The maximum load of phosphorus to attain the maximum permissible concentration of total P in the reservoir was estimated in 63.2 tonnes P/ year. The current external P load to the reservoir is estimated in 324 tonnes P / year and must be severely reduced to improve the water quality for water supply and allow the implementation of aquaculture projects that could contribute to the socio-economic development of the region / ?O presente estudo teve como objetivo descrever os padr?es espaciais e temporais de varia??o do estado tr?fico e sua rela??o com a estrutura e din?mica da comunidade planct?nica de um grande reservat?rio localizado na regi?o tropical semi-?rida do Nordeste Brasileiro. O reservat?rio Armando Ribeiro Gon?alves ? o maior reservat?rio do Estado do Rio Grande do Norte e ? respons?vel pela acumula??o de cerca de 53 % de toda a ?gua doce superficial represada no Estado. As amostragens de ?gua e de pl?ncton foram realizadas mensalmente em 10 pontos de coleta distribu?dos ao longo do eixo longitudinal do reservat?rio e ao longo de um ciclo hidrol?gico completo. As amostras foram coletadas para determina??o das concentra??es de f?sforo total, nitrog?nio total, clorofila a e s?lidos suspensos (fixos e vol?teis) e para determina??o da composi??o e abund?ncia de esp?cies fitoplanct?nicas e zooplanct?nicas. Durante o per?odo de estudo, o reservat?rio caracterizou-se como eutr?fico e n?o houve tend?ncia de aumento do estado tr?fico do reservat?rio no per?odo de estiagem. As concentra??es de f?sforo total e de s?lidos fixos em suspens?o diminu?ram no sentido da montante para a jusante do reservat?rio enquanto que as raz?es N:P aumentaram no mesmo sentido devido ? redu??o nas concentra??es de f?sforo e relativa const?ncia nas concentra??es de nitrog?nio. As raz?es N:P observadas foram indicativas de maior limita??o por f?sforo do que por nitrog?nio. No entanto, como as concentra??es de ambos os nutrientes foram elevadas e a transpar?ncia da ?gua muito reduzida, geralmente n?o ultrapassando um metro de profundidade do disco de Secchi, ? muito prov?vel que a produ??o prim?ria planct?nica do reservat?rio seja mais limitada pela disponibilidade de luz do que pela disponibilidade de nutrientes. Elevadas concentra??es de nutrientes aliadas ? baixa disponibilidade de luz podem explicar a persistente domin?ncia de cianobact?rias filamentosas como Cylindrospermopsis raciborskii, no pl?ncton do reservat?rio. Tais cianobact?rias s?o potencialmente t?xicas e representam um grave problema ambiental pois comprometem a qualidade da ?gua para o abastecimento p?blico, a recrea??o e a pesca quando presentes em elevadas densidades, assim como as observadas neste estudo. O mesozoopl?ncton do reservat?rio foi dominado pelo cop?podo calan?ida Notodiaptomus cearensis e pelo clad?cero Diaphanosoma spinulosum. Em geral, a estrutura da comunidade zooplanct?nica parece ser especialmente influenciada pela varia??o espacial das cianobact?rias. Os resultados das an?lises de regress?o mostram que tanto a clorofila a quanto o biovolume de cianobact?rias estiveram mais fortemente correlacionados com o nitrog?nio do que com o f?sforo e que a transpar?ncia da ?gua esteve mais fortemente correlacionada com a biomassa algal do que com as demais fontes de turbidez. A carga m?xima de f?sforo que pode ser lan?ada no reservat?rio visando manter a concentra??o m?xima de P total permitida foi estimada em 63,2 toneladas P/ano. A carga atual que entra no reservat?rio, estimada em 324 ton P/ano, precisa ser drasticamente reduzida a fim de possibilitar a implanta??o de atividades de piscicultura que contribuiriam para o desenvolvimento s?cio-econ?mico da regi?o