Diagnosis of the phytoplankton community of a reservoir in the semiarid Northeast

O estudo foi realizado no reservatÃrio OrÃs, localizado no estado do Cearà o qual està inserido na regiÃo semiÃrida brasileira. Esta pesquisa teve por objetivo estudar a comunidade fitoplanctÃnica e a variabilidade da qualidade das Ãguas superficiais do reservatÃrio OrÃs, entre os anos de 2008 à 2011, identificando a dinÃmica das classes de maior frequÃncia, bem como as espÃcies de cianobactÃrias mais abundantes existentes nessas Ãguas e seu potencial de risco à saÃde humana. Realizou-se em intervalo bimestral 17 campanhas de coleta em sete pontos do reservatÃrio dos seguintes parÃmetros limnolÃgicos (Clorofila a; transparÃncia; fÃsforo total; nitrato; temperatura e pH), perfazendo um total de 714 amostras (17 campanhas x 7 pontos x 6 parÃmetros). As medidas de transparÃncia, temperatura, bem como o pH foi realizada em campo, enquanto as demais amostras para anÃlise foram coletadas diretamente na Ãgua a 30 cm de profundidade, acondicionadas em frascos previamente lavados e descontaminados (polietileno e vidro Ãmbar) e mantidas resfriadas em caixas tÃrmicas atà o local de anÃlises. De acordo com os resultados as concentraÃÃes de clorofila aumentaram ao longo dos quatro anos de estudos, porÃm ainda se encontram em consonÃncia com os padrÃes do CONAMA, que permite atà 30Âg.L-1 para a classe II. Observa-se o aumento das mÃdias desse atributo com o tempo, enquanto que ocorre o oposto para a transparÃncia. Com relaÃÃo aos nutrientes, o fÃsforo possui um aumento gradativo, tendo uma leve queda em 2010, quando houve menor precipitaÃÃo e consequentemente um baixo escoamento superficial, o mesmo pode-se observar para os valores de nitrato. A temperatura mÃdia da Ãgua esteve entre 28 ÂC e 30 ÂC, indicando que o OrÃs possui Ãguas quentes, caracterÃsticas de regiÃes semiÃridas. Quanto aos valores de pH pode-se notar que sempre estiveram alcalinos, devido o solo deste ambiente ser rico Ãons de bicarbonato. A composiÃÃo do fitoplÃncton foi composta por chlorophyceae, cyanophyceae, bacillariophyceae, euglenophyceae, xantophyceae e zygnemaphyceae, destacando-se chlorophyceae com maior nÃmero de espÃcies e cyanophyceae apesar do nÃmero menor de espÃcies as quantidades de indivÃduos foram sempre superiores aos indivÃduos dos outros grupos. A frequÃncia do grupo de cianobactÃrias chegou entre 50 e 60% das amostras coletadas. TambÃm foramam realizadas as anÃlises quantitativa e qualitativa do grupo de cianobactÃrias, sendo que este grupo foi o que predominou durante o perÃodo de estudo e o mais preocupante à que grande parte de seus indivÃduos sÃo potencialmente tÃxicos. PÃde-se observar que as quantidades de cÃlulas sempre foram superiores as quantidades estipuladas pela resoluÃÃo CONAMA nÂ357/2005. Quando realizou-se a abundÃncia das espÃcies de cianobactÃrias pÃde-se observar que a espÃcie Aphanocapsa sp. foi mais abundante nos trÃs primeiros anos, porÃm foi substituÃda em 2011 pela Planktotrix agardhii, sendo que ambas as espÃcies sÃo consideradas pela literatura como potencial tÃxico.In the semiarid region of Brazil, in addition to water deficit, another serious problem of water availability is limiting water quality due to eutrophication, resulting from the use and occupation of space in the vicinity of water bodies and contributions in the areas of the reservoirs. This study was conducted at Oros reservoir in the state of Cearà which is inserted in the Brazilian semiarid region. This research aimed to study the variability of phytoplankton community and the quality of surface water reservoir OrÃs, between the years 2008 to 2011, identifying the dynamics of the class with the highest frequency and the most abundant species of cyanobacteria existing in these waters and their potential health risk humana.Para answer this question were performed in the range 17 bimonthly collection campaigns in seven points of the tank the following limnological parameters (chlorophyll a, transparency, total phosphorus, nitrate, temperature and pH), totaling 714 samples (17 campaigns x 7 x 6 points parameters). Transparency measures, temperature, and pH was performed in the field, while the other samples for analysis were collected directly in water 30 cm deep, placed in vials previously washed and decontaminated (polyethylene and amber glass) and kept refrigerated in coolers to the site analysis. According to the results of chlorophyll concentrations increased over the four years of study, but are still in line with the standards of CONAMA, which allows up 30μg.L-1 to class 2. It is observed that the increase of the mean attribute with time, whereas the opposite happens for transparency. With respect to nutrients, phosphorus has gradually increased, with a slight decline in 2010, when there was less precipitation and consequently a low runoff, the same can be observed for the nitrate values. The average water temperature was between 28  C and 30  C, indicating that the Oros has warm waters, characteristics of semiarid regions. The values of pH may be noted that were always alkaline soil because this environment is rich in bicarbonate ions. The phytoplankton composition was composed by Chlorophyceae, Cyanophyceae, Bacillariophyceae, Euglenophyceae, xantophyceae and Zygnemaphyceae, especially with larger Chlorophyceae and Cyanophyceae species despite the smaller number of species quantities of individuals were always higher than the other groups of individuals. The frequency of the cyanobacteria group arrived between 50 and 60% of the samples collected. Were also carried out quantitative and qualitative analyzes of the cyanobacterial group, and this group was the one that prevailed during the study period and more worrying is that most of his subjects are potentially toxic. It was observed that the amounts of cells were always higher than the amounts stipulated by CONAMA Resolution NÂ. 357/2005. When there was the abundance of species of cyanobacteria could be observed that the species Aphanocapsa sp. was most abundant in the first three years, but was replaced in 2011 by Planktotrix agardhii, since both species are considered in the literature as potentially toxic. The diversity decreased over the years, inferring that this reservoir is in a state of eutrophication