Dinâmica e produtividade primária da comunidade fitoplanctônica em reservatório do semiárido brasileiro.

Abstract

The semiarid region of Northeast Brazil is characterized by a system of seasonal rains,variable in space and time, prolonged droughts and annual recurrent droughts interannual and high temperatures and almost constant during the year. This natural scenario justifies the natural water scarcity in the region, which depends on the construction of reservoirs as a strategic measure to its socioeconomic development. The semi-arid climatic conditions have influenced the structure and composition of phytoplankton community of the reservoirs and therefore the phytoplankton primary productivity. Thus, the objective of this research was to identify and evaluate the seasonal dynamics and primary productivity of phytoplankton community Pereira reservoir Miranda, municipality of Pentecoste, Ceará, and link them to climate variables, hydrological and limnological. Water samples were collected monthly in 2015 to determine physical variables (temperature, water clarity and turbidity), chemical (dissolved oxygen, conductivity, pH, total phosphorus, orthophosphate, ammonia, nitrite, nitrate and silica) and biological ( chlorophyll a and primary productivity), and phytoplankton collections for identification, counting and calculating the Shannon diversity index - Wiener. The data were statistically analyzed by analysis of variance (ANOVA) for primary productivity and multivariate principal component analysis (PCA) to order the physical and chemical variables and express the relationships between them. As a result, there were changes in limnological characteristics with prolonged drought. There was no significant difference (p> 0.05) in primary productivity during the months studied. However, there was a higher primary productivity in the rainy season. Thirty have been identified and a phytoplankton species, especially Microcystis sp. (Unitary), with dominance in the rainy season, and plenty of Aphanocapsa elachista in the dry season. The Shannon diversity index - Wiener was down for both periods, with plenty of few species, and increase from the end of the rainy season. Thus, it can be inferred that the dry scenario observed during the study interfered with limnologic conditions and phytoplankton diversity in Pereira de Miranda reservoir, i.e., changes in physical and chemical factors of water, enhanced by prolonged drought affected adversely the primary productivity of Pereira de Miranda reservoir.