Influência dos parâmetros ambientais na composição do fitoplâncton do Açude Jaburu I, Ceará, Brasil

Abstract

In the Brazilian semi-arid tropic, the study of the phytoplankton of the reservoirs allows to evaluate the participation of toxic species that produce cyanotoxins, your occurrence characterizes public health risks, mainly due to the difficulties of removing these compounds in conventional drinking-water treatment. Jaburu I Reservoir is the main reservoir of water supply in the Ibiapaba region, in Ceará. This research has as main aim to correlate the phytoplankton composition with the environmental factors. The sampling performed in february, may, august and november, between the periods of 2014 to 2017, by COGERH. Multivariate analyzes were performed, as well as statistical analyzes, including chemical, physical and biological variables. The cyanobacteria dominated the samplings, predominating microcystin producing genera. The low turbidity and the state of mesotrophy of the reservoir favored the frequent dominance of the genus S-strategist Microcystis. The more representative the other classes are to the detriment of cyanobacteria, the lower the total population densities. Using non-metric multidimensional scaling (NMDS), based on the Bray-Curtis index, we identified two distinct groups, differentiated by the absence of the genus Microcystis, and subsequently confirmed by Analysis of similarities (ANOSIM). The turbidity, pH, chlorophylla, phosphorus gradients differentiated the two groups. The pH increase favored Cylindropermopsis sp., also influenced positively the specific richness of the samplings and the reduction of the dominance. Increased turbidity was decisive for increasing specific richness, indicating that this parameter reduces the effects of possible oxidative stress, which may be intensified by the release of microcystin. The increase of assimilation of total phosphorus, as much as of total nitrogen, in algal biomass meant increased the participation of the other classes in detriment of the cyanobacteria. The increase in chlorophyll-a was directly related to the increase of sodium in the reservoir. Thus, the richness of species and classes regulate the growth of phytoplankton by the increase in interspecific competition, being influenced by pH, turbidity and macronutrient assimilation. It should be noted that control of the nitrogen compounds in the dry period are important, since the nitrogen demand in this period is crucial for the algal development, even as the difficulty of indexes and parameters based on chlorophyll-a to monitor the algal growth in Jaburu I Resevoir.