Caracterização da comunidade fitoplanctônica da lagoa de Maracanaú (Ceará, Brasil)

Abstract

Inland aquatic ecosystems function as natural reservoirs of water, such as lagoons, being a suitable place for the development of a microbiota of its own, which makes these ecosystems the stage of a balanced dynamic that favors the diversity of life. The objective of this work was to analyze the phytoplankton community of Lagoa de Maracanaú, located in the municipality of Maracanaú in the State of Ceará. Precipitation data was obtained from the Funceme website. In the period from April to October 2017, biweekly collections were carried out at two points to obtain data on water temperature, transparency, salinity and pH of the water, as well as dissolved oxygen, phosphate, ammonia and nitrite. In the phytoplankton collection, a plankton net with a mesh opening of 25 μm and a mouth diameter of 20 cm was used, and 100 liters of water were filtered. The collected material was concentrated to 10.0 mL, fixed in Transeau solution, 4% formaldehyde, in a ratio of 1: 1. Ten subsamples of 0.1 mL were analyzed in Optron TIM - 2008 microscope at the Bioecology Laboratory - Labec. The Carlson trophic state index (EIT) was calculated, based on phosphate levels and water transparency. It was identified 53 species, inserted in 11 Families and 31 Classes. As Navicula sp. and Cyclotella sp. were abundant at both sites, the Navicula cuspidata, Chroococcus sp. and Pseudostaurastrum gracile were not abundant and the others were classified as rare. During the period of the work precipitation was more concentrated in the months of March and April. The water temperature was between 30 and 32 ° C. The transparency was below 30 cm. The amount of dissolved oxygen was within optimal range (between 7 and 8mg / L). Nitrite and ammonia were within the acceptable levels (<1.0 mg / L), but the phosphate was well above the acceptable amount (> 0.01 mg / L). According to the Carlson Index the Lagoon can be considered eutrophic.