Dinâmica espacial e temporal de variáveis limnológicas e sua influência sobre cianobactérias em um reservatório eutrofizado: açude Acarape do Meio-CE.

Abstract

This study aimed to analyze the relationship among physical, chemical, and biological parameters as well as the occurrence of cyanobacteria in the Acarape do Meio water supply reservoir located in the metropolitan region of Fortaleza-CE. The monitoring of the water quality was carried out monthly from January to December 2008, with sub-surface samples from seven collection stations distributed in order to cover the entire water source. The results for the following parameters: wind speed, depth, transparency, temperature, pH, electrical conductivity, total alkalinity, dissolved oxygen, DB05 , total ammonia nitrogen, nitrate, nitrite, total Kjeldahl nitrogen, total nitrogen, total phosphorus, soluble orthophosphate, "a" chlorophyll, "a" phaeophytin, thermotolerant coliforms, Escherichia coli, as well as identification and counting of cyanobacteria indicated a strong spatial-temporal variation mainly due to climatic, morphological, and anthropogenic influences. The major contributions of organic matter to the water source occurred in the rainy season, reflecting the high concentrations of DBO5, mainly in the coastal region. The reservoir is in an advanced state of eutrophication, mainly due to the intake of macronutrients (nitrogen and phosphorus), which contribute to the high density of cyanobacteria (748,592 cells/mL in the rainy season and 621,786 cells/mL in the dry season). 9 taxons have been identified distributed in 3 orders, 5 families, and 9 genders, being Aphanocapsa spp, Merismopedia spp, Snowella cfatomus, Cylindrospermopsis raciborskii, Geitlerinema spp, Planctolyngbya spp, Pseudoanabaena sppl., Pseudoanbaena spp2., Planktothrix Agardhi the species identified. The Cylindrospermopsis raciborskii presented dominance in the seasons of the year, with alternation in the dry period with Planktothrix agardhii. These species were the only ones to have 100% of frequency, both being potentially toxic. There were positive correlations between the density of cyanobacteria and concentrations of phosphorus (r=0,37; p<0,05 rainy season and r=0,52; p<0,05 dry season), and through the N.P ratio one can infer that phosphorus is the possible limiting nutrient in this ecosystem.