The climatic rhythm and blooms of cyanobacteria in a tropical reservoir in São Paulo, Brazil.

I Ogashawara,Jg Tundisi,Ja Zavattini

doi:10.1590/1519-6984.17412

Abstract

The present study sought to develop a methodology to analyse water quality based on the concepts and methods of climate and climatology. Accordingly, we attempted to relate hydro- and limnometeorological techniques and methodologies to a rhythmic analysis technique developed within the context of the Brazilian geographical climatology. Our goal was to assess and analyse cyanobacterial blooms, the main index of water quality for the reservoirs of the "Alto Tietê" Basin and, consequently, the Metropolitan Region of São Paulo, an area of high environmental complexity due to its high degree of development and high population density. The meteorological data used were collected by the Institute of Astronomy, Geophysics and Atmospheric Sciences at the University of São Paulo meteorological station, and the limnological data were collected through the Hydrological Monitoring System implemented by SABESP in the Billings and Guarapiranga Reservoirs and the laboratory of the same entity. The rhythmic and integrated analysis showed that the process of cyanobacterial blooms is dependent on a combination of meteorological factors as temperature and wind intensity that may disrupt the stability of the reservoir, providing the conditions necessary for the development of cyanobacteria during the stabilisation process. The pace of the Atlantic Polar Front Entrance during the winter in São Paulo is a limiting factor for the growth of cyanobacteria because of their high frequency, thus maintaining the balance of the reservoir throughout this period. The weather types those could cause a instability in the water column were: Cold Front entrance (66.67%), conflict between masses (22.22%) and the Tropical Instability Line (11.11%). The possibility for prevention and forecasting periods advise when these reservoirs should not be used, mainly with regard to recreational activities.

Highlights

The effect of climate on aquatic environments was revealed in 1920 by the geographer Emmanuel de Martonne in his book Traité de géographie physique: climat, hydrographie, relief du sol, biogéographie in which he wrote that the climate could be an important factor for the stability of the aquatic environment (Martonne, 1920)
The following behaviour was noted: a) the highest cyanobacterial density levels occurred during weeks 1 to 12 and 43 to 52, levels that were much higher than the density permitted by the Brazilian Council for the Environment (CONAMA) no 357/2005 (Brasil, 2005), which is 20,000 cells per mL; b) the lowest concentrations levels were registered during weeks 13 to; and, c) the concentration was slightly higher than the limit established by law during weeks to 42
The most critical events, with a density of cyanobacteria of more than 30000 cel/mL, were related to the Instability Line (34324.5 cel/mL) and to the Stationary Polar Atlantic Front (37761.9 cel/mL). These results demonstrate that the mechanism of mixing and stratification proposed by Tundisi et al (2010) could occur both with the front enters and with other weather types that disturb the water column

Summary

Introduction

The effect of climate on aquatic environments was revealed in 1920 by the geographer Emmanuel de Martonne in his book Traité de géographie physique: climat, hydrographie, relief du sol, biogéographie in which he wrote that the climate could be an important factor for the stability of the aquatic environment (Martonne, 1920). The vertical structure of tropical reservoirs is susceptible to stratification and the mixing process originating from weather events, as documented in Tundisi et al (2004, 2010) and Moraes et al (2010) These studies showed that, according to the variability of wind stress and regimes, aquatic ecosystems present several responses in their physical, chemical, and biological variables. As demonstrated by Court (1957), “climate is not static”, which means that, in some situations, climatic characteristics based on the averaged courses of meteorological elements appear to have restricted use because they do not provide any information regarding the correlations between them This fact was previously observed by Ward (1914) in a paper published in the Annals of the Association of American Geographers in which he wrote that the annual, monthly and diurnal averages of the different climatic elements, when given numerically or even when charted, are often misleading. The same view is accepted by the American geographer William Morris Davis: according to Skaggs (2004, p. 446), “[...] it is clear that Davis did not really approve of climatological research based on a definition of climate as average weather.”

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