A comunidade fitoplanctônica no reservatório de Itupararanga (Bacia do Rio Sorocaba, SP)

Abstract

Reservoirs are artificial aquatic systems which show similar features to lakes and rivers, like the dynamic horizontal characteristics of rivers and the vertical ones of lakes. Due to these properties, there are many factors which are responsible for the distribution and composition of phytoplankton, as there are: stability of the water column, hydraulic retention time, dam operation, availability of nutrients, photosynthetically active solar radiation (PASR), and temperature. As a result of human actions during the past years, the reservoirs are undergoing a process of eutrophication, and therefore contributing to the growth of cyanobacteria, causing problems for wells and thus compromising the health of the population, as these organisms can produce highly aggressive toxins. The study of phytoplankton in the Itupararanga Reservoirs has so become more and more important, as it is a place for recreation, irrigation, public water supply for the counties Votorantim and Sorocaba, and the generation of electricity. The objective of this research is to study the temporal variability (in a seasonal or daily context) and spatial heterogeneity (horizontal axle and diferents deep) in the phytoplankton and to evaluate the potential toxic of predominant cyanobacteria species in this reservoir. In order to reach this aim, a sample collection took place at two sitesone near the dam and the other near the headwatersduring the rainy season (February 2011) and the dry season (July 2011), at a rhythm of every four hours during 10 consecutive days at different depths of the water column. The Phytoplankton community was characterized in relation to its structure (biomass and diversity) and its analysis of cyanotoxins (microcrystin, cylindospermopsin and saxitoxin), using the ELISA method. In order to relate the biological variables, hydrometeorological and abiotic variables have been analyzed. During the studied period, the Itupararanga Reservoir could be classified as polymictic, showing thermal stratification in the rainy season and circulation of the water column in the dry season. Variations in the phytoplankton structure could not be observed on a daily but only a seasonal basis. The average total phytoplankton density was 41,86x10 3 ind.mL-1 in the rainy season, and in the dry season 39,31x10 3 ind.mL-1. Two phytoplankton species altered in their dominance, in the rainy season the Chlorophyceae Monoraphidium contortum showed more presence, whereas in the dry season Cyanobacteria Cylindrospermopsis raciborskii was found in a higher quantity. There was a high relation between the total nutrients (NT:PT) and the dissolved ones (NID:PTD), in both periods, as well as no limitation in the nitrogen level. Microcrystin and cylindrospermposin could not be detected, and the concentrations of saxitoxin were below the limit set by the Brazilian Ministry of Health-MS n°2.914/2011 (3μg.L-1). However, it is essential to achieving a sustainable management plan for the catchment of Sorocaba and Middle Tiête, aimed at monitoring the occurrence...

Trophic State Evolution over 15 Years in a Tropical Reservoir with Low Nitrogen Concentrations and Cyanobacteria Predominance

“…A database of cyanobacteria numbers and the concentrations of chlorophyll-a (Chl), total phosphorus (TP), ammonia, nitrite, nitrate, and total Kjeldahl nitrogen was compiled from the CETESB annual reports for the period 2000-2014(CETESB 20012003;2004;2007;2008;2010;2014;. Information concerning the numbers of cyanobacteria was available after 2004.…”

“…Alteration of the composition of the phytoplankton community could be a key factor for understanding the eutrophication process. Increases in the proportion of cyanobacteria in the phytoplankton community were observed in 2011 (Casali 2014) and 2013 (Lira et al 2013), in an environment previously dominated by chlorophyceae (Cunha and Calijuri 2011b). This seems to be supported by the present data, with rapid increases in the concentrations of both cyanobacteria (Fig.…”

“…The conditions observed in the Itupararanga reservoir suggest that the possibility of contamination of the water by toxins is likely to increase over time, given that the predominant organisms are recognized as potential toxin producers (Wood et al 2014). The presence of saxitoxin (albeit still at safe levels) has already been detected in the Itupararanga reservoir, attributed to high levels of Cylindrospermopsis raciborskii (Woloszynska) Seenayya and Subba (Casali 2014).…”

Growth of Raphidiopsis raciborskii and Monoraphidium contortum from a subtropical Brazilian Reservoir: interaction, saxitoxin production and response to the trophic state

“…The dissolved nutrient concentrations tested in the assays were based on the results obtained from the São Paulo Research Foundation (FAPESP) Thematic Project. 26 The total of average concentrations obtained from the water column of nitrogen forms (nitrite, nitrate and ammonia) and dissolved phosphorus (orthophosphate) were used, as well as the average of micronutrient concentrations determined by atomic absorption spectrometry. 27 According to these results, changes were made to the composition of the standard ASM-1 culture medium, 19 to simulate the mesotrophic reservoir, and the concentrations were estimated for the supereutrophic condition (Table 1).…”

Dinâmica do fitoplâncton e assimilação de nitrato, amônio e ureia em reservatórios subtropicais com diferentes graus de trofia

“…Isto indica que a comunidade fitoplanctônica nesses reservatórios, provavelmente, não foi limitada pelas concentrações de N. Casali (2014) também não detectou limitação por N na comunidade fitoplanctônica em Itupararanga.…”