Effects of copper and chromium on the zooplankton community : a mesocosms experimental study / Efeitos do cobre e cromo na comunidade zooplanctônica : um estudo experimental em mesocosmos

AUTOR(ES)
DATA DE PUBLICAÇÃO

2004

RESUMO

The urban and industrial development has been contributing to the introduction of great amounts of heavy metals in the aquatic ecosystems, exposing its biota and the whole food chain to the contamination with these elements. A lot of studies about the behavior of heavy metals in the aquatic environment have been developed, since heavy metals represent an environmental problem due to its persistence and no biodegradability in the environment. However, little is known about the ecological effects of heavy metals on the structure and function of the aquatic communities. This work contributes for a better knowledge of these effects on the zooplankton community in field experiments. The purpose of this work was to evaluate the effects of chromium and copper on the zooplankton community structure in mesocosms experiments at the Lobo-Broa reservoir (CHREA/USP). The mesocosms were constituted of three 5000 liters transparent PVC littoral enclosures in contact with the bottom sediment. One mesocosms was maintained as control (not contaminated), and two were contaminated with the CONAMA/86 maximum concentrations allowed for copper (20µg/L) and chromium (40µg/L). The experiment was conducted from March 28 to April 30, 2002, when samples of water (for limnological analyses) and plankton were collected before and after the contamination in intervals of two to seven days. The zooplankton samples were counted and the species of the three main groups (Copepoda, Cladocera and Rotifera) were identified, eggs and population classes of Cladocera and Copepoda were quantified, and ecological indexes were calculated. According to the results, the concentrations of metals applied caused several effects on the zooplankton community. The ecological indexes showed that the effects of the chromium contamination were more severe over the zooplankton community than copper. However, the effects of the contamination were different for each metal, zooplankton group and species, and for the evaluation of these effects, the analysis based on population data was more efficient than the analyses based on ecological indexes. Copper caused more deleterious effects over the Crustaceans than chromium, but these effects were different for each species. It was observed a different sensibility among the species and the development stages of Copepoda. A more severe reduction in the population abundance and production of eggs of Calanoida occurred in the copper contaminated mesocosms than in the chromium one. Cyclopoida were more resistant to the metal contamination than Calanoida. Cladocera were the most sensitive group, reducing Its abundance and egg production in the contaminated mesocosms, and presenting acute and chronic effects for both metals. It was observed differences in the sensibility among the species of Cladocera, and the competition for resources demonstrated to be an important factor in the succession of species. Several species of Rotifera were more sensitive to chromium than copper, and indirect effects of contamination, like changes in the competition for resources and predation, were important factors in the determination of the Rotifera population structure

ASSUNTO(S)

zooplankton cromo toxicidade toxicity copper zooplâncton cobre mesocosmos mesocosms broa reservoir chromium represa do broa

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