Distribution of Cladocera (Branchiopoda) populations on medium and low Tietê river reservoirs: a spatial and temporal analysis / Distribuição das populações de Cladocera (Branchiopoda) nos reservatórios do médio e baixo Tietê: uma análise espacial e temporal

AUTOR(ES)

Lucí Helena Zanata

DATA DE PUBLICAÇÃO

2005

RESUMO

Artificial reservoirs are ecosystems with broad economic and social importance; however, they modify hydrological and ecological characteristics of the environment, interfering on the organization of biotic communities, which, in turn, play fundamental role in the transference of energy in the ecosystem. Spatial and temporal organization may occur on these environments, resulting in distinct communities composition and distribution. Aiming to verify this organization, the zooplanktonic community had been evaluated, focusing on Cladocera populations. The analysis was based on samples collected on stations distributed along the longitudinal axis of the medium and low Tietê river reservoirs (SP), in february, may, july, and october, 2000. Data obtained had been correlated to environmental parameters, such as pH, conductivity, temperature, dissolved oxygen, suspended material, nutrients, and chlorophyll-a. The results indicated an expected differentiation on physical and chemical characteristics along the longitudinal axis of Tietê river, as much as on the organismsabundance and distribution. The reservoirs from medium Tietê were found to be more eutrophicated than those from low Tietê, in the periods analyzed, a result probably related to the pollutant discharge coming from the more urbanized and industrialized region of São Paulo state, which enriches the system. Most of this material form sediment or becomes assimilated on the first reservoirs, resulting in significant improvement of the water quality on the cascade longitudinal axis, for the majority of the variables analyzed. Similarly to physical and chemical characteristics, the biological community also showed differentiation in the longitudinal axis of the cascade system. Higher abundance of organisms occurred on the medium Tietê, where the Cladocera community had been composed mostly by small sized species, mainly of the genus Ceriodaphnia, while significant reduction of these values was observed on low Tietê, where higher size species of the genus Daphnia and Simocephalus were relatively more abundant. The species diversity was higher on the regions with elevate abundance of organisms. The environmental characteristics found in the system caused the emergence of organisms with several degrees of morphological alterations; in some cases, the malformations can be congenital and, in others, the attack by microorganisms was evident

ASSUNTO(S)

spatial and temporal distribution cladocera zooplâncton cladocera zooplankton reservatórios distribuição espacial e temporal reservoirs

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