Influence of trophic status and habitat in the distribution of diatoms in reservoirs of the Mid Tietê river/Alto Sorocaba basin (SP, Brazil).

Abstract

The Mid Tietê River/Alto Sorocaba basin (BMT/AS) is located in the Center-Southeast of São Paulo State, and comprises one of the most developed regions of the State. Most of the water supply in this region comes from reservoirs susceptible to anthropogenic impacts. Among the biological indicators of environmental changes, the use of diatoms has greatly increased in eutrophication studies. This project intends to analyze the spatial and temporal distribution of diatoms in different habitats (planktonic, periphytic and surface sediments) in four reservoirs with distinct trophic status from the BMT/AS (Barra Bonita, Itupararanga, Prainha and Ipaneminha reservoir), aiming to (a) evaluate the ecological quality of these systems, (b) compare the bioindicating potential of diatoms from distinct habitats, and (c) to broaden the knowledge on the distribution and ecology of tropical diatom species. In each reservoir three to four sampling stations will be established. Planktonic and periphytic diatoms will be sampled in the rainy and dry periods, and the surface sediments in the dry one. Samplings will include physical and chemical analysis for water and sediments. Water variables are: temperature, pH, electric conductivity, transparency, dissolved oxygen, alkalinity, nitrogen and phosphorus inorganic forms, total nitrogen and total phosphorus, soluble reactive silica and chlorophyll-a, and variables for sediments are: total organic carbon, total nitrogen and its stable isotopes (d13C e d15N), total phosphorous and granulometry. Diatom species will be identified and quantified. Ecological information of the taxa will be based on literature review, electronic addresses and the OMNIDIA program. Diversity indices will be calculated and associations of bioindicating species will be characterized. Data will be analyzed using multivariate statistical analysis (ordination, classification and clustering). The present proposal is pioneer for the Mid Tietê River basin and the second in Brazil to compare the bioindicating potential of diatoms from different habitats in reservoirs with distinct trophic status. As part of a larger project, it will provide limnological and ecological (diatoms) information to develop a regional database, targeting the development of an inferential model (diatom-phosphorus) presently nonexistent for tropical regions.