Estudo paleolimnológico de acidificação antrópica em dois lagos amazônicos utilizando assembléias de diatomâceas como bioindicadores

Abstract

Paleolimnological techniques have been used successfully to investigate the history of acidification in acid-sensitive ecosystems since the early 80's. One common method for inferring historical trends in acidification is to develop a transfer function which relates contemporary fóssil diatom assemblage composition and surface pH leveis in lakes. In the present study, a transfer function based on this pnnciple was developed for 15 lakes in the central Amazon which included data from 10 lakes surveyed during an earlier study and 5 lakes investigated here. A commonly used biotic index of acidity, B, based on the relative percentage of diatoms with different tolerances to acidity, was evaluated in each lake and related to the measured pH. A simple linear regression between pH and log B explained 90% of the variability in the data. This regression equation was significantly different from those reported for temperate regions and is apparently unique to the Central Amazon. Once established, this relationship was used to irrfer the history of anthropogenic acidification in lakes from the analysis of fóssil diatom assemblages in Pb dated sediment cores. The history of acidification was investigated in two lakes, lago Cururu, a lake located in the urban area of Manaus, impacted by emissions from a petroleum refinery and thermoelectric plants, and Lago Sumaúma, a lake located in the Jamari river basin, impacted by emissions from forest buming. The paleolimnological study of lago Sumaúma indicated strong peaks of acidification associated with periods of intense forest buming. The paleolimnological analysis of lago Curum indicated a gradual increase m acidity associated with a progressive rise in urban population and industrial development. These results demonstrate that anthropogenic acidification is occurring in aquatic ecosystems in the Amazon and that the paleolimnological method used provides a powerfiil tool for investigating these changes.