Environmental reconstruction of a region under anthropic influence: a review of the last 200 years at Guaíba Lake (RS)

Author(s)

Carolina Miyoshi

• Document type: Master's Dissertation
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Instituto Oceanográfico (IO/DIDC)
• Defense date: 2017-03-08

Examining board members

Rubens Cesar Lopes Figueira; Lucildes Pita Mercuri; Elírio Ernestino Toldo Junior

• Advisor: Rubens Cesar Lopes Figueira

Abstract

The new epoch Anthropocene is marked by the increase of population and industrial development. These anthropic alterations have had as consequences environmental and climatic changes, especially in the last two hundred years. The Guaíba River, located at the Brazilian State of Rio Grande do Sul, is extremely important for different attributes: (1) it is the main source of potable water to the capital Porto Alegre; (2) it is an important navigation route, that connects the State central region with the Patos Lagoon and the Atlantic Ocean; and (3) it harbors the main industries of Porto Alegre. The principal objective of this study was to obtain environmental reconstructions for three sediment cores from Guaíba River. To accomplish this goal, we determined the concentrations of trace elements (As, Cr, Cu, Ni, P, Pb, Sc and Zn) and proceeded the analysis of recent geochronology, which was acquired through 210Pb and 137Cs activities with the CRS model. Furthermore, we calculated geoaccumulation indices: Enrichment Factor, Pollution Load Index and Sediment Pollution Index. The sediment cores G1 and G2 presented results that expressed the consequences of the sand mining that occurs at Jacuí River. Approximately after 1998, there has been better control of the dredges that operate on the river and the depositional dynamics were changed again. The G3 reconstruction had different conclusions compared with the others. Grain size alterations were explained by climatic events, like El Niño and La Niña; and the concentration increase of trace elements, mainly Cr, Pb, P and Zn, was connected with possible anthropogenic sources. In this study of environmental reconstruction, the utilization of the CRS model and of metals concentrations and grain size as proxies proved to be adequate, especially in the case of the sand mining at Jacuí River and its consequences. (AU)

• FAPESP's process: 15/02290-1 - Environmental reconstruction of a region under anthropogenic influence: a review of the last 200 years at Guaíba Lake (RS)
• Grantee: Carolina Miyoshi
• Support Opportunities: Scholarships in Brazil - Master