A MULTI PROXY ASSESSMENT OF LONG-TERM ANTHROPOGENIC IMPACTS IN PATOS LAGOON, SOUTHERN BRAZIL

Sediments preserve environmental information at the time of deposition which is a useful tool to evaluate the extent of the environmental change from its pristine condition. We evaluated historic environmental trends in the sedimentary record by analysing three sediment cores collected within the freshwater region of Patos Lagoon (southern Brazil). As, Ba, Cr, Cu, Ni, Pb, and Zn were analysed by inductively coupled plasma optical emission spectrometry. C/N ratios and delta C-1(3) values were also determined. Contamination indices such as Enrichment Factor, Geoaccumulation Index, Sediment Pollution Index and Pollution Load Index were calculated to evaluate the influence of anthropic activities. Multipleelemental indices showed a general overview of the environmental conditions of the lagoon throughout time. Furthermore, single-element indices explained which elements triggered the observed changes in the environmental trends. Near Camaqua River mouth, we inferred fairly undisturbed conditions and did not seem to be affected by the mining activities upstream Camaqua River. The influence of these activities was observed upstream the lagoon, between Camaqua and Guaiba rivers, probably as a consequence of the hydrodynamics of the lagoon. Especially, As, Ba and Pb showed moderately polluted levels after 2009 AD. In Guaiba site, a progressive deterioration of the lagoon quality was observed after 1980 reaching the worst environmental degradation by 2000 AD. However, Enrichment Factor values only showed moderate pollution levels suggesting a considerable dilution process within the system given its large size. Similar 6 13 C signature was observed in the whole lagoon prior to the anthropogenic influence. However, such a condition changed differentially after the anthropogenic fingerprint. Recent sediments reflected a shift in the plant cover, and particularly in Guaiba, the influence of urban and industrial activities of Porto Alegre City were reflected in the sedimentary record. Overall, metals together with organic matter composition proxies allowed us to determine the anthropic-related changes in Patos Lagoon.