RECORDS OF VARIABLE MERCURY INPUTS DURING THE LATE HOLOCENE IN A PRISTINE LAKE OF THE NORTHERN PATAGONIA ANDEAN RANGE (LAKE TONCEK, NAHUEL HUAPI NATIONAL PARK)

RIBEIRO GUEVARA, S.; MEILI, M.; RIZZO, A.; DAGA, R.; ARRIBÉRE, M.A.

S. C. de Bariloche

Congreso; IV Congreso Argentino de Limnología; 2008

High mercury levels were measured in previous works in Nahuel Huapi National Park (NHNP) ecosystems, particularly mercury concentrations 3 to 5 fold over background were observed in lacustrine sedimentary sequences in layers dated 300 to 400 years ago. A short sedimentary sequence extracted from lake Tonèek was studied to investigate mercury cycling in NHNP during last 1000 years. The mercury concentration profile was measured together with other elements significant to evaluate environmental changes, as well as organic matter and biogenic silica. The sequence was dated by 210Pb and 137Cs techniques. Two regions were identified in the mercury concentration profile with increased values up to 10 fold over background (50 ng.g-1), corresponding to the 18th and 19th centuries the upper, and around the 13th century the lower. No correlation was observed with the environmental tracers studied, nor with tephra layers. Extended fires is a potential source to be considered since these events were recorded in the region in 13th century, and also in 18th and 19th centuries, concurrent in both cases with ENSO events suggesting the incidence of natural and anthropogenic phenomena. Volcanic and geothermal activities are other potential sources to be considered.