Mercury in an ultraoligatrophic North Patagonian Andean lake (Argentina): concentration patterns in different components of the water column

ARRIBÉRE, M., DIÉGUEZ, M.C., RIBEIRO GUEVARA, S., QUEIMALIÑOS, C. P., FAJON, V., REISSIG, M. AND M. HORVAT

JOURNAL OF ENVIRONMENTAL SCIENCES

Elsevier

Año: 2010 vol. 22 p. 1171 - 1178

0022-0906

Piedmont deep ultraoligotrophic lakes of Northern Patagonia (Argentina) are located in pristine areas along a wide latitudinal range. Several studies have reported moderate to high total Hg concentrations and contrasting Methyl-Hg production at different lake compartments. Sources of Hg for eastern Patagonian terrestrial and aquatic ecosystems are still not clear, however, while point sources could be ruled out, atmospheric deposition might be recalled as a plausible natural source perhaps contributing Hg from close active volcanic areas west of the Andes. In this investigation we report a noticeably seasonal, horizontal (between sampling sites) and vertical (between water column strata) heterogeneity in the Total [Hg] found in the pelagic zone of lake Moreno. Sterile water samples taken in a depth profile in lake Moreno showed up moderate to high values of natural [CH3Hg+] in fall with a decreasing pattern of [CH3Hg+] with depth. Overall our results indicate that Hg is mostly allocated in the upper 20 m, the euphotic (epilimnetic) zone of the lake where the plankton fraction between 10-53 µm dominates mostly due to the high numbers attained by two species of the dynoflagellate Gymnodinium. Planktonic size fraction between 53-200 µm comprising rotifers, ciliates and inmature stages of crustaceans, and the > 200 µm fraction made up by calanoid copepods and cladocerans, presented strinkingly lower total Hg levels which suggest a low magnification of Hg at the planktonic consumers level.