Hg2+ incorporation in Andean Patagonian ultraoligotrophic lakes: insights into the role of pelagic protists

DIEGUEZ, MARÍA DEL CARMEN; SOTO CÁRDENAS, CAROLINA; RIBEIRO GUEVARA, SERGIO; CLAUDIA, QUEIMALIÑOS

Simposio; International Symposium on Mercury in Biosphere: Environmental and Geochemical Aspects; 2022

Catchments of Andean North Patagonia are impacted by active volcanoes of the Southern Volcanic Zone. Deep piedmont ultraoligotophic lakes concentrate natural Hg2+ deposited in their catchments, presenting elevated THg:DOC ratios and thus, remarkable high Hg2+ availability for fractionation/bioaccumulation. In such lakes, THg levels are consistently highest in the smaller planktonic fraction (10-53 μm) including picoplanktonic and nanoplanktonic species, the main constituents of the microbial loop, than in larger planktonic fractions (53-200 μm and >200 μm). Organisms of the microbial loop incorporate Hg2+ form the dissolved phase and transfer it to higher levels of pelagic food webs.AIM: Evaluation of the uptake of Hg2+ in key components of microbial assemblages of Andean lakes: the picocyanobacteria Synechococcus sp., the photoautotrophic phytoflagellate Gymnodinium paradoxum (Chromista, Dinophyceae), and the mixotrophic ciliates Stentor araucanus and Ophrydium naumanni (Protozoa, Ciliophora, Heterotrichida), bearing the endosymbiontic green alga Chlorella. We hypothesize that the passive incorporation of Hg by the different species is determined by morphological traits [surface (S), volume (V), S:V)], while the active Hg2+ incorporation depends on the trophic transfer through picoplankton consumption.