Inorganic mercury (Hg2+) accumulation in autotrophic and mixotrophic planktonic protists: implications for Hg trophodynamics in ultraoligotrophic Andean Patagonian lakes

MARÍA DIÉGUEZ; MARIANA GEREA; SERGIO RIBEIRO GUEVARA; CAROLINA SOTO CÁRDENAS; CLAUDIA QUEIMALIÑOS; MARÍA DIÉGUEZ; MARIANA GEREA; SERGIO RIBEIRO GUEVARA; CAROLINA SOTO CÁRDENAS; CLAUDIA QUEIMALIÑOS

CHEMOSPHERE

PERGAMON-ELSEVIER SCIENCE LTD

Lugar: Amsterdam; Año: 2018 p. 223 - 231

0045-6535

Microbial assemblages are typical of deep ultraoligotrophic Andean Patagonian lakes and comprisepicoplankton and protists (phytoflagellates and mixotrophic ciliates), having a central role in the Ccycle, primary production and in the incorporation of dissolved inorganic mercury (Hg2þ) into lakefood webs. In this study we evaluated the mechanisms of Hg2þ incorporation in hetero- and autotrophicbacteria, in the autotrophic dinoflagellate (Gymnodinium paradoxum) and in two mixotrophicciliates (Stentor araucanus and Ophrydium naumanni) dominating the planktonic microbial assemblage.The radioisotope 197Hg was used to trace the Hg2þ incorporation in microbiota. Hg uptake wasanalyzed as a function of cell abundance (BCF: bioconcentration factor), cell surface (SCF: surfaceconcentration factor) and cell volume (VCF: volume concentration factor). Overall, the results obtainedshowed that these organisms incorporate substantial amounts of dissolved Hg2þ passively (adsorption)and actively (bacteria consumption or attachment), displaying different Hg internalization andtherefore, varying potential for Hg transfer. Surface area and quality, and surface:volume ratio (S:V)control the passive uptake in all the organisms. Active incorporation depends on bacteria consumptionin the mixotrophic ciliates, or on bacteria association to surface in the autotrophic dinoflagellate. Hgbioaccumulated by pelagic protists can be transferred to higher trophic levels through plankton andfish feeding, regenerated to the dissolved phase by excretion, and/or transferred to the sediments byparticle sinking. In ultraoligotrophic Andean Patagonian lakes, picoplankton and planktonic protistsare key components of lake food webs, linking the pelagic and benthic Hg pathways, and therebyplaying a central role in Hg trophodynamics.