MERCURY IN ULTRAOLIGOTROPHIC DEEP LAKES OF ANDEAN PATAGONIA

RIZZO, A; QUEIMALIÑOS, C; ARCAGNI, M; PÉREZ CATÁN, S; SOTO CARDENAS, EC; RIBEIRO GUEVARA, S; DIÉGUEZ, MC

Ciudad del Cabo

Conferencia; 15th International Conference of Mercury as a Global Pollutant; 2022

Ultraoligotrophic lakes of Andean Patagonia show variable levels of Hg in water and moderate to high THg levels in lake sediments. High total Hg (THg) to dissolved organic carbon concentrations, determine that THg is highly bioavailable in the water column. Interestingly, THg levels in fish are far higher in benthic feeders than in pelagic foragers, indicating that lake bottom has particular conditions promoting differential Hg bioaccumulation. In this investigation we studied THg in the water column, sediment-water interphase and pore water in relation with dissolved organic matter (DOM) concentration and quality in the warm monomictic deep lakes Moreno East (ME) and Moreno West (MW). Littoral, sublittoral and pelagic sites (Zmax: ca. 20, 40 and 100 m, respectively) were sampled during stratification (April) and mixing (November) periods. THg and dissolved organic carbon (DOC) concentrations were measured in water column, water-sediment and pore water samples of both lakes, using CVAF and combustion catalytic oxidation, respectively. DOM was characterized through optical techniques. THg levels and DOC concentrations were highest in pore water followed by interphase and at last by water column samples, regardless spatial (between and within lakes)/temporal differences, suggesting potential diffusion from the sediments.  DOC-THg concentration showed idiosyncratic patterns among lake compartments, however THg levels related positively with DOM allochthonous optical signals, particularly in littoral and sublittoral areas and during mixing periods. During stratification, higher THg levels in pore water extracted from sediments of the deepest zone related with changes in redox conditions likely promoted by lower O2 levels.