Mercury in shallow and deep lakes within a Hg hotspot of the southeastern Patagonian Andes: insights into seasonal and spatial patterns.

DIEGUEZ, MARÍA DEL CARMEN; FERNANDEZ, ZAIDA; SOTO CÁRDENAS, CAROLINA; ARCAGNI, MARINA; PEREZ CATAN SOLEDAD; RIZZO, ANDREA

Cape Town

Conferencia; 16th International Congress of Mercury as a Global Pollutant; 2024

ICMGP

On the eastern side of the Patagonian Andes (Argentina), deposition of mercury (Hg) from volcanicsources and reemission from the Pacific Ocean, favored by atmospheric transport by the westerlywinds and orographic precipitation, create Hg hotspots in headwater catchments. We studied theseasonal dynamics of Hg in two connected lakes, the shallow lake Pire and the deep lake BrazoRincón, within a natural Hg hotspot inside Nahuel Huapi National Park. Hg2+ was found as thedominant species in lake water (>98%) and in-lake THg dynamics were related to seasonal hydrologic inputs and terrestrial dissolved organic matter (DOM) fluxes. In both lakes, THg concentrations in water were related directly to allochthonous DOM signatures, particularly in the wet season, indicating terrestrial origin and hydrologic mobilization. In the shallow lake, the highest THg concentration (21.30 ng/L) and the lowest (2.22 ng/L) were found in summer and spring,respectively. In contrast in the deep lake the highest concentration (1344.58 ng/L) was recorded inwinter and the lowest (1.73 ng/L) in summer. In both lakes, deeper strata displayed higher THg inwinter and summer while more even concentrations across depths were found in spring. Overall, the high values recorded of THg:DOC (due to extremely low DOC) and of THg:chlorophyl a, and thepositive correlation between THg and chl a in both lakes, indicate the high Hg availability and uptake by phytoplankton. These results suggest that, independent of lake depth, Hg inputs from thecatchment determine THg levels in the water column, while DOC levels and MOD quality collectivelycontrol Hg availability and uptake at the base of pelagic food webs. Temporal overlap of high Hgavailability and high phytoplankton primary production would favor Hg entry into pelagic food websin ultraoligotrophic Andean-Patagonian lakes.