QUEIMALIÑOS claudia Patricia
The microbial mercury link in oligotrophic lakes: Bioaccumulation by picocyanobacteria in natural gradients of dissolved organic matter
SOTO CÁRDENAS, CAROLINA; QUEIMALIÑOS, CLAUDIA; RIBEIRO GUEVARA, SERGIO; GEREA, MARINA; DIÉGUEZ, MARÍA C.
PERGAMON-ELSEVIER SCIENCE LTD
Año: 2019 vol. 230 p. 360 - 368
Andean Patagonian lakes are oligotrophic systems characterized by low dissolved organic carbon (DOC) levels and moderate to high Hg concentration that determine naturally high Hg/DOC ratios and bioavailability. In these lakes, microbial food webs are extremely important in Hg trophodynamics, being that the picophytoplankton fraction is a major entrance path of Hg 2+ into pelagic food webs. This study analyzed the bioaccumulation of Hg 2+ by the picocyanobacteria Synechococcus sp. using the radiotracer 197 Hg 2+ and water from four Andean Patagonian lakes presenting a natural gradient of DOM concentration and quality. Hg 2+ bioaccumulation by Synechococcus was calculated as the uptake of Hg 2+ per biovolume unit (volume concentration factor VCF; pL μm −3 ). Hg uptake showed a wide variation (13 < VCF< 300 pL μm −3 ) in the natural DOC gradient tested (0.7?4 mg L −1 ; Hg 2+ /DOC ratio: 1.8?14 ng mg −1 ). The bioaccumulation of Hg 2+ in Synechococcus decreased exponentially with DOC concentration. Differences in the quality of dissolved organic matter (DOM) among lake water influenced also Hg 2+ bioaccumulation. Naturally degraded DOM, with low molecular weight/size, promoted higher Hg uptakes in Synechococcus compared to humic DOM, rich in high molecular weight/size aromatic compounds, that retained Hg in the dissolved phase. In Andean Patagonian lakes picocyanobacteria are pivotal organisms in the Hg cycling, taking dissolved Hg 2+ and transferring it to pelagic food webs, as well as fueling the benthic Hg pathway through sedimentation.