Inorganic mercury (Hg 2+ ) accumulation in autotrophic and mixotrophic planktonic protists: Implications for Hg trophodynamics in ultraoligotrophic Andean Patagonian lakes

SOTO CÁRDENAS CAROLINA; GEREA, MARINA; QUEIMALIÑOS, CLAUDIA; GUEVARA, SERGIO RIBEIRO; DIÉGUEZ, MARÍA C.

CHEMOSPHERE

PERGAMON-ELSEVIER SCIENCE LTD

Año: 2018 vol. 199 p. 223 - 231

0045-6535

Mi­cro­bial as­sem­blages are typ­i­cal of deep ul­tra­olig­otrophic An­dean Patag­on­ian lakes and com­prise pi­coplank­ton and pro­tists (phytofla­gel­lates and mixotrophic cil­i­ates), hav­ing a cen­tral role in the C cy­cle, pri­mary pro­duc­tion and in the in­cor­po­ra­tion of dis­solved in­or­ganic mer­cury (Hg2+) into lake food webs. In this study we eval­u­ated the mech­a­nisms of Hg2+ in­cor­po­ra­tion in het­ero- and au­totrophic bac­te­ria, in the au­totrophic di­nofla­gel­late (Gymno­dinium para­doxum) and in two mixotrophic cil­i­ates (Sten­tor arau­canus and Ophry­dium nau­manni) dom­i­nat­ing the plank­tonic mi­cro­bial as­sem­blage. The ra­dioiso­tope 197Hg was used to trace the Hg2+ in­cor­po­ra­tion in mi­cro­biota. Hg up­take was an­a­lyzed as a func­tion of cell abun­dance (BCF: bio­con­cen­tra­tion fac­tor), cell sur­face (SCF: sur­face con­cen­tra­tion fac­tor) and cell vol­ume (VCF: vol­ume con­cen­tra­tion fac­tor). Over­all, the re­sults ob­tained showed that these or­gan­isms in­cor­po­rate sub­stan­tial amounts of dis­solved Hg2+ pas­sively (ad­sorp­tion) and ac­tively (bac­te­ria con­sump­tion or at­tach­ment), dis­play­ing dif­fer­ent Hg in­ter­nal­iza­tion and there­fore, 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 con­sump­tion in the mixotrophic cil­i­ates, or on bac­te­ria as­so­ci­a­tion to sur­face in the au­totrophic di­nofla­gel­late. Hg bioac­cu­mu­lated by pelagic pro­tists can be trans­ferred to higher trophic lev­els through plank­ton and fish feed­ing, re­gen­er­ated to the dis­solved phase by ex­cre­tion, and/​or trans­ferred to the sed­i­ments by par­ti­cle sink­ing. In ul­tra­olig­otrophic An­dean Patag­on­ian lakes, pi­coplank­ton and plank­tonic pro­tists are key com­po­nents of lake food webs, link­ing the pelagic and ben­thic Hg path­ways, and thereby play­ing a cen­tral role in Hg tropho­dy­nam­ics.