Mercury trophodynamics in the food web of Lake Nahuel Huapi (North Patagonia, Argentina)

ARCAGNI, M.; RIZZO, A.; CAMPBELL, L.; ARRIBÉRE, M.A.; PAVLIN, M.; JUNCOS, R.; FAJON, V.; HORVAT, M.; RIBEIRO GUEVARA, S.

Conferencia; 11th International Conference on Mercury as a Global Pollutant; 2013

Total mercury (THg) and methylmercury (MeHg) trophodynamics was studied in the food web of Lake Nahuel Huapi, one of the largest ultraoligotrophic systems in North Patagonia. Fish, macroinvertebrates, and plankton, were sampled at two sites (Bahía López-BL in the south and Brazo Rincón-BR in the north) which present different geographic, hydrogeomorphic, and environmental characteristics. Food web dynamics were assessed using stable nitrogen (¦Ä15N) and carbon (¦Ä13C) isotopes, THg concentrations ([THg]) were determined by INAA and by DMA, and MeHg concentrations ([MeHg]) via GC-separation on an automated MeHg analyzer. The highest [THg] were recorded in plankton, ranging from 0.1 to 250 g g-1 dry weight (DW), although [MeHg] ranged from 0.003 to 0.029 g g-1 DW. [THg] in macroinvertebrates were higher for the decapods Aegla sp. (crab) and Samastacus (crayfish) muscle (0.09-2.7 g g-1 DW), with [MeHg] ranging from 0.06 to 1.4 g g-1 DW. Snails (Chilina sp.) had elevated [THg] (0.12-1.0 g g-1 DW), but with lower [MeHg] (0.016-0.020 g g-1 DW). In mussels (Diplodon chilensis), [THg] ranged from 0.08 to 0.56 g g-1 DW, with [MeHg] from 0.01 to 0.03 g g-1 DW. Insect larvae including Ephemeroptera and Trichoptera, had mid-range [THg] (0.04-0.4 g g-1 DW) and [MeHg] between 0.006 and 0.04 g g-1 DW. The fish species, including the small native Galaxias maculatus, the large native Percicthys trucha and the large introduced salmonid species had [THg] in muscle tissue ranging between 0.05 and 2.3 g g-1 DW, while the % of MeHg were high at 70 to 100 % of THg. Percicthys trucha exhibited higher [THg] (0.1-2.3 g g-1 DW; average 0.96 g g-1 DW) than Oncorhynchus mykiss (0.04-0.26 g g-1 DW; average 0.11 g g-1 DW) and Salmo trutta (0.05-0.47 g g-1 DW; average 0.23 g g-1 DW). This is explained by the different feeding habits of P. trucha, that relies mostly on benthic organisms which showed high [MeHg], whereas O. mykiss and S. trutta are more piscivorous, preying on G. maculatus. This small fish is an important planktivorous in Patagonian lakes, combining pelagic and benthic feeding habits. [THg] did not correlate with trophic level (¦Ä15N) or with carbon source (¦Ä13C) in the food web of both sites. On the other hand, [MeHg] correlated positively with ¦Ä15N in BL but not in BR. However, an increment of [MeHg] with increasing ¦Ä15N was observed in the food web of BR. Percicthys trucha, O. mykiss, and S. trutta exhibited similar ¦Ä15N (~13 ¡ë), occupying the highest trophic level of the system. These results show that although the highest [THg] were determined in plankton, higher [MeHg] were observed in upper trophic levels with more benthic diet (P. trucha), remarking the relevance of the benthic-pelagic coupling in Hg food web transfer.