Total mercury concentration in different plankton fractions in Lake Moreno (Patagonia, Argentina) in relation with ä15N

ARCAGNI, M.; RIZZO, A.; CAMPBELL, L.; ARRIBERE, M.A.; KYSER, K.; KLASSEN, K.; RIBEIRO GUEVARA, S.

Halifax, Nova Scotia

Conferencia; 10th International Conference on Mercury as a Global Pollutant; 2011

The aim of this work was to assess association between total mercury (THg) and D15N (stable nitrogen isotope ratios) values in the plankton community in Lake Moreno (Northwest Patagonia, Argentina), an ultraoligotrophic double-basined lake. The Moreno East (ME) and West (MW) basins each have differing hydrogeomorphic and catchment features, allowing us to compare plankton dynamics. THg and D15N were measured in three plankton fractions (F1: 10-53 µm, F2: 53-200 µm, F3: >200 µm). F1 is composed of phytoplankton and mixotrophic ciliates, while both F2 and F3 contain mostly consumers such as ciliates, rotifers, copepods and cladocerans. THg concentrations were not significantly different between ME and MW. Within each basin, the smallest fraction had significantly higher THg concentrations relative to F2 and F3. In both basins, fraction size was positively correlated with D15N values, with F1having lowest values. The largest fraction F3 had higher ä15N values in ME than MW. However, there were no other significant between basin differences for F1 or F2. THg concentrations and D15N values were negatively correlated in MW, but there were no significant correlations for ME plankton. The difference observed in the D15N values between ME and MW in the F3 fraction may be due to the relative species contribution; e.g. it is suspected that ME may have a higher proportion of species in F3 which presents higher D15N values than the dominant species in MW F3 samples. A different proportion of N-fixing algae or higher waste inputs in one basin than in the other could be also the cause for the different D15N observed between ME and MW. However, there is no significant difference in the D15N values of F1 and F2 between the basins, and an absence of heterocyst indicative of N-fixation in potential N-fixing algae from this lake. Despite the smallest plankton fraction can be partially consumed by the larger fractions, it seems that only a small proportion of the THg is transferred to the consumers in F2 and F3 fractions.