Trace elements in sediments and plankton from two high-altitude lakes in a volcanic area from North Patagonia, Argentina.

This study analyzes the distribution of nine potentially toxic trace elements (arsenic, antimony, bromine, cobalt, chromium, mercury, rubidium, selenium, and zinc) in sediments and plankton from two small mesotrophic lakes in a non-industrialized area impacted by the Caviahue-Copahue volcanic complex (CCVC). The two lakes have different plankton community structures and received different amounts of pyroclastic material after the last CCVC eruption. Trace element concentrations of surface sediments differed between lakes, according to the composition of the volcanic ashes deposited in the lakes. The size of organisms was the principal factor influencing the accumulation of most trace elements in plankton within each lake, being trace element concentrations generally higher in the microplankton than in the mesozooplankton. The planktonic biomass in the shallower lake was dominated by small algae and copepods, while mixotrophic ciliates and different-sized cladocerans dominated the deeper lake. These differences in the community structure and species composition influenced the trace element bioaccumulation, especially in microplankton, while habitat use and feeding strategies seem more relevant in mesozooplankton bioaccumulation. This work contributes to the scarce records of trace elements and their dynamics in plankton from freshwater ecosystems impacted by volcanic activity.

Variations in anthropogenic silver in a large Patagonian lake correlate with global shifts in photographic processing technology.

At the beginning of the 21st century, digital imaging technology replaced the traditional silver-halide film photography which had implications in Ag contamination. Lake Nahuel Huapi is a popular Patagonia tourist destination impacted by municipal silver (Ag) contamination from photographic processing facilities since 1990's. Silver concentrations in a dated sediment core from the lake bottom showed a 10-fold increase above background levels in the second half of the 20th century, then a decrease. This trend corresponds well with published annual global photography industry demand for Ag, which clearly shows the evolution and replacement of the traditional silver-halide film photography by digital imaging technology. There were significant decreases in Ag concentrations in sediments, mussels and fish across the lake between 1998 and 2011. Lower trophic organisms had variable whole-body Ag concentrations, from 0.2-2.6 µg g-1 dry weight (DW) in plankton to 0.02-3.1 µg g-1 DW in benthic macroinvertebrates. Hepatic Ag concentrations in crayfish, mussels and predatory fish were significantly elevated relative to muscle which often have Ag concentrations below the detection limit (0.01-0.05 µg g-1 DW). Trophodynamic analyses using δ15N and whole-body invertebrate and muscle Ag concentrations indicated food web biodilution trends. High sedimentation rates in conjunction with the reduction of silver waste products discharged to the lake, as a result of the change to digital image processing technologies, are resulting in unplanned but welcome remediation of the Ag contamination in Lake Nahuel Huapi.

Historical records of mercury in southern latitudes over 1600 years: Lake Futalaufquen, Northern Patagonia.

Mercury is released to the environment from natural and anthropogenic sources, and through atmospheric transport is distributed globally. Lake Futalaufquen (42.8°S) is an oligotrophic lake located in Los Alerces National Park (Northern Patagonia), providing a remote and unpolluted study system. A lacustrine sedimentary sequence revealed 1600 years of Hg deposition, identifying natural baselines and marked peaks not correlated with long-range atmospheric transport. Organic matter and catchment erosion were discarded as Hg drivers. Natural background, pre-1300 CE Hg concentrations, ranged between 27 and 47 ng g(-1) (accumulation rates from 8 to 15µg m(-2) y(-1)). From 1300 CE on, the Hg background profile did not follow the generally increasing Hg pattern observed in both Southern and Northern Hemisphere since pre-industrial times. It was not until the last century that a 1.6-fold increase is observed in the Hg accumulation rate, considered among the lowest increments in southern South America. Noteworthy local/regional sources of Hg for this area, along with global transport, are forest fires and volcanic activity. Between approx. 1340 and 1510 CE, sharp increase in Hg concentration and accumulation rate (up to 204 ng g(-1) and 51 µg m(-2) y(-1), respectively) were clearly associated with extended fire episodes. Furthermore, high Hg peaks during the last 300 years were associated with volcanic eruptions in northernmost Patagonia together with fairly irregular fire episodes, caused by anthropogenic burning by settling population in the Andes.

Source identification of volcanic ashes by geochemical analysis of well preserved lacustrine tephras in Nahuel Huapi National Park.

Well preserved volcanic ashes produced in recent events, recovered from sedimentary sequences extracted from three lakes belonging to Nahuel Huapi National Park, Northern Patagonia, were geochemically characterized in order to reveal patterns that allow the identification of the source. Two water bodies are situated in the direct impact area of volcanoes Calbuco and Puyehue-Cordón Caulle, while the third, lake Moreno, is situated in-between. The sedimentary sequences were dated by (210)Pb and (137)Cs techniques; the elemental composition was determined by Instrumental Neutron Activation Analysis. Distinctive patterns were found out when comparing glass shards, and also white pumice but in a lesser degree, of tephra layers extracted from lake Ilón, related mostly to volcano Calbuco events, and lake Nahuel Huapi (Brazo Rincón site), associated to Puyehue-Cordón Caulle eruptions. The geochemical parameters that showed decisive differences were SiO(2) and Na(2)O+K(2)O contents, the Eu anomaly, Rare Earth element ratios; the concentration of incompatible elements Cs, Rb, Th, Hf, Ta and Zr, and the compatible elements Cr and V. The six upper tephra layers extracted from lake Moreno showed geochemical patterns that allowed clear association with Calbuco and Puyehue-Cordón Caulle sources. These results set up the base for tephrochronological applications in historical periods in Nahuel Huapi National Park area.