Mercury in Aquatic Systems of North Patagonia (Argentina): Sources, Processes and Trophic Transfer

Abstract

Andean Patagonian catchments comprise large freshwater networks along a sharp west-to-east bioclimatic gradient. The Nahuel Huapi National Park (Argentina) includes the headwaters of the largest fluvial network of North Patagonia characterized by mountain and piedmont aquatic systems draining toward the Atlantic and Pacific oceans. Several studies in the region have recorded moderate to high mercury (Hg) levels in different environmental compartments of Andean catchments. Lake sediment sequences have revealed that the departure of Hg concentrations from background levels, attributable to global circulation of this toxic metal, is connected to frequent disturbances caused by active volcanoes of the Andean belt (Southern Volcanic Zone of South America) and wildfires. Freshwaters of the region are oligo- to ultraoligotrophic, with extremely low concentrations of dissolved organic matter, displaying high total Hg to dissolved organic carbon ratios which reflect in high Hg availability. This work reviews the evidence from different studies performed in Nahuel Huapi lake catchment, which explored the sources of Hg, the terrestrial and aquatic pathways of its biogeochemical cycling, as well as its circulation in lake food webs. Moreover, potential changes in the cycle of Hg in Andean Patagonian catchments are discussed in the context of the global and regional climate trends. In this regard, changes in Hg cycling in ecosystems of the region are expected to be manyfold because different components influencing this process (Hg stored in ecosystems, processing rates, the lateral transport to aquatic end points, methylation, etc.) are climate-sensitive.