An Invisible Threat to Natural Heritage: Examples of Large Protected Areas with Hg-Enriched Freshwater Environments

Freshwater environments of large protected areas such as national parks and biosphere reserves concentrate a significant amount of natural heritage. An active release of mercury (Hg) to the global environment may challenge the state of this heritage. The present work synthesizes tentatively the information on Hg-enrichment in freshwater environments of large protected areas. A major bibliographical database was used to find the related literature (articles in international journals), which then was filtered to leave only the most relevant sources. Their content was analyzed to extract the necessary information. This bibliographical survey permitted us to find a few dozen examples of protected areas with freshwater environments enriched in mercury and methylmercury. These areas are present in the different parts of the world, and most commonly the Americas. The researchers paid more attention to mercury in biota than in water and sediments. The reported factors of Hg-enrichment differ, with the prevalence of those anthropogenic. The role of volcanism and long-distance dispersal of mercury by air and water is also significant. Interpreting the examples faces various uncertainties, but it is generally clear that Hg-enrichment can be regarded as a potential threat to natural heritage of protected areas on the global scale. It is proposed that Hg-hotspots (e.g., in Nova Scotia in Canada and Patagonia in Argentina) are rare phenomena constituting a new category of heritage. This interpretation extends the vision of the overall natural heritage of national parks and biosphere reserves. Several recommendations to natural heritage management in large protected areas with Hg-enriched freshwater environments are specified.