Using Tree-Rings to Discern Historical Emissions of Mercury from Geogenic and Anthropogenic Activities
Abstract
Mercury is a contaminant of global concern as it can be transformed into extremely toxic methylmercury that bioaccumulates in aquatic ecosystems and causes severe health impacts in humans. Primary emissions of mercury occur from both natural (i.e., volcanic) and anthropogenic (i.e., fossil fuel combustion, industry, and mining) sources with anthropogenic sources making up the majority of these emissions. While modern day primary emissions are generally well understood, reconstructing historical emissions is more challenging. Typically, we turn to natural, environmental archives such as sediment and peat cores, and, more recently, tree rings, to reconstruct past mercury levels and emissions. Dendrochronology is an effective technique for reconstructing historical atmospheric mercury levels and emissions as stomatal assimilation (during photosynthesis) is the primary mechanism of mercury uptake in trees. Such studies have largely examined mercury levels near industrial sources or in background areas, with little examination of natural, volcanic or geogenic emissions. This study examines the mercury concentration in ~300-year tree ring record of a high-altitude Araucaria araucana (monkey puzzle) stand at the Chile-Argentina border in the Andes, which is generally downwind of two active volcanoes, Lonquimay and Llaima. Data from the Pino Hachado A. araucana tree rings show higher mercury concentrations compared to more background sites, indicating that eruptions and passive degassing from nearby volcanoes are significant sources of atmospheric mercury. There is an overall increasing trend, consistent with increasing mercury emissions with industrialization, though not as significant as seen in other studies. Increased mercury concentration is seen in sapwood of all cores, showing sapwood enrichment. Other increases in mercury concentration are possibly related to major volcanic eruptions, increased gold mining using mercury amalgamation in Chile, and Chilean railway expansion. Further research will be done to decipher the main historic mercury emission sources in this area and the relative contribution of volcanic eruptions.Supervisor: Dr. David McLagan