Spatiotemporal Characterization of Mercury Isotope Baselines and Anthropogenic Influences in Lake Sediment Cores

Abstract

Mercury is a globally distributed atmospheric pollutant, which travels long distances in the form of gaseous elemental mercury (Hg 0 ). Gaseous Hg 0 is removed from the atmosphere via the foliar uptake (Demers et al., 2013;Zhou et al., 2021) or via oxidation to Hg 2+ , which is readily deposited to the biosphere following sorption to particles (Hg P ) and/or precipitation (Selin, 2009). Since industrialization, anthropogenic activities alone have increased mercury emission by a factor of approximately 5 (Streets et al., 2017). Increased mercury loading to aquatic ecosystems can enhance microbial production of monomethylmercury (MeHg) (Benoit et al., 2003;Lindberg et al., 2007), which is a bioaccumulative toxin in food webs (Mergler et al., 2007). Humans are primarily exposed to MeHg via the consumption of fishery products (Sunderland, 2007).In 2017, the Minamata Convention on Mercury (MC), a multilateral agreement to mitigate anthropogenic mercury emissions and human health from mercury pollution, has entered into force (UNEP, 2019). As a part of the MC, provisions have been established for a global monitoring program and a convention effectiveness evaluation (Article 19, 22) to understand spatiotemporal changes in mercury levels as well as its sources, processes, and fate in various environmental media. Since then, numerous studies have assessed temporal trends of mercury in diverse atmospheric samples (Hg 0 , Hg 2+ , Hg P , precipitation) (Cheng et al., 2017;Dommergue et al., 2016) and biota (fish, bird eggs, polar bear) (Blukacz-Richards et al., 2017;Lee et al., 2016;McKinney et al., 2017) to gather insights on the changes in emissions, deposition, and ecosystem fate of mercury. Natural archives of sediment, peat, and ice cores have also been used to quantify long-term changes in the deposition of various atmospheric mercury species (Engstrom et al., 2014;Enrico

Tracking the legacy of early industrial activity in sediments of Lake Zurich, Switzerland: using a novel multi-proxy approach to find the source of extensive metal contamination

“…Other studies have found that sediments in North American lakes track anthropogenic changes in mercury cycling and saw an increase in the global 202 Hg and Δ 199 Hg coinciding with industrialisation (Lepak et al 2020) and that atmospheric deposition of Hg from coal combustion in Australian lake sediments allow for tracking of Hg point sources (Schneider et al 2021). Further discussion about the use of Hg isotope signatures as tracers for anthropogenic Hg inputs into sediments can be found in Kwon et al (2020) and Lee et al (2021).…”

Climatic Controls on a Holocene Mercury Stable Isotope Sediment Record of Lake Titicaca

“…Another central question emerging from recent studies is the degree to which the natural Hg isotope baseline varies between different lake sediments. 8,41 Lepak et al 41 suggested that the baseline Hg stable isotope signature is mainly controlled by watershed characteristics, with large watershed to lake surface areas receiving a higher proportion of litterfall-derived atmospheric Hg(0), and therefore lower δ 202 Hg, Δ 199 Hg, and Δ 200 Hg. Lake Titicaca is a sentinel of climate change in the southern tropical Andes and has experienced large fluctuations of the lake level over the Holocene due to changes in precipitation regimes.…”

“…In the Northern Hemisphere (NH), atmospheric Hg(0) concentrations and Hg­(II) deposition have decreased significantly since monitoring started in the 1970s. , This decrease is attributed to a reduction in anthropogenic Hg(0) emissions related to air pollution control measures in coal-fired power plants and incinerators . Changes in natural drivers, such as the effect of increasing gross terrestrial primary production or precipitation intensity over the last century, may also have affected regional and global Hg deposition superimposed on the anthropogenic emission signal. Understanding how anthropogenic and natural factors affect global Hg cycling improves the quality of model predictions of future Hg burden under different anthropogenic emission and climate change scenarios.…”

“…Hg stable isotope records of lake sediments have shown promise in the reconstruction of the history of anthropogenic pollution. ,,,− A common pattern in many sediment cores is the increase of Δ 199 Hg and Δ 200 Hg with industrialization from the 1850s to present. Lepak et al suggested that this increase in Δ 199 Hg and Δ 200 Hg in the sediment reflects a change in global atmospheric Hg stable isotope signatures of anthropogenic emissions.…”

“…Other authors suggested that changes in redox transformations in the atmosphere and within the lake water, or decreases in ice coverage, caused the observed variations. Another central question emerging from recent studies is the degree to which the natural Hg isotope baseline varies between different lake sediments. , Lepak et al suggested that the baseline Hg stable isotope signature is mainly controlled by watershed characteristics, with large watershed to lake surface areas receiving a higher proportion of litterfall-derived atmospheric Hg(0), and therefore lower δ 202 Hg, Δ 199 Hg, and Δ 200 Hg.…”