Atmospheric Mercury Deposition in Estuarine Ecosystems and Coastal Lagoons: Contribution to The Global Hg Cycle

Dear Colleagues,

Atmosphere dedicates this Special Issue to atmospheric mercury deposition in estuarine ecosystems and coastal lagoons: Contribution to the Hg global cycle. Mercury (Hg) is a global pollutant that bioaccumulates and persists in the environment. It can travel long distances within air masses and water currents, undergo methylation into its most concern organic form, monomethylmercury (MMHg; CH₃Hg⁺), the more bioavailable and toxic form, and biomagnifies and drives most human health advisories and concerns for wildlife impacts. Additionally, Hg transport, transformations, bioaccumulation, and exposure are affected by numerous interacting processes and phenomena, such as climate change, nutrient loading, land use/cover, food web dynamics, and human behavior and decisions. Atmospheric speciation and deposition are important in the understanding of Hg as a global pollutant and especially to determine the capacity of the atmosphere to transport Hg over a long distance and its role in the Hg biogeochemical cycle in various environmental ecosystems. This Special Issue reinforces the need for improvement on the current understanding of the global cycling of Hg between major global reservoirs, mostly atmosphere and aquatic ecosystems.

The global Hg cycle is highly dependent on air/water exchange, as it is one of the primary pathways to deliver Hg to the atmosphere. It has become clear that atmosphere is a key component of the biogeochemical cycle of Hg, acting as a reservoir, transport mechanism, and facilitator of chemical reactions. As such, the atmosphere is the major transport pathway for the global distribution of Hg. The chemical and physical behavior of atmospheric Hg determines how, when, and where emitted Hg pollution impacts ecosystems. A part of the emissions entering the atmosphere is locally deposited to aquatic and terrestrial ecosystems. Another part is transported with air masses in directions dependent on many factors, including wind direction and speed and Hg behavior during this transport. As a consequence, Hg emitted in one part of the world can be transported to another. However, the spatial distribution of Hg concentrations and deposition is quite uneven.

Knowledge on Hg releases into the atmosphere, atmospheric transport and deposition, and the linkage between environmental contamination and potential impacts to human health needs to be improved in particular ecosystems as estuaries and coastal lagoons. These types of aquatic environments are unique systems that offer a large number of goods and services. They are highly productive and include important fisheries and aquaculture exploitations, playing an important role in biogeochemical cycles, protecting and promoting the genetic diversity of the species that inhabit or use them as refuge or nursery. Although open water systems appear to be net sinks for Hg sequestration, nearshore wetland systems may be significant sources of Hg emission due to the biogenic release from plant leaves and the increased quantity and quality of dissolved organic carbon. Because estuarine environments are naturally and anthropogenically enriched in Hg, the evasion of Hg from contaminated wetlands, particularly estuaries, may be a critically important and currently underestimated flux of Hg to the atmosphere. With this Special Issue, we intend to answer an important question: How much atmospheric mercury could be deposited, retained and re-emitted to the atmosphere in estuaries and coastal lagoons during different seasons? The eventual deposition and retention of mercury in its various chemical forms in soils and waterbodies, its wide distribution and cycling in different ecosystems, mainly in aquatic ones, and the resultant risks to human and wildlife health constitute a major environmental management issue that should be considered in future actions by the decision makers.

In ligh of the above, we invite you to contribute articles to this Special Issue by reporting developed studies and new data about atmospheric mercury deposition in estuarine ecosystems and coastal lagoons. Solicited contributions include (but are not limited to): atmospheric mercury deposition, mercury fluxes between atmosphere/water, physical and chemical processes, transport and fate of mercury in atmosphere and aquatic environments (pristine and contaminated ones), and the impact of mercury/methylmercury environmental transformations to human health. Articles on chemical analysis and development of new methodologies to evaluate the bahavior of mercury species in several reservoirs, mostly in atmosphere and aquatic ecosytems, are also encouraged.

Dr. Rute Cesário
Guest Editor

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• Atmosphere as an important part of the global mercury biogeochemical cycle
• Atmospheric mercury speciation and deposition
• Mercury wet and dry depositions
• Impact of climate changes in mercury species, processes, and fluxes
• Mercury biogeochemistry in estuarine environments and coastal lagoons
• Mercury fluxes between atmosphere/water/sediments