Does anoxia affect mercury cycling at the sediment-water interface in the Gulf of Trieste (northern Adriatic Sea)? Incubation experiments using benthic flux chambers

Emili, Andrea (author), Koron, Neža (author), Covelli, Stefano (author), Faganeli, Jadran (author), Acquavita, Alessandro (author), Predonzani, Sergio (author), De Vittor, Cinzia (author)

Coastal areas in the northernmost part of the northern Adriatic Sea (Gulf of Trieste and adjacent Grado lagoon) are characterized by high levels of mercury (Hg) in sediments and water column mainly originating from the suspended material inflowing through the Isonzo - Soča river, originating from the Idrija (NW Slovenia) mining district, into the Gulf of Trieste. The Hg pollution is a result of 500-year mining activity reflected in a wide public health concern. Hzpoxic and anoxic conditions at the sediment-water interface are frequently observed in the Gulf of Trieste and in the lagoon due to stronglate summer density stratification and high organic matter input. Hg mobility at the sediment-water interface was investigated at three sampling points located in the Gulf of Trieste (AA1, CZ) and Grado Lagoon (BAR). Experiments were conducted under laboratory conditions at in situ temperature using a dark flux chamber simulating an oxic-anoxic transition.Temporal variations of dissolved Hg and MeHg as well as O2, NH4+, NO3-, PO43-, H2S, Fe2+, dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC) concentrations were monitored simultaneously. Fluxes of solutes across the sediment-water interface were calculated from linear regressions of the variation of solute concentrations, measured in oxic and anoxic conditions with incubation time. Our results show low benthic Hg effluxes and even influxes in oxic conditions and effluxes in the anoxic phase of the experiment. MeHg release was less noticeable (low or absent) in the oxic phase, probably due to similar methaylation and demethylation rates, but high in the anoxic phase of the experiment. In this context, the MeHg flux was linked to sulphate reduction and dissolution of Fe (and Mn), oxyhydroxides, and formation of sulphides and carbonates. The impact of DOM on Hg and MeHg oxic and anoxic fluxes was of minor importance, suggesting that the majority of dissolved Hg and MeHg are not linked to DOM. In the reoxigenation phase, studied at sampling point CZ by opening the chamber after a period of two weeks, the concentrations of MeHg and Hg dropped rapidly probably due to re-adsorption onto Fe (Mn) hydroxides and enhanced demethylation. Sediments, especially during anoxic events, should be, hence, considered as a primary source of MeHg for the water column in the northern Adriatic coastal areas.

• Language: English
• Keywords: hypoxic conditions, anoxic conditions, methylmercury, benthic chambers, mercury recycling, methylation, benthic fluxes, coastal environments, Gulf of Trieste
• Work type: Not categorized
• Typology: 1.08 - Published Scientific Conference Contribution
• Organization: BF - Biotechnical Faculty
• Year: 2011
• Number of pages: Str. 194-204
• Numbering: Vol. 26, issue 2
• PID: 20.500.12556/RUL-37443
• UDC: 574
• ISSN on article: 0883-2927
• DOI: 10.1016/j.apgeochem.2010.11.019
• COBISS.SI-ID: 2307919
• Publication date in RUL: 10.07.2015

Record is a part of a proceedings

• Title: Mercury biogeochemical cycling in mercury contaminated environments
• COBISS.SI-ID: 1447260

Record is a part of a journal

• Title: Applied geochemistry
• Shortened title: Appl. geochem.
• Publisher: Elsevier
• ISSN: 0883-2927
• COBISS.SI-ID: 5134855