Inorganic and methylated mercury dynamics in estuarine water of a salt marsh in Massachusetts, USA. (1st February 2022)

• Record Type: Journal Article
• Authors: Wang, Ting; Obrist, Daniel
• Is Part Of: Environmental pollution. Volume 294(2022)
• Publication Date: 2022-02-01
• Subjects: New England coastal estuary -- Mercury source -- Vegetation uptake -- Intertidal dynamic -- Riverine export -- Upper marsh; Pollution -- Periodicals; Pollution -- Environmental aspects -- Periodicals; Environmental Pollution -- Periodicals; Pollution -- Périodiques; Pollution -- Aspect de l'environnement -- Périodiques; Pollution -- Effets physiologiques -- Périodiques; Pollution; Pollution -- Environmental aspects; Periodicals; Electronic journals; 363.73
• DOI: 10.1016/j.envpol.2021.118657
• Languages: English
• ISSNs: 0269-7491

Abstract

Abstract: Salt marsh estuaries serve as sources and sinks for nutrients and elements to and from estuarine water, which enhances and alleviates watershed fluxes to the coastal ocean. We assessed sources and sinks of mercury in the intertidal Plum Island Sound estuary in Massachusetts, the largest salt marsh estuary of New England, using 25-km spatial water sampling transects. Across all seasons, dissolved (FHg) and total (THg) mercury concentrations in estuarine water were highest and strongly enhanced in upper marshes (1.31 ± 0.20 ng L −1 and 6.56 ± 3.70 ng L −1, respectively), compared to riverine Hg concentrations (0.86 ± 0.17 ng L −1 and 0.88 ± 0.34 ng L −1, respectively). Mercury concentrations declined from upper to lower marshes and were lowest in ocean water (0.38 ± 0.10 ng L −1 and 0.56 ± 0.25 ng L −1, respectively). Conservative mixing models using river and ocean water as endmembers indicated that internal estuarine Hg sources strongly enhanced estuarine water Hg concentrations. For FHg, internal estuarine Hg contributions were estimated at 26 g yr −1 which enhanced Hg loads from riverine sources to the ocean by 44%. For THg, internal sources amounted to 251 g yr −1 and exceeded riverine sources six-fold. Proposed sources for internal estuarine mercury contributions include atmospheric deposition to the large estuarine surface area and sediment re-mobilization, although sediment Hg concentrations were low (average 23 ± 2 μg kg −1 ) typical of uncontaminated sediments. Soil mercury concentrations under vegetation, however, were ten times higher (average 200 ± 225 μg kg −1 ) than in intertidal sediments suggesting that high soil Hg accumulation might drive lateral export of Hg to the ocean. Spatial transects of methylated Hg (MeHg) showed no concentration enhancements in estuarine water and no indication of internal MeHg sources or formation. Initial mass balance considerations suggest that atmospheric deposition may either be in similar magnitude, or possibly exceed lateral tidal export which would be consistent with strong Hg accumulation observed in salt marsh soils sequestering Hg from current and past atmospheric deposition. Graphical abstract: Image 1 Highlights: Salt marshes served as internal mercury sources to tidal water. Internal salt marsh Hg sources accounted for 86% of total mercury watershed export. Salt marsh mercury sources may originate from plant depositon and soil mobilization. Our study showed no detectable in-situ production of methyl-mercury.