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Ulus Y, Tsui MTK, Sakar A, Nyarko P, Aitmbarek NB, Ardón M, Chow AT. Declines of methylmercury along a salinity gradient in a low-lying coastal wetland ecosystem at South Carolina, USA. Chemosphere 2022; 308:136310. [PMID: 36088973 DOI: 10.1016/j.chemosphere.2022.136310] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/08/2022] [Revised: 08/26/2022] [Accepted: 08/30/2022] [Indexed: 06/15/2023]
Abstract
Wetlands are widely regarded as biogeochemical hotspots of highly toxic methylmercury (MeHg), mainly mediated by sulfate-reducing bacteria. In low-lying coastal wetlands, sea level rise, a phenomenon caused by global climate change, is slowly degrading numerous healthy freshwater forested wetlands into salt-degraded counterparts with a nickname "ghost forests", and eventually converting them to saltmarshes. However, little is known about the changes of mercury (Hg) methylation, bioaccumulation, and biomagnification along the forest-to-saltmarsh gradient. Here, we conducted extensive field sampling in three wetland states (healthy forested wetlands, salt-degraded forested wetlands, and saltmarsh) along a salinity gradient (from 0 to 9.4 ppt) in Winyah Bay, South Carolina, USA. We found that in our study wetland systems the saltmarshes had the lowest levels of both total Hg and MeHg in sediments and biota, as compared to healthy forested wetlands and saltwater-degraded ghost forests. Our results suggest that the slow conversion of forested wetland to saltmarsh could reduce net MeHg production in our study wetland systems, which we hypothesized that could be attributed to increased sulfate reduction and excessive buildup of sulfide in sediment that inhibits microbial Hg methylation, and/or reduced canopy density and increased photodegradation of MeHg. However, it should be noted that biogeochemical MeHg responses to salinity changes may be site-specific and we urge more similar studies in other wetland systems along a salinity gradient. Therefore, long-term salinization of coastal wetlands and the slow conversion of forests to marshes could decrease long-term exposure of toxic MeHg levels in coastal food webs that are similar to our system, and ultimately reduce human exposure to this neurotoxin.
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Affiliation(s)
- Yener Ulus
- Department of Environmental Studies, Davidson College, Davidson, NC, 28035, USA; Department of Biology, University of North Carolina at Greensboro, Greensboro, NC, 27402, USA
| | - Martin Tsz-Ki Tsui
- Department of Biology, University of North Carolina at Greensboro, Greensboro, NC, 27402, USA; School of Life Sciences, Earth and Environmental Sciences Programme, State Key Laboratory of Agrobiotechnology, The Chinese University of Hong Kong, Shatin, Hong Kong SAR, China.
| | - Aslihan Sakar
- Department of Biology, University of North Carolina at Greensboro, Greensboro, NC, 27402, USA
| | - Paul Nyarko
- Department of Biology, University of North Carolina at Greensboro, Greensboro, NC, 27402, USA
| | - Nadia B Aitmbarek
- Department of Biology, University of North Carolina at Greensboro, Greensboro, NC, 27402, USA
| | - Marcelo Ardón
- Department of Forestry and Environmental Resources, North Carolina State University, Raleigh, NC, 27695, USA
| | - Alex T Chow
- Biogeochemistry and Environmental Quality Research Group, Clemson University, Georgetown, SC, 29442, USA
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