The impact of salt marsh restoration on mercury fate and biogeochemistry
LE3 .A278 2013
Bachelor of Science
Environmental & Sustainability Studies
The Bay of Fundy is an area of concern for mercury (Hg) contamination because it is a staging point for migratory shorebirds. Coastal salt marsh restoration on dyked farmland is being explored along the bay's coast, however little is known about the effects of reclamation on mercury concentration and speciation in sediments. In this study, sediment cores were sampled (0-15 cm) before and after a dyke was breached in 2011 and compared to cores sampled from the neighbouring mudflat, salt marsh, and field. Three cores were sampled from each of the post-breach reclaimed area, salt marsh, mudflat, and field, and two from the reclaimed area pre-breach. Sediment cores were sectioned and solids analyzed for total mercury (THg) and methylmercury (MeHg) , as well as electrical conductivity (EC), pH, oxidation-reduction potential (ORP), water-extractable organic carbon (WEOC), organic matter (%OM), and clay content (%Clay). All parameters were significantly altered by tidal inundation. From pre- to post-breach THg doubled, EC increased 240%, pH increased from 5.25 to 7.40, %OM increased 64%, %Clay increased 74%, and WEOC increased 98%, whereas ORP decreased 104% and MeHg decreased 23%. Increases in pH, EC, WEOC, %OM, and %Clay are known to decrease the bioavailability of MeHg through several processes including: (i) increased particle binding and sedimentation; (ii) formation of dissolved gaseous mercury and volatilisation to the atmosphere; and (iii) demethylation of MeHg. This research suggests that methylmercury does not increase in restored salt marshes in the short-term (< 1 year), however more research is required to confirm these results.
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