LE3 .A278 2022

2022

O'Driscoll, Nelson
Mallory, Mark

Acadia University

Master of Science

Masters

Environmental Science

Earth & Environmental Sciences

Estuaries are ecologically sensitive areas that are vulnerable to bioaccumulation of methylmercury (MeHg), a potent neurotoxin that readily bioaccumulates and biomagnifies in ecosystems resulting in negative impacts on organism health. Studies on MeHg bioaccumulation in coastal invertebrates in Eastern Canada are limited, and these data are necessary to determine risk for bioaccumulation in higher trophic level organisms like fish and birds. Particularly, the Minas Basin, Bay of Fundy is an important site for fish spawning and for foraging birds during migration. Fourteen species of invertebrates were collected from five intertidal sites in the Minas Basin during summer 2021 and analysed for concentrations of MeHg and total mercury (THg), and stable isotopes of 13C, 15N, and 34S. The mean concentration of MeHg of all individuals (12.78  11.23 ng/g dry weight (dw)) was approximately an order of magnitude below the Canadian tissue residue guideline for the protection of wildlife consumers like fish and birds of 157.20 ng/g dw. Species with the highest concentrations of Hg were the gastropod Ilyanassa obsoleta, and predatory polychaetes from the families Goniadidae and Maldanidae. Values were generally consistent with those found in other studies in Eastern Canada and the United States. Trophic position (15N) was strongly positively correlated with bioaccumulation of Hg (THg: r208 = 0.14, p = 0.04 and MeHg: r208 = 0.34, p < 0.0001). The Trophic Magnification Factor (TMF) and Trophic Magnification Slope (TMS) were much higher for MeHg than THg (TMF: 16.41 and 2.60, TMS: 1.21  0.30 and 0.41  0.28 respectively), and the TMF for MeHg greatly exceeded those reported in other studies of food webs containing higher trophic level organisms. Stable isotopes of sulfur (34S) (measured in three species; Corophium volutator, Ilyanassa obsoleta, and Littorina littorea) were positively related to MeHg in invertebrates, and when used in combination with 15N values improved predictions of Hg concentrations in biota. To evaluate the effects of environmental chemistry on Hg production and bioaccumulation, bulk sediments from all sites were analysed for THg, %LOI (carbon), and 34S, and concentrations of MeHg, TOC, sulfate, and sulfide were measured in porewaters. MeHg in porewater was the best predictor of invertebrate MeHg, but sediment 34S, which can be used as an indicator of sulfate reduction and thus Hg methylation, was also a relatively strong predictor and should be included in studies on Hg bioaccumulation moving forward to improve predictive models. Predictions of Hg concentrations in biota using sediment and porewater chemistry were strongest for the amphipod Corophium volutator, highlighting this species as potentially useful bioindicator of Hg contamination in the Bay of Fundy. This research was reviewed to assess the various geochemical, biological, and physical factors that impact MeHg production and bioavailability in estuaries, which will help to identify ecosystems that are at greater risk for MeHg retention and bioaccumulation.

The author retains copyright in this thesis. Any substantial copying or any other actions that exceed fair dealing or other exceptions in the Copyright Act require the permission of the author.

https://scholar.acadiau.ca/islandora/object/theses:3881