Proximity to Riparian Wetlands Increases Mercury Burden in Fish in the Upper St. Lawrence River

Autumn Osgood,Thomas M Holsen,Michael R Twiss,Evie S Brahmstedt,Matthew J.S Windle

doi:10.3390/w14010070

Abstract

Mercury deposited in the Upper St. Lawrence River watershed by atmospheric deposition accumulated in riparian wetlands and is at risk of remobilization due to water level fluctuations. To examine if riparian wetlands are a source of mercury to fish, 174 yellow perch (Perca flavescens) and 145 round gobies (Neogobius melanostomus) were collected in 2019 from eight wetland and seven non-wetland habitats throughout the Upper St. Lawrence River. Mercury levels were significantly (p < 0.01) higher in fish collected from wetlands than those collected from non-wetland habitats for both yellow perch and round goby. Perch had mercury concentrations of 74.5 ± 35.4 ng/g dry wt in wetlands compared to 59.9 ± 23.0 ng/g dry wt in non-wetlands. Goby had mercury concentrations of 55.4 ± 13.8 ng/g dry wt in wetlands and non-wetland concentrations of 41.0 ± 14.0 ng/g dry wt. Riparian wetlands are areas of elevated mercury methylation and mobilization in the Upper St. Lawrence River and consequences to predators should be considered from the perspective of both wildlife preservation as well as fish consumption advisories for public health concerns.

Highlights

Rules for determining distances among sites were as follows: (1) Sites being compared must be on the same contiguous shoreline, assuming that the young fish will not be crossing the main channel, which has been shown to be a distinct water mass [29], to nearby islands; (2) sites on islands without any sites on the same contiguous island or nearby island separated by shallow water were not compared to other sites given the assumption (1) above; (3) straight lines were used when possible, but exceptions were made for peninsulas where a conservative number of straight lines were used to estimate distance traveled around the land feature
Each fish species was separated into two groups: Fish caught adjacent to wetlands and fish caught in areas with no adjacent wetlands
The test for normality failed for mercury content, yellow perch and round goby passed the equal variance test, indicating the variance within the samples is approximately the same throughout all samples

Summary

Introduction

The St. Lawrence Seaway allowed an increased opportunity for abundant hydropower production and transcontinental trade into the United States and Canada by connecting the American Great Lakes to the Atlantic Ocean. The construction of the MosesSaunders hydropower dam (1958) and the St. Lawrence Seaway (1959) on the Upper. Prior to the construction of the dam, water levels fluctuated naturally with season- and decadal-scale climate variability. The construction of the dam maintained stable water levels in the Upper St. Lawrence River

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