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also exposed to high concentrations of methyl-mercury . Over the past two decades , the number of bird species adversely affected by mercury has increased by a factor of six . It also has adverse effects on the reproduction of fish , which are exposed to humans through consumption . Higher concentrations are found in large , long-lived fish-eating species such as walleye , largemouth bass , and lake trout compared to lower trophic level species such as yellow perch .
Mercury contamination and concentration have certain patterns over time . Sediment cores from inland lakes within the Great Lakes region indicate that declines in local and regional mercury emissions have decreased mercury delivery to inland lakes across the region by about 20 percent since the mid-1980s . Mercury concentrations in walleye , largemouth bass , lake trout , and herring gull eggs in the Great Lakes region show downward trends in recent decades , consistent with declines in regional emissions and sediment accumulation in inland lakes . In certain areas within the region , mercury concentrations in some fish and wildlife species have been trending upward in the last 10 to 15 years . The challenge
Rusty Black Bird of interpreting patterns and change in mercury contamination and methylmercury in fish and wildlife underscores the need for comprehensive mercury monitoring at multiregional or national scales and over decadal time scales .
In general , fish mercury concentrations tend to be higher in the northern and eastern parts of the region and the inland lakes . The northern reaches of the Great Lakes region contain forests which enhance mercury deposition through litterfall . The mercury sensitivity of an area is determined by characteristics that influence the inputs , transport , and bioavailability ( i . e ., methylation and trophic transfer ) of mercury in aquatic food webs . Areas of high mercury concentrations in fish are positively correlated with areas of high forest cover and wetland area . The forested areas in the northern reaches of the region receive a higher dry deposition of mercury and exacerbate the impacts of mercury emissions and deposition . Agricultural lands that release large amounts of nutrients into local water bodies can have the effect of decreasing mercury in fish as the nutrients result in a bio dilution effect .
Mercury level in the environment of the Great Lakes region has declined over the last four decades , concurrent with a decreased level of air emissions from the regional and U . S . sources . While the timing and magnitude of the response will vary , further controls on mercury emission sources are expected to lower mercury concentrations in the food web yielding multiple benefits to fish , wildlife , and people in the Great Lakes region . It is anticipated that improvements will be greatest for inland lakes and will be roughly proportional to declines in mercury deposition , which most closely track trends in regional and
Atlantic Salmon
U . S . air emissions . The findings from this binational scientific synthesis indicate that mercury remains a pollutant of major concern in the Great Lakes region ; that the scope and intensity of the problem are greater than previously recognized .
Hirendra Bista Environmental Science
Batch 2017
Nature and Social Concern Society 51