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Seasonal variation of total mercury burden in the American alligator (Alligator mississippiensis) at Merritt Island National Wildlife Refuge (MINWR), Florida



Frances Nilsen, Jonathan E. Dorsey, Stephen E. Long, Tracey B. Schock, John A. Bowden, Russell H. Lowers, Louis J. Guillette Jr.


Seasonal variation of mercury (Hg) is not well studied in free-ranging wildlife. Atmospheric deposition patterns of Hg have been studied in detail and have been modeled for both global and specific locations with great accuracy and correlates to environment impact. However, monitoring these trends in wildlife is complicated due to local environmental parameters (e.g., rainfall, humidity, pH, bacterial composition) that can affect the transformation of atmospheric Hg to the biologically available forms. Here, we utilized an abundant and healthy population of American alligators (Alligator mississippiensis) at Merritt Island National Wildlife Refuge (MINWR), FL, and assessed Hg burden in whole blood samples over a span of 7 years (2007 – 2014; n = 174) in an effort to assess seasonal variation of total [Hg]. While the majority of this population is assumed healthy, 18 individuals with low body mass indices (BMI, defined in this study) were captured throughout the 7 year sampling period. These individual alligators exhibited [Hg] that were not consistent with the observed overall seasonal [Hg] variation, and were statistically different from the healthy population of alligators. The alligators with low BMI had elevated concentrations of Hg compared to their age/sex/season matched counterparts with normal BMI. Statistically significant differences were found between the winter and spring seasons for animals with normal BMI. The data in this report supports the conclusion that organismal total [Hg] do fluctuate directly with seasonal deposition rates as well as other seasonal environmental parameters, such as average rainfall and prevailing wind direction. This study highlights the unique environment of MINWR to permit annual assessment of apex predators, such as the American alligator, to determine detailed environmental impact of contaminants of concern.
Science of the Total Environment


Nilsen, F. , Dorsey, J. , Long, S. , Schock, T. , Bowden, J. , Lowers, R. and Guillette, L. (2017), Seasonal variation of total mercury burden in the American alligator (Alligator mississippiensis) at Merritt Island National Wildlife Refuge (MINWR), Florida, Science of the Total Environment, [online], (Accessed May 24, 2024)


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Created July 8, 2017, Updated August 16, 2017