Fellow: Melani L. Tescher, Department of Biology, UND
Advisor: Sally Pyle, Assistant Professor of Biology, UND
Matching Support: UND central administration
Degree Progress: M.S. August 2000

Thesis Abstract.

Although, methylmercury contributes only a small fraction to the total mercury pool in aquatic ecosystems, it is an increasingly common pollutant around the world. It is believed that contaminants like methylmercury are responsible for declines many avian populations through the reduction in habitat, food quality and quantity, reproductive impairment and low nesting success. Kellys Slough is a National Wildlife Refuge with a main purpose of waterfowl production and therefore makes a prime test system because it surrounded by land that has been cultivated for generations. 

The purpose of this study was to examine methylmercury bioaccumulation in waterfowl raised on Kellys Slough National Wildlife Refuge in Grand Forks County, North Dakota. To better understand the dynamics of bioaccumulation, baseline total mercury concentrations were assessed in the sediments. Environmental variables such as pH, dissolved oxygen, microorganisms and sediment clay content was also assessed. These variables aid or hinder the transformation of mercury to methylmercury. The food sources for the ducklings (macroinvertebrates and vegetation) for the young mallards were also studied.

Sediment analysis showed total mercury concentration ranged from 24.70 ng/g-86.50 ng/g with a mean concentration of 42.12 ng/g ± SD 25.44. These levels are below the EPA standard (0.1-0.2 mg/g) for freshwater systems. Vegetation and macroinvertebrates were analyzed for total mercury content. The levels ranged form 4.94 ng/g to 86.50 ng/g (x = 45.65 20.034s) in the vegetation and 4.16 ng/g-10.50 ng/g (x = 7.59 2.702) for the invertebrates. Liver tissue was analyzed for inorganic and methylmercury. The reason behind the dual analysis was to determine the amount of inorganic mercury crossing the gut and the body. Due to the assumption that inorganic mercury does not cross the gut, the muscle tissue was analyzed only for methylmercury. Levels for each tissue showed ranged form 88.90 ng/g to 238.0 ng/g methylmercury (x = 138.79 ng/g 40.573) and 10.00 ng/g to 24.91ng/g inorganic mercury (x = 24.91 ng/g 16.682) in the liver and 44.40 ng/g to 107.0 ng/g  (x = 73.05 ng/g ± 22.629) in muscle tissue. 

Regression analysis showed a positive correlation between total mercury concentration of sediment and vegetation. However, a negative correlation was seen between sediment and invertebrates, and vegetation and invertebrates. No significant difference was measured between the means of any of the groups. 

Methylmercury concentrations found from liver and muscle tissue were analyzed with a Paired t-test. There was a significance difference between the means for these to tissues (<0.001). We also saw a correlation factor 0.780. Paired differences showed a mean of 65.74 + SE 8.524 (t-value = 7.712, df = 9, sig. 0.000). The data collected were conclusive in determining differences in the bioaccumulation of methylmercury concentrations between the liver and muscle tissue.

A copy of the thesis can be obtained from Professor Sally Pyle.