Masters Theses

Date of Award

6-1976

Degree Type

Thesis

Degree Name

Master of Science

Major

Wildlife and Fisheries Science

Major Professor

Ralph W. Dimmick

Committee Members

Michael R. Pelton, John C. Rennie

Abstract

Juvenile wood ducks (50) and six environmental components (foods and sediment) were collected from three zones within a 51.5 km. segment of the Holston River between July, 1972 and May, 1973. Samples of liver, breast muscle and body fat from each duckling were analyzed for total mercury content by the atomic absorption technique. Foods sampled were those known to be of value in the diet of juvenile wood ducks. Those foods analyzed were black fly larvae (Simuliidae), tubers of sago pondweed (Potamogeton pectinatus), and leaf and stem portions of tapegrass (Vallisneria americanus), water stargrass (Heteranthera dubia), and Elodea. Sediments were also analyzed to form a more complete picture of mercury movements in the food chain of wood ducks. Mean mercury concentrations in the wood ducks were below the FDA guideline of 0.5 parts per million (ppm). Liver tissues contained the highest mean concentration (0.42 ppm) with levels ranging from 0.13 - 1.1 ppm. Mercury concentrations in breast muscle and body fat averaged 0.15 ppm and 0.10 ppm, respectively, and in both the highest level was 0.40 ppm. Liver concentrations averaged 37 percent higher than breast muscle. Several very consistent trends were evident from the data. In wood duck tissues and food samples there was an increase in mercury levels at the lower end of the study area. Due to a wide range in sample sizes, it was not shown that these differences between zones were statistically significant in every case. Sorting the data for the wood ducks by zone and year provided the best indication of mercury distribution in the study area. Significant differences (P<.10) occured in five cases. The wide range in sample sizes probably contributed to the low proportion of instances for which these differences were significant. An examination of 29 proventricular contents from collected ducks was made to determine the predominant foods in the diet of juvenile wood ducks on the Holston River. All stages of the black fly (Simulium vittatum) comprised almost one-fourth of the total diet and occurred in 20 stomachs. Exhibiting a diet of wide diversity, the ducks fed primarily on three other items: leaves and stems of curly-leaved pondweed (Potamogeton crispus), tubers of sago pondweed (P. pectinatus), and adult terrestrial Coleoptera. Sago pondweed was the only plant species which occurred in all zones and was the only plant species which was statistically tested. Of all components, sediments had the highest mean concentration (0.76 ppm) ranging from 0.12 - 1.70 ppm. Sediment values were highest in zone 2. Black fly larvae and all of the aquatic plants had mean levels below 0.10 ppm. Mercury concentrations in these components followed the same pattern as those in the wood ducks with a progressive increase going downstream. Concentrations in zone 3 were higher than those in zones 1 and 2 for both black flies and sago pondweed. The levels of mercury found in wood ducks apparently pose no immediate threat to the wood duck population. From the standpoint of human health, concentrations of mercury in the breast muscle of wood ducks from the Holston River should be safe since none exceed 0.4 ppm. Long-term, low-dose exposure to mercury compounds may present problems easily overlooked. More research is needed in this area to predict these possible effects. Increased methylation of mercury in sediments due to the presence of conditions which promote this process could explain the higher mercury levels found in all aquatic organisms in the lower end of the study area. Mercury levels in sediments were highest in zone 2 and this would be expected because zones 2 and 3 had very different sets of conditions which affect methylation. Zone 3 represented a transition zone between flowing river and reservoir. Flow rates decreased sharply as the Holston River merged with the upper end of John Sevier Lake. Deposition increased levels of organic matter and water temperature. Active organic matter decomposition with increased microbial activity could have caused increased methylation rates to occur in zone 3, followed by subsequent accumulation in aquatic organisms.

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