Mercury Distribution in Sediments and Bioaccumulation by Fish in Two Oregon Reservoirs: Point-Source and Nonpoint-Source Impacted Systems

Abstract

Mercury pollution was compared in two Oregon reservoirs of similar size and age, located within the same ecoregion. Cottage Grove Reservoir was distinguished by a history of mercury mining and processing within its watershed, while Dorena Reservoir was not. Mercury concentrations in sediments of the reservoirs, tributary streams, and three species of fish were measured. Sediment mercury concentrations in the main tributary of Cottage Grove Reservoir, which drains the subbasin where past mercury mining occurred, was tenfold higher than mercury in sediments from other reservoir tributaries. There were no significant differences between sediment mercury concentrations in the tributaries of Dorena Reservoir. The average mercury concentration in the basin sediment of Cottage Grove Reservoir (0.67 +/- 0.05 microg/g dry wt) was higher than for Dorena Reservoir (0.12 +/- 0.01 microg/g dry wt). At Cottage Grove Reservoir, maximum mercury concentrations were near or exceeded 1 microg/g wet wt for largemouth bass (Micropterus salmonides) and bluegill (Lepomis macrochirus) epaxial muscle. Muscle mercury concentrations in largemouth bass and crappie (Pomoxis nigromaculatus) from Cottage Grove Reservoir were significantly higher than from the same species from Dorena Reservoir. Numbers of bluegill of the same age available from both reservoirs were too small for statistical comparisons. Mercury concentrations in largemouth bass muscle fluctuated annually in both reservoirs. Fish ages were consistently positively correlated with muscle mercury concentrations in only the point-source-impacted reservoir. These results indicated that a point source, Black Butte Mine, contributed amounts of mercury greatly in excess of mobilization from natural deposits, atmospheric deposition, and small-scale uses of the metal as an amalgamating agent in gold mining.

Seasonal Variations in the Use of Profundal Habitat among Freshwater Fishes in Lake Norsjø, Southern Norway, and Subsequent Effects on Fish Mercury Concentrations

“…A. charr may then be starving during winter, which leads to near significantly higher Tot-Hg-concentrations [22], and significantly higher Tot-Hg-concentrations in spring before the onset of the growth season. Similar seasonal variations related to growth rates and condition have been reported in littoral and pelagic habitat and streams [23][24][25][26][27][28][29][30]. The different residual variances per season are likely caused by different sample sizes, however, the highest variance in winter may also be supported by different reactions to starvation.…”

“…Contrarily, increasing weight at the same length or age results in lower Hg-concentrations, either by somatic growth dilution (SGD) [11,[15][16][17][18][19][20][21], or by further concentrating Hg during starvation [22]. The combination of these two effects results in seasonal variations in Hg-concentrations in fish [23][24][25][26][27][28][29][30], however, some studies suggest that this is not the case in all populations [31][32][33].…”

Adverse Effects of Mercury and Some Management Options to Reduce Dental Amalgam Waste

“…Sediment mercury levels follow a similar pattern; mercury levels were lowest in the Middle Fork that is considered a more pristine area and highest in the Coast Fork (Cottage Grove) where there is historic mining activities and mercury contaminated mine tailings (Park and Curtis, 1997). Mercury levels were the highest in piscivorous (fish-eating) fish and the lowest in invertevorous (invertebrate-eating) fish, reinforcing mercury's bioaccumulative properties throughout the food web (Hope and Rubin, 2005).…”

Final Report on the Aquatic Mercury Assessment Study

“…Aqueous mercury levels are affected by many factors including oxygen concentration, precipitation, temperature, water level, and wetland runoff (Sellers et al 2001, Hurley et al 1998a, Regnell et al 1997. Although less variation would be expected in fish muscle tissue (Downs et al 1998, Foster et al 2000, where the biological half life of mercury can be one to three years (McKim et al 1976, Burrows andKrenkel 1973), at least one study suggests substantial seasonal variation in fish tissue mercury as a possible consequence of variations in mercury uptake (Park and Curtis 1997). Also, localized aggregations of fish from the same water body may exhibit significant spatial variations in mercury concentration as a likely result of differences in mercury bioavailability among foraging areas (Munn and Short 1997).…”