Some of the highest concentrations of wet atmospheric deposition of mercury for the U.S. are recorded in Mesa Verde National Park in the southwest corner of Colorado, and several nearby reservoirs have fish consumption advisories for mercury. We asked whether or not similarly high concentrations of mercury are deposited at two sites near a high-elevation, class one Wilderness Area, which is farther from potential local sources of mercury emissions than the National Park but receives more annual precipitation. Back trajectory analyses were used to investigate sources of the mercury in the deposition samples. We further asked how much mercury is incorporated into the zooplankton of 28 lakes and reservoirs in this region and investigated biological and physical sources of variability. Sediment cores from four of the high-elevation lakes were analyzed to understand changes in mercury flux over time.
Results/Conclusions Wet deposition samples collected from April to October 2007 had concentrations of 3-70 ng Hg/L, which were slightly lower than samples from the National Park. Back trajectory analyses suggest that samples with high mercury concentration often are associated with source areas to the south and southwest that have coal-fired power plants. Mercury in zooplankton varied greatly among size fractions and lakes, ranging from undetectable to 89 ng MeHg/g dry for the 80-300 um size class and 5-185 ng MeHg/g dry. Mercury flux measured by sediment cores increased from preindustrial levels beginning ~1870 and either peaked from 1970-1990 before declining to mid-levels after 1990 or increased rapidly starting at about 1960 but did not demonstrate much of a decline after 1990. These data show that atmospheric mercury is being deposited at high concentrations at high-elevation sites downwind of a coal-fired energy production area, but that the effect on aquatic food webs is variable. Sources of variability will be discussed.
