FACTORS AFFECTING MERCURY BIOMAGNIFICATION IN RIVERINE FOOD WEBS IN THE ROCKY MOUNTAINS: CLARK FORK RIVER BASIN, MONTANA, U.S.A.

A number of studies suggest that Hg biomagnification in aquatic systems are dependent on two factors: a source of mercury and the potential for this mercury to become methylated. To compare the importance of these two factors in a riverine system I examine sites with varying sediment total mercury concentrations (source term) and varying environmental conditions affecting mercury methylation (wetland abundance, and riparian abundance) resulting in mercury concentration in three riverine trophic levels (aquatic invertebrates, fish, and osprey). I find that the mercury concentrations of low trophically positioned species, like aquatic invertebrates, are extremely dependent on mercury source concentrations (p=0.0143). While, species in subsequent trophic positions, such as fish see substantial influence from both the source term (p\u3c0.0001) and environmental conditions (wetland abundance, p\u3c0.0001 and riparian abundance, p=0.0008. Top trophic level species, such as osprey, have THg concentrations that are heavily dependent on environmental conditions (wetland abundance p\u3c0.0001 and riparian abundance, p=0.0001) and less on the sediment source of THg (p=.1234). Specifically, for these higher trophic levels, wetland abundance is the most explanatory environmental condition in determining the mercury methylation potential