Terrestrial Invertebrates Reflect Increases in Mercury Mobilization across a Riparian Gradient

Elevated mercury concentrations among arthropods collected
from
a saturated riparian zone suggest that extreme flooding increases
the level of mercury mobilization. Total mercury was analyzed among
Oniscidea (sow bugs; Malacostraca), Opiliones (harvestmen; Arachnida),
and Succineidae (amber snails; Gastrapoda) along a riparian gradient
with varying water levels, including an area flooded by a rare event.
Four areas were compared: a dry upland, a flooded interface, a normal
interface, and a consistently saturated wetland. Average total mercury
concentration in harvestmen increased 426% in the flooded interface
relative to a dry location where individuals averaged 3.21 ±
14.4 ng Hg/g dry weight. Mercury concentrations in sow bugs increased
by 34% between the dry and flooded interface and reached an average
of 198 ± 42.6 ng Hg/g dry weight at the wetland center, a 97%
increase from the dry location concentration. Average mercury concentration
in snails increased by 48% in the normal interface relative to the
flooded interface (41.1 ± 15.9 ng Hg/ng dry weight), whereas
snails collected within the wetland had a 23% greater mercury burden
compared to those in the normal interface. Increased mercury in invertebrates
is associated with increased proximity to the wetland center, and
newly saturated soils mobilize mercury into invertebrates during flooding
moments.