Riparian Methylmercury Production Increases Riverine Mercury Flux and Food Web Concentrations

Area of Science:

• Environmental Chemistry
• Ecotoxicology
• Aquatic Ecology

Background:

• Methylmercury (MeHg) contamination poses a global threat to aquatic ecosystems.
• Rivers are complex systems for studying MeHg dynamics, making source identification critical for management.
• Riparian zones are recognized as biogeochemical hotspots for MeHg production but are understudied as riverine sources.

Purpose of the Study:

• To quantify hydrologic and biogeochemical processes influencing MeHg in a river system.
• To investigate the role of riparian zones as MeHg sources to the Snake River.
• To assess MeHg bioaccumulation in aquatic invertebrates within the study area.

Main Methods:

• Conducted field sampling at 16 locations along the Snake River.
• Quantified MeHg concentrations and loads in surface water and riparian porewater.
• Analyzed MeHg levels in benthic invertebrates (snails and clams).

Main Results:

• Approximately one-third of the Snake River's MeHg load was not accounted for by upstream sources.
• Increased MeHg loads in the river correlated significantly with MeHg in riparian porewaters.
• Surface water MeHg concentrations were positively correlated with MeHg in benthic snails and clams.

Conclusions:

• Riparian zones are a likely significant source of MeHg to the agriculturally intensive Snake River.
• MeHg produced in riparian zones is assimilated into local aquatic food webs.
• Findings provide insights for mitigating MeHg pollution in riverine environments.