| Mercury (Hg) is an important environmental pollutant. Studies have investigated Hg cycling in aquatic environments, but the fate and transport of Hg in terrestrial environments has been little studied even though as much as 75% of Hg in lakes is derived from terrestrial systems. Hg exhibits a strong affinity for organic matter in soils and surface waters. The terrestrial processes and pathways that drive the transport of organic carbon (OC) also influence the transport and watershed cycling of Hg. Peatlands, the major source of OC exiting many watersheds in the boreal zone, play an important role in determining the availability of Hg for surface water transport. I determined the fluxes of Hg and OC through forested watershed systems and the effect that OC has on those fluxes. I characterized Hg and OC in each watershed hydrologic compartment and investigated the relationship between Hg and OC among and within hydrologic compartments. The main source of Hg in the terrestrial system is the forest canopy with deposition twice that in the open (13.0 {dollar}rmmu g msp{lcub}-2{rcub} yrsp{lcub}-1{rcub}{dollar} vs. 6.5 {dollar}rmmu g msp{lcub}-2{rcub} yrsp{lcub}-1{rcub}).{dollar} Canopy cover type strongly influences Hg deposition with increased deposition under conifers. Soils are sinks of Hg in the watershed. Hg concentration shows moderately strong relationships with dissolved OC (DOC) in throughfall, stronger relationships with DOC in stemflow and moderate to strong relationships with particulate OC (POC) in upland runoff, bog runoff, lagg waters and streamflow. Hg associated with POC accounts for 52% to 80% of the Hg transported from the six watersheds studied, with total transport ranging from 0.70 to 3.65 {dollar}rmmu g msp{lcub}-2{rcub} yrsp{lcub}-1{rcub}{dollar} (based on watershed area). Watershed geometry and hydrology both play an important role in determining the effect OC has on Hg transport. Partitioning of Hg to DOC, mobile POC, and solid immobile fractions of OC is related to the contact time between Hg and carbon sources. This study addresses the knowledge gaps that exist regarding the terrestrial transport of Hg, and provides an integrated, landscape-scale view of the major hydrologic and organic fluxes responsible for the transport of Hg from terrestrial to aquatic systems. |
