Biogeochemical cycling of methylmercury in lakes and tundra watersheds of Arctic Alaska.
The fate of atmospherically deposited and environmentally active Hg is uncertain in the Arctic, and of greatest toxicological concern is the transformation to monometh-ylmercury (MMHg). Lake/watershed mass balances were developed to examine MMHg cycling in four northern Alaska lakes near the ecological research station at Toolik Lake (68 degrees 38' N, 149 degrees 36' W). Primary features of the cycle are watershed runoff, sedimentary production and mobilization, burial, and photodecomposition in the water column. The principal source of MMHg is in situ benthic production with 80-91% of total inputs provided by diffusion from sediments. The production and contribution of MMHg from tundra watersheds is modest. Photodecomposition, though confined to a short ice-free season, provides the primary control for MMHg (66-88% of total inputs) and greatly attenuates bioaccumulation. Solid-phase MMHg and gross potential rates of Hg methylation, assayed with an isotopic tracer, vary positively with the level of inorganic Hg in filtered pore water, indicating that MMHg production is Hg-limited in these lakes. Moreover, sediment-waterfluxes of MMHg (i.e., net production at steady state) are related to sediment Hg loadings from the atmosphere. These results suggest that loadings of Hg derived from atmospheric deposition are a major factor affecting MMHg cycling in arctic ecosystems. However, environmental changes associated with warming of the Arctic (e.g., increased weathering, temperature, productivity, and organic loadings) may enhance MMHg bioaccumulation by stimulating Hg methylation and inhibiting photodecomposition.
Department of Marine Sciences, University of Connecticut, Groton, Connecticut 06340, USA. methylhg@whoi.edu
Chad R
CR
Hammerschmidt
William F
WF
Fitzgerald
Carl H
CH
Lamborg
Prentiss H
PH
Balcom
C Mao
CM
Tseng
D000413:Alaska; D004784:Environmental Monitoring; D005618:Fresh Water / Q000032:analysis; D019015:Geologic Sediments / Q000032:analysis; D008628:Mercury / Q000032:analysis; D008767:Methylmercury Compounds / Q000032:analysis* / Q000528:radiation effects; D010777:Photochemistry; D014466:Ultraviolet Rays; D014874:Water Pollutants, Chemical / Q000032:analysis* / Q000528:radiation effects; D014881:Water Supply / Q000032:analysis; D014887:Weather
D008767:Methylmercury Compounds; D014874:Water Pollutants, Chemical; D008628:Mercury