Whole-ecosystem study shows rapid fish-mercury response to changes in mercury deposition.
Methylmercury contamination of fisheries from centuries of industrial atmospheric emissions negatively impacts humans and wildlife worldwide. The response of fish methylmercury concentrations to changes in mercury deposition has been difficult to establish because sediments/soils contain large pools of historical contamination, and many factors in addition to deposition affect fish mercury. To test directly the response of fish contamination to changing mercury deposition, we conducted a whole-ecosystem experiment, increasing the mercury load to a lake and its watershed by the addition of enriched stable mercury isotopes. The isotopes allowed us to distinguish between experimentally applied mercury and mercury already present in the ecosystem and to examine bioaccumulation of mercury deposited to different parts of the watershed. Fish methylmercury concentrations responded rapidly to changes in mercury deposition over the first 3 years of study. Essentially all of the increase in fish methylmercury concentrations came from mercury deposited directly to the lake surface. In contrast, <1% of the mercury isotope deposited to the watershed was exported to the lake. Steady state was not reached within 3 years. Lake mercury isotope concentrations were still rising in lake biota, and watershed mercury isotope exports to the lake were increasing slowly. Therefore, we predict that mercury emissions reductions will yield rapid (years) reductions in fish methylmercury concentrations and will yield concomitant reductions in risk. However, a full response will be delayed by the gradual export of mercury stored in watersheds. The rate of response will vary among lakes depending on the relative surface areas of water and watershed.
Harris
Reed C
RC
Tetra Tech Inc., 180 Forestwood Drive, Oakville, ON, Canada L6J 4E6.
Rudd
John W M
JW
Amyot
Marc
M
Babiarz
Christopher L
CL
Beaty
Ken G
KG
Blanchfield
Paul J
PJ
Bodaly
R A
RA
Branfireun
Brian A
BA
Gilmour
Cynthia C
CC
Graydon
Jennifer A
JA
Heyes
Andrew
A
Hintelmann
Holger
H
Hurley
James P
JP
Kelly
Carol A
CA
Krabbenhoft
David P
DP
Lindberg
Steve E
SE
Mason
Robert P
RP
Paterson
Michael J
MJ
Podemski
Cheryl L
CL
Robinson
Art
A
Sandilands
Ken A
KA
Southworth
George R
GR
St Louis
Vincent L
VL
Tate
Michael T
MT
D000818:Animals; D017753:Ecosystem; D005399:Fishes / Q000378:metabolism*; D005618:Fresh Water / Q000737:chemistry*; D019015:Geologic Sediments / Q000737:chemistry*; D008629:Mercury Isotopes / Q000032:analysis; D008767:Methylmercury Compounds / Q000032:analysis* / Q000378:metabolism; D014877:Water Pollution, Chemical / Q000032:analysis*
D008629:Mercury Isotopes; D008767:Methylmercury Compounds