Lacustrine responses to decreasing wet mercury deposition rates--results from a case study in northern Minnesota.
We present a case study comparing metrics of methylmercury (MeHg) contamination for four undeveloped lakes in Voyageurs National Park to wet atmospheric deposition of mercury (Hg), sulfate (SO4(-2)), and hydrogen ion (H+) in northern Minnesota. Annual wet Hg, SO4(-2), and H+ deposition rates at two nearby precipitation monitoring sites indicate considerable decreases from 1998 to 2012 (mean decreases of 32, 48, and 66%, respectively). Consistent with decreases in the atmospheric pollutants, epilimnetic aqueous methylmercury (MeHgaq) and mercury in small yellow perch (Hgfish) decreased in two of four lakes (mean decreases of 46.5% and 34.5%, respectively, between 2001 and 2012). Counter to decreases in the atmospheric pollutants, MeHgaq increased by 85% in a third lake, whereas Hgfish increased by 80%. The fourth lake had two disturbances in its watershed during the study period (forest fire; changes in shoreline inundation due to beaver activity); this lake lacked overall trends in MeHgaq and Hgfish. The diverging responses among the study lakes exemplify the complexity of ecosystem responses to decreased loads of atmospheric pollutants.
U.S. Geological Survey, 2280 Woodale Drive, Mounds View, Minnesota 55112, United States.
Mark E
ME
Brigham
Mark B
MB
Sandheinrich
David A
DA
Gay
Ryan P
RP
Maki
David P
DP
Krabbenhoft
James G
JG
Wiener
D000818:Animals; D017753:Ecosystem; D060106:Lakes / Q000032:analysis* / Q000737:chemistry; D008628:Mercury / Q000032:analysis*; D008767:Methylmercury Compounds / Q000032:analysis*; D008910:Minnesota; D010471:Perches / Q000378:metabolism; D014874:Water Pollutants, Chemical / Q000032:analysis*
D008767:Methylmercury Compounds; D014874:Water Pollutants, Chemical; D008628:Mercury