Trend reversal of mercury concentrations in piscivorous fish from Minnesota lakes: 1982-2006.
The trend of mercury concentrations in standardized length northern pike (NP55) and walleye (WE40) was evaluated for a 25-year period, 1982-2006, based on a data set of 1707 cases from 845 lakes throughout Minnesota. Two lines of evidence--changes within individual lakes and regression analyses for all lakes together--indicate a downward trend before the mid-1990s and an upward trend thereafter. Within lakes,the evidence is based on the difference between two years of data at least 5 years apart. Before 1995, 64% decreased and 31% increased; after 1995,35% decreased and 60% increased. Three regression models-linear, quadratic, and two-segment linear piecewise-were evaluated for best fit using the Akaike Information Criteria (AIC). The two-segment linear piecewise regression model, with a breakpoint of 1992, was the best fit, while the quadratic model, with an inflection point of 1995, also had substantial support. The linear model was not supported (deltaAIC > 10). Based on least-squares linear regressions applied separately to 1982-1992 and 1992-2006, mercury concentrations in NP55 and WE40 decreased 4.6 +/- 1.3% (95% CI) per year from 1982 to 1992 and increased 1.4 +/- 0.8% per year from 1992 to 2006.
Monson
Bruce A
BA
Minnesota Pollution Control Agency, 520 Lafayette Road No., St. Paul, Minnesota, USA. bruce.monson@state.mn.us
D000818:Animals; D005399:Fishes / Q000378:metabolism* / Q000502:physiology*; D005506:Food Contamination; D008628:Mercury / Q000737:chemistry*; D008910:Minnesota; D011235:Predatory Behavior / Q000502:physiology*; D013997:Time Factors; D014874:Water Pollutants, Chemical / Q000737:chemistry*
D014874:Water Pollutants, Chemical; D008628:Mercury