ISSN:
1573-515X
Keywords:
ANC
;
DOC
;
mercury
;
labile methylmercury
;
water
;
zooplankton
Source:
Springer Online Journal Archives 1860-2000
Topics:
Chemistry and Pharmacology
,
Geosciences
Notes:
Abstract Twelve softwater lakes in NE Minnesota were sampled in spring, summer, and fall of 1992 and 1993 for labile (unextracted) methyl-Hg, total (extracted) methyl-Hg, and total Hg in lake water and net plankton (≥300 µm). The lakes are small (5.6–56 ha), low productivity, headwater drainage or seepage lakes. They are acid-sensitive (ANC ≤200 µeq/L) but not low pH lakes (average pH 6.6). The lakes ranged in color from 8.5 to 70 PCU. Statistical analysis of the water chemistry variables and mercury species support the conclusion that these were a homogeneous set of lakes; therefore, seasonality of mercury forms was analyzed on combined (mean) data from the 12 lakes. Methyl-Hg in water declined throughout the growing season. HgT also declined sharply from spring to summer but increased again in the fall. In contrast to the methyl-Hg and Hg in water, concentrations in plankton were at the lowest levels in spring and rose to higher levels in summer. The mass of mercury in plankton increased from spring to fall, as did the methyl-Hg fraction, which increased from 20% of HgT in spring to 52% in autumn. Bioaccumulation factors (BAF) for methyl-Hg in net plankton increased over the growing season. Overall, log BAF for HgT in net plankton (wet wt.) was 4.45. Log BAF for methyl-Hg in plankton was 4.90 to 5.43 depending on the analytical form of methyl-Hg in water (labile or total). Seasonal patterns of methyl-Hg and HgT did not covary in water, but did covary in plankton. These results support the conclusion that measurement of Hg in water is not adequate in itself to determine the amount of bioavailable Hg (i.e., methyl-Hg) in a lake. Labile (unextracted) methyl-Hg could be a useful measurement of bioavailable Hg. Labile methyl-Hg exhibits the same seasonal patterns as total methyl-Hg, but does not require the extraction steps necessary for measuring total methyl-Hg.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1023/A:1005967413585
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