Abstract
Twenty-five small, mainly oligotrophic, forest Swedish lakes were treated in different ways (e.g. liming) during 1987 in order to reduce the Hg levels in fish. The temporal variation of Hg concentration in sediments and water, and the extent that this variation can be related to normal lake characteristics and/or altered chemical conditions due to lake remedial measures was studied. Yearly mean alkalinity was increased from 0.07 to 0.18 meq l−1 and pH from 6.0 to 6.5 due to the treatments. The Hg concentration, as well as the Hg:C ratio, in seston was reduced after treatment; the median Hg/C ratio in seston decreased from 1.6 µg g−1 during 1986 to 0.8 µg g−1 during 1988. In the water column the concentration of the reactive plus non-reactive Hg fraction (RIHg, detected after reduction with NaBH4) showed a similar inter-year variation to the Hg content in seston, in contrast to the total Hg concentration in water column which was not decreased after the treatments. The increase in pH due to the remedial measures appeared to be the main cause of the decreased RIHg concentration, although the humic content (measured as colour) also explained a large part of the variation in RIHg concentration between the lakes. The decrease in the RIHg concentration in the lake water is the probable reason for the reduced Hg levels observed in the seston.
Published Version
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