John Wiley & Sons, Ltd.

The potentiation of zinc toxicity by soil moisture in a boreal forest ecosystem

Northern boreal forests often experience forest dieback as a result of metal ore mining and smelting. The common solution is to lime the soil which increases pH, reducing metal toxicity and encouraging recovery. However, in certain situations, such as Flin Flon, Manitoba, Canada, liming has only yielded moderate benefits with some locations responding well to liming and other locations, not at all. Here, in an effort to increase the effectiveness of the ecorestoration strategy, we investigated if these differences in liming responsiveness were linked to differences in toxicity. Toxicity of metal impacted Flin Flon soils on the oribatid mite Oppia nitens and the collembolan Folsomia candida were assessed, with a view to identify the metal of concern in the area. The effects of moisture content on metal sorption, uptake and toxicity to the invertebrates were also investigated. Toxicity tests with the invertebrates were conducted using either Flin Flon soils or artificial soils with moisture content adjusted to 30, 45, 60 or 75% of the maximum water holding capacity of the soil samples. The Relative to Cd Toxicity Model identified Zn as the metal of concern in the area and this was confirmed with validation tests with field contaminated soils. Further, increasing moisture content in soils increased the amount of mobile Zn available for uptake with the ion exchange resin. Survival and reproduction of both invertebrates were reduced under Zn exposure as moisture level increased. Thus moisture collecting landforms, which are often also associated with high Zn concentrations at Flin Flon, have as a result, higher Zn toxicity to the soil ecosystem due to increases in soil moisture. This article is protected by copyright. All rights reserved

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