Bait-Lamina Test in the Assessment of Polluted Soils: Choice of Exposure Duration

Abstract

Measurement of feeding activity of soil saprophages by the consumption of bait made of plant material—the bait-lamina test—is used for solving many problems of functional ecology. It is important to choose the correct exposure duration of bait to obtain unbiased data. This requires the analysis of time dependence of bait consumption, however, it has not been performed for technogenically polluted soils. We have compared two study sites of spruce–fir forest in the area affected by long-term emissions of the Middle Ural Copper Smelter: background (30 km away from the plant) and strongly polluted by heavy metals (1 km away). The feeding activity was evaluated on days 3, 6, 9, 12, and 15. The dependence of the consumed bait portion on the exposure duration sharply differs at the background and polluted sites: it is clear linear in the period from the third till the twelfth day on the former and is absent on the latter. This is related to the difference not only in the abundance, but also in the species composition of saprophages. The pollution effect is the most pronounced on the ninth day of exposure, and deviations from this period for more than two days both to the higher and smaller sides are undesirable. The recalculations of the original values should be carefully applied: the linear interpolation may be used to recalculate the activity in the background area to adjust it to the exposure duration in the polluted site, but not vice versa.