Can laboratory toxicity tests explain the pattern of field communities of algae, plants, and invertebrates along a toxicity gradient of post-mining sites?

The responses of soil algae, vascular plants, and invertebrates to soils collected along a toxicity gradient of post-mining sites were measured in laboratory toxicity tests, and the responses were compared with field pattern of communities of these organisms along this gradient. The study was performed in the Sokolov coal mining district (Czech Republic) where three types of soil materials were sampled: highly acidic coal-rich clays (pH 2.8 +/- 0.4), slightly acidic tertiary volcanic ashes (4.6 +/- 1.6), and alkaline tertiary clays (8.2 +/- 0.1). Laboratory tests with eight species of algae, two species of invertebrates (Enchytraeus crypticus and Folsomia candida), and one plant species (Sinapis alba) gave similar results and showed that besides low pH and the associated solubility of Al, As content and high conductivity were the major factors correlated with toxicity of post-mining substrates. Communities consisting of 69 species of soil algae, 21 species of vascular plants, and 44 morphospecies of soil macrofauna were found during field survey of post mining sites. The toxicity tests explained about 21% of the data variability for the algal community in the field but did not explain any of the data variability for the plant or invertebrate community in the field. The poor ability of laboratory tests to predict the data obtained from surveys of natural communities may result from environmental factors and biotic interactions that have strong effects in the field but not in the laboratory. The study shows that understanding the effects of toxic agents in a complex environmental gradient may require more research on the interaction between toxicity and environmental factors. (C) 2011 Elsevier B.V. All rights reserved.