The impact of metal pollution on soil faunal and microbial activity in two grassland ecosystems

In this study the influence of metal pollution on soil functional activity was evaluated by means of Bait lamina and BIOLOG® EcoPlates™ assays. The in situ bait lamina assay investigates the feeding activity of macrofauna, mesofauna and microarthropods while the BIOLOG® EcoPlate™ assay measures the metabolic fingerprint of a selectively extracted microbial community. Both assays proved sensitive enough to reveal changes in the soil community between the plots nearest to and further away from a metal pollution source. Feeding activity (FA) at the less polluted plots reached percentages of 90% while plots nearer to the source of pollution reached percentages as low as 10%. After 2 and 6 days of incubation average well color development (AWCD) and functional richness (R′) were significantly lower at the plots closest to the source of pollution. While the Shannon Wiener diversity index (H′) decreased significantly at sites nearer to the source of pollution after 2 days but not after 6 days of incubation. Arsenic, Cu and Pb correlated significantly and negatively with feeding activity and functional indices while the role of changing environmental factors such as moisture percentage could not be ruled out completely. Compared to the Bait lamina method that is used in situ and which is therefore more affected by site specific variation, the BIOLOG assay, which excludes confounding factors such as low moisture percentage, may be a more reliable assay to measure soil functional activity.