Microarthropoda and Enchytraeidae (Oligochaeta) in Naturally Lead-Contaminated Soil: A Gradient Study

Abstract

The microarthropod and enchytraeid fauna of a natural lead-contaminated soil in a Norwegian spruce, Picea abies (L.) Karst., forest was studied in gradients from unpolluted soil to the middle of a vegetation-free area. Because of dissolved lead from the bedrock, about 50 m2 of the forest floor lacked vegetation, and another 50 m2 had weakly developed vegetation. The lead content in the raw humus was up to 10–15% dry wt. Increasing levels of lead gave a gradual reduction in species numbers among plants and microarthropods. Microarthropod species varied in their ability to live in lead-polluted soil. Four groups were recognized: (1) sensitive species associated with normal vegetation, (2) less sensitive species occurring even in areas with strongly reduced vegetation, (3) tolerant species extending their range into vegetation-free areas, and (4) microarthropods favored by strong lead pollution ( Isotoma olivacea Tullberg among Collembola and Nanorchestes sp. among mites). Because a few species increased strongly in the vegetation-free area, the total abundance of microarthropods remained almost the same throughout the gradient. Changes in vegetation cover along the lead gradient is a confounding factor, but sensitive species proved to react equally negatively to increased lead levels when the vegetation factor was kept constant. Possible adaptations to lead during the postglacial period are discussed.