Colonisation, survival and spread of earthworms on a partially restored landfill site

Allolobophora chlorotica and Aporrectodea longa were inoculated into a clay landfill site cap at Calvert, Buckinghamshire during the Spring of 1992,. Monitoring of these animals, their offspring and natural colonists of the s ite using a variety of methods, has occurred since then. Both inoculated sp ecies have established sustainable populations, with an index of cast-count ing showing that A. longa numbers have at least doubled. The spread of this species has been steady, but slow through the compacted day cap, with worm s moving up to 10 m from points of inoculation after 5 years (mean value 2. 3 m). From digging and hand-sorting of samples, A. chlorotica has been show n to move comparable distances and earthworm densities overall are now at l east 110 m(-2). Numbers of A. chlorotica were significantly (p < 0.05) high er in areas where both species were inoculated, compared to areas where the y were inoculated in isolation. Other species found on site include Eisenie lla tetraedra and Lumbricus rubellus. Although the inoculated earthworm pop ulations appear to be expanding and flourishing, physical soil conditions h ave not changed significantly over the study period. The rate of ameliorati on of this type of material would appear to be extremely slow and introduct ion of earthworms can only partially meet this requirement.