The first popularly published assessments of earthworm populations came from Charles Darwin, who baited earthworms around his estate with scraps of paper rubbed with lard (1881). The study of earthworm populations has come a long way since– with researchers utilizing capture methods that include hand sorting, electroshocking, formalin, and using mustard and its extracts. Unfortunately, these surveys have either been in low pollution, idealized forests and agricultural areas or in highly specific polluted sites like mine tailings and slag heaps.
The primary purpose of this study was to understand what oligochaete populations are present in both non-polluted (pristine) and post-industrial brownfield soils laden with metal toxicants (polluted) in the same general region. In order to assess earthworm biodiversity and population counts across both polluted and pristine sites, the use of ground mustard powder in warm water was chosen as a liquid vermifuge. Earthworms were sampled across northeastern Pennsylvania and New Jersey, USA (a transect of 110 km) in forests, agricultural areas, post-industrial brownfields and superfund sites.
Almost all (97%) of the earthworms found across 90 sites were of three species, two of which are exotic (Lumbricus terrestris and L. rubellus), and one of which is highly invasive (Amynthas agrestis). Interestingly, there were more earthworms found in polluted sites, but they had significantly less biomass per specimen. Multivariate analyses of pollution level and environmental conditions, although indicative, are not completely diagnostic for spatial, temporal, or habitat distributions of earthworm species or population numbers. The next step in this biosurvey is to continue building a network of sampling sites across the USA and Canada in order to track earthworm populations, utilizing undergraduate researchers, ecology classes, and citizen scientists.