Earthworms: Development and Testing of a Sampling Methodology, Assessment of a Field Guide to their Identification, and Investigation of the Relationship with Soil Contamination

By James Bone: September 2008

Supervisors: Dr Nick Voulvoulis and Dr Martin Head
Collaborators: Natural History Museum: Dr David Jones, Dr Paul Eggleton, and Dr Steve Brooks

Introduction

James taking samples in Hounslow Heath

This research aims to optimise and assess the effectiveness of the OPAL soil and earthworm field guide to collect earthworm population and diversity information by non-specialists.

Earthworms are known to increase rainfall infiltration rates through soil, improve soil aeration and allow greater root development. The incorporation of organic matter (dead leaves, plants etc.) through the action of casting and the removal of surface litter into the mineral soil leads to enhanced nutrient availability and soil fertility.

Existing distribution records for earthworm species in the UK are poor, a function of under recording rather than earthworm absence. A methodology was developed taking into account past studies, relevant standards, and data needs, and a recording form was also developed taking into account existing recording forms.

The field guide was tested through pilot studies - participants collected and identified earthworms, recorded results and collected specimens. Participant’s identifications were compared to expert identifications; using a hand lens and using a microscope.

Method

The relationship between earthworm population and diversity and soil contamination was investigated through sampling of earthworms over a soil contaminant concentration gradient. Geographic Information System (GIS) software was used to compile plots of relative hazard to earthworms using literature toxicity values. Plots were compiled that illustrated recovered earthworms and their distributions, for each species, for earthworm ecological groupings, and for total earthworms recovered.

Pilot study 1 - involved assessment of the field guide with three socioeconomic groups; in total 19 locations were sampled. Adult earthworms were recovered from 6 locations; with identifications at 4; of these the rate of correct identification was 50%.

Pilot study 2 - involved 16 participants; adult earthworms were recovered by 2 participants and none of the identifications were correct. Comparison of expert hand lens identification with microscope identifications showed that hand-lens users were correct 70% of the time.

Pilot study 3 - involved assessment of the field guide on primary school children; 1 adult was identified but expert identification revealed it to be a juvenile.

Results and conclusion

Analysis of earthworm species and environmental variables demonstrated that there was a significant relationship only between nickel and Allolobophora chlorotica. A significant relationship was found to exist between the endogeic ecological group and the environmental variables arsenic and copper.

Testing the field guide revealed participants can make positive identifications using the guide but that the error level is potentially high. Improvements in layout of the guide and level of support provided to participants may improve its effectiveness. Expert identification using the field guide and lens with those made using a microscope demonstrated a high level of agreement.

Assessment of the relationship between earthworm population, diversity and soil contamination revealed no causal relationship can be determined from this study, likely to be due to confounding variables, and a lack of data due to earthworm seasonal dormancy. Arsenic was found to have a significant positive relationship with the endogeic earthworm ecological group; this may be due to adaptation.

Following testing of the identification guide, in conjunction with the soil properties questionnaire, the final version was produced in collaboration with the Field Studies Council for incorporation into the survey field guide. This work and following investigations will have policy implications for soil and soil biodiversity such as the Soil Strategy for England, and the EU Soil Thematic Strategy.

Download the full project summary (PDF, 1.4MB)

Take part in the Soil and Earthworm Survey

 

 

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