Digging for earthworms in Dorset

As much as I enjoy working at my computer analysing data, it felt good to get out to get outside and collect some data of my own recently. I was sampling earthworms in Purbeck, Dorset with the help of Soil Biodiversity Group volunteers John Chesebro and Fevziye Hasan (https://twitter.com/fezidae), Rachel Efrat of the British Geological Survey (https://twitter.com/RachelEfrat) and my boyfriend Andrew.

The study site is part of a long-term study into heathland restoration. Heathlands are found in areas of free-draining infertile, acidic soils, and are dominated by shrubs such as heather and gorse. Part of this heath was converted to agricultural land in the 1950s by the application of large quantities of fertiliser to increase nutrients, and lime to increase the pH of the naturally acidic soils. Since then there has been a move to restore the original heathland vegetation, which is a habitat for rare species.

The original study compared different methods of making the soil more acidic, by removing the topsoil, adding sulphur or iron sulphates, these were then sown with cuttings from the nearby heathland. Not all the plots were successful, but it did result in a long gradient of different soil pH levels, which I am using to investigate the influence of pH on earthworms.

Heathland in the foreground with restored plot amongst pasture in background
Heathland in the foreground with restored plot amongst pasture in background

Earthworms are known to prefer alkaline conditions, and species vary in their tolerance to pH levels but the data we already have is confounded by being collected across different soil types and locations. At this site the plots are on the same soil type, so hopefully the data will show the pattern of earthworm abundance and species with pH which can then be compared with the overall data set to see if the patterns are similar or different.

I had a GPS device with the co-ordinates of the plots, and had chosen ones with a good range of pH measurements. Once we had found them the fieldwork was straightforward, we take measurements of soil pH, moisture and temperature and then dig a standard sized hole and collect any earthworms we find.

Volunteers Fez and John sorting soil for earthworms (thanks to Rachel Efrat for photo)
Volunteers Fez and John sorting soil for earthworms (thanks to Rachel Efrat for photo)

Any earthworms found in the soil were preserved in methylated spirits to be identified back in the laboratory.

Earthworms collected from soil in Dorset (thanks to Rachel Efrat for photo)
Earthworms collected from soil in Dorset (thanks to Rachel Efrat for photo)

We were fortunate to have three days of good weather, which was a novelty as my previous experiences of earthworm sampling has been in the cold and rain! The dry spring did mean the soils were not as wet as I expected however, which necessitated some changes to the sampling in order to maximise the number of earthworms sampled – hopefully it will be enough.

Earthworm sampling is dirty work!
Earthworm sampling is dirty work!
Post-fieldwork ice cream!
Post-fieldwork ice cream!

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