More earthworm sampling, or the mystery of the farty mustard

Another county, another field… Last Monday and Tuesday I was again away with the Natural History Museum Soil Biodiversity Group, this time heading up to Leicestershire, for more earthworm sampling. Not as scenic as Somerset, we were sampling in a research farm near Loddington, in addition to myself, Sholto was again volunteering, I also met for the first time Salma and we were joined by Irfaan on Tuesday.

Another earthworm is sampled by Irfaan, with Salma and Sholto
Salma is trained in the correct way to retract the tape measure

In the previous week there was a problem with the mustard solution, which had developed a pungent smell of hydrogen sulphide (egg-fart gas). This was a concern because the smell was so strong it could be killing the worms in their burrows before they could emerge. Could the change be because of a faulty batch of mustard powder, or change to the ingredients? This week different batch numbers of mustard powder were purchased to test this.

David checks the bouquet of the mustard solution

Sniffing the mustard solution before pouring was now a necessary step, after the first mixing the smell was promising but by the morning some bottles had deteriorated. A new hypothesis was proposed that some sort of bacterial contamination was causing the smell and then it was realised the problem started after the mustard solution was made up using water from the soil laboratory back at the the Museum. The water in the labs comes from the museum’s own borehole and often has a slightly sulphurous smell, could some sulphur-reducing bacteria dwelling in the supply have caused the problem? It was decided to use fresh water bottles on the next trip.

Tuesday evening we travelled back to London and on Wednesday I spent the afternoon helping in the soil laboratory preparing the kit for Thursday and Friday and changing the alcohol in the earthworm samples. Earthworms have a high water content and this dilutes the alcohol, if the liquid is not replaced with fresh spirit the earthworms can start  to decompose which makes identification difficult (and stinky). Then Wednesday evening we left for Dorset – the final county being sampled in.

Soil Biodiversity Group earthworm samples
That’s a lot of earthworms!

Living in just the next county I have had many family holidays in Dorset and it was a pleasure to be back in beautiful Purbeck. Our site was near a quarry were limestone (Purbeck ‘marble’) is extracted and on Friday we got to view a blasting, which was very exciting.

Quarry manager Simon discusses the site with David
Quarry manager Simon discusses the site with David

The shallow soil did not yield many big anecic worms but large numbers of smaller species, since earthworms have a preference for areas of high pH. As might be expected there were also large numbers of snail shells which I tried my best not to be distracted by, although I think I may sneak a few specimens when we return next week!

The Soil Biodiversity Group at the end of a hard day's earthworm sampling
Off for a well-earned meal after a hard day’s earthworm sampling

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