After what feels like ages (actually, 5 months is quite a long time!) I have finished my fieldwork, hurrah! I sampled soil and leaf-litter invertebrates, and microbes, in total of 38 sites in 6 different land-use types (deciduous forest, coniferous forest, heathland, pasture, cropland and urban areas) with the aim to compare how species differ between them.
The majority of invertebrates hibernate during the winter, since they do not produce their own body heat like mammals and birds it is too cold for them to be active. However, 10cm under the ground the soil is often a few degrees warmer than the air and many soil animals are still active, including earthworm, so I am still busy out in the cold and rain digging them up for my PhD research – I recently found 16 earthworms from a 20 cm x 20 cm soil pit at a farm where the soil temperature was 4°C!
When temperatures fall below 0°C and water in the soil freezes many earthworms simply burrow into deeper layers where they can survive but earthworms which live on the surface instead rely on chemical defences to tolerate cold temperatures. Earthworms can avoid freezing by increasing the amount of sugars in their body fluids, this reduces the temperature at which they will freeze – in the same way putting antifreeze in your car washer fluid keeps it liquid.
Most of the danger from freezing is that water expands when it becomes solid, which damages the tissues of the earthworm. This damage can be reduced by reducing the water content of the body – adult earthworms are not very good at surviving dehydration, but their cocoons are so earthworm cocoons are very resistant to cold. The cocoons of the earthworm Dendrodrilus rubidus is known to survive temperatures below −40°C and in the laboratory have survived immersion in liquid nitrogen at −196°C!
The award for chilliest worm has to go to the ‘ice worms’, these are a type of potworm, (family Enchytraeidae), cousins to earthworms, and live exclusively within the ice of glaciers. They are so adapted to the cold that they die at temperatures above 5°C. You won’t find any in the UK, although you may find their relatives – small white segmented worms – while digging in the soil or in compost heaps.
For the last couple of months I have been doing fieldwork in the New Forest – a National Park in my home county of Hampshire. The New Forest was previously sampled by the Natural History Museum Soil Biodiversity Group during the New Forest Qualitative Inventory in 2010 and I have been revisiting some of the sites and also new ones. The aim of my sampling is to collect soil and leaf litter invertebrates, and soil cores for microbial analysis in six different land uses which correspond to those used in the PREDICTS project: mature secondary vegetation, immature secondary vegetation (heathland), plantation forest, grassland, cropland and urban areas.
Many of the methods I am using are the same as I used in my MSc project, I dig a hole to collect earthworms and other soil animals, and sieve leaf litter which are placed in Winkler bags to extract invertebrates living in the leaves. I have also being doing pitfall trapping, which is the first time I have done it as part of a research project rather than casual recording of beetles. I really dislike pitfall trapping!
What a pitfall trap?
A pitfall trap is one of the simplest forms of collecting invertebrates for ecological surveys, it is simply a cup set into the ground so that the rim is at ground level. As the invertebrates run across the surface they fall in and are trapped. Usually the cup is filled with liquid which kills and preserves the animals until the trap is collected, although you can run them dry if they are checked often to prevent the captives eating one another. There are several variations of pitfall traps, including putting bait and using baffles to herd the animals in the trap, but I used the basic type for my research. They are not a very representative way of collecting invertebrates as they only catch things that run around on the surface – particularly predatory beetles, and I am not entirely happy with them as a way of comparing communities. However, they are commonly used for ecological surveys and I don’t think I could have got away without doing them, and I am not using them as a method alone. Eminent entomologist Prof Simon Leather discusses pitfall traps in much more detail than this on his blog – which I highly recommend.
The New Forest is famous for its free roaming livestock, especially the New Forest ponies, but also cattle, donkeys and, in the autumn, pigs. It is also open to the public and popular with tourists, walkers, dog-walkers etc. so I ensured I used non-toxic preservative and covered the pitfall traps with a lid raised of the ground to try and prevent animals drinking from them. The lids also had my contact details and information on the project to avoid them being interfered with my well-meaning passers by. Unfortunately ponies do not read so I did loose three to being trampled and thrown about by ponies! So that is irritation number one.
The pitfall traps were left and collected after a week, this was irritation number 2 as it meant coming back to the sites the next week, it was also sometimes challenging to find them even with GPS co-ordinates! One we never managed to find as the co-ordinates had not been recorded correctly. After all that work, here is what you get:
This was a particularly nasty one with lots of specimens and not much preservative, some of the others were not as bad. The worse invertebrate to find in your pitfall trap are slugs, they go horribly bloated and get slime all over the other specimens, but thankfully I did not have too many cases of those. The specimens are then rinsed off and preserved in alcohol until its time to identify them – that’s for another post!
Today I look back at my volunteer work sorting leaf litter samples with the Natural History Museum Soil Biodiversity Group.
This week’s #throwbackthursday looks back at fieldwork as part of the Natural History Museum Soil Biodiversity Group NVC project.
This week’s Throwback Thursday looks back at the Earthworm Society of Britain field trip to Richmond Park in 2014.
This week’s #throwbackthursday chronicles the final part of field work on the NERC BESS earthworm project in 2013 – hard to believe two years have past since we finished!
Two years ago I was volunteering on yet another week of earthworm sampling on the NERC BESS project, this time in Leicestershire and Dorset. This week features farty mustard solution and an exciting day in an active quarry!
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.
 |
|
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 blasting (guess who made the excited squeal!) |
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!
 |
|
Off for a well-earned meal after a hard day’s earthworm sampling |
Analysis of the NERC BESS Earthworm project is still on going, and a paper is in progress. The Dorset site had particularly high earthworm numbers, with over 200 found in one pit! I will discuss that in another #throwbackthursday. I also plan to use the NERC BESS data to compare with my PhD data so taking time out to volunteer on the project is paying off well!
Over one year into my PhD now, and I had been hoping to blog a little reflection on this but things have been rather hectic! Instead here is a look back to some more earthworm fieldwork I volunteered on in November 2013, digging holes in Somerset and Berkshire.
For eight days in November I returned for more earthworm survey work with the Natural History Museum Soil Biodiversity Group, this time in Somerset and Berkshire. A small team of volunteers this time, just myself and long-time SBG volunteer Irfaan, travelled first to the Somerset site to continue work started the previous week. We had been informed the Somerset site was the most beautiful yet but when we arrived on Monday the fog was so thick we had to take David’s word for it! Thankfully, by Tuesday the sun had returned to reveal a superb landscape, the countryside you imagine from hundreds of years ago, with little patchwork fields fringed with ancient hedgerows.
What a difference a day makes in Somerset
Four fields are sampled per farm, covering a spectrum of management intensity, such as how often the field is grazed, how much fertiliser (animal or artificial) is added and whether it has been ploughed or used for crops in the past. The field we worked first was the lowest intensity field at the Somerset site, not surprisingly as it was some distance from the nearest track, was steep and had springs running through it. This field had never been ploughed, giving an odd feeling of being possibly the first people to disturb the soil. It also had the biggest Yellow Meadow Ant (Lasius flavus) mounds I have ever seen!
Horse battered Yellow Meadow Ant (Lasius flavus) mound, at least two foot tall
 |
 |
Digging and coring in Somerset, quite possibly the first time the soil has been broken by man!
Shire Horses in Somerset
Dipterological distraction: Noon Fly (Mesembrina meridiana) in Somerset (thanks to Georgie for this photograph from the previous week’s visit)
If he had fallen over I could have bagged £300 pounds!
Once the location is marked with a flag it’s time to start over again taking measurements, digging a pit, taking samples and hunting for worms!
Irfaan and I intently sorting soil for worms
There’s one!
Blue-grey worm (Octolasion cyaneum)
On Thursday we left Somerset for Berkshire, unfortunately still with a field left to finish. The site in Berkshire was the Organic Research Centre Elm Farm.
Excitingly the very first pit had a bumper crop of the UK’s largest earthworm – Lumbricus terrestris emerge when the mustard solution was added, some were bigger than by baby snakes at home! Could this be because of higher organic inputs in this field than Somerset? The statistics will tell us in time (hopefully!).
Lumbricus terrestris expelled by mustard solution
Must get on with planning my own fieldwork!
Just in time for UK Fungus Day this week’s #throwbackthursday looks back at a training course on the identification of fungi I attended in October 2013.
