Earthworm Watch

Despite being important for ecosystem function, below-ground organisms are rarely the focus of Citizen Science projects. Earthworms are the most accessible of soil invertebrates - ubiquitous, easy to find and of known importance in soil productivity, carbon storage and flood mitigation.

Earthworm Watch is a Citizen Science project aiming to improve knowledge of how humans affect earthworms and how this influences soil health. The project launched April 2016 and is expected to run for at least two years - focussing on spring and autumn to coincide when earthworms are most active.

Photo of an earthworm by Victoria Burton

Project Background

Earthworms are known to influence soil carbon storage, plant productivity and rates of water drainage but mapping the benefits they provide is not yet possible because earthworm distribution and diversity is under-studied1. Data from urban soils is particularly lacking, despite gardens and other green spaces making up a large percentage of urban space, (e.g., 14% of Greater London2). Globally, soils store approximately 80% of terrestrial carbon3 but the UK's carbon stock in domestic garden soils has not been quantified, and the effects of human management on this stock - and on the other benefits earthworms provide - are yet to be studied.

Earthworm Watch will map key ecosystem benefits - productivity, flood mitigation and carbon storage - that are mediated by earthworms in the UK, now and under different possible future land-management scenarios. The survey will include optional experiments to test how gardens and other urban green spaces can be managed to promote earthworm populations and enhance the benefits they provide.

Study design

Photo showing two sampling plots

The survey requires digging a soil pit in two areas of different habitat e.g., lawn/flowerbed (pictured) or management e.g., mulched/unmulched. For each soil pit the habitat, number and types of earthworms, and soil properties are recorded. This paired study design controls for differences in effort and ability between participants, avoiding the main problem with analysing citizen science data.

In addition, participants have the opportunity to do an experiment by making a change to one of the two plots (e.g., adding nutrients in the form of vegetable waste) waiting a month, and then sampling both plots.

Scientific aims

The new surveys undertaken by citizen scientists will provide suitably structured data to answer the following questions:

  • How do abundance and functional diversity of earthworms respond to different land use and land management as well as to other environmental gradients (e.g., soil moisture, texture)?
  • How do three key ecosystem benefits mediated by earthworms - soil carbon storage, soil productivity and flood mitigation - vary geographically across the U.K.; and what is the total carbon stock in UK domestic garden soils?
  • Do these ecosystem benefits co-vary positively (forming ecosystem service 'bundles') or negatively (implying trade-offs), and does the answer depend on spatial scale?
  • What land management approaches are conducive to earthworm assemblages that provide good levels of ecosystem services?
  • How are earthworms and the ecosystem services they mediate projected to respond to future scenarios of land-use change?

Analysis

We will use mixed-effects models (as used in [4]) to focus on comparisons between plots sampled by the same participant to model earthworm abundance and diversity and to estimate soil carbon across the U.K. Maps of ecosystem benefits will be generated by combining data on water tables, soil type and climate with relationships between earthworm assemblages, soil fertility and drainage rates.

Audience and outputs

There has been pressure for a policy for improvements in soil quality (as has been seen for water and air) and the results of this project will feed into the necessary underpinning science. The project will inform management outcomes on both a local scale for gardeners and allotment holders, and on a city scale to inform policy decisions on urban landscape planning. In particular, there is a recognised need to understand factors determining carbon storage in U.K. soils and to improve our understanding of the relationships between soil carbon and soil health. The impact on participants will be to enthuse and inform them on the value of the life beneath their feet and its importance for the wider environment - they will also gain first-hand experience of the scientific process.

An additional incentive for participants will be the opportunity for acknowledgement in outputs, in the form of a massively co-authored publication on the database to be submitted to the Biodiversity Data Journal, and have their name against data in the Natural History Museum Data Portal. Particularly keen citizen scientists will be invited to participate in writing papers on the less analytic aspects of the project.

The Team

Earthworm Watch is a partnership between the Earthwatch Institute and the Natural History Museum in association with the Earthworm Society of Britain.

For further information, contact Victoria Burton or visit the Earthworm Watch website.

@EarthwormWatch on Twitter.

References

  1. Carpenter, D. et al. Mapping of earthworm distribution for the British Isles and Eire highlights the under-recording of an ecologically important group. Biodiversity and Conservation 21(2) 475-485 (2012).
  2. Smith, C. London: Garden city? (2010) IPCC. Summary for Policymakers. In Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.
  3. Newbold, T. et al. [Global effects of land use on local terrestrial biodiversity](http://www.nature.com/nature/journal/v520/n7545/full/nature14324.html Nature 520, 45-50 (2015).