Environmental significance of earthworm secreted calcium carbonate

Project summary

This project is seeking to determine production rates of the calcium carbonate granules that earthworms secrete into soils.

We are also seeking to determine how long the granules survive in soils, whether their isotope systematics can be used to help palaeo-environmental interpretation and the chemistry and mineralogy of the granules, particularly with respect to contaminated soils and the stabilisation of the amorphous calcium carbonate found in the granules.

Background

The importance of earthworms in a variety of soil processes is well established, e.g. mixing and aeration of soil, breakdown of organic matter. It is less well appreciated that many earthworm species produce millimetre sized aggregates of calcite crystals called granules. Calcite granules have been known about since the groundbreaking work of Charles Darwin but little work has been carried out on them since.

A close up of a granule showing individual calcium carbonate rhombs The few studies that have been undertaken show that they are commonplace in soils but have not investigated production rates in a systematic fashion. Canti has produced estimates of earthworm granule production on the basis of production in initially granule free material. He suggests rates of up to 241 g of calcite m^-2 yr^-1 for a typical earthworm density of 300 m^-2, i.e. earthworm calcite granule production processes up to c. 60 kgC ha^-1 yr^-1. Typical CO₂ soil fluxes are 5 - 315 mol CO₂ m^-2 yr^-1 and typical soil C sequestration measures would remove 300 to 800 kgC ha^-1 yr^-1. Thus earthworm calcite granules are potentially highly significant in the terrestrial C cycle.

Funding

This has been obtained from The Natural Environment Research Council (NERC), Diamond and the Undergraduate Research Opportunities Programme.

Personnel

Mark Hodson, Denise Lambkin, Graham Langworthy, Anne Fraser, Caroline Layton, Kerry Gwilliam (University of Reading)
Trevor Piearce (University of Lancaster )
Matt Canti (English Heritage)
Paul Schofield (Natural History Museum)
Martin Lee (University of Glasgow)
Fred Mosselmans (Diamond)