Analytical Methods:Biological Activity

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1 Monitoring Biological Activity

[edit] Monitoring Biological Activity

[edit] Degradation processes linked to biological activity

Soil biodiversity and biological activity in archaeological deposits will be affected by the nature of the substrate (soil or anthropogenic deposit), the physical and chemical conditions in the soil or burial environment, and, in the upper parts of the profile at least, by land use and management. There are three aspects to biological activity:

Roots
- Physical disruption of structures through penetration and tree throw,
- Localised compaction,
- Localised changes in soil chemistry and enhanced earthworm and microbial activity.
Soil macrofauna (rabbits, moles, termites, earthworms etc.)
- Physical disruption of structures through burrowing and undermining
- Mixing (bioturbation) of stratigraphy
- Burial of surface objects by earthworms casting at the surface
Microbes
- Decomposition of organic materials
- Development of reducing conditions

[edit] Approaches to monitoring biological activity

Soil macrofauna activity can often be monitored by assessing the surface evidence, for example the number of worm casts or the frequency and size of rabbit burrow entrances. However, the level of surface activity can be hard to relate to subsurface destruction, and it is also important that at the outset an assessment is made of the level of stratigraphic preservation of the site. The sub-surface effects can only be described and measured by direct observation, itself a destructive process.

Soil microbial activity can be measured in terms of microbial biomass and / or soil respiration rates. For agricultural soil quality the presence of key microfaunal groups is also used (Litterick et al., 2005), but to date too little is known about the interactions between different microbes and archaeological remains to make this a useful measurement.

Microbial biomass reflects the living microbial community of the soil, and it is this community that regulates the decomposition of soil and archaeological organic materials. However, microbial biomass is closely linked to soil organic matter content, so in soils where there are likely to be changes in organic matter content,e.g. through manuring, soil microbial activity will be a much poorer reflection of what is happening to the archaeological deposits.

Soil respiration rates give a good indication of decomposition processes in soil (Anderson, 1982). Respiration rates are sensitive to changes in soil moisture, temperature, oxidation etc., hence soil respiration can be used to monitor the effect of changes in these properties on decomposition rates. However, it doesn't provide any information on the nature of the carbon being used. Whilst an increase in soil respiration rates may indicate an increased rate of loss of archaeological organic matter, it may also be linked to losses of younger soil organic carbon.

[edit] Sampling strategies

Disturbance can significantly affect soil biology, hence where possible in-situ measurements are desirable. It also means that measurement of microbial activity before, during and after disturbance events such as excavation, drainage etc. can be very revealing about their likely effects on the archaeological remains (particularly organic remains).

[edit] References

Anderson, J.P.E. (1982) Soil respiration, methods of soil analysis, part 2. American Society of Agronomy, Madison, Wisconsin.
Litterick, A., Ball, B., Merrilees, D., Rees, B. and Sinclair, A. (2005) Indicators of soil resilience for Scotland and Northern Ireland. Final report of SNIFFER Project, LQ06, Edinburgh.