WATERLOGGED : RECOVERY
Packing and storage of samples
Uncarbonized waterlogged plant material is very delicate and can easily be destroyed, so it is very important to handle it properly. After recovery, samples must be immediately packed in air-tight containers in their actual wet state. There are different ways of packing the samples, depending on the nature of the plant remains, on the sediment type or on special issues.
Packing type 1
For a normal sediment sample, it is sufficient to put it into a polyethylene bag of good quality, close this bag carefully and then wrap it in a second plastic bag, which again should be sealed in a air-tight way. Sealed plastic buckets are an alternative.
Packing type 2
Fragile remains such as layers of flax stems, dung remains, human coprolithes, moss pads etc. should be packed in hard plastic boxes. In this way they are protected much better and still remain in their original context.
Packing type 3
Sampling and packing in short plastic pipes (cut from a drainpipe) is possible for peat or fine sediments without coarse gravel by pressing the pipes from top into the sediment. This method is very useful for systematic sampling, because standardized samples can easily be recovered in this way.
Packing type 4
A profile column or block sample can be taken with the help of a plastic or metallic box, which has to be cut into the profile wall. If single large plant remains like hazelnuts or fruit stones are sampled separately, they can, with a good deal of additional water, be put into small plastic bags and then carefully set in boxes.
For labelling, water and light resistant pens or pencils and plastic labels are a must. In the case of profile columns or short plastic pipes, the labelling of profile-top and profile-bottom must not be forgotten. Judgement samples should be labelled in a different way to distinguish them from the systematic programme samples. Also they should be annotated with some remarks on their content or with a question to the archaeobotanist in the excavation notes or sample sheet. Places from where samples are taken should be recorded on the excavation notes.
For transport and storage, the packed samples should be stowed in solid plastic containers with a cover. If packed carefully, long term storage up to several years is possible under cool (<5oC), moist, above all dark conditions.
Before sieving: sediment analysis, pre-treatments and measurement
To obtain all the information that a sample contains, it is important to examine it before sieving with the naked eye and under low magnification. Only in its original state can the composition, consistency and texture of a sediment be analysed. Fragile plant remains such as tree leaves, flimsy stems, or complete inflorescenses, may still be complete in their original position, but after sieving broken by the jet of water. So these remain should better be picked out before sieving. A sediment analysis describing colour, water-state, texture, lithology of the sediment as well as inclusions may also be helpful (Kenward & Hall 1995).
It is necessary to reserve a small amount of the unprocessed sample material for slide scans of the fine matrix of the sediment. For that several microscopic preparations should be analysed under a microscope with 100-400-fold magnification. Fine cereal bran, tiny leave and wood fragments, plant hairs, different plant tissues inclusive epidermis fragments, stone cells, eggs from intestinal parasites, charcoal dust and other objects can be identified in this way.
While samples of "packing type 1" can often be processed immediately, the other types need some preparation before further processing. Profile columns, drillings and sometimes also the short pipe samples must stratigraphically be subsampled to get a vertical sample series, which can then be handled just like ordinary samples. It is often useful to make a drawing taken samples vertically. In the case of "packing type 2" samples the fragile plant remains still in situ, the moss pads or the coprolithes must be carefully separated from the surrounding sediment.
In some cases, especially if the sample is loamy, it may be soaked in water for at least 12 hours. The addition of chemicals should be avoided, because delicate plant tissues can loose their colour or may even be damaged.
Before sieving, each sample must be quantified by measuring the weight and the volume. There are two different ways to determine the volume. The best way to determine the volume is to put the sample into a bucket with volume measuments and to add a defined quantitiy of water, so that the sample is totally covered. The entire volume is measured. The volume of the sample is the difference between the entire volume and the added water. In the case of solid block samples (cuboid samples, samples from profile columns or pipe samples) the volumen can also be calculated.
As samples from waterlogged sites are usually of small volume, sieving often takes place in the lab and not on the excavation. However there may be exceptions, when large quantities of sediment are sieved to obtain fruit stones or other objects of a larger size, as for example, applied for the “bulk samples” mentioned by Kenward & Hall (1995) with a minimum of 30 kg, which were sieved to 1 mm only.
In the case of waterlogged sediments wet-sieving or wash-over is usually performed rather than flotation, because the water-saturated plant remains do not always float to the surface. For wet sieving, several sieves with different mesh sizes are used. The minium is a set of two sieves with 0.5 and 2.0 mm mesh as used in Arbon Bleiche 3 (Jacomet et al. 2004) while, for answering ecological questions a 0.25 mm sieve must be added to retrieve the tiny diaspores of Juncus sp., Typha sp. and Characeae. It is quite common to use a set of six stacked sieves with different mesh sizes (Jacomet et al.1989, Maier 2001, Van der Veen 1996) The soaked sediment is put into the upper sieve and washed through the whole sieve set with a jet of water. Unfortunately it is possible, that fragile plant remains may be destroyed, so this process should be done as carefully as possible (Hosch and Zibulski 2003).
Wash-over is a gentler method and that potentially causes less damage to the waterlogged remains. First place the sample in a bucket and fill the bucket with water until it is about one third full. Swirl the bucket to force the organics into suspension and then decant the suspended organic remains into the a stack of sieves with different mesh sizes. This process is repeated until no more organic remains are released into suspension (Kenward et al. 1980, p. 11).
After sieving, the residues in the different sieves must be kept continuously wet. If they are ot kept wet, fragile and many other plant remains will simply disappear. If they are scanned immediately, the sieve contents are put into plastic boxes with a cover together with a small amount of water. If the residues have to be stored for several days, they may be kept in polyethylen bags with water, put in the fridge or another cool place. It is not necessary to add any preservatives.
- Kenward, H.K., Hall, A.R. (1995). Biological Evidence from Anglo-Scandinavian Deposits at 16-22 Coppergate. The Archaeology of York. Vol. 14: The Past Environment of York, Fascicule 7, p. 435-797.
- Jacomet, S., Leuzinger, U., Schibler, J. (2004). Die jungsteinzeitliche Seeufersiedlung Arbon/Bleiche 3. Umwelt und Wirtschaft. Archäologie im Thurgau, Band 12. Veröffentlichungen des Amtes für Archäologie des Kantons Thurgau, 458 S.
- Jacomet, S., Brombacher, Ch., Dick, M. (1989). Archaeobotanik am Zuerichsee. Berichte der Züricher Denkmalpflege, Monographien 7. Zürich 348 p.
- Kenward, H.K., Hall, A.R. and Jones, A.K.G. (1980). A tested set of techniques for the extraction of plant and animal macrofossils from waterlogged archaeological deposits. Science and Archaeology 22, p. 3-15.
- Maier, U. (2001). Archäobotanische Untersuchungen in der neolithischen Ufersiedlung Hornstaad-Hörnle I A am Bodensee. Siedlungsarchäologie im Alpenvorland VI. Foschungen und Berichte zur Vor- und Frühgeschichte in Baden-Württemberg 74, 9-384. Stuttgart.
- Van der Veen, M. (1996). Plant remains. In Jackson, R.P.J., T.W. Potter: Excavations at Stonea. Cambridgeshire 1980-85. p. 613-636, British Museum Press.
- Hosch, S., Zibulski, P. (2003). The influence of inconsistent wetsieving procedures on the macroremain concentration in waterlogged sediments. Journal of Archaeological Science, vol. 30, issue 7, 849-857.
- Badham, K., Jones, G. (1985). An experiment in manual processing of soil samples for plant remains. Circaea 3, 1, 15-26.