Reburial studies, Isle of Wight

Isle of Wight Council

Background

The area to be examined during the proposed study of the reburial of sensitive archaeological sites and features is located on the north east coast of the Isle of Wight. It encompasses the area previously studied during the course of the Wootton-Quarr survey and includes the wetlands in the Wootton Creek valley particularly those adjacent to Firestone Copse. During the course of archaeological surveys covering the intertidal zone between Fishbourne and Binstead more than 150 archaeological features ranging in date from the early Neolithic to the post-medieval period have been recorded. These include a large number of wooden structures including trackways and fishtraps. The function of other clusters and alignments of wooden posts remains unclear. Posts from many of these structures were recovered for dating and analysis. The long term storage and conservation requirements of these posts now need to be addressed.

Preliminary investigations into the stability of the Wootton-Quarr project area, both the physical environment and the chemistry of the intertidal sediments, suggest that the silts are eroding, leading to the exposure of new archaeological structures and the destruction of others. An environment which has previously provided conditions of stability, enabling the preservation of large amounts of organic material, is currently eroding. This is causing structures to become exposed and their condition to deteriorate.

Previous work

Previous monitoring of the water chemistry at various sites within the intertidal area during the Wootton-Quarr project has suggested that erosion of the intertidal silt causes changes in the chemical environment. As erosion occurs and timbers are exposed, the chemistry of the environment changes from a relatively protective anaerobic system to a more exposed and active aerobic one. In this changing environment the material becomes increasingly susceptible to degradation caused by wave action and by biological agencies which flourish in these conditions. Water chemistry has been monitored using water extracted from dipwells inserted at various depths into the silts at selected sites within the intertidal zone. The chemical parameters which have been examined are pH, conductivity levels and oxygen content.

The field survey and environmental studies which formed part of the Wootton-Quarr survey served to illustrate the quantity and importance of the archaeological remains within the area. Surveying and chemical monitoring during the course of this project have demonstrated the fragility of these remains and their vulnerablilty to the changes in the physical and chemical environment which are caused by erosion.

The circumstances of the project

Chemical monitoring and geomorphological surveys have clearly illustrated that erosion within the intertidal zone is causing destruction of archaeological remains. Continued survey has proved that sites are being actively eroded. Two categories of wooden object are considered in this proposal:

• Waterlogged timbers recovered from sites in the intertidal zone are exhibiting obvious signs of deterioration in the holding tank where they are stored at Quarr Abbey.
• A seventeenth century wreck in the silts at Fishbourne beach. This wreck will be lost from the archaeological record if action is not taken to rebury it.

It is proposed to use this waterlogged wood to conduct monitored experiments in intertidal and inshore reburial. A brackish wetland environment has been identified at Firestone Copse, a Site of Special Scientific Interest, where early Holocene organic remains have survived in a stable anaerobic environment. It is proposed to use this location to conduct reburial experiments which can be regularly monitored. This procedure will make a valuable contribution to the national problem of sustaining large quantities of waterlogged wooden artefacts.

Burial and retrieval of samples will continue for a three year period, providing a sufficiently long time span for significant changes to occur. The water chemistry will be monitored for the duration of the project and samples will be removed for analysis. Micro-biological sampling will also be undertaken. The archive produced by the project will be deposited with the Isle of Wight Council Museum Service.

Aims and objectives

Academic or research design

The primary aim of the study is to identify a wetland site with a geomorphological and chemical environment which may be suitable for the natural storage of waterlogged organic archaeological remains. Large amounts of organic material are difficult and expensive to conserve, but they can provide data on past climates, woodland management and woodworking techniques. It is highly likely that it will be possible to extract further information from this archive in the future.

Waterlogged wood deteriorates if it remains untreated for long periods, entailing an irretrievable loss of information. Reburial may offer an inexpensive means of preserving organic remains in a relatively stable condition within the natural environment. Scientific analysis into the condition of waterlogged remains and into bacterial activity within both objects and sediments will form part of a wider research project proposed by English Heritage and the Mary Rose Trust. Environmental monitoring and research will complement research into wetland environments already being conducted by other environmental agencies, in particular the Royal Holloway Institute for Environmental Research, University of London.

Future research could encompass studies into the rate and causes of deterioration of organic materials within waterlogged environments. Research may indicate specific parameters which are required to maintain objects in good condition. The monitoring of chemical parameters and microbiological factors should provide data concerning the organisms living in particular chemical environments and their effect upon the buried material. Monitoring may provide sufficient data to enable the construction of predictive models indicating whether a site is liable to be protective or destructive and whether it would be suitable for use as a natural environment store. The project will provide opportunities for experimental investigations of the soil chemistry and microbiological activity within these sediments. The retrieval and analysis of wood samples will allow the causes, processes and rates of deterioration to be identified and quantified.

Methods statement

A series of methodologies will be employed during the reburial study.

• The wetland at Firestone Copse will be analysed to assess its suitability for the storage of the waterlogged organic remains retrieved during the course of the Wootton-Quarr project.
• Methods of site protection and monitoring will be investigated.
• Chemical and biological analyses and environmental sampling will be carried out in the areas selected for reburial experiments.
• The chemical environment of the wetland will be assessed by regularly monitoring the levels of pH, redox potential and conductivity. Specific chemical parameters will be identified where appropriate by spot sediment sampling and colorimetry.
• A wide area of wetland will be assessed using cotton strip assay to monitor the rate of degradation of cellulose in the wetland environment. The redox potential will be measured at each location chosen for this experiment by the insertion of redox probes. This experiment will be repeated once each season during year 1 to establish any variation and patterns in decay rates.
• Sediment columns will be removed from the various sites used in the cotton strip assessment. These columns will provide cross sections of the experimental sites and will be analysed chemically using colorimetry. The moisture content will be calculated at various depths to assess whether the area remains permanently waterlogged.
• After completion of the initial rapid assessment of the wider area, a site will be selected for the reburial of the waterlogged timber currently in the holding tank at Quarr Abbey.
• A methodology will be devised for the reburial, recording and selective sampling of the waterlogged wood.
• The reburial site will be intensively monitored to assess the changes in chemistry caused by the burial of the archaeological material. The continuous monitoring of chemical parameters will provide information on how quickly the wetland returns to its original chemical condition. It will also establish whether the chemical microbiological regime in the area is altered.
• Microbiological techniques will be used to enumerate and identify anaerobic bacteria which might be present. The presence or absence of cellulose degrading bacteria will also be investigated. It is intended that this work will be carried out by a CASE funded student based in the archaeology department at Southampton University.
• Wood samples will be buried in the wetland at various depths to assess their rates of deterioration. The samples will comprise sterilised and unsterilised wood of a number of species. Samples from wood recovered from the intertidal zone at Quarr will also be used in the experiments. Fast decaying cellulolytic material such as linen and paper will also be buried.
• The samples will be weighed and measured prior to burial. Some will be waterlogged and the maximum moisture contents calculated.
• The fast decaying materials and a certain number of wood samples will be recovered regularly over a three year period. These samples will be examined using Scanning Electron Microscopy.
• Decay in the wood samples will be examined using NMR spectrometry. The use of a Bruker MSL 3000 spectrometer will allow analysis of wood chemistry and decay in sediments. Additional analysis of water in wood blocks will be carried out using MRI imaging.
• Wood blocks will be inoculated with test organisms and decay will be assessed after exposure in sediments for one to three years. Assessment will be by weight loss measurement supported by Scanning Electron Microscopy.

Timetable

It is envisaged that the project will run for three years in total. It is intended that the waterlogged wood from the Wootton-Quarr archaeological survey should be buried after the first year, by which time a suitable site should have been identified. The programme of sample retrieval and monitoring will continue after this date to assess the longer term effects on the buried samples and the impact of reburial on the surrounding environment.