three options: Passive preservation, i.e.leave the site as it is, the environment
is safe; Active preservation, i.e.influence environmental parameters around
the site in order to enhance preservation conditions; Excavation, i.e.mitiga-
tion strategies will be too expensive or ineffective and the best option to
ensure that archaeological information survives would be to excavate and
conserve or re-deposit (re-bury) artefacts in an environment more conducive
to their preservation. It is important to remember that in situpreservation is
not a panaceaand may not be feasible in all situations. However, approach-
ing and assessing a site in this way can provide a more objective rationale for
the management of archaeological sites.
This chapter provides a recommended approach to in situpreservation of
waterlogged archaeological sites containing wooden and iron artefacts, and
complements the chapters on deterioration of wood and metals. It draws on
research carried out at the waterlogged site of Nydam, an Iron Age sacrificial
site in southern Denmark, which has been preserved in situsince 1997. The
techniques used will be outlined, and an overview of the results and their impli-
cations will be given. Although Nydam is a waterlogged site, the recommended
framework is applicable to underwater sites as the processes of deterioration
are the same even though the specific agents of deterioration may differ.
2 Environmental Monitoring
Waterlogged soils in wetlands are normally characterised by reduced condi-
tions and the lack of oxygen from a certain depth. Apart from this common
feature they cover a large range of pH values and concentrations of nutrients and
other species. These parameters may influence the deterioration of archaeo-
logical artefacts, and it is thus necessary to monitor the conditions at each
individual site in order to evaluate the feasibility of in situpreservation. A range
of different methods have been used for environmental monitoring at archae-
ological sites in waterlogged soils.
2.1 Water Level
The hydrology of a site is very important, in particular the water level around
artefacts. If, for example, wooden artefacts lie above the water table they will be
exposed to deterioration by a whole range of micro- and macro-organisms,
which will lead to their complete destruction within years. More importantly,
depending upon their state of preservation they may suffer from collapse with
a resultant loss of archaeological information. Water level is normally measured
using dipwells/piezometers. Dipwells are the simplest form of piezometer and
consists of an open-ended tube, which is either perforated near the base of the
tube or along the length, and is inserted into a borehole. Measurements of water
310 Chapter 12