Monitoring and Mitigation Works in Unsaturated Archaeological Deposits

Monitoring of the archaeological deposits at the World Heritage Site Bryggen in Bergen has been ongoing since 2001. In latter years a large-scale project of mitigation works has been carried out, resulting in the creation of a water-management system aimed at raising groundwater-levels and increasing soil moisture content in areas with poor preservation conditions. Oxygen is a key parameter in the decay of archaeological material in the unsaturated zone, and the monitoring at Bryggen includes in situ monitoring of oxygen concentrations and comparison to soil moisture content, temperature, groundwater-level, precipitation and soil reactivity. This is used to document where and when decay takes place and to estimate “how wet is wet enough” in order to reduce the oxygen diffusion and the decay rate to an acceptable level. The results show that even small changes in the soil moisture can have a large impact on the oxygen dynamics in the ground.     

Research on Conservation State and Preservation Conditions in Unsaturated Archaeological Deposits in Oslo

Abstract

Archaeological, biological, and geochemical investigations of soil sample series from a section and five boreholes have been studied to evaluate the state of preservation at the time of investigation and the preservation conditions of urban archaeological deposits from medieval Oslo, Norway. Focus has been put on the most fragile deposits in the unsaturated and fluctuation zones. Even with limited investigations, it is possible to assess the archaeological conservation state and the preservation conditions. Further work should focus on interpreting measured results and on mitigation strategies.     

The Influence of Soil Moisture,Temperature and Oxygen on the Oxic Decay of Organic Archaeological Deposits

The sensitivity of organic‐rich archaeological layers at Bryggen in Bergen, Norway, to changes in soil temperatures, water contents and oxygen concentrations is investigated. This is done by linking measurements of oxic decay at varying temperatures and water contents with on‐site monitoring data using a one‐pool decomposition model. The results show that the model can be used to elucidate the current in situ decay and to evaluate where and when the decay takes place. Future investigations need to include long‐term incubation experiments and decay studies at zero or very low oxygen contents in order to improve the robustness of predictions.     

Monitoring and Management Options in the Preservation of Urban Waterlogged Deposits,Nantwich, UK

A baseline survey in 2007 characterized the physical and chemical conditions for preservation within waterlogged remains at Nantwich. Installation of eighteen dipwells has allowed a five-year monitoring programme to be conducted from 2011. Two add-on projects supplemented this monitoring programme by examining the different methods for redox measurement, and for soil moisture measurement using Time Domain Reflectometry (TDR).

Initial results show two main zones of preservation, with reducing conditions attributed to location of the deposits in the floodplain, and a second zone uphill with more variable conditions for preservation. This study shows that sediment-coring programmes combined with dipwell installations can provide useful data to assess and monitor in situ preservation conditions, which can help to formulate management strategies for conservation of waterlogged archaeological deposits. This paper focuses on the efficacy of the methodology, referencing in particular comparative monitoring techniques and lists a series of recommendations for future studies.     

Research and Monitoring on Conservation State and Preservation Conditions in Unsaturated Archaeological Deposits of a Medieval Farm Mound in Troms and a Late Stone Age Midden in Finnmark,Northern Norway

This paper presents archaeological observations and results of palaeoecological and geo-chemical analyses of archaeological deposits from two rural sites in northernmost Norway. These are combined with climate data and the first period of continuous monitoring of soil temperature, moisture, and redox potential in sections. This data constitutes the basic research material for evaluations of conservation state and preservation conditions. The data has been collected in collaboration with the partners of a cross-disciplinary project: ‘Archaeological Deposits in a Changing Climate. In situ Preservation of Farm Mounds in Northern Norway’ funded by the Norwegian Council for Research (http://www.niku.no/en/archaeology/environmental_monitoring/archaeological_deposits_in_a_changing_climate_in_situ_preservation_of_farm_mounds/). This is an important Norwegian research initiative on monitoring of rural archaeological deposits, and the results have consequences for heritage management of a large number of sites from all periods. Palaeoecological analyses and redox measurements have revealed ongoing decay that might not otherwise have been detected. Decay studies indicate that both site types may be at risk with the predicted climate change. Some mitigating acts are suggested.     

In Situ Preservation of Wetland Heritage: Hydrological and Chemical Change in the Burial Environment of the Somerset Levels,UK

Abstract

In situ preservation is a core strategy for the conservation and management of waterlogged remains at wetland sites. Inorganic and organic remains can, however, quickly become degraded, or lost entirely, as a result of chemical or hydrological changes. Monitoring is therefore crucial in identifying baseline data for a site, the extent of spatial and or temporal variability, and in evaluating the potential impacts of these variables on current and future in situ preservation potential.

Since August 2009, monthly monitoring has taken place at the internationally important Iron Age site of Glastonbury Lake Village in the Somerset Levels, UK. A spatial, stratigraphic, and analytical approach to the analysis of sediment horizons and monitoring of groundwater chemistry, redox potential, water table depth and soil moisture (using TDR) was used to characterize the site.

Significant spatial and temporal variability has been identified, with results from water-table monitoring and some initial chemical analysis from Glastonbury presented here. It appears that during dry periods parts of this site are at risk from desiccation. Analysis of the chemical data, in addition to integrating the results from the other parameters, is ongoing, with the aim of clarifying the risk to the entire site.