Michel Vorenhout

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.

Organic Loss in Drained Wetland Monuments: Managing the Carbon Footprint

Abstract The recent installation of land drains at Star Carr, Yorkshire, UK, has been linked with loss of preservation quality in this important Mesolithic buried landscape, challenging the PARIS principle. Historically captured organic carbon, including organic artefacts, is being converted to soluble organic compounds and less soluble carbon gases. At the same time sulphur and nitrogen compounds are oxidized to species that are chemically destructive of artefacts and ecofacts. Two of the carbon products, CO2 and methane, are ‘greenhouse gases’ whose environmental impact can be costed in terms of carbon equivalents, which can be set against an assessment of the gain in agricultural productivity of the land arising from drainage, at Star Carr being the improved cereal crop. Wetland studies elsewhere suggest that such decay processes could be slowed by restoring the historic soil environment, and even reversed to create carbon capture, enabling the farmer to claim carbon credits.

Implementation of sustainable urban drainage systems to preserve cultural heritage – pilot Motte Montferland

The shallow subsurface in historic cities often contains extensive archaeological remains, also known as cultural deposits. Preservation conditions for naturally degradable archaeological remains are strongly dependent on the presence or absence of groundwater. One of the main goals at such heritage sites is to establish a stable hydrological environment. Green infrastructural solutions such as Sustainable Urban Drainage Systems (SUDS) can support preservation of cultural deposits. Several cases show that implementation of SUDS can be cost effective at preservation of cultural deposits. These include Motte of Montferland, City mound of Vlaardingen, Weiwerd in Delfzijl, and the Leidse Rijn area. In all cases, the amount of underground infrastructure is minimised to prevent damaging cultural layers. SUDS have been implemented to preserve cultural heritage. The first monitoring results and evaluation of the processes give valuable lessons learned, transnational knowledge exchange is an important element to bring the experiences across boundaries.

Effects of a New Hydrological Barrier on the Temperatures in the Organic Archaeological Remains at Bryggen in Bergen, Norway

The World Heritage Site of Bryggen in Bergen, Norway, has experienced significant degradation of archaeological deposits as a consequence of changes in the soil water and groundwater balance after urban redevelopment adjacent to the heritage site. Additionally, groundwater temperatures below the heritage site were found to be significantly higher closer to the redeveloped area. One of the main mitigation measures taken to reduce the degradation of the archaeology has been the construction of a hydrological barrier along the sheet piling that divides the redeveloped area and the historic site. A shallow subsurface infiltration system was designed to achieve groundwater levels and flow conditions that are optimal for the preservation of archaeological remains directly along the sheet pile, while reducing drainage and subsidence also further upstream. Monitoring of groundwater level and temperatures after implementation of the hydrological barrier shows that groundwater levels and flow conditions have improved with respect to optimal preservation conditions, and groundwater temperatures have generally been reduced by up to 2 °C.

Preserving Medieval Farm Mounds in a Large Stormwater Retention Area

The Netherlands has denoted large areas as stormwater retention areas. These areas function as temporary storage locations for stormwater when rivers cannot cope with the amount of water. A large area, the Onlanden — 2,500 hectares — was developed as such a storage area between 2008 and 2013. This peat area contains up to 300 medieval housing areas. These ‘peatmounds’, named after the current visible small mound, were explicitly mentioned as a preservation goal in the project. The preservation of the peatmounds during and after the project has been guaranteed by a combination of protective measures, research, and monitoring actions. At first a risk evaluation was performed, followed by a monitoring project focusing on the preservation of the organic part of the mounds. This evaluation showed that the rewetting of the mounds might improve the overall preservation. A total of fifteen monitoring stations were a-selectively distributed over the total area, covering the four main types of land use. The measured parameters at these stations focus on the desiccation/rewetting effects. The second threat, as determined in the risk evaluation, is the growth of deep penetrating plants. These roots might disturb the archaeological profile. Preventive coverage with plastic and up to a metre of soil could prevent root growth into the archaeology. An experimental coverage showed the effectiveness of this technique, but also the risks. This paper focuses on the lessons that can be learned from this six-year project, the monitoring results, and clearly shows the benefits of a combined approach in large-scale projects.