Rapportage Archeologische Monumentenzorg 207

The third round of archaeological monitoring at the UNESCO World Heritage site at Schokland was carried out in 2009 – 2010. The present report on this monitoring round also contains monitoring data on two sites from 2006. Four sites were monitored in total; two sites (E170-Schokkerhaven and J125) represent Stone Age river dune sites in the landscape surrounding the island. The third site (P14) is a Stone Age and Bronze Age site on a boulder clay outcrop. De Zuidert is a Medieval and subrecent dwelling mound (terp) on the former island. These last two sites are situated on the former island. Monitoring of groundwater levels, moisture contents, redox, botanical remains and bone was planned, along with micromorphological and soil chemical analysis and interpretation of dipwells monitored by the water board. The plan was to compare these data with those from previous monitoring rounds. Unfortunately, the monitoring of groundwater levels, moisture contents, redox and bone failed. Comparison with micromorphological slides from previous rounds proved to be impossible because the samples were missing. Analysis of groundwater levels from the water board shows variable behaviour of the water table in different areas surrounding the former island. From this data, it is clear that the water table has risen considerably in the northern part of the zone (including the P14 area). In the central and southern parts of the zone (dipwells 3 - 8) the differences are marginal, however. The hydrological zone is wetter during wet spells, but the water levels during dry periods drop to the same levels as those outside the zone. Apparently, the water level in some areas of the hydrological zone may temporarily drop below the minimum level desired. Soil chemical analysis and micromorphology demonstrate that three major degradation processes are affecting the archaeological sites: desiccation, desiccation-driven pyrite oxidation and tillage. Pyrite oxidation is a particular cause for concern, as it results in damage by acidification or by fragmentation of materials due to gypsum formation. The worst damage due to desiccation and pyrite oxidation was observed at E170-Schokkerhaven, and in the upper layers of De Zuidert. Analysis of botanical remains shows no clear trend towards better or worse preservation. In fact, the 1999 measurements appear to differ from those from 2001 and 2010 in that the former show less variation within one sample, while at the same time they include more extreme values. Any differences between 2001 and 2010 are very minor. At E170-Schokkerhaven, interpretable botanical remains show that the site has not deteriorated completely, but it is clear that there has been some damage, and that there still is a wealth of archaeological information that will be lost if degradation processes continue. The creation of the hydrological zone has had a positive effect on the archaeological sites to the east of the island, especially in the P14 area. The other monitored sites are outside its zone of influence. Based on the results of this monitoring rounds - and on a comparison with the results of the previous rounds - the following recommendations are made for each of the sites: P14 has a burial environment that is very suitable for preserving the archaeological remains, thanks to the successful implementation of the hydrological zone. Monitoring by the water board will be sufficient in the future; as long as the water table remains high, the site is safe. De Zuidert terp shows degradation processes in its upper layers that have probably been occurring for at least a hundred years. The mound effectively forms a hydrological system that is independent of its surroundings. The burial environment cannot therefore be changed without doing major damage to the site, especially its visual value. The well-preserved deeper layers with good future prospects combined with the inadvisability of trying to change the burial conditions means intensive monitoring is not necessary. For the future, the only relevant form of monitoring would consist of low-frequency site inspections to make sure the site is not threatened by deep-rooted vegetation. E170-Schokkerhaven is desiccating, suffering from pyrite oxidation, and under cultivation. Rates of decay are notoriously difficult to predict, but with the present state of knowledge is assumed that the site will lose a very significant portion of its archaeological value within the next few decades. For future preservation, measures need to be taken to improve the burial conditions and preserve the site in situ. If this is not possible, excavation of the site for preservation ex situ should be considered. As long as the situation remains unchanged, it does not make much sense to continue monitoring for in situ preservation. J125 seems to be in good condition, and the burial environment does not give immediate reason for concern. An increase in the depth of tillage and some degree of pyrite oxidation are, however, potential threats. At this site, it would be advisable to continue monitoring the burial environment. The intensive land-use at J125 makes long-term monitoring of groundwater/ moisture/redox unfeasible. A better strategy for future monitoring may therefore be to obtain good-quality cores from more representative locations at this site for macroscopic observations, and for micromorphological and chemical analysis