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Environmental conditions


Biological, chemical and physical factors affect the preservation of the Vrouw Maria. It is therefore important to summarize the environmental condition before discussing the condition of the wreck.

The wreck and its surroundings were investigated within the EU Culture 2000 - Programme MoSS Project (Monitoring, Safeguarding and Visualizing North-European Shipwreck Sites: Common European Underwater Cultural Heritage - Challenges for Cultural Resource Management). At the Vrouw Maria site data about environmental factors such as pH, dissolved oxygen, temperature and turbidity was monitored by different data-loggers, and topographical and geological mapping of the area were also carried out. A more detailed monitoring of the environment was carried out between September 2002 and August 2003 by the Finnish Institute of Marine Research. A comprehensive article about the environment of the Vrouw Maria will be published by Leino et all in 2010 (IJNA). Furthermore, in the summer of 2009 sediment samples were collected in order to study the bottom animals.

The wreck is located in the outer archipelago at the depth of 41 meters. It can be said that the hydrological conditions at the site are typical for the surrounding archipelago area, meaning that the conditions are relatively favorable for long-term preservation of the wood of the wreck. Salinity and oxygen levels are low, it is dark, cold - seldom above 6 degrees Celsius - and currents and other water movements are quite weak. These are all good features for preservation of materials. It should be noted, though, that the conditions are not stable on a yearly basis. In the summer season the water column stratifies because of thermal difference between surface and bottom water, which means that the oxygen level nearer the bottom decreases due to the decomposition of organic matter. This might lead to anoxic conditions if there is much decomposing organic matter such as dead algae. In wintertime the temperature difference diminishes and the water column mixes from surface to bottom, bringing more oxygen down to the wreck site. The yearly cycle is also not totally regular, as storms might break the stratification and suddenly alter the conditions.

Thanks to the depth, the effects of ice-formation do not reach the wreck, but other water movements pose potential risks due to the wreck standing almost completely exposed on the sea-bed. Wave action reaches the wreck only weakly, but it has been proven by a specially designed device that the masts move to and fro within the waves. While this is not considered as an imminent risk, on the long term this might lead to damages. Currents are generally weak, but they nevertheless slowly erode the decomposing wood-surface all over the wreck, which can be observed in the samples brought up so far.

As for biological factors, there is no marine vegetation obscuring the hull. Lack of natural light excludes primary producers such as macro algae from the site, but sessile animals can attach on the wreck. Indirectly also loose dead algae might have an effect by drifting by the sides of the wreck and forming "mats", under which anoxic conditions might develop and thus cause local changes to conditions. On microscopic level fungi and bacteria are certainly active, but due to environmental conditions the most destructive wood decomposers such as the "shipworm" Teredo Navalis have not been found in the site.  

According to the sediment samples collected in 2009 by Monivesi Oy the populations are typical for the area and there are no endangered species. The largest populations are of Machoma baltica and Marenzelleria spp.

The mercury in the cargo is of relevance when discussing the environmental issues. There should be more than 100 kg (8,4 liters) of Mercury in the hold. A sediment sample from the vicinity of the wreck did not reveal increased mercury level, so the mercury is presumably still in the original packages in the hold. The toxicity of mercury has to be notified, at least in the case of any kind of interventive actions are taken.

 



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Last updated 30.10.2015
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