The effect of sewage enrichment upon the integrity of the fabric of marine sites of archaeological importance
This research programme was instigated in response to concerns regarding the
potential impact of sewage contamination from a long sea-outfall commissioned in
1991 in Portsmouth, Hampshire, on the long-term quality of local, historic wreck
timbers. Information pertaining to the quality of seawater and the degradation of
sacrificial wood samples, with particular emphasis on the action of the wood-boring
crustacean, Limnoria spp, was collected and is presented in this thesis. The data was
collected from three wreck sites in the Solent and surrounding waters: the Mary Rose
(1509 - 1545), HMS Invincible (1744 - 1758) and HMS Hazardous (1698 - 1706).
Both the Mary Rose and HMS Invincible sites are situated in an area of the Solent
that was contaminated by sewage discharge. The site of HMS Hazardous is in
cleaner water at Bracklesham Bay and was therefore designated as the control.
Limnoriid activity was found to be higher at the HMS Invincible site than at the
Mary Rose site - the HMS Invincible site also recorded the highest levels of sewage
contamination. However, limnoriid activity was greater still at the "clean" control
site of HMS Hazardous, thereby ruling out a conclusive link with sewage
contamination. Water quality analyses showed the existence of vertical layering in
the water column for many of the parameters determined.
L. quadripunctata dominated the limnoriid population at the three sites but there was
a significant presence of L. lignorum at the deeper Mary Rose site. On one occasion
(winter 93/94), L. lignorum dominated the limnoriid population at the Mary Rose
site. At the same time, the affinity for Scots pine wood observed during the rest of
the study was not apparent.
Faecal indicator bacteria were isolated from the biofouling layer of the wood blocks
at both the Mary Rose and HMS Invincible sites and microbiological activity
appeared to be greatest at the Mary Rose site. Fouling barnacles on the wood
samples appeared to offer some protection from limnoriid activity in the short-term
but had no long-term protective effect.