Mireille Consalvey PhD Thesis - University of St Andrews

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3.3.2. Laboratory Investigation into biofilm growth
Visual obscrvations
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The colouration of the sediment in the petri dishes rapidly changed from
brown to the golden brown colour associated with diatornaceous biofilms. After
45 days patches of green had also appeared, which would suggest a shift in the
taxonomic groups. As the biofilm developed, bubbles of oxygen were visibly
adhered to the biofilm, both above and below the surface, indicating high rates of
primary productivity. By day 45, the biofilm was blistering away from the
sediment surface as well as growing on the water surface and adhering to the side
of the tank. There was also some bacterial growth; evident from an oily meniscus
on the water/biofilm surface.
LTSEM analysis revealed that pennate diatoms (- 10 gm) were the first
to colonise the sediments. These were followed by chain forming and other large
species (planktonic and benthic forms). Some bacterial growth was also evident,
By day 13, the biofilm was well developed; a diverse algal community embedded
in matrix of EPS covered the sediment surface. At the end of the study densely
packed areas of cyanobactena were also evident. The samples were highly
hydrated and the cells were embedded in an EPS layer preventing taxonomic
identification
Bulk density
(Figure 3.7).
Over the course of the experiment bulk density did not significantly
change from the initial value of 0.78 + 0.24 g CM-3 on day 0.
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