Mireille Consalvey PhD Thesis - University of St Andrews

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resulted in a visible increase in surface water at the site. However, the water
content of the newly exposed sediments was significantly lower than prior to
disturbance. Deeper sediments have a higher bulk density and this result may be
explained by a reduction in the available pore space for water drainage. The
increase in water content over time may be explained by the deposition of new
sediments, these forming a less compact surface layer.
In the laboratory study, there was an immediate increase in the water
content as water was absorbed into the freshly immersed sediments. Subsequent
to this there was little change and it is likely that the biofilms were saturated
because of constant submersion. The water content did not change with depth,
but in a natural system where water can drain into the sediments, as well as be
subject to evaporation, a change in water content may be observed with depth.
Biomass
The chlorophyll a contents in both studies were comparable to values
obtained in situ by Underwood and Paterson (1997), Kelly et al. (2001) and de
Brouwer and Stal (2001). The in situ removal of sediments removed 95% of the
biomass. The remaining 5% was likely to be PIB (Photosynthetically Inactive
Biomass; Kelly et al. 2001). Within 5 days the biomass had significantly
increased, a time scale comparable to the findings of Underwood and Paterson
(1993) and subsequent to this there was no significant increase. The biomass
source was unknown, but the uneven distribution of newly formed b1ofilin
patches, as well as the slow rate of cell movement, makes colonisation from the
edges unlikely to be the main source of imported biomass. Depth distribution
profiles show a concentration of biomass in the top 200 pm (Kelly et al. 2001)
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