Mireille Consalvey PhD Thesis - University of St Andrews

(IM
The balance between all these parameters and their respective effects on
the fluorescence yields are still not clear, clearly further work is required to
resolve these questions. However, Ser6dio et al. (1997) concluded that any effect
on F, will be comparatively small compared to the large variations seen as a
result of migration.
A dark adaptation time of 15 min was selected by Kromkamp et al.
(1998), Honeywill (200 1) and Honeywill et al. (2002) aiming to achieve the fine
balance between achieving a true measure of minimum fluorescence but also
limiting the effect of cells dramatically changing their position. Kromkamp et al.
(1998) estimated that 75% of the signal detectable by PAM fluorescence
techniques emanates from the upper 150 [tm of the sediment. By considering the
theoretical distance that cells might travel (Table 8.1) it can be seen that cells
could travel greater than 150 pm in 15 min, therefore one cannot assume that the
same population of cells will be present before and after dark adaptation. The
data obtained in Chapter 7 suggested that some cells did migrate away during the
15 min dark adaptation period.
Table 8.1: Theoretical distances travelled
Distance travelled
gm
Speed I min 15 mins I hour Notes
GIM S-1)
Happey-wood 2.5 150 2250 9000 Horizontal
and Jones (19 8 8) 9 540 8100 32400
Hay et al. (1993) 4.7 282 4230 16920 Horizontal
0.17 10.2 153 612 Vertical
0.19 11.4 171 684 Vertical
Hopkins (1963) 0.28- 116.8 ] 252 1 1008 Vertical
Harper (1977) 0.25 115 1 225 ] - 900 --I Vertical 1
240