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presumably with increasing light levels or maintained ice thickness causing
photosynthetic inhibition. During the 1999/2000 summer Pendant Lake showed
significantly higher primary production than Ace Lake (Laybourn-Parry et al., 2002).
However, chlorophyll a concentrations were also shown to decrease throughout the
1999/2000 summer from November through February, which correlates with the data
from the current study where February 2000 levels were lower than November 2000 (Fig
3.1 Ob).
Bacterial abundance (Fig 3.11 b) fluctuated considerably throughout the year.
However, there was a general trend to an increase in abundance with depth. which might
indicate the presence of a deep chlorophyll maxima at 1 Om, as was seen in Ace Lake.
This correlates well with chlorophyll a data which shows a maximum concentration at
l Om throughout the year (Fig 3.1 Ob).
HNAN abundance showed a strong correlation with bacterial abundance (Fig
3.20). HNAN utilise bacteria as a food source, but there was a peak in bacterial
abundance during September which is not utilised by the HNAN (Fig 3.20). However, the
peak is mainly influenced by a huge abundance of bacteria at l Om where no HNAN were
isolated during September (Fig 3.12b). This point at 10m during September also shows
no recorded PNAN. The PNAN population was virtually entirely made up of
Stichococcus bacillaris (Laybourn-Parry et al., 2002). PNAN were recorded at
moderately low abundance during February (500 x105 L-) (Laybourn-Parry et al., 2002).
Reasons for this low abundance are unknown.
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