ý.,,: V. ý ýý . - Nottingham eTheses - University of Nottingham

Inorganic nitrogen (NO2, NO3 and NH4) was generally higher in Pendant Lake
than Ace Lake (Gibson, 1999; Laybourn-Parry et al., 2002). Ammonium and nitrate
concentrations were probably higher due to the complete mixing of the Pendant Lake
water column; whereas in Ace Lake, inorganic nitrogen settles out of the mixolimnion
into the monimolimnion
through the breakdown and diffusion of organic matter down the
water column (Hand & Burton, 1981). However, nutrients do diffuse upwards across the
chemocline, providing a localised nutrient pool just above the chemocline (Bell &
Laybourn-Parry, 1999b). Nitrite concentrations (Fig. 3.6b) were virtually the same in
both lakes (2µg
1-1). Generally, inorganic nitrogen species were always measurable, and
therefore not limiting.
Inorganic phosphate (SRP; Fig 3.8b) was higher in Pendant Lake compared to the
mixolimnion of Ace Lake. It was not nutrient limiting, reaching its highest concentration
during July at 8-1 Om. SRP dynamics are heavily influenced by biogeochemical processes
in the sediment (Laybourn-Parry et al., 2002). Since Pendant Lake was not stratified, the
levels of SRP in the water column would have been influenced by the sediment processes
which would not have occurred in the permanently stratified
Ace Lake.
Dissolved organic carbon (DOC; Fig 3.9b) showed little fluctuation with depth
and time. Overall there was less DOC in Pendant Lake than Ace Lake (Fig 3.9a & b;
Laybourn-Parry et al., 2002). There was a slight decrease in concentration from Om to
I Om during November, which might coincide with an increase in phytoplankton activity
in the upper waters due to increased light levels during the early summer. Laybourn-Parry
et al. (2002) recorded the highest concentrations in November during the summer of
1999/2000. However, the ice thickness during this month was only 72% of November
2000 (Fig 3.1 b), therefore the greater ice thickness would cause greater light attenuation,
which could reduce photosynthetic activity and thus DOC output. DOC was higher
during February compared with the winter, due to an increase in light conditions and a
reduction in ice thickness allowing increased light penetration and intensity.
Chlorophyll a concentrations (Fig 3. l Ob) were generally higher in Pendant Lake
than Ace Lake, showing that the meromictic status of Ace Lake probably limits primary
productivity within the oxylimnion (Laybourn-Parry et al., 2002). Chlorophyll a peaked
at 10m during September (-35µg 1-1) levels then decreased during November,
99