Wahleach Project Water Use Plan Wahleach Reservoir ... - BC Hydro

TN:TP
120
100
80
60
40
20
0
June 2004
July 2004
Aug 2004
Sept 2004
Oct 2004
Nov 2004
May 2005
June 2005
July 2005
Aug 2005
Sept 2005
May 2006
June 2006
July 2006
Aug 2006
Sept 2006
Oct 2006
P Limitation
N Limitation
Figure 8. Mean TN:TP (wt:wt) ratios in the epilimnion of Wahleach Reservoir, 2004-
2006. Red dashed lines indicate ratio that suggests either N or P limitation.
4.4 Phytoplankton
Phytoplankton cell densities ranged from 2,320 cells·ml -1 in 2004 (one station only;
no measure of variance available) to 3,770 ± 400 cells·ml -1 in 2006 (Fig. 9).
Although densities increased ~50% in 2006 from 2004, likely due to higher fertilizer
loading in 2006, the densities were on average 30% lower than the densities
observed in oligotrophic Okanagan Lake (Stockner in Andrusak et al 2004). The low
densities observed in 2004 and 2005 are similar to densities found for unfertilized
Elsie Lake, a fast flushing ultra-oligotrophic coastal system (Perrin and Harris, 2006)
suggesting that the fertilizer loading in 2004 and 2005, which were below the levels
recommended by Perrin et al (2006), may have had limited effect on productivity.
Phytoplankton biomass ranged from 0.53 mm 3 ·ml -1 in 2004 to 1.47 ± 0.09 mm 3 ·ml -1
in 2006 (Fig. 9). Despite fertilization of Wahleach, the low density and biomass
clearly reflect a phytoplankton community typical of oligotrophic conditions (Wetzel
2001).
Wahleach Reservoir Fertilization Project, 2004-2006.
20