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

Zooplankton Density
(cells·L -1 )
30
25
20
15
10
5
0
Density
Biomass
May 04
June 04
July 04
Aug 04
Sept 04
Oct 04
Nov 04
May 05
June 05
July 05
Aug 05
Sept 05
Oct 05
Nov 05
May 06
June 06
July 06
Aug 06
Sept 06
Oct 06
Nov 06
Figure 13. Mean growing season zooplankton densities and biomass in Wahleach
Reservoir, 2002-2004.
120
100
80
60
40
20
0
Zooplankton Biomass
(µg·L -1 )
The zooplankton density was numerically dominated by cladocerans (other cladocera
and Daphnia), which averaged between 79 and 91% of the zooplankton community
(Fig. 14). This finding is consistent with values reported for earlier years of the
fertilization program (Perrin et al 2006). During the sampling period (2004-2006)
cladocera other than Daphnia accounted for between 54% and 63% of the zooplankton
community, while Daphnia accounted for between 17% and 30% of the total
zooplankton density. Other cladocera were mainly dominated by Eubosmina
longispina, Chydorus sp. and Holopedium gibberum. Populations of cladocera other
than Daphnia sp peaked early in the growing season in June and July, until Daphnia sp.
emerged in August and numerically dominated the zooplankton assemblage well into
the fall (Fig. 14). The density of cladocera other than Daphnia doubled during the study
period, from approximately 3 individual·L -1 to 5 individual·L -1 in 2006. During this same
period the density of Daphnia rosea also doubled, from approximately 1 individual·L -1 to
2 individual·L -1 . While the actual density of Daphnia rosea is low, the densities are
nearly 14 fold higher relative to earlier densities of less than 0.17 1 individual·L -1
reported in 1999 (Perrin et al 2006).
Wahleach Reservoir Fertilization Project, 2004-2006.
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