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

Nitrogen Load
(mg·N·m -2 )
140
120
100
80
60
40
20
0
June 4
June 13
2006
2005
2004
June 20
June 27
July 4
July 11
July 18
Figure 3. Weekly loading of nitrogen in Wahleach Reservoir, 2004-2006.
July 25
Aug 1
The annual P load from fertilizer was 176–204 mg⋅P⋅m -2 (Table 1). In 2006, the
annual phosphorus loading rate was increased based on the recommendation by
Perrin et al (2006) that in order to improve the production of the Daphnia sp,
zooplankton that are crucial for sustaining planktivorous kokanee populations (Perrin
et al 2006), the annual loading rates must not be less than 200 mg⋅P⋅m -2 . These
loading rates were in the range of those used in fertilization experiments at other
oligotrophic lakes (102–164 mg⋅P⋅m -2 by Langeland and Reinertsen (1982), 27-100
mg⋅P⋅m -2 by Clarke et al (1997), 100–600 mg⋅P⋅m -2 by Johnston et al (1999), 66–100
mg P⋅m -2 by Stockner and MacIsaac (1996) and 271 mg P⋅m -2 by Ashley et al (1999)).
As a consequence of the higher P loading in 2006, the annual nitrogen load was also
increased (Fig. 3). Nitrogen must be added concurrently to ensure that epilimnetic N
concentrations remain above ~20 µg L -1 , the concentration of nitrogen considered
limiting to phytoplankton growth (Wetzel 2001) and to ensure that the N:P ratio
remains high. Low N:P ratios may promote the growth of large blue-green algae,
which can be toxic (Schindler, 1977 Watson and Kalff 1981; Pick and Lean 1987;
Stockner and Shortreed 1988, 1989) and unpalatable to zooplankton and are
therefore considered carbon sinks.
Wahleach Reservoir Fertilization Project, 2004-2006.
Aug 8
Aug 15
Aug 22
Aug 29
Sept 5
Sept 12
Sept 19
Sept 26
Oct 3
Oct 10
Oct 17
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