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

More documents

Recommendations

Info

5. Discussion The building blocks of phytoplankton, the basis of all food chains, are carbon, nitrogen and phosphorus. Typically, although not always, phytoplankton contain these elements in ratios called Redfield Ratios, of 106 units of carbon:16 units of nitrogen:1 unit of phosphorus (Redfield 1934). As a result, in order for phytoplankton to grow, all three elements are required and if a water body is deficient in one of the building blocks then growth and ecosystem productivity are stressed and ultimately limited. While there are exceptions, the most important nutrient causing a shift from a lesser productive system to a more productive system are phosphorus and nitrogen. There is an overwhelming amount of evidence supporting the relationship between the quantity of nitrogen and phosphorus entering a lake and the measured response to that input. Vollenwieder (1976) developed a quantitative relationship describing the trophic conditions that result from a nutrient load and has shown unequivocally that increased phosphorus loading leads to higher productivity lakes. Our fertilization strategy is utilizing this known link between nutrient loading, algal production, and food availability for planktivorous fish in the hopes that the kokanee and in turn rainbow trout stocks are successfully restored. The importance of a monitoring component to the success of a fertilization project has long been recognized. A program monitoring the response of the ecosystem, allows for adaptive management and allows for the effectiveness of restoration strategies to be evaluated. It is not our intention to shift Wahleach Reservoir from a nutrient poor, low productivity oligotrophic system to a nutrient rich, high productivity eutrophic system. Optimally, each carbon atom assimilated should be transferred up the food chain to support higher trophic levels. Trophic classification is based on a sliding scale of productivity and uses basic parameters to determine the location of a particular lake or reservoir on the productivity scale. At the low end of the scale, lakes are called ultra-oligotrophic which are extremely nutrient poor and have low productivity while at the extreme end of the scale are nutrient rich, high productivity called hypereutrophic. Wahleach Reservoir has many users and we must ensure our restoration strategies do not negatively impact water quality for any stakeholder. It should be noted that instead of using proxy indicator parameters, one can directly determine productivity using either radio-labelled carbon, oxygen production or dissolved inorganic carbon uptake measurement, all of which require a high degree of technical expertise and considerable effort. The value of primary productivity measurements is, unlike biomass measurements that are confounded by losses such as grazing, sinking and transport or alternatively by accumulation of inedible algae, primary productivity allow for a direct assessment of the “health” or productivity of the system. Primary productivity data is not available for Wahleach, therefore, our results will be compared to criteria that are commonly used to determine the trophic state of lakes (Wetzel 2001). Wahleach Reservoir Fertilization Project, 2004-2006. 42
Table 5 lists the range and the mean values for 4 different parameters of each trophic classification as defined by Wetzel (2001). Also included is the range and mean values found in Wahleach during the 2004–2006 period. Using this approach, Wahleach Reservoir is classified as an oligotrophic system based on TP and TN concentrations and mesotrophic based on chl a concentrations and Secchi depth. It should be pointed out that Secchi depth is linked to chlorophyll a concentrations, therefore the two parameters do not provide two separate independent assessments of trophic state. The ranges measured for chlorophyll are within the ranges reported by Perrin et al (2006). It is important to remember that large filamentous phytoplankton chains are difficult for zooplankton to assimilate and therefore when conditions favors their growth, the biomass tend to accumulate rather than being assimilated by herbivorous zooplankton. Our taxonomic analysis did identify a number of large sized phytoplankton cells, particularly in the late summer period, which were identified as carbon sinks, this may explain in part, the apparent discrepancy between the differing classification based of different parameters. Regardless, the mean and the range of the chl a values in Wahleach are at the low end of mesotrophy. Table 5. General trophic state classification based on criteria defined by Wetzel (2001). All units are (µg·L -1 ), unless otherwise stated. Highlighted cell indicates trophic classification of Wahleach Reservoir with respect to particular parameter. Table modified from Wetzel (2001). Parameter TP TN Wahleach Values * Trophic classification oligotrophic mesotrophic eutrophic range 2 - 17 3 -18 11 - 96 16 - 386 mean 5.7 8 27 84 range 50 - 320 307 - 1630 361 - 1387 393 - 6100 mean 158 661 753 1875 Chl a range 0.9 – 6.4 0.3 – 4.5 3 - 11 3 - 78 mean 3.6 m 1.7 4.7 14 Secchi (m) range 2.2 – 7.1 5.4 – 29.3 1.5 – 8.1 0.8 – 7.0 mean 4.3 m 9.9 4.2 2.5 * values based on mean of 2004, 2005 and 2006 values Wahleach Reservoir Fertilization Project, 2004-2006. 43
Page 1 and 2:
Wahleach Project Water Use Plan Wah
Page 3 and 4: Citation: Harris, S.L., D. Sebastia
Page 5 and 6: spawners, from 0 spawners at the st
Page 7 and 8: Table of Contents EXECUTIVE SUMMARY
Page 9 and 10: List of Figures Figure 1 Map of stu
Page 11 and 12: List of Tables Table 1. Annual fert
Page 13 and 14: 1 Introduction The Wahleach Reservo
Page 15 and 16: 3. Methods 3.1 Fertilizer Additions
Page 17 and 18: Photo 1. Old tank farm, consisting
Page 19 and 20: Nitrogen Load (mg·N·m -2 ) 140 12
Page 21 and 22: Vertical profiles of dissolved oxyg
Page 23 and 24: y gravid females and the lengths of
Page 25 and 26: hydroacoustic surveys was used in o
Page 27 and 28: 4. Results 4.1 Reservoir elevation
Page 29 and 30: 4.3 Water Chemistry The mean pH was
Page 31 and 32: Silicic acid is used by diatoms to
Page 33 and 34: Density (cells mL -1 ) 4000 3000 20
Page 35 and 36: Chrysoflagellates and Chryptoflagel
Page 37 and 38: 4.5 Zooplankton The zooplankton com
Page 39 and 40: Density (individuals·L -1 ) Biomas
Page 41 and 42: 4.6 Spawner Surveys The number of k
Page 43 and 44: providing some spawning opportuniti
Page 45 and 46: Kokanee spawners 10000 8000 6000 40
Page 47 and 48: Catch Per Unit Effort (# Fish·Net
Page 49 and 50: Weight (mm) Fork Length (mm) 60 55
Page 51 and 52: 4.8 Hydroacoustics Good weather pro
Page 53: strengths suggested these fish were
Page 57 and 58: Wahleach Reservoir had lower total
Page 59 and 60: 6. Recommendations 1) Fertilization
Page 61 and 62: 7. References APHA. 1985. Standard
Page 63 and 64: Pick, F.R. and D.R.S. Lean. 1987. T
Page 65 and 66: Appendix 1. Phytoplankton species a
show all

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

Create successful ePaper yourself

Delete template?

Save as template?