Kootenay Lake Fertilization Experiment, Year 15 (North Arm) and Year 3 (South Arm) (2006) Report
- Fish and Wildlife Science and Allocation, Ministry of Environment, Province of British Columbia
This report summarizes results from the fifteenth year (2006) of nutrient additions to the North Arm of Kootenay Lake and three years of nutrient additions to the South Arm. Experimental fertilization of the lake has been conducted using an adaptive management approach in an effort to restore lake productivity lost as a result of nutrient uptake in upstream reservoirs. The primary objective of the experiment is to restore kokanee (Oncorhynchus nerka) populations, which are the main food source for Gerrard rainbow trout (Oncorhynchus mykiss) and bull trout (Salvelinus confluentus). The quantity of agricultural grade liquid fertilizer (10-34-0, ammonium polyphosphate and 28-0-0, urea ammonium nitrate) added to the North Arm in 2006 was 44.7 tonnes of P and 248.4 tonnes of N. The total fertilizer load added to the South Arm was 257 tonnes of nitrogen; no P was added. Kootenay Lake has an area of 395 km{sup 2}, a maximum depth of 150 m, a mean depth of 94 m, and a water renewal time of approximately two years. Kootenay Lake is a monomictic lake, generally mixing from late fall to early spring and stratifying during the summer. Surface water temperatures generally exceed 20 C for only a few weeks in July. Results of oxygen profiles were similar to previous years with the lake being well oxygenated from the surface to the bottom depths at all stations. Similar to past years, Secchi disc measurements at all stations in 2006 indicate a typical seasonal pattern of decreasing depths associated with the spring phytoplankton bloom, followed by increasing depths as the bloom gradually decreases by the late summer and fall. Total phosphorus (TP) ranged from 2-7 {micro}g/L and tended to decrease as summer advanced. Over the sampling season dissolved inorganic nitrogen (DIN) concentrations decreased, with the decline corresponding to nitrate (the dominant component of DIN) being utilized by phytoplankton during summer stratification. Owing to the importance of epilimnetic nitrate that is required for optimal phytoplankton growth discrete depth water sampling occurred in 2006 to measure more accurately changes in the nitrate concentrations. As expected there was a seasonal decline in nitrate concentrations, thus supporting the strategy of increasing the nitrogen loading in both arms. These in-season changes emphasize the need for an adaptive management approach to ensure the nitrogen to phosphorus (N:P) ratio does not decrease below 15:1 (weight:weight) during the fertilizer application period. Phytoplankton composition determined from the integrated samples (0-20m) was dominated by diatoms, followed by cryptophytes and chrysophytes. The contribution of cryptophytes to total biomass was higher in 2006 than in 2005. Cryptophytes, considered being edible biomass for zooplankton and Daphnia spp., increased in 2006. Phytoplankton in the discrete depth samples (2, 5, 10, 15 and 20m) demonstrated a clear north to south gradient in average phytoplankton density and biomass among the three stations sampled, with highest values at the North Arm station (KLF 2) and lowest values in the most southern station in the South Arm (KLF 7). Populations were dominated by flagellates at all stations and depths in June and July, then dominated by diatoms in August and September in the North and South arms of the lake. There were no large bluegreen (cyanobacteria) populations in either arm of the lake in 2006. Seasonal average zooplankton abundance and biomass in both the main body of the lake and in the West Arm increased in 2006 compared to 2005. Zooplankton density was numerically dominated by copepods and biomass was dominated by Daphnia spp. The annual average mysid biomass data at deep stations indicated that the North Arm of Kootenay Lake was more productive than the South Arm in 2006. Mysid densities increased through the summer and declined in the winter; mean whole lake values remain within prefertilization densities. Kokanee escapement to Meadow Creek declined in 2006 to approximately 400,000 spawners. The Lardeau River escapement also declined with approximately 100,000 spawners. Escapement in the South Arm tributaries in 2006 was similar to 2005 with virtually no spawners. The mean size of female and male kokanee from Meadow Creek was larger than the past three years (24.9 cm and 25.2 cm, respectively) and larger than the long term average (25.2 cm). This is indicative of a density dependent growth response as a decline in in-lake abundance and returning spawners occurred. Spring hydroacoustic estimates indicated low densities of South Arm kokanee with most of the North Arm fry remaining at the most northerly stations. By the fall, the distribution of kokanee from the North Arm to the South Arm was fairly uniform, a normal occurrence in Kootenay Lake. Fall hydroacoustic estimates in 2006 increased to approximately 22 million kokanee.
- Research Organization:
- Bonneville Power Administration (BPA), Portland, OR (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- 39133
- OSTI ID:
- 962648
- Report Number(s):
- P112333; R&D Project: 1994-049-00; TRN: US200917%%67
- Resource Relation:
- Related Information: Fisheries Project Report No. RD 126 2009
- Country of Publication:
- United States
- Language:
- English
Similar Records
Arrow Lakes Reservoir Fertilization Experiment; Years 4 and 5, Technical Report 2002-2003.
Effect of the Operation of Kerr and Hungry Horse Dams on the Reproduction Success of Kokanee in the Flathead River System, 1986 Annual Progress Report.