| Citation |
E.U. Schindler, R. Rae, K.I. Ashley, L. Vidmanic, D. Sebastian, H. Andrusak, G. Scholten, P. Woodruff, J. Stockner, F. Pick, L.M. Ley, P.B. Hamilton, G.F. Andrusak, L. Fleck (2008) Kootenay Lake Fertilization Experiment, Year 13 (North Arm) and Year 1 (South Arm) 2004, Ministry of Environment, Sumac Writing and Editing, Limno-Lab Ltd., Redfish Consulting Ltd., BC Conservation Foundation, Eco-Logic Ltd., University of Ottawa, University of British Columbia, Canadian Museum of Nature, Crystal Springs Contracting. |
| Abstract/Description or Keywords |
This report summarizes results from the thirteenth year (2004) of the North Arm Kootenay Lake experimental fertilization and Year 1 (2004) of fertilizing the South Arm. Experimental fertilization has occurred in the lake 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). 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 2004 was 37.6 tonnes of P and 243.5 tonnes of N. The total fertilizer load added to the South Arm was 124 tonnes of nitrogen; no P was added. As in previous years a tug and barge was used to dispense the fertilizer equally over a 10 km stretch in the North Arm from 3 km south of Lardeau, BC to 3 km south of Schroeder Creek. South Arm fertilizer was dispensed in a similar manner from a point 8 km north of Mountain Shores to a point 8 km north of Boswell BC, a distance of 12.5 km each way. Kootenay Lake an area of 395 km2, 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. The warmest surface water temperatures in 2004 were recorded on August 10 at 20.5 ľC in the North Arm (KLF 3) and at 20.9 ľC in the South Arm (KLF 6). The entire water column was oxygen-saturated throughout the sampling season with values ranging from about 8-16 mg/L. Secchi depth followed the expected seasonal pattern for an oligo-mesotrophic lake; decreasing values in May, June, and early July, concurrent with the spring phytoplankton bloom, while increasing again as the summer advanced and phytoplankton biomass decreased.. The pattern was similar among all stations, except at KLF 7 in the South Arm, where water clarity was low from April to July and then increased through the summer to display the greatest clarity of all stations by November. Total phosphorus (TP) ranged from 2-10 _g/L in the North Arm, 2-13 _g/L in the South Arm, and 2-17 _g/L in the West Arm. These values tended to decrease as summer advanced. With average TP values generally in the range of 3-10 _g/L, Kootenay Lake is now considered to be an oligotrophic to oligo-mesotrophic lake. Total dissolved phosphorus (TDP) followed the same seasonal trends as TP and ranged from 2-9 _g/L in the North and West arms and from 2-8 _g/L in the South Arm. A spring TDP peak similar to the TP peak was not observed at any station in 2004, but TDP increased in the fall at stations KLF 1-5 and KLF 8. TDP in the hypolimnion was also low throughout the spring and summer, increasing in the fall. Dissolved inorganic nitrogen (DIN) concentrations showed a more pronounced declining trend than P over the sampling season, with the decline corresponding to nitrate (the dominant component of DIN) being used by phytoplankton during summer stratification. DIN in the epilimnion ranged from 20-167 _g/L in the North Arm, from 20-141 _g/L in the South Arm, and from 27-135 _g/L in the West Arm. In late fall, DIN increased from its summer low, more so at South Arm and West Arm stations than at North Arm stations. As in 2003, discrete depth water sampling occurred in 2004, and a more detailed examination of the nitrate concentrations in the epilimnion was undertaken. There was a seasonal decline in nitrate concentrations, which supports the strategy of increasing the nitrogen loading in both arms and applying an adaptive management strategy for a nitrogen to phosphorus (N:P) ratio of approximately 15:1 (weight:weight) during the fertilizer application period. Chlorophyll a (Chl a) concentrations in 2004 ranged from 0.5-4.4 _g/L in the North Arm, 0.5-4.3 _g/L in the South Arm, and 1.2-4.4 _g/L in the West Arm. Over the sampling season, Chl a at all stations generally increased in the spring corresponding with the phytoplankton bloom, although the Chl a peak was measured in May rather than in June, when the TP concentrations peaked. Following the spring peak, Chl a decreased and then remained low or increased gradually during the summer except in the West Arm. With mixing of the water column in the fall, a second peak was measured, and at most stations, the fall peak was higher than the spring peak. By October at some stations and November at others, the Chl a concentration had declined again to the winter phytoplankton minimum. The overall trend observed throughout the 2004 sampling season was of fairly constant algal biomass at the North Arm and South Arm stations. Unlike previous years biomass was slightly higher in September and October in North Arm stations due to slight increases in pennate diatoms, in particular Fragilaria crotonensis and subsequently Tabellaria. In contrast, declines in biomass were observed by September in all South Arm stations. Kootenay Lake continues to be a diatom dominated lake (66 - 71% of total average biomass). However, 2004 was somewhat unique in that centric diatoms were more important than pennate diatoms in the North Arm. The annual average and the summer average biomasses in the North Arm were the lowest since fertilization began in 1992. Furthermore, additional fertilization of the South Arm with nitrogen during August did not appear to have had any significant effect on phytoplankton biomass. Fertilizer applications will need to commence earlier in the year in 2005. Seasonal phytoplankton composition was dominated by diatoms and secondarily by flagellates and by cyanobacteria. The timing of peaks of maximum abundance and minimum abundance differed in the two arms. There was variation of total phytoplankton abundance between depths and among dates sampled. The majority of the phytyoplankton was distributed in the upper 15 m of the epilimnion with a consistent low abundance at 20 m depth at most stations. There were no apparent high concentrations of phytoplankton ‘deep plates’ found at any station suggestive of deep chlorophyll maximums. Bacteria samples were sampled and analyzed in Kootenay Lake in 2004. The range of free-living bacteria in Kootenay Lake was 650-700,000 cells/mL, well within the range of estimates from several fertilized BC coastal lakes. In these lakes the average population densities ranged from 650 – 750,000 cells/mL, with population peak densities often exceeding 1-1,500,000 cells/mL in late summer. During 2004, seston fatty acid samples were collected and analyzed. The total fatty acid concentration in Kootenay Lake had very high July concentrations ranging from 38-109 _g.L-1. The concentrations decreased markedly for August, September, and October to a range of 16-35 _g.L-1. The sum of w3 fatty acids showed a similar trend and represented 24-32% of fatty acids in Kootenay Lake. The w3:w6 ratio at a South Arm station fluctuated in the range of 2.5:1 and 4.5:1, while at a North Arm station it stayed relatively constant at just over 4:1. Beneficial fatty acids, in particular the w3 fatty acids, in algae are particularly nutritious for zooplankton. This has a positive effect on kokanee by increasing their capacity to gain the necessary fatty acids for overwinter survival since kokanee graze on zooplankton. The zooplankton populations in Kootenay Lake were comprised of a diverse species assemblage, with total population density lower in 2004 compared to 2003. The zooplankton density was numerically dominated by copepods, which averaged 94% of the population in 2004. Daphnia spp. comprised 1%, and cladocerans other than Daphnia spp. comprised 5%. The decline in the proportion of cladocerans in 2004 may have been due to the decrease in the biomass of grazeable phytoplankton (nanoplankton, 2–22 _m). The 2004 decline in Daphnia density could be due to much lower phytoplankton biomass hence less food and or due to higher grazing rates from kokanee and mysids. Zooplankton biomass in 2004 had similar downward trends in both the North and South Arms. Total biomass decreased as did the biomass of other cladocerans and of Daphnia. The zooplankton biomass in 2004 was comprised of 66% copepods, 26% Daphnia spp., and 8% cladocerans other than Daphnia spp. Daphnia biomass decreased approximately seven times lower in the North Arm and approximately four times lower in the South Arm compared to 2003 estimates. In 2004 mysid densities were higher than the previous two years. These values remain within the range of pre-fertilization values. Since 1993 mysid densities at deep stations have fluctuated along the length of the lake with higher values usually occurring in North Arm stations. During the season, densities increased through summer and declined in winter. Mysid density and biomass tended to be higher at the deep sites than at near-shore sites. Estimated kokanee escapement to Meadow Creek and the Lardeau Rivers was 1.13 million and 0.25 million, respectively in 2004. The Meadow Creek escapement increased substantially from the 2000-2003 estimates that were all < 1 million. Escapement to the Lardeau River was slightly higher than in previous years. Kokanee returning to South Arm tributaries in 2004 were very few in numbers with most streams having either none or < 100 spawners. The mean size of 2004 female kokanee was 216 mm while male mean size was 217 mm, slightly smaller than the 38 year average of 221 mm for females and 224 mm for females. The 2004 fecundity was determined to be 245 eggs, higher than the 2003 estimate of 208 but still below the long-term average of 259. The 2004 estimate of Meadow Creek fry production was ~16 million with ~91% produced in the spawning channel. Fall hydroacoustic surveys in 2004 indicated a decrease of kokanee from the previous two years but remain higher than the pre-fertilization years. The Meadow Creek 2004 fry production was lower than the near record years of 2002 and 2003. However, the 2004 estimate for ages 1-3 was higher than the early 1990s when fertilization commenced. A good relationship exists between the fall fry acoustic estimates and the spring spawning channel fry estimates. The peak count of Gerrard rainbow trout increased from the 2003 results. Rainbow trout sport fisheries evidently improved in 2004 compared to the previous three years. Nutrient additions are scheduled for the South Arm in 2005 with additions commencing earlier in the year than 2004. Results of the thirteenth year of the Kootenay Lake fertilization experiment (North Arm) indicate that kokanee restoration has been successful in replacing nutrients lost as a result of upstream impoundments. The data illustrates that all trophic levels have responded to the nutrient additions with kokanee numbers reflecting this successful bottom up approach. |
