| Citation |
E.U. Schindler, H. Andrusak, K.I. Ashley, G.F. Andrusak, L. Vidmanic, D. Sebastian, G. Scholten, P. Woodruff, J. Stockner, F. Pick, L.M. Ley and P.B. Hamilton (2008) Kootenay Lake Fertilization Experiment: Year 14 (North Arm) and Year Two (South Arm) - 2005, Ministry of Environment, Limno-Lab Ltd., Redfish Consulting Ltd., BC Conservation Foundation, University of Ottawa, University of British Columbia, Canadian Museum of Nature, Eco-Logic Ltd. |
| Abstract/Description or Keywords |
This report summarizes results from the fourteenth year (2005) of fertilizing the North Arm Kootenay Lake and Year 2 (2005) of fertilizing 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). 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 2005 was 44.1 tonnes of P and 246.9 tonnes of N. The total fertilizer load added to the South Arm was 234 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 using a tug and barge 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 has 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 2005 were recorded on August 08 at 21.9 ľC in the North Arm (KLF 3) and at 23.0 ľC in the South Arm (KLF 5). 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. Secchi depth measurements reflected the typical seasonal phytoplankton growing pattern with low measurements recorded during the spring phytoplankton bloom. Summer measurements remained low due to nutrient additions that promoted good growth but these depth measurements increased as the bloom gradually decreased during the late summer and fall. Although slight differences occurred between stations, this pattern was similar for all stations in 2005. Total phosphorus (TP) ranged from 2-8 _g/L in the North Arm, 2-5 _g/L in the South Arm, and 2-3 _g/L in the West Arm. These values tended to decrease as summer advanced. With average TP values generally in the range of 2-4 _g/L, Kootenay Lake is considered to be an oligotrophic lake. Total dissolved phosphorus (TDP) followed the same seasonal trends as TP and ranged from 2-8 _g/L in the North Arm, 2-4 _g/L in the South Arm and 2 _g/L in the West Arm. Over the sampling season dissolved inorganic nitrogen (DIN) concentrations showed a more pronounced declining trend than P, with the decline corresponding to nitrate (the dominant component of DIN) being utilized by phytoplankton during summer stratification. DIN in the epilimnion ranged from 18-156 _g/L in the North Arm, from 11-135 _g/L in the South Arm, and from 12-140 _g/L in the West Arm. These concentrations trended downwards as the summer advanced only to increase again during the fall-winter months in all three arms. Owing to the importance of epilimnion nitrate that is required for optimal phytoplankton growth discrete depth water sampling occurred in 2005 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 a nitrogen to phosphorus (N:P) ratio of 15:1 (weight:weight) during the fertilizer application period. Chlorophyll a (Chl a) concentrations in 2005 ranged from 0.5-4.5 _g/L in the North Arm, 0.5-3.4 _g/L in the South Arm, and 0.5-3.9 _g/L in the West Arm. Although station-to-station variability was high the pattern of increasing Chl a concentrations from spring to summer was evident for most stations throughout the lake. Results for South Arm stations indicated a late summer bloom (September) compared to the North Arm (July). Phytoplankton composition determined from the integrated samples (0-20m) was dominated by diatoms, followed by chrysophytes. Cryptophytes were most dominant in the spring but at station KLF 2 in July they were also dominant. The annual average cryptophyte biomass in the North Arm was twice the annual average of biomass in the South Arm. The overall contribution of cryptophytes to total biomass was much greater in the North Arm than in the South ArmThe overall average biomass was not different between the North and the South Arm but the summer biomass (June, July, August) was higher in the N+P fertilized North Arm(0.62 g m-3) versus the N-fertilized South Arm (0.47 g m-3). Phytoplankton in the discrete depth samples (2, 5, 10, 15 and 20m) was dominated by diatoms, followed by flagellates and then cyanobacteria. Compared to 2004 the 2005, whole-lake average increased in abundance by 20% and increased in biomass by 30% The largest populations were found at north basin stations similar to the results from the integrated samples. The majority of phytoplankton was distributed in the upper 10-15 m of the epilimnion and there was a consistent low population density at 15-20 m at most stations. There were no deep phytoplankton plates found at any station to suggest the presence of a persistent deep chlorophyll maximum in Kootenay Lake. A significant change in 2005 occurred compared to 2004 where species composition shifted to a higher biomass of flagellates and a decrease in nitrogen-fixing blue-green algae. Inedible diatom biomass decreased in 2005 from 2004 but was abundant in August and September in all stations within the lake. A higher biomass of flagellates provides a greater forage base for zooplankton. Zooplankton average density decreased in 2005 compared to the previous five years. Zooplankton density is numerically dominated by copepods, which include calanoids and cyclopoids. The zooplankton community in the North Arm comprised of 90% copepods, 1% Daphnia spp., and 9% cladocerans other than Daphnia spp. The South Arm population in the 2005 sampling season comprised of 86% copepods, 3% Daphnia spp., and 11% cladocerans other than Daphnia spp. Estimated zooplankton biomass in 2005 was similar in both the North and South Arms. The zooplankton biomass was comprised of 72% copepods, 18.5% Daphnia spp and 9.7% cladocerans other than Daphnia spp. Biomass of copepods and cladocerans other than Daphnia spp increased slightly from 2004 while Daphnia spp decreased slightly. In 2005, mysid density and biomass was higher in the North Arm and lower in the South Arm than in 2004. 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 escapements to Meadow Creek and the Lardeau Rivers was 1.03 million and 0.23 million, respectively in 2005. The Meadow Creek escapement was similar to the 2004 results. Escapement to the Lardeau River was slightly higher than in previous years. Kokanee returning to South Arm tributaries in 2005 were very few in numbers with most streams having either none or < 100 spawners. The mean size of 2005 female kokanee was 216 mm while male mean size was 217 mm, slightly smaller than the 39 year average of 221 mm for females and 224 mm for males. These results were identical to those measured in 2004 but slightly smaller than the 39- year average. The 2005 fecundity was determined to be 227 eggs, slightly lower than the 2004 fecundity of 245 eggs/female, and also lower than the long-term average of 259 eggs/female. The 2005 estimate of Meadow Creek spawning channel fry production was ~25 million, the second highest level of production during the four decades of channel operation. Fall hydroacoustic survey estimates in 2005 was similar to 2004 with a total of 16 million kokanee in the lake. There was a significant decrease in the number of fry based on the fall hydroacoustic survey compared to the estimated spring fry production. During 2005 the distribution of kokanee was highly skewed to the north end of the lake. The fry in the North Arm may have been subjected to high predation. During most years of this study, the kokanee usually distribute evenly throughout the North and South Arms during the fall surveys. Nutrient additions are scheduled for the South Arm in 2006 with additions commencing at the same time as in 2005. Results of the fourteenth 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. |
