Kootenay Lake Fertilization Experiment, Year 15 (North Arm) and Year 3 (South Arm) (2006) Report

Abstract

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 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 ºC 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 µg/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 Kootenay Lake Fertilization Experiment, Year 15 (North Ar...

Worldwide status of burbot and conservation measures

“…Although alternate hypotheses have been proposed, it is likely that decreases in copepod density are linked to increases in introduced mysis shrimp (Mysis relicta, Mysidae), which are copepod predators and competitors, in combination with reductions in lake productivity after construction of upstream dams (Duncan and Libby Dams : Zyblut 1967;Northcote 1972;Binsted and Ashley 2006). Remediation for the decrease in copepods has included adding nutrients to Kootenay Lake as part of a larger ecosystem rehabilitation project (Ashley et al 1999;Schindler et al 2007). This lake fertilization project has resulted in increased copepod densities close to levels at the time of historic recruitment.…”

The life history characteristics, growth and density of Mysis diluviana in Lake Pend Oreille, Idaho, USA

“…In Kootenay Lake of southern B.C., Canada, managers employed a nutrient enhancement program to stimulate a bottom-up trophic cascade and ensure a sufficient density of desirable zooplankton prey to sustain fish fry (Ashley et al, 1997, Schindler et al, 2009. The intentional application of nutrients to entire lakes is counter to nutrient abatement programs and federal statues such as the US Clean Water Act promulgated in response to the general eutrophication of aquatic ecosystems.…”

The fishing and natural mortality of large, piscivorous Bull Trout and Rainbow Trout in Kootenay Lake, British Columbia (2008–2013)

“…Lake levels and temperatures are influenced by the upstream Duncan and Libby Dams and by the downstream Corra Linn Dam (Hamblin & McAdam, 2003). For more information on Kootenay Lake see Daley et al (1980), Schindler et al (2014) and Kurota et al (2016).…”

“…As a result Kokanee ( Oncorhynchus nerka ), which provide the primary food source for the piscivorous trout (Andrusak & Parkinson, 1984), also declined. In response, the North Arm of Kootenay Lake began to be fertilized in 1992 (Schindler et al, 2014). However, between 1997 and 2000, the fertilizer inputs were temporarily experimentally reduced before returning to pre-1997 levels in 2001.…”

“…However, between 1997 and 2000, the fertilizer inputs were temporarily experimentally reduced before returning to pre-1997 levels in 2001. Most recently, in 2004, the fertilization program was expanded to also include the South Arm (Schindler et al, 2014). …”