Kinbasket and Revelstoke Reservoirs Ecological Productivity and Kokanee Population Monitoring – 2008-2016 (Years 1 to 9) Synthesis Report

Author: K. Bray, T. Weir, R. Pieters, S. Harris, D. Brandt, D. Sebastian, L. Vidmanic

The goal of the related studies (CLBMON02, CLBMON03, and CLBMON56) is to provide the information necessary to inform future water use plans on options and decisions for operating Kinbasket and Revelstoke Reservoirs with respect to ecological productivity (CLBMON03 and 56) and Kokanee abundance (CLBMON02). The objectives for Kokanee Population Monitoring (CLBMON-2) are to monitor trends in the biological characteristics, distribution, and abundance of kokanee and to provide information required to link the influence of reservoir operation to population levels. The objectives for the Ecological Productivity Monitoring program (CLBMON-3) are to understand reservoir limnology and to determine if changes in pelagic productivity are associated with reservoir operations (BC Hydro 2007a). CLBMON-56 was required under the Mica Unit 5 and 6 Environmental Assessment, and focuses on the incremental effect of two additional generating units at Mica Dam on pelagic production and kokanee populations. The work will focus on measuring temperature data in both reservoirs at a fine scale through the use of moored arrays.

Nutrient availability, light conditions, and temperature in the photic zone are considered to exert critical influences on pelagic production. No evident trends in tributary nutrient (nitrogen and phosphorus) inputs were evident over the study years. Reservoir nutrient chemistry and primary production demonstrate that both reservoirs are ultra-oligotrophic (very low in productivity) and limited by phosphorus. Primary production is dominated by smaller phytoplankton (pico- and nano-plankton) as would be expected a low nutrient system. An overall declining trend in phyto- and zooplankton density and biomass was observed over the study period, although with a small period of increase midway. We found no correlation between these primary and secondary trophic levels as might be otherwise expected; however, we have found correlations between zooplankton and kokanee metrics.

The time at which the zooplankton Daphnia (preferred food of kokanee) become available for kokanee forage is sensitive to water temperature. Winter conditions are shown to affect both the onset of stratification in spring and water temperature during this time. In Revelstoke Reservoir we have found that operations, particularly outflows from Mica Dam and Generating Station, exert a strong influence on the dynamics of the interflow of Mica water through Revelstoke Reservoir, and thus nutrient inputs into the photic zone. We will continue to investigate these connections between physical and biological processes and trophic level interactions in these reservoirs as they pertain to the study.

Relative to the long-term dataset, a number of kokanee metrics were noted as declining or low in this second phase of the study, roughly from 2011 to 2016. Kokanee abundance in Kinbasket and Revelstoke Reservoirs has been suppressed since 2011 and the lowest estimates of biomass density (kg/ha) were recorded in the last three to four years of the study period. Age 0 to age 1 survival trends were declining (Kinbasket) or at consistent lows (Revelstoke) since 2011, similar to spawner index trends.

Nutrient availability, light conditions, and temperature in the photic zone are considered to exert critical influences on pelagic production. No evident trends in tributary nutrient (nitrogen and phosphorus) inputs were evident over the study years. Reservoir nutrient chemistry and primary production demonstrate that both reservoirs are ultra-oligotrophic (very low in productivity) and limited by phosphorus. Primary production is dominated by smaller phytoplankton (pico- and nano-plankton) as would be expected a low nutrient system. An overall declining trend in phyto- and zooplankton density and biomass was observed over the study period, although with a small period of increase midway. We found no correlation between these primary and secondary trophic levels as might be otherwise expected; however, we have found correlations between zooplankton and kokanee metrics.

The time at which the zooplankton Daphnia (preferred food of kokanee) become available for kokanee forage is sensitive to water temperature. Winter conditions are shown to affect both the onset of stratification in spring and water temperature during this time. In Revelstoke Reservoir we have found that operations, particularly outflows from Mica Dam and Generating Station, exert a strong influence on the dynamics of the interflow of Mica water through Revelstoke Reservoir, and thus nutrient inputs into the photic zone. We will continue to investigate these connections between physical and biological processes and trophic level interactions in these reservoirs as they pertain to the study.

Relative to the long-term dataset, a number of kokanee metrics were noted as declining or low in this second phase of the study, roughly from 2011 to 2016. Kokanee abundance in Kinbasket and Revelstoke Reservoirs has been suppressed since 2011 and the lowest estimates of biomass density (kg/ha) were recorded in the last three to four years of the study period. Age 0 to age 1 survival trends were declining (Kinbasket) or at consistent lows (Revelstoke) since 2011, similar to spawner index trends.