Monitoring Study No. CLBMON-44 (Year 9) Lower Columbia River Physical Habitat and Ecological Productivity, Study Period: 2016

Author: R. Plewes, H. Larratt, M.A. Olson-Russello

CLBMON-44 is a multi-year study of physical habitat and ecological productivity on the Lower Columbia River (LCR) between the outflow of the Hugh L. Keenleyside Dam (HLK) and the Birchbank gauging station. The aim of the study is to examine the influence of three different flow periods on select physical habitat and ecological productivity measures: - January 1 March 31, Mountain Whitefish (MWF); - April 1 June 30, Rainbow Trout (RBT); and - September 1 October 31, Fall fluctuating flows (FFF).

The occurrence of the nuisance algae Didymo was highest in winter. To test if differences in winter flow conditions cause Didymo growth, a statistical CART model was run (Appendix-A6). The most important predictor of Didymo growth was low water temperature, followed by site. Generally, sites with back-watering from the Kootenay River (S4, S5, and S7) had higher relative abundance of Didymo than the sites S1, S2, S3, and S6. These conditions provide favourable Didymo growth conditions – rocky substrates with cool, clear, moderate flows (Bergey et al. 2009; Bothwell et al., 2009).
Periphyton in LCR showed significant variations in production and community structure between seasons and between years. Many factors that influenced periphyton production gradients are related to LCR flows contributed by reservoir releases. Our field observations agree well with the statistical models that measures of flow variability and velocity are the important factors influencing periphyton production in LCR. These results suggest a direct link between productivity and operations. Although discharge clearly plays a role on the periphyton community, the smaller nuances of managed fish flows (MWF, RBT and FFF) is more difficult to discern. Each managed flow period and relevant hypothesis is considered separately in the following sections.

The occurrence of the nuisance algae Didymo was highest in winter. To test if differences in winter flow conditions cause Didymo growth, a statistical CART model was run (Appendix-A6). The most important predictor of Didymo growth was low water temperature, followed by site. Generally, sites with back-watering from the Kootenay River (S4, S5, and S7) had higher relative abundance of Didymo than the sites S1, S2, S3, and S6. These conditions provide favourable Didymo growth conditions – rocky substrates with cool, clear, moderate flows (Bergey et al. 2009; Bothwell et al., 2009).
Periphyton in LCR showed significant variations in production and community structure between seasons and between years. Many factors that influenced periphyton production gradients are related to LCR flows contributed by reservoir releases. Our field observations agree well with the statistical models that measures of flow variability and velocity are the important factors influencing periphyton production in LCR. These results suggest a direct link between productivity and operations. Although discharge clearly plays a role on the periphyton community, the smaller nuances of managed fish flows (MWF, RBT and FFF) is more difficult to discern. Each managed flow period and relevant hypothesis is considered separately in the following sections.