CLBMON-15b Middle Columbia River Ecological Productivity Monitoring

Author: J. Schleppe, R. Plewes, H. Larratt, A. Duncan

CLBMON-15B is long-term monitoring study on ecological productivity in the Middle Columbia River. The key objectives of this monitoring program are to 1) provide long term data on the productivity of benthic communities, 2) assess how the recommended minimum flow releases influence benthic productivity as it relates to the availability of food for fishes in the MCR and 3)to quantify the relationship between habitat attributes and benthic composition, abundance, and biomass in the section of the MCR most likely to be influenced by minimum flows and REV 5 operations. A key environmental objective of the minimum flow release is to enhance the productivity and diversity of benthic communities. The benthic community of MCR is viewed as a key monitoring component in the Revelstoke Flow Management Program because the productivity and diversity of the benthic community may reflect ecosystem health, and the benthic community supports juvenile and adult life stages of fish populations.

Q.1. What is the composition, distribution, abundance and biomass of periphyton and benthic invertebrates in the section of MCR subjected to the influence of minimum flows?
The spatial area supporting benthic communities increased with minimum flows, predominantly in Reach 4, but also in Reach 3 during periods when ALR reservoir did not create backwater conditions. The spatial area of productive habitat is determined by the BC Hydro operating regime because the operating regime is directly responsible for the wetted history. The operating regime creates three typical bands of growth that moved across the channel in relation to mean low flows and duration of daily high flows. During certain operating regimes, the total productive area is determined by factors such as high daily average flows, backwatering from Arrow Lakes Reservoir, and weather conditions. The spatial model developed during 2017 and 2018, currently considers chlorophyll-a and invertebrate biomass. The results of the model indicate that minimum flows increased productivity during periods of low ALR reservoir elevations, and the minimum flow effects were more apparent for periphyton and invertebrates in Reach 4 than in Reach 3.
Q.2. What is the effect of implementing minimum flows on the area of productive benthic habitat?
Given no other operating constraints, we conclude that minimum flows in combination with daily, weekly, monthly and annual operating regimes positively affect the total biomass within the MCR. Peak or total biomass was greatest in permanently wetted areas adjacent to the channel edge at average low flows and in areas directly below average low flows. ALR backwatering increases the total area of productive habitat in the MCR, but does not appear to alter the accrual rates.
The overall benefits of minimum flow are greatest under the following conditions:
– Periods of low daily flows (400 to 600 m3/s) that exceed 24 hours with low humidity and >10-15C or <0C average daytime temperatures - Repeated exposure events in excess of 12 hours, particularly during more extreme temperatures. Q3. What is the effect of implementing minimum flows on the accrual rate of periphyton biomass in the MCR? Is there a long-term trend in accrual? Accrual rates in permanently wetted areas that occurred in the mid-channel, with the highest water velocity and depth during high flows did not appear to have a different accrual rate under current minimum flows management when compared to pre-implementation of minimum flows. The physical characteristics such as velocity, light, and substrate were more important determinants of periphyton accrual than minimum flows within these areas. Thus, minimum flows are expected to have minimal effects on accrual. Peak flows associated with REV 5 or other high water events appear to reduce periphyton accrual rates and standing crop in permanently submerged habitats. We conclude that minimum flows do not affect areas that are periodically dewatered (located above the minimum flow line), but they do have an effect in areas that were regularly exposed before the minimum flow operating regime because increased accrual would have occurred as observed in time series sampling in the spring and fall. Daytime submergence, seasonal patterns, algal immigration from Revelstoke Reservoir and operating cycles were also important determinants of periphyton accrual and must also be considered. Q.4. What is the effect of implementing minimum flows on the total abundance, diversity and biomass of benthic organisms in the section of the MCR subjected to the influence of minimum flows? Is there a long term trend in benthic productivity? Permanently submerged areas were the most productive and diverse, but frequently submerged varial zone areas also had comparable levels of productivity and diversity. The area of productive invertebrate habitat was bounded by average daily low flows and its upper limit was determined by average daily submergence. Determining the benefits of minimum flows is not currently possible because of other confounding factors such as the duration of daily high flows. Without any other operating constraints, minimum flows do affect the total abundance, biomass and diversity of benthic communities because they establish a minimum area of productive habitat and ensure there are organisms for recolonization in addition to those provided by tributary inflows. However, other factors such as the life history strategies of different benthic invertebrates or periphyton species may also be equally or possibly even more important to overall productivity. We conclude that minimum flows have not affected abundance/biomass/diversity in permanently wetted areas. However, our data suggest that other aspects of operation, such as high peak flows associated with high water events may be important determinants of invertebrate production. Thus, consideration of all aspects of flow regulation must occur in conjunction with minimum flows to understand potential effects. We conclude that minimum flows do not affect areas periodically dewatered located above the minimum flow elevation, but they probably had an effect in areas that were regularly exposed before the minimum flow operating regime because the data indicate that benthic invertebrate abundance, diversity, and biomass are positively associated with submergence. Daytime submergence, seasonal patterns and operating cycles were also important determinants of benthic accrual and must also be considered. Q5. If changes in the benthic community associated with minimum flow releases are detected, what effect can be inferred on juvenile or adult life stages of fishes? Food for fish was assessed using a Fish Food Index (FFI) in 2013 and the total biomass of EPT and Dipteran taxa in 2014 to 2015. The FFI consisted of three parameters for each benthic taxon, 1) invertebrate abundance, 2) relative invertebrate biomass, and 3) fish food preference for a given benthic taxon. The overall benefits of minimum flow are greatest under the following conditions: - Periods of low daily flows that exceed 24 hours with freezing or high average daytime temperatures; - Dewatering periods greater than 12 hours. Substrates submerged for 450 to 500 hours (10 to 11 hours per day over approximately 45 days) during daytime hours had the greatest availability of preferred fish food items, which are generally EPT and Diptera. EPT and Dipteran biomass was greatest in areas submerged for at least 750 to 1000 hours over at least 46 days. Both periphyton and invertebrates showed similar responses, suggesting that overall productivity and food for fish is directly affected by the operational cycles that create either submerged or dry conditions, where increased periods of submergence result in an overall increase in productivity. In addition to the area wetted by minimum flows acting as a species reservoir, tributaries such as the Jordan River may be important donors of invertebrate species utilized by fish and these donations would assist with MCR recovery from exposure events.

Q.1. What is the composition, distribution, abundance and biomass of periphyton and benthic invertebrates in the section of MCR subjected to the influence of minimum flows?
The spatial area supporting benthic communities increased with minimum flows, predominantly in Reach 4, but also in Reach 3 during periods when ALR reservoir did not create backwater conditions. The spatial area of productive habitat is determined by the BC Hydro operating regime because the operating regime is directly responsible for the wetted history. The operating regime creates three typical bands of growth that moved across the channel in relation to mean low flows and duration of daily high flows. During certain operating regimes, the total productive area is determined by factors such as high daily average flows, backwatering from Arrow Lakes Reservoir, and weather conditions. The spatial model developed during 2017 and 2018, currently considers chlorophyll-a and invertebrate biomass. The results of the model indicate that minimum flows increased productivity during periods of low ALR reservoir elevations, and the minimum flow effects were more apparent for periphyton and invertebrates in Reach 4 than in Reach 3.
Q.2. What is the effect of implementing minimum flows on the area of productive benthic habitat?
Given no other operating constraints, we conclude that minimum flows in combination with daily, weekly, monthly and annual operating regimes positively affect the total biomass within the MCR. Peak or total biomass was greatest in permanently wetted areas adjacent to the channel edge at average low flows and in areas directly below average low flows. ALR backwatering increases the total area of productive habitat in the MCR, but does not appear to alter the accrual rates.
The overall benefits of minimum flow are greatest under the following conditions:
– Periods of low daily flows (400 to 600 m3/s) that exceed 24 hours with low humidity and >10-15C or <0C average daytime temperatures - Repeated exposure events in excess of 12 hours, particularly during more extreme temperatures. Q3. What is the effect of implementing minimum flows on the accrual rate of periphyton biomass in the MCR? Is there a long-term trend in accrual? Accrual rates in permanently wetted areas that occurred in the mid-channel, with the highest water velocity and depth during high flows did not appear to have a different accrual rate under current minimum flows management when compared to pre-implementation of minimum flows. The physical characteristics such as velocity, light, and substrate were more important determinants of periphyton accrual than minimum flows within these areas. Thus, minimum flows are expected to have minimal effects on accrual. Peak flows associated with REV 5 or other high water events appear to reduce periphyton accrual rates and standing crop in permanently submerged habitats. We conclude that minimum flows do not affect areas that are periodically dewatered (located above the minimum flow line), but they do have an effect in areas that were regularly exposed before the minimum flow operating regime because increased accrual would have occurred as observed in time series sampling in the spring and fall. Daytime submergence, seasonal patterns, algal immigration from Revelstoke Reservoir and operating cycles were also important determinants of periphyton accrual and must also be considered. Q.4. What is the effect of implementing minimum flows on the total abundance, diversity and biomass of benthic organisms in the section of the MCR subjected to the influence of minimum flows? Is there a long term trend in benthic productivity? Permanently submerged areas were the most productive and diverse, but frequently submerged varial zone areas also had comparable levels of productivity and diversity. The area of productive invertebrate habitat was bounded by average daily low flows and its upper limit was determined by average daily submergence. Determining the benefits of minimum flows is not currently possible because of other confounding factors such as the duration of daily high flows. Without any other operating constraints, minimum flows do affect the total abundance, biomass and diversity of benthic communities because they establish a minimum area of productive habitat and ensure there are organisms for recolonization in addition to those provided by tributary inflows. However, other factors such as the life history strategies of different benthic invertebrates or periphyton species may also be equally or possibly even more important to overall productivity. We conclude that minimum flows have not affected abundance/biomass/diversity in permanently wetted areas. However, our data suggest that other aspects of operation, such as high peak flows associated with high water events may be important determinants of invertebrate production. Thus, consideration of all aspects of flow regulation must occur in conjunction with minimum flows to understand potential effects. We conclude that minimum flows do not affect areas periodically dewatered located above the minimum flow elevation, but they probably had an effect in areas that were regularly exposed before the minimum flow operating regime because the data indicate that benthic invertebrate abundance, diversity, and biomass are positively associated with submergence. Daytime submergence, seasonal patterns and operating cycles were also important determinants of benthic accrual and must also be considered. Q5. If changes in the benthic community associated with minimum flow releases are detected, what effect can be inferred on juvenile or adult life stages of fishes? Food for fish was assessed using a Fish Food Index (FFI) in 2013 and the total biomass of EPT and Dipteran taxa in 2014 to 2015. The FFI consisted of three parameters for each benthic taxon, 1) invertebrate abundance, 2) relative invertebrate biomass, and 3) fish food preference for a given benthic taxon. The overall benefits of minimum flow are greatest under the following conditions: - Periods of low daily flows that exceed 24 hours with freezing or high average daytime temperatures; - Dewatering periods greater than 12 hours. Substrates submerged for 450 to 500 hours (10 to 11 hours per day over approximately 45 days) during daytime hours had the greatest availability of preferred fish food items, which are generally EPT and Diptera. EPT and Dipteran biomass was greatest in areas submerged for at least 750 to 1000 hours over at least 46 days. Both periphyton and invertebrates showed similar responses, suggesting that overall productivity and food for fish is directly affected by the operational cycles that create either submerged or dry conditions, where increased periods of submergence result in an overall increase in productivity. In addition to the area wetted by minimum flows acting as a species reservoir, tributaries such as the Jordan River may be important donors of invertebrate species utilized by fish and these donations would assist with MCR recovery from exposure events.