CLBMON-55: Revelstoke Reservoir Macrophyte Assessment Program

Author: Consulting Ltd

1. What are the diversity and distribution of macrophytes in Revelstoke Reservoir?

All seven (7) species of aquatic macrophytes observed in Phase 1 were also observed in Phase 2: Potamogeton amplifolius, Potamogeton alpinus, Potamogeton foliosus, Eleocharis acicularis, Nitella sp., Myriophyllum spicatum, and Ranunculus aquatilis.

In Phase 1, Potamogeton amplifolius was found to be dominant at down reservoir sites (Sites 1 to 4), where it is generally deeper, and Nitella sp. was dominant at up reservoir sites (Sites 8 to 11), where it was generally shallower. In Phase 2 (2014) similar trends were noticed for Potamogeton amplifolius (dominant at Sites 1 and 2) and Nitella sp. (dominant species at Sites 8 and 9), and Eleocharis acicularis observed as dominant at Sites 10 and 11.

In Phase 2, P. amplifolius, a species that prefers deeper water, was observed to have moved to lower elevations at several down-reservoir sites (Sites 2 and 5 and potentially 3 and 4). Species that do well in shallow and disturbed areas such as E. acicularis were observed to have increased in relative abundance within many near-shore zones in Phase 2.

2. Did changes in reservoir drawdown and frequency, due to fifth-unit (REV5) operation at Revelstoke Dam, have any impact on aquatic macrophytes in Revelstoke Reservoir?

Average monthly water elevation in Revelstoke Reservoir (August 1984 to February 2010) was 572.55 m while post REV5 operation levels (December 2010 to December 2014) were lower (572.36 m). There was some evidence to suggest that reduced water elevations in the reservoir, post REV5, influenced relative abundance of certain species (e.g., E. acicularis).

3. Which species of aquatic macrophytes were most likely (if at all) affected by the operation of REV5?

In Phase 1, E. acicularis was observed at four (4) longterm study sites (Sites 5, 7, 10 and 11). These sites were potentially influenced by low drawdown and it was anticipated that low drawdown might increase distribution of this species where water regulation restricted other species growth (i.e., reducing interspecies competition). In Phase 2, E. acicularis was the most dominant species and observed at 2 additional sites (Site 1, 5, 7, 8, 10 and 11) suggesting that conditions were more favourable for E. acicularis post REV5, reflective of lower average water level elevations.

4. What are the best mitigating strategies to minimize any impact to aquatic macrophytes?

Overall, the same macrophyte species were observed in Revelstoke Reservoir between Phase 1 and Phase 2; however, some macrophyte species tend to be more tolerant to lower water levels and others showed improved growth under such conditions. The ability of macrophytes to adapt to changes in water level suggested that the overall macrophyte communities observed in Revelstoke Reservoir were not substantially impacted by REV5 operations.

1. What are the diversity and distribution of macrophytes in Revelstoke Reservoir?

All seven (7) species of aquatic macrophytes observed in Phase 1 were also observed in Phase 2: Potamogeton amplifolius, Potamogeton alpinus, Potamogeton foliosus, Eleocharis acicularis, Nitella sp., Myriophyllum spicatum, and Ranunculus aquatilis.

In Phase 1, Potamogeton amplifolius was found to be dominant at down reservoir sites (Sites 1 to 4), where it is generally deeper, and Nitella sp. was dominant at up reservoir sites (Sites 8 to 11), where it was generally shallower. In Phase 2 (2014) similar trends were noticed for Potamogeton amplifolius (dominant at Sites 1 and 2) and Nitella sp. (dominant species at Sites 8 and 9), and Eleocharis acicularis observed as dominant at Sites 10 and 11.

In Phase 2, P. amplifolius, a species that prefers deeper water, was observed to have moved to lower elevations at several down-reservoir sites (Sites 2 and 5 and potentially 3 and 4). Species that do well in shallow and disturbed areas such as E. acicularis were observed to have increased in relative abundance within many near-shore zones in Phase 2.

2. Did changes in reservoir drawdown and frequency, due to fifth-unit (REV5) operation at Revelstoke Dam, have any impact on aquatic macrophytes in Revelstoke Reservoir?

Average monthly water elevation in Revelstoke Reservoir (August 1984 to February 2010) was 572.55 m while post REV5 operation levels (December 2010 to December 2014) were lower (572.36 m). There was some evidence to suggest that reduced water elevations in the reservoir, post REV5, influenced relative abundance of certain species (e.g., E. acicularis).

3. Which species of aquatic macrophytes were most likely (if at all) affected by the operation of REV5?

In Phase 1, E. acicularis was observed at four (4) longterm study sites (Sites 5, 7, 10 and 11). These sites were potentially influenced by low drawdown and it was anticipated that low drawdown might increase distribution of this species where water regulation restricted other species growth (i.e., reducing interspecies competition). In Phase 2, E. acicularis was the most dominant species and observed at 2 additional sites (Site 1, 5, 7, 8, 10 and 11) suggesting that conditions were more favourable for E. acicularis post REV5, reflective of lower average water level elevations.

4. What are the best mitigating strategies to minimize any impact to aquatic macrophytes?

Overall, the same macrophyte species were observed in Revelstoke Reservoir between Phase 1 and Phase 2; however, some macrophyte species tend to be more tolerant to lower water levels and others showed improved growth under such conditions. The ability of macrophytes to adapt to changes in water level suggested that the overall macrophyte communities observed in Revelstoke Reservoir were not substantially impacted by REV5 operations.