This report is an examination of the overall level of biological productivity within the Arrow Reservoir in 1997/98. Bathymetry, hydrology, water quality, nutrients, phytoplankton, zooplankton, Mysids, Kokanee Salmon and paleolimnology are all considered. The study finds that there is a sequence of decreased productivity occurring following impoundment. Oligotrophication is often caused by hydroelectric development, which is prevalent within the Arrow Lake water system. Also, Mysis relicta were introduced in Arrow Reservoir in a misguided attempt to provide an additional food resource for salmonids. Although the mysids did not cause the collapse of the Arrow ecosystem, their presence likely accelerated the rate of decline of the kokanee population by competing with them for their preferred food items, i.e., Daphnia. There are several reported instances where mysids and Daphnia co-exist at mesotrophic levels of productivity (e.g., Kalamalka Lake, Emerald Bay in Lake Tahoe, Kootenay Lake), therefore, the negative effect of mysid introduction is most strongly observed in ecosystems that are naturally oligotrophic or undergoing oligotrophication through hydroelectric development. However, the inescapable loss of nutrients trapped by upstream impoundments, the loss of littoral productivity, the blockage of marine derived nutrients and the modification of the seasonal hydrograph lead us to conclude that hydroelectric development is the primary cause of oligotrophication in Arrow Reservoir, with mysids playing a secondary role.
Pieters, Roger, Thompson, Lisa C.; Vidmanic, Lidija; Pond, Steve; Stockner, John; Hamblin, Paul; Young, Mark; Ashley, Ken; Lindsay, Bob; Lawrence, Greg; Sebastian, Dale; Scholten, George; Lombard, Darci L.. 1998. Arrow Reservoir Limnology and Trophic Status - Year 1 (1997/98) Report. BC Ministry of Environment, Lands and Parks. Fisheries Project Report. RD 67