Factors influencing Gonyostomum semen blooms in a small boreal reservoir lake

Blooms of the nuisance alga Gonyostomum semen occurred in Lake 979 (Experimental Lakes Area), a small brown-water lake, that was subjected to several years of an experimental flooding regime. During periods of flooding, blooms of G. semen developed when light decreased below 100molm^–2s^–1 and total phosphorous concentrations increased to >30gl^–1. Gonyostomum semen biomass was significantly correlated with total P and DOC concentrations. In addition, G. semen abundance increased at times when Daphnia rosea had rapidly declined to<10 animals l^–1. Daphnia egg ratios suggest that declines in Daphnia abundance were the result of shifts in mortality and not causally linked to changes in G. semen densities. The results observed in Lake 979 were supported by a laboratory experiment where the appearance of G. semen from Lake 979 sediment was stimulated by altering chemical and biological variables. The stimulation of G. semen blooms appears to be dependant on multiple variables rather than a single variable.