Abstract
The bloom-forming freshwater alga Gonyostomum semen is associated with acidic, mesotrophic brown water lakes in boreal regions. However, researchers have been unable to conclusively link G.semen abundance and bloom formation to typical brown water lake traits, that is, high water color and DOC (dissolved organic carbon) concentrations. Iron is a main driver of water color in boreal lakes, and a recent study of lake monitoring data indicated a connection between lakes with high G.semen abundance and iron concentrations >200µg·L-1 . Thus, iron may be the missing link in explaining G.semen abundance and growth dynamics. We experimentally assessed the effects of different iron concentrations above or below 200µg·L-1 on the growth of G.semen batch monocultures. Iron concentrations <200µg·L-1 limited G.semen growth, while iron concentrations >200µg·L-1 did not. Moreover, the iron concentration of the medium required for growth was higher than for other common phytoplankton (Microcystis botrys and Chlamydomonas sp.) included in the experiment. These results indicate that G.semen requires high levels of iron in the lake environment. Consequently, this and previous findings using lake monitoring data support the hypothesis that high concentrations of iron favor the formation of high-density G.semen blooms in boreal brown water lakes. As lakes get browner in a changing climate, monitoring iron levels could be a potential tool to identify lakes at risk for G.semen blooms, especially among lakes that provide ecosystem services to society.
Highlights
The bloom-forming freshwater alga Gonyostomum semen is associated with acidic, mesotrophic brown water lakes in boreal regions
At iron concentrations >200 μg Á L−1 (Fe03 and Fe04), Gonyostomum semen strains 1 and 3 grew exponentially during the entire testing period, increasing up to 10-fold compared to the starting cell densities (Fig. 1). This response was stronger in strain 1 (maximum r = 0.11, standard deviation (SD) = 0.008) than strain 3
At iron concentrations
Summary
The bloom-forming freshwater alga Gonyostomum semen is associated with acidic, mesotrophic brown water lakes in boreal regions. The iron concentration of the medium required for growth was higher than for other common phytoplankton (Microcystis botrys and Chlamydomonas sp.) included in the experiment These results indicate that G. semen requires high levels of iron in the lake environment. In less nutrient-rich brown water lakes in boreal regions, such cyanobacterial blooms are uncharacteristic and flagellates (such as Gonyostomum semen) are the most common bloom-forming alga (Ilmavirta 1983). Those lake ecosystems may require a different management approach to ensure good water quality and to protect ecosystem services, such as drinking water and recreation. Gonyostomum semen is a noxious alga that typically occurs in Northern-European brown water lakes (Cronberg et al 1988, Rengefors et al 2012), where
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