Växtplankton i Storvänern 2021

The seasonal average phytoplankton biovolumes were on a higher level than normal for the three sampling sites in Lake Vänern. As typical for the lake, the phytoplankton community was dominated by diatoms both in April and in May, although chryptophytes made a comparatively large portion of the totals in May. In June there was a more mixed situation over which phytoplankton groups that dominated at the three monitoring stations. In August the total biovolumes were higher than normal, with diatoms as a major part of the volumes. The ecological status is high according to the average total biovolumes in August 2019-2021. This is also true for the whole period from 1979, even though the total biovolumes have slowly increased over time. Assessments using the phytoplankton trophic index PTI indicates in general a slightly lower water quality than for the biovolumes and chlorophyll. This is most likely due to a large proportion of cyanobacteria in the phytoplankton community, a proportion that is slightly increasing over time, although the total amount of cyanobacteria is comparatively low.