Effects of lake water level regulation on aquatic macrophyte stands in northern Finland and options to predict these impacts under varying conditions

A comparative study on the relationship between lake water level regulation and aquatic macrophyte growth was conducted between 1984 and 1986 in two lakes in northern Finland, regulated Ontojärvi and unregulated Lentua. In Ontojärvi, the most apparent effect was an almost complete disappearance of large isoetids (Isoetes lacustris and Lobelia dortmanna). The frequence of helophytes and nymphaeids in this lake was also lower. Alternatively, small isoetids such as the Ranunculus reptans were much more common in Ontojärvi. Helophytes were affected primarily by changes in the water level fluctuation regime, whereas large isoetids and some nymphaeids were eliminated by a more direct exposure to ice.