Effects of Ca (OH)2 additions on phytoplankton communities under ice cover in eutrophic hardwater lakes

Abstract

The effects of Ca(OH) 2 treatment during the open-water season on phytoplankton communities under ice cover were examined for up to three winters (Nov. Apr.) in three eutrophic hardwater lakes in central Alberta. Phytoplankton communities were compared between treated and untreated lakes, and between pre- and posttreatment periods within a treatment lake. In all study lakes, phytoplankton biomass tended to be high at ice-on, decrease after November, and remain low (<2mg/L) from January to early March, when light conditions and water temperatures were also low. After late March to early April, phytoplankton biomass started to increase exponentially because of higher light conditions and water temperature. Most phytoplankton species that were common under ice also occurred during the open-water season. Although phytoplankton species composition was diverse under ice, the biomass of most species, except for flagellates, did not increase before mid-March. Species composition and biomass of some phytoplankton groups varied without clear trends among winters in treated and untreated lakes. Therefore, Ca(OH) 2 treatment during the open-water season did not appear to affect winter phytoplankton communities.