|CS29 Phytoplankton & Primary Production|
|Date: Tuesday, June 11, 2002|
|Location: Poster Session - VCC|
|Forsstrom, L, , University of Helsinki, Helsinki, Finland, Laura.Forsstrom@Helsinki.Fi|
|Sorvari, S, , University of Helsinki, Helsinki, Finland, Sanna.Sorvari@Helsinki.Fi|
|Rautio, M, , University of Helsinki, Helsinki, Finland, Milla.Rautio@Helsinki.Fi|
|Korhola, A, , University of Helsinki, Helsinki, Finland, Atte.Korhola@Helsinki.Fi|
|PHYTOPLANKTON DYNAMICS IN TWO SUBARCTIC LAKES WITH DIFFERENT THERMAL STRUCTURES|
|Phytoplankton species composition and succession during the open water season was studied in two subarctic lakes in Finnish Lapland. Both lakes are oligotrophic clear water lakes with low nutrient concentrations and low productivity, but they have different morphometries. Lake Saanajarvi is a 24 m deep dimictic lake. The open water season lasts for approximately three months, of which the lake is thermally stratified for almost two months. Lake Masehjavri is 11 m deep and mixes constantly during the ice-free season.
In Lake Saanajarvi the phytoplankton biomass grew constantly throughout the season and was greatest during the autumn turnover. No spring maximum in the biomass could be detected. In Lake Masehjavri the maximum biomass was observed one week after the ice break and it then declined towards the end of the season. The phytoplankton community in Lake Saanajarvi consisted mainly of chrysophytes and diatoms, whereas in Lake Masehjavri the community was dominated by cryptophytes and chrysophytes. Multivariate analyses demonstrate that the differences in species composition and succession are mostly related to physical factors, such as temperature, light regime and thermal stability.