LAKE WATER SALINITY AND PERIPHYTIC DIATOM SUCCESSION IN 3 SUB-ARCTIC LAKES, YUKON-TERRITORY, CANADA

Seasonal changes in water chemistry and periphytic diatom assemblages were monitored for a saline, a subsaline, and a freshwater lake in the central Yukon Territory. Athalassic saline lakes, such as these, are believed to be extremely rare in arctic regions. All three study lakes exhibited a gradual shoreline retreat over the season (28 May to 22 A ugust 1992) due to evaporative water loss. As the season progressed, t he saline lake exhibited a marked increase in conductivity and salinit y, similar to changes observed for inland salt lakes in more southern regions. The seasonal changes in water chemistry were less pronounced in the subsaline and freshwater lakes. The periphytic diatom populatio ns of the saline lake closely tracked changes in the lake's salinity, exhibiting a successional shift from taxa with low salt tolerances (e. g., Nitzschia cf. commutata and N. cf. palea) to those with high salt tolerances (e.g., Amphora acutiuscula) over the study period. Periphyt ic diatoms in the subsaline and freshwater lakes also exhibited marked successional changes, shifting to almost complete dominance by a sing le species (Cocconeis placentula and Achnanthes minutissima respective ly), but these shifts were not related to lake water salinity alone.