TROPHIC STATUS OF LAKES IN THALA HILLS, ANTARCTICA : RECORDS FROM THE YEARS 1967-68 AND 1988 (19th Symposium on Polar Biology)

Major ions, nutrients and primary production of phytoplankton (PP) investigated in lakes of the Thala Hills, East Antarctica during 1967-68 and 1988 were compared to discuss changes in environmental conditions Lakes Glubokoye and Lagernoye revealed chemical stratification during the former and uniform chemical profiles during the latter period. The contents of phosphates in lake waters during the 1967-68 period reached 750 μg Pl^ and those of ammonia 1300 μg N/l^, 1-2 orders of magnitude higher than in the 1988 period and in most of East Antarctic lakes These high contents are explained by higher summer air temperatures which brought about more intensive flushing of the active layer of permafrost with meltwater, and possibly triggered accumulated human impact. Accordingly, high nutrient levels revealed that in the ice-free water bodies during 1967-68, PP were approaching characteristic levels in nutrient-enriched Antarctic lakes. During 1988 the PP measured in ice-covered lakes were 1-2 orders of magnitude lower and comparable to other Antarctic lakes without animal or human impact. Global warming leading to increased thawing of the permafrost can result in exposure of subsurface organic material to meltwater throughflow which may trigger an increase of trophic level of Antarctic lakes