Biological evolution of Antarctic lakes

Beaver Lake, a large epishelf lake in Eastern Antarctica was sampled on two occasions during the austral summer of 2000. Two sites, one 1km offshore and another 6km offshore were sampled at intervals to depths of 40m and 110m respectively. The lake is an end member of ultra-oligotrophic lake systems with a very low carbon pool. Dissolved organic carbon concentrations ranged between 95-652 micro grams per litre. Nutrient levels were generally low with soluble reactive phosphorus ranging from undetectable to 8.4 micro grams per litre, ammonium ranged between 1.8-5.0 micro grams per litre, nitrate from undetectable to 161 micro grams per litre and nitrite 1.1-5.3 micro grams per litre. Chlorophyll a concentrations ( 0.39 - 4.38 micro grams per litre) showed an unusual distribution with the highest levels close to the lake bottom at the offshore site (110m) where the phototrophic nanoflagellates displayed strong autofluorescence. Bacterial concentrations were low, with a maximum of 7.60 x 107 per litre, as were the concentrations of heterotrophic nanoflagellates that exploit them. Primary production ranged between 19.7 - 25.49 micro grams C per litre day-1 and bacterial production from 0.32 - 1.15 micro grams C per litre day-1. In common with other continental Antarctic lakes, the system was dominated by a microbial plankton. However, a dwarf variety of the calanoid copepod, Boeckella poppei, occurred below 25m at concentrations of 3-5 per litre. The data suggest that primary production and bacterial production were not limited by nutrient availability, but by other factors e.g. in the case of bacterial production by organic carbon concentrations and primary production by low temperatures.The fields in this dataset are:EvolutionBiologicallakesalinitydepth mciliates per litrecystsboeckellabacteriaglucoseglycineparticulate organic carbon (POC)total organic carbon (TOC)DiAskenasia 15/2/00sloved organic carbon (DOC)MonodiniumAskenasiaStrombidiumHeliozoascuticociliatesHolophyraPNAN = Phototrophic nanoflagellates HNAN= heterotrophic nanoflagellates