Hydrobiologia

Fossil coenobia of the green algae group Pediastrum are well preserved in lake sediments. Integrated ecological and paleolimnological research as a basis for more exact palaeoecological inferences, however, is lacking almost completely so far. Here, we report the Pediastrum concentration and taxon composition in surface sediment samples from 36 large lakes (area >100 ha) and 32 ponds (area <1 ha) covering broad summer temperature and salinity gradients on the Tibetan Plateau, and additionally study 23 assemblages from the large freshwater lake Taro Co. Pediastrum algae are identified as relatively common algal compound of the still pristine alpine freshwater ecosystems. A salinity of ~2 g l−1 TDS seems to inhibit the growth of most of the Pediastrum taxa already. No large overall differences in the taxonomic inventory of ponds and large lakes are detected. The in-lake variation of assemblages in Taro Co is low. Factors driving the species composition of assemblages, however, seem to differ between both ecosystem types. Whereas taxonomic shifts in Pediastrum assemblages from ponds occur along the summer temperature gradient, shifts in taxon composition along the salinity gradient indicate the possible use of the algae group as an indicator for past salinity changes in large lakes.