Periphytic diatom assemblages from ultra-oligotrophic and UV transparent lakes and ponds on Victoria Island and comparisons with other diatom surveys in the Canadian Arctic

Periphytic diatoms are potentially powerful indicators of environmental change in climatically-sensitive high latitude regions. However, only a few studies have examined their taxonomic and ecological characteristics. We identified and enumerated diatom assemblages from sediment, rock, and moss habitats in 34 ultra-oligotrophic and highly transparent lakes and ponds on Victoria Island, Arctic Canada. The similar limnological characteristics of the sites allowed us to examine the influence of habitat, independent of water chemistry, on the diatom assemblages. As is typical in shallow arctic water bodies, benthic taxa, including species of Achnanthes , Caloneis , Cymbella , Navicula , and Nitzschia , were most widely represented. Minor gradients in our measured environmental variables did not significantly explain any variance in diatom species, but there were marked differences in diatom assemblages among sites. Pond ephemerality seems to explain some diatom variation, because aerophilic taxa such as Achnanthes kryophila Petersen and A. marginulata Grunow were dominant in shallow sites that had undergone appreciable reductions in volume. We identified several taxa that exhibited strong habitat preferences to sediment, moss, or rock substrates and also found significant differences (P<0.01) in diatom composition among the three habitats. In comparisons with three similar diatom surveys extending over 1200 km of latitude, we determined that surface sediment assemblages differed significantly (P<0.001) among all regions examined. Diatom species diversity was inversely related to latitude, a result likely explained by differences in the lengths of growing seasons. These data contribute important ecological information on diatom assemblages in arctic regions and will aid in the interpretation of environmental changes in biomonitoring and paleolimnological studies.